Implement DnsResolver for Windows - #129302

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Implement DnsResolver for Windows#129302
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@rzikmrzikm commented Jun 11, 2026

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Implements the API approved in #19443:

  • New Dns.Resolve*[Async] static methods for A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
  • New DnsResolver / DnsResolverOptions for instance-based resolution with optional custom DNS servers.
  • Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord, PtrRecord, NsRecord.
  • DnsResponseCode enum and DnsResult envelope carrying ResponseCode, Records, and NegativeCacheTtl.

Windows implementation uses DnsQueryEx. Non-Windows platforms get PlatformNotSupportedException stubs pending follow-up implementations (splitting to multiple stacked PRs for easier review).

CopilotAI review requested due to automatic review settings June 11, 2026 16:57
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rzikm requested a review from a teamJune 11, 2026 16:58
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Pull request overview

This PR adds a new DNS query API surface area to System.Net.NameResolution (new Dns.Resolve* static entry points plus an instance-based DnsResolver), and implements the Windows PAL using DnsQueryEx. It also introduces functional tests, including deterministic loopback-server-driven tests for record parsing/handling.

Changes:

  • Adds new public APIs: Dns.Resolve* (A/AAAA/SRV/MX/TXT/CNAME/PTR/NS), DnsResolver, DnsResolverOptions, record structs, DnsResult<T>, and DnsResponseCode.
  • Implements Windows DNS querying/parsing via DnsQueryEx (sync + async paths), plus non-Windows PNSE stubs.
  • Adds functional tests (outer-loop network tests + loopback DNS server tests) and extends NameResolution telemetry to handle string[] answers.

Reviewed changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated 18 comments.

Show a summary per file
FileDescription
src/libraries/System.Net.NameResolution/tests/FunctionalTests/System.Net.NameResolution.Functional.Tests.csprojAdds new functional test sources to the project
src/libraries/System.Net.NameResolution/tests/FunctionalTests/LoopbackDnsServer.csAdds an in-process UDP/TCP loopback DNS server for deterministic tests
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResponseBuilder.csAdds a fluent builder for DNS response bytes used by loopback tests
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverTest.csAdds outer-loop functional tests for the new APIs (real DNS)
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.csAdds deterministic loopback-server-driven tests for parsing/behavior/metrics
src/libraries/System.Net.NameResolution/src/System/Net/NameResolutionTelemetry.csExtends telemetry answer handling to support string[]
src/libraries/System.Net.NameResolution/src/System/Net/DnsResult.csIntroduces DnsResult<T> envelope type
src/libraries/System.Net.NameResolution/src/System/Net/DnsResponseCode.csIntroduces DnsResponseCode enum
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.csImplements Windows PAL via DnsQueryEx, record parsing, cancellation, glue, TTL extraction
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Unsupported.csAdds non-Windows PNSE PAL stubs
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverOptions.csAdds options type for custom server selection
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.csAdds instance-based resolver API + telemetry wrapping
src/libraries/System.Net.NameResolution/src/System/Net/DnsRecords.csAdds record structs (Address/Srv/Mx/Txt/CName/Ptr/Ns)
src/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.csAdds new static Dns.Resolve* APIs backed by a default resolver
src/libraries/System.Net.NameResolution/src/System/Net/Dns.csMakes Dns partial to host the new Dns.Resolve* partial
src/libraries/System.Net.NameResolution/src/System.Net.NameResolution.csprojWires new sources and Windows Dnsapi interop into the build
src/libraries/System.Net.NameResolution/src/Resources/Strings.resxAdds SR string for unsupported custom DNS ports
src/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.csAdds new public API contract entries
src/libraries/Common/src/Interop/Windows/Interop.Libraries.csAdds Libraries.Dnsapi constant
src/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsTypes.csAdds DnsQueryEx/DNS_RECORD-related structs/constants
src/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsApi.csAdds LibraryImport declarations for DnsQueryEx/DnsCancelQuery/DnsFree

Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs Outdated
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs Outdated
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs Outdated
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs Outdated
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs Outdated
Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs Outdated
Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs Outdated
Comment threadsrc/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsApi.cs Outdated
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs Outdated
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs Outdated
MihaZupan
MihaZupan reviewed Jun 11, 2026
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First pass through.

Just curious, will there be a way to opt-in to using the managed implementation even on Windows, or would there be no reason to want to do that anyway?

Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs Outdated
Comment on lines +75 to +82
public System.Net.DnsResult<System.Net.AddressRecord> ResolveAddresses(string name) { throw null; }
public System.Net.DnsResult<System.Net.AddressRecord> ResolveAddresses(string name, System.Net.Sockets.AddressFamily addressFamily) { throw null; }
public System.Net.DnsResult<System.Net.SrvRecord> ResolveSrv(string name) { throw null; }
public System.Net.DnsResult<System.Net.MxRecord> ResolveMx(string name) { throw null; }
public System.Net.DnsResult<System.Net.TxtRecord> ResolveTxt(string name) { throw null; }
public System.Net.DnsResult<System.Net.CNameRecord> ResolveCName(string name) { throw null; }
public System.Net.DnsResult<System.Net.PtrRecord> ResolvePtr(string name) { throw null; }
public System.Net.DnsResult<System.Net.NsRecord> ResolveNs(string name) { throw null; }

@MihaZupanMihaZupanJun 11, 2026

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Suggested change
publicSystem.Net.DnsResult<System.Net.AddressRecord>ResolveAddresses(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.AddressRecord>ResolveAddresses(stringname,System.Net.Sockets.AddressFamilyaddressFamily){thrownull;}
publicSystem.Net.DnsResult<System.Net.SrvRecord>ResolveSrv(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.MxRecord>ResolveMx(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.TxtRecord>ResolveTxt(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.CNameRecord>ResolveCName(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.PtrRecord>ResolvePtr(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.NsRecord>ResolveNs(stringname){thrownull;}

I think we should talk about this with the team :)

My stance continues to be that exposing sync APIs here is a mistake, especially if we have real plans to eventually add support for resolution over HTTPS/QUIC.
The fact that e.g. Resolve silently has 2x the latency compared to the async variant makes the argument that we need sync APIs for perf wrong IMO.

@rzikmrzikmJun 17, 2026

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I am also not entirely happy with having synchronous versions as well, we can bring it in a team discussion and push back if more of us feel strongly about this :)

Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs Outdated
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs Outdated
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs Outdated
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs Outdated
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs Outdated
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs Outdated
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs Outdated
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs Outdated
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs Outdated
This was referenced Jun 11, 2026
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Pull request overview

Copilot reviewed 21 out of 21 changed files in this pull request and generated 4 comments.

Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/LoopbackDnsServer.cs Outdated
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs Outdated
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs Outdated
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs Outdated
@MichalPetryka

MichalPetryka commented Jun 17, 2026•
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I've worked with DNS apis here before so here's what I wanted to note:

  • This needs to account for this pre Windows 11 bug and fallback to DnsQueryW for affected cases (it's only when DnsQueryEx would return synchronously).
  • IIRC DnsQueryEx is also broken under impersonization, so this needs identical handling like the GetAddrInfoW handling today has.

CopilotAI review requested due to automatic review settings June 18, 2026 11:38
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Pull request overview

Copilot reviewed 21 out of 21 changed files in this pull request and generated 6 comments.

Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs Outdated
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs Outdated
Comment threadsrc/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsTypes.cs Outdated
Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs Outdated
Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs Outdated
Comment on lines +48 to +54
[OuterLoop("Binds the loopback DNS port 53 and issues real DnsQueryEx calls.")]
[Collection(nameof(DisableParallelization))]
[PlatformSpecific(TestPlatforms.Windows)]
public class DnsResolverLoopbackTest : IClassFixture<WindowsLoopbackServer>
{
private static DnsResolver CreateResolver(LoopbackDnsServer server)
=> new DnsResolver(new DnsResolverOptions { Servers = { server.EndPoint } });
Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs Outdated
This was referenced Jun 18, 2026
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CopilotAI review requested due to automatic review settings June 25, 2026 11:15
@rzikmrzikm closed this Jun 25, 2026
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Copilot wasn't able to review any files in this pull request.

@rzikmrzikm mentioned this pull request Jun 25, 2026
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rzikm added a commit that referenced this pull request Jul 8, 2026
@rzikm
Implement DnsResolver for Windows (#129845)
e6e4d8d
Replacement for #129302 (thanks,
`gh stack submit` 😠)
Implements the API approved in
#19443:
New Dns.Resolve*[Async] static methods for
A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
New DnsResolver / DnsResolverOptions for instance-based resolution with
optional custom DNS servers.
Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord,
PtrRecord, NsRecord.
DnsResponseCode enum and DnsResult envelope carrying ResponseCode,
Records, and NegativeCacheTtl.
Windows implementation uses DnsQueryEx. Non-Windows platforms get
PlatformNotSupportedException stubs pending follow-up implementations
(splitting to multiple stacked PRs for easier review).
---------
Co-authored-by: rzikm <rzikm@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
@MihuBotMihuBot mentioned this pull request Jul 14, 2026
Open
eiriktsarpalis pushed a commit that referenced this pull request Jul 15, 2026
@rzikm
@eiriktsarpalis
Implement DnsResolver for Windows (#129845)
1afd7a2
Replacement for #129302 (thanks,
`gh stack submit` 😠)
Implements the API approved in
#19443:
New Dns.Resolve*[Async] static methods for
A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
New DnsResolver / DnsResolverOptions for instance-based resolution with
optional custom DNS servers.
Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord,
PtrRecord, NsRecord.
DnsResponseCode enum and DnsResult envelope carrying ResponseCode,
Records, and NegativeCacheTtl.
Windows implementation uses DnsQueryEx. Non-Windows platforms get
PlatformNotSupportedException stubs pending follow-up implementations
(splitting to multiple stacked PRs for easier review).
---------
Co-authored-by: rzikm <rzikm@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
@github-actionsgithub-actionsBot locked and limited conversation to collaborators Jul 26, 2026
Sign up for freeto subscribe to this conversation on GitHub. Already have an account? Sign in.

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Implement DnsResolver for Windows - #129302
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@rzikm
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Implements the API approved in #19443:
  • New Dns.Resolve*[Async] static methods for A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
  • New DnsResolver / DnsResolverOptions for instance-based resolution with optional custom DNS servers.
  • Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord, PtrRecord, NsRecord.
  • DnsResponseCode enum and DnsResult envelope carrying ResponseCode, Records, and NegativeCacheTtl.
Windows implementation uses DnsQueryEx. Non-Windows platforms get PlatformNotSupportedException stubs pending follow-up implementations (splitting to multiple stacked PRs for easier review).
CopilotAI
review requested due to automatic review settings
June 11, 2026 16:57
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from a teamJune 11, 2026 16:58
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Tagging subscribers to this area: @karelz, @dotnet/ncl

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Pull request overview
This PR adds a new DNS query API surface area to System.Net.NameResolution (new Dns.Resolve* static entry points plus an instance-based DnsResolver), and implements the Windows PAL using DnsQueryEx. It also introduces functional tests, including deterministic loopback-server-driven tests for record parsing/handling.
Changes:
  • Adds new public APIs: Dns.Resolve* (A/AAAA/SRV/MX/TXT/CNAME/PTR/NS), DnsResolver, DnsResolverOptions, record structs, DnsResult<T>, and DnsResponseCode.
  • Implements Windows DNS querying/parsing via DnsQueryEx (sync + async paths), plus non-Windows PNSE stubs.
  • Adds functional tests (outer-loop network tests + loopback DNS server tests) and extends NameResolution telemetry to handle string[] answers.
Reviewed changes
Copilot reviewed 21 out of 21 changed files in this pull request and generated 18 comments.
Show a summary per file
FileDescription
src/libraries/System.Net.NameResolution/tests/FunctionalTests/System.Net.NameResolution.Functional.Tests.csprojAdds new functional test sources to the project
src/libraries/System.Net.NameResolution/tests/FunctionalTests/LoopbackDnsServer.csAdds an in-process UDP/TCP loopback DNS server for deterministic tests
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResponseBuilder.csAdds a fluent builder for DNS response bytes used by loopback tests
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverTest.csAdds outer-loop functional tests for the new APIs (real DNS)
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.csAdds deterministic loopback-server-driven tests for parsing/behavior/metrics
src/libraries/System.Net.NameResolution/src/System/Net/NameResolutionTelemetry.csExtends telemetry answer handling to support string[]
src/libraries/System.Net.NameResolution/src/System/Net/DnsResult.csIntroduces DnsResult<T> envelope type
src/libraries/System.Net.NameResolution/src/System/Net/DnsResponseCode.csIntroduces DnsResponseCode enum
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.csImplements Windows PAL via DnsQueryEx, record parsing, cancellation, glue, TTL extraction
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Unsupported.csAdds non-Windows PNSE PAL stubs
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverOptions.csAdds options type for custom server selection
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.csAdds instance-based resolver API + telemetry wrapping
src/libraries/System.Net.NameResolution/src/System/Net/DnsRecords.csAdds record structs (Address/Srv/Mx/Txt/CName/Ptr/Ns)
src/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.csAdds new static Dns.Resolve* APIs backed by a default resolver
src/libraries/System.Net.NameResolution/src/System/Net/Dns.csMakes Dns partial to host the new Dns.Resolve* partial
src/libraries/System.Net.NameResolution/src/System.Net.NameResolution.csprojWires new sources and Windows Dnsapi interop into the build
src/libraries/System.Net.NameResolution/src/Resources/Strings.resxAdds SR string for unsupported custom DNS ports
src/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.csAdds new public API contract entries
src/libraries/Common/src/Interop/Windows/Interop.Libraries.csAdds Libraries.Dnsapi constant
src/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsTypes.csAdds DnsQueryEx/DNS_RECORD-related structs/constants
src/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsApi.csAdds LibraryImport declarations for DnsQueryEx/DnsCancelQuery/DnsFree
Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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Comment threadsrc/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsApi.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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First pass through.
Just curious, will there be a way to opt-in to using the managed implementation even on Windows, or would there be no reason to want to do that anyway?
Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs
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Comment on lines

+75
 to 
+82

 public System.Net.DnsResult<System.Net.AddressRecord> ResolveAddresses(string name) { throw null; }
 public System.Net.DnsResult<System.Net.AddressRecord> ResolveAddresses(string name, System.Net.Sockets.AddressFamily addressFamily) { throw null; }
 public System.Net.DnsResult<System.Net.SrvRecord> ResolveSrv(string name) { throw null; }
 public System.Net.DnsResult<System.Net.MxRecord> ResolveMx(string name) { throw null; }
 public System.Net.DnsResult<System.Net.TxtRecord> ResolveTxt(string name) { throw null; }
 public System.Net.DnsResult<System.Net.CNameRecord> ResolveCName(string name) { throw null; }
 public System.Net.DnsResult<System.Net.PtrRecord> ResolvePtr(string name) { throw null; }
 public System.Net.DnsResult<System.Net.NsRecord> ResolveNs(string name) { throw null; }
@MihaZupanMihaZupanJun 11, 2026

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Suggested change

publicSystem.Net.DnsResult<System.Net.AddressRecord>ResolveAddresses(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.AddressRecord>ResolveAddresses(stringname,System.Net.Sockets.AddressFamilyaddressFamily){thrownull;}
publicSystem.Net.DnsResult<System.Net.SrvRecord>ResolveSrv(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.MxRecord>ResolveMx(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.TxtRecord>ResolveTxt(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.CNameRecord>ResolveCName(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.PtrRecord>ResolvePtr(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.NsRecord>ResolveNs(stringname){thrownull;}
I think we should talk about this with the team :)
My stance continues to be that exposing sync APIs here is a mistake, especially if we have real plans to eventually add support for resolution over HTTPS/QUIC.

The fact that e.g. Resolve silently has 2x the latency compared to the async variant makes the argument that we need sync APIs for perf wrong IMO.
@rzikmrzikmJun 17, 2026

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I am also not entirely happy with having synchronous versions as well, we can bring it in a team discussion and push back if more of us feel strongly about this :)
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Pull request overview
Copilot reviewed 21 out of 21 changed files in this pull request and generated 4 comments.
Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/LoopbackDnsServer.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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I've worked with DNS apis here before so here's what I wanted to note:
  • This needs to account for this pre Windows 11 bug and fallback to DnsQueryW for affected cases (it's only when DnsQueryEx would return synchronously).
  • IIRC DnsQueryEx is also broken under impersonization, so this needs identical handling like the GetAddrInfoW handling today has.
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Pull request overview
Copilot reviewed 21 out of 21 changed files in this pull request and generated 6 comments.
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsTypes.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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 [OuterLoop("Binds the loopback DNS port 53 and issues real DnsQueryEx calls.")]
 [Collection(nameof(DisableParallelization))]
 [PlatformSpecific(TestPlatforms.Windows)]
 public class DnsResolverLoopbackTest : IClassFixture<WindowsLoopbackServer>
 {
 private static DnsResolver CreateResolver(LoopbackDnsServer server)
 => new DnsResolver(new DnsResolverOptions { Servers = { server.EndPoint } });
Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs
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@rzikm
Implement DnsResolver for Windows (#129845)
e6e4d8d
Replacement for #129302 (thanks,
`gh stack submit` 😠)
Implements the API approved in
#19443:
New Dns.Resolve*[Async] static methods for
A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
New DnsResolver / DnsResolverOptions for instance-based resolution with
optional custom DNS servers.
Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord,
PtrRecord, NsRecord.
DnsResponseCode enum and DnsResult envelope carrying ResponseCode,
Records, and NegativeCacheTtl.
Windows implementation uses DnsQueryEx. Non-Windows platforms get
PlatformNotSupportedException stubs pending follow-up implementations
(splitting to multiple stacked PRs for easier review).
---------
Co-authored-by: rzikm <rzikm@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
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@rzikm
@eiriktsarpalis
Implement DnsResolver for Windows (#129845)
1afd7a2
Replacement for #129302 (thanks,
`gh stack submit` 😠)
Implements the API approved in
#19443:
New Dns.Resolve*[Async] static methods for
A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
New DnsResolver / DnsResolverOptions for instance-based resolution with
optional custom DNS servers.
Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord,
PtrRecord, NsRecord.
DnsResponseCode enum and DnsResult envelope carrying ResponseCode,
Records, and NegativeCacheTtl.
Windows implementation uses DnsQueryEx. Non-Windows platforms get
PlatformNotSupportedException stubs pending follow-up implementations
(splitting to multiple stacked PRs for easier review).
---------
Co-authored-by: rzikm <rzikm@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
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Implement DnsResolver for Windows - #129302
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Implements the API approved in #19443:
  • New Dns.Resolve*[Async] static methods for A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
  • New DnsResolver / DnsResolverOptions for instance-based resolution with optional custom DNS servers.
  • Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord, PtrRecord, NsRecord.
  • DnsResponseCode enum and DnsResult envelope carrying ResponseCode, Records, and NegativeCacheTtl.
Windows implementation uses DnsQueryEx. Non-Windows platforms get PlatformNotSupportedException stubs pending follow-up implementations (splitting to multiple stacked PRs for easier review).
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Pull request overview
This PR adds a new DNS query API surface area to System.Net.NameResolution (new Dns.Resolve* static entry points plus an instance-based DnsResolver), and implements the Windows PAL using DnsQueryEx. It also introduces functional tests, including deterministic loopback-server-driven tests for record parsing/handling.
Changes:
  • Adds new public APIs: Dns.Resolve* (A/AAAA/SRV/MX/TXT/CNAME/PTR/NS), DnsResolver, DnsResolverOptions, record structs, DnsResult<T>, and DnsResponseCode.
  • Implements Windows DNS querying/parsing via DnsQueryEx (sync + async paths), plus non-Windows PNSE stubs.
  • Adds functional tests (outer-loop network tests + loopback DNS server tests) and extends NameResolution telemetry to handle string[] answers.
Reviewed changes
Copilot reviewed 21 out of 21 changed files in this pull request and generated 18 comments.
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FileDescription
src/libraries/System.Net.NameResolution/tests/FunctionalTests/System.Net.NameResolution.Functional.Tests.csprojAdds new functional test sources to the project
src/libraries/System.Net.NameResolution/tests/FunctionalTests/LoopbackDnsServer.csAdds an in-process UDP/TCP loopback DNS server for deterministic tests
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResponseBuilder.csAdds a fluent builder for DNS response bytes used by loopback tests
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverTest.csAdds outer-loop functional tests for the new APIs (real DNS)
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.csAdds deterministic loopback-server-driven tests for parsing/behavior/metrics
src/libraries/System.Net.NameResolution/src/System/Net/NameResolutionTelemetry.csExtends telemetry answer handling to support string[]
src/libraries/System.Net.NameResolution/src/System/Net/DnsResult.csIntroduces DnsResult<T> envelope type
src/libraries/System.Net.NameResolution/src/System/Net/DnsResponseCode.csIntroduces DnsResponseCode enum
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.csImplements Windows PAL via DnsQueryEx, record parsing, cancellation, glue, TTL extraction
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Unsupported.csAdds non-Windows PNSE PAL stubs
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverOptions.csAdds options type for custom server selection
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.csAdds instance-based resolver API + telemetry wrapping
src/libraries/System.Net.NameResolution/src/System/Net/DnsRecords.csAdds record structs (Address/Srv/Mx/Txt/CName/Ptr/Ns)
src/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.csAdds new static Dns.Resolve* APIs backed by a default resolver
src/libraries/System.Net.NameResolution/src/System/Net/Dns.csMakes Dns partial to host the new Dns.Resolve* partial
src/libraries/System.Net.NameResolution/src/System.Net.NameResolution.csprojWires new sources and Windows Dnsapi interop into the build
src/libraries/System.Net.NameResolution/src/Resources/Strings.resxAdds SR string for unsupported custom DNS ports
src/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.csAdds new public API contract entries
src/libraries/Common/src/Interop/Windows/Interop.Libraries.csAdds Libraries.Dnsapi constant
src/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsTypes.csAdds DnsQueryEx/DNS_RECORD-related structs/constants
src/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsApi.csAdds LibraryImport declarations for DnsQueryEx/DnsCancelQuery/DnsFree
Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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Comment threadsrc/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsApi.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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First pass through.
Just curious, will there be a way to opt-in to using the managed implementation even on Windows, or would there be no reason to want to do that anyway?
Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs
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 public System.Net.DnsResult<System.Net.AddressRecord> ResolveAddresses(string name) { throw null; }
 public System.Net.DnsResult<System.Net.AddressRecord> ResolveAddresses(string name, System.Net.Sockets.AddressFamily addressFamily) { throw null; }
 public System.Net.DnsResult<System.Net.SrvRecord> ResolveSrv(string name) { throw null; }
 public System.Net.DnsResult<System.Net.MxRecord> ResolveMx(string name) { throw null; }
 public System.Net.DnsResult<System.Net.TxtRecord> ResolveTxt(string name) { throw null; }
 public System.Net.DnsResult<System.Net.CNameRecord> ResolveCName(string name) { throw null; }
 public System.Net.DnsResult<System.Net.PtrRecord> ResolvePtr(string name) { throw null; }
 public System.Net.DnsResult<System.Net.NsRecord> ResolveNs(string name) { throw null; }
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Suggested change

publicSystem.Net.DnsResult<System.Net.AddressRecord>ResolveAddresses(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.AddressRecord>ResolveAddresses(stringname,System.Net.Sockets.AddressFamilyaddressFamily){thrownull;}
publicSystem.Net.DnsResult<System.Net.SrvRecord>ResolveSrv(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.MxRecord>ResolveMx(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.TxtRecord>ResolveTxt(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.CNameRecord>ResolveCName(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.PtrRecord>ResolvePtr(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.NsRecord>ResolveNs(stringname){thrownull;}
I think we should talk about this with the team :)
My stance continues to be that exposing sync APIs here is a mistake, especially if we have real plans to eventually add support for resolution over HTTPS/QUIC.

The fact that e.g. Resolve silently has 2x the latency compared to the async variant makes the argument that we need sync APIs for perf wrong IMO.
@rzikmrzikmJun 17, 2026

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I am also not entirely happy with having synchronous versions as well, we can bring it in a team discussion and push back if more of us feel strongly about this :)
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Pull request overview
Copilot reviewed 21 out of 21 changed files in this pull request and generated 4 comments.
Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/LoopbackDnsServer.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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@MichalPetryka
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I've worked with DNS apis here before so here's what I wanted to note:
  • This needs to account for this pre Windows 11 bug and fallback to DnsQueryW for affected cases (it's only when DnsQueryEx would return synchronously).
  • IIRC DnsQueryEx is also broken under impersonization, so this needs identical handling like the GetAddrInfoW handling today has.
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Pull request overview
Copilot reviewed 21 out of 21 changed files in this pull request and generated 6 comments.
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsTypes.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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Comment on lines

+48
 to 
+54

 [OuterLoop("Binds the loopback DNS port 53 and issues real DnsQueryEx calls.")]
 [Collection(nameof(DisableParallelization))]
 [PlatformSpecific(TestPlatforms.Windows)]
 public class DnsResolverLoopbackTest : IClassFixture<WindowsLoopbackServer>
 {
 private static DnsResolver CreateResolver(LoopbackDnsServer server)
 => new DnsResolver(new DnsResolverOptions { Servers = { server.EndPoint } });
Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs
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Copilot wasn't able to review any files in this pull request.
@rzikmrzikm
mentioned this pull request
Jun 25, 2026
 Merged

rzikm added a commit
that referenced
this pull request
Jul 8, 2026
@rzikm
Implement DnsResolver for Windows (#129845)
e6e4d8d
Replacement for #129302 (thanks,
`gh stack submit` 😠)
Implements the API approved in
#19443:
New Dns.Resolve*[Async] static methods for
A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
New DnsResolver / DnsResolverOptions for instance-based resolution with
optional custom DNS servers.
Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord,
PtrRecord, NsRecord.
DnsResponseCode enum and DnsResult envelope carrying ResponseCode,
Records, and NegativeCacheTtl.
Windows implementation uses DnsQueryEx. Non-Windows platforms get
PlatformNotSupportedException stubs pending follow-up implementations
(splitting to multiple stacked PRs for easier review).
---------
Co-authored-by: rzikm <rzikm@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
@MihuBotMihuBot
mentioned this pull request
Jul 14, 2026

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eiriktsarpalis pushed a commit
that referenced
this pull request
Jul 15, 2026
@rzikm
@eiriktsarpalis
Implement DnsResolver for Windows (#129845)
1afd7a2
Replacement for #129302 (thanks,
`gh stack submit` 😠)
Implements the API approved in
#19443:
New Dns.Resolve*[Async] static methods for
A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
New DnsResolver / DnsResolverOptions for instance-based resolution with
optional custom DNS servers.
Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord,
PtrRecord, NsRecord.
DnsResponseCode enum and DnsResult envelope carrying ResponseCode,
Records, and NegativeCacheTtl.
Windows implementation uses DnsQueryEx. Non-Windows platforms get
PlatformNotSupportedException stubs pending follow-up implementations
(splitting to multiple stacked PRs for easier review).
---------
Co-authored-by: rzikm <rzikm@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
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} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
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var __m = "*";
var __re = new RegExp('^' + ".*" + '

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Implement DnsResolver for Windows - #129302
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Implements the API approved in #19443:
  • New Dns.Resolve*[Async] static methods for A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
  • New DnsResolver / DnsResolverOptions for instance-based resolution with optional custom DNS servers.
  • Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord, PtrRecord, NsRecord.
  • DnsResponseCode enum and DnsResult envelope carrying ResponseCode, Records, and NegativeCacheTtl.
Windows implementation uses DnsQueryEx. Non-Windows platforms get PlatformNotSupportedException stubs pending follow-up implementations (splitting to multiple stacked PRs for easier review).
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Pull request overview
This PR adds a new DNS query API surface area to System.Net.NameResolution (new Dns.Resolve* static entry points plus an instance-based DnsResolver), and implements the Windows PAL using DnsQueryEx. It also introduces functional tests, including deterministic loopback-server-driven tests for record parsing/handling.
Changes:
  • Adds new public APIs: Dns.Resolve* (A/AAAA/SRV/MX/TXT/CNAME/PTR/NS), DnsResolver, DnsResolverOptions, record structs, DnsResult<T>, and DnsResponseCode.
  • Implements Windows DNS querying/parsing via DnsQueryEx (sync + async paths), plus non-Windows PNSE stubs.
  • Adds functional tests (outer-loop network tests + loopback DNS server tests) and extends NameResolution telemetry to handle string[] answers.
Reviewed changes
Copilot reviewed 21 out of 21 changed files in this pull request and generated 18 comments.
Show a summary per file
FileDescription
src/libraries/System.Net.NameResolution/tests/FunctionalTests/System.Net.NameResolution.Functional.Tests.csprojAdds new functional test sources to the project
src/libraries/System.Net.NameResolution/tests/FunctionalTests/LoopbackDnsServer.csAdds an in-process UDP/TCP loopback DNS server for deterministic tests
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResponseBuilder.csAdds a fluent builder for DNS response bytes used by loopback tests
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverTest.csAdds outer-loop functional tests for the new APIs (real DNS)
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.csAdds deterministic loopback-server-driven tests for parsing/behavior/metrics
src/libraries/System.Net.NameResolution/src/System/Net/NameResolutionTelemetry.csExtends telemetry answer handling to support string[]
src/libraries/System.Net.NameResolution/src/System/Net/DnsResult.csIntroduces DnsResult<T> envelope type
src/libraries/System.Net.NameResolution/src/System/Net/DnsResponseCode.csIntroduces DnsResponseCode enum
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.csImplements Windows PAL via DnsQueryEx, record parsing, cancellation, glue, TTL extraction
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Unsupported.csAdds non-Windows PNSE PAL stubs
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverOptions.csAdds options type for custom server selection
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.csAdds instance-based resolver API + telemetry wrapping
src/libraries/System.Net.NameResolution/src/System/Net/DnsRecords.csAdds record structs (Address/Srv/Mx/Txt/CName/Ptr/Ns)
src/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.csAdds new static Dns.Resolve* APIs backed by a default resolver
src/libraries/System.Net.NameResolution/src/System/Net/Dns.csMakes Dns partial to host the new Dns.Resolve* partial
src/libraries/System.Net.NameResolution/src/System.Net.NameResolution.csprojWires new sources and Windows Dnsapi interop into the build
src/libraries/System.Net.NameResolution/src/Resources/Strings.resxAdds SR string for unsupported custom DNS ports
src/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.csAdds new public API contract entries
src/libraries/Common/src/Interop/Windows/Interop.Libraries.csAdds Libraries.Dnsapi constant
src/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsTypes.csAdds DnsQueryEx/DNS_RECORD-related structs/constants
src/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsApi.csAdds LibraryImport declarations for DnsQueryEx/DnsCancelQuery/DnsFree
Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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Comment threadsrc/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsApi.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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First pass through.
Just curious, will there be a way to opt-in to using the managed implementation even on Windows, or would there be no reason to want to do that anyway?
Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs
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 public System.Net.DnsResult<System.Net.AddressRecord> ResolveAddresses(string name) { throw null; }
 public System.Net.DnsResult<System.Net.AddressRecord> ResolveAddresses(string name, System.Net.Sockets.AddressFamily addressFamily) { throw null; }
 public System.Net.DnsResult<System.Net.SrvRecord> ResolveSrv(string name) { throw null; }
 public System.Net.DnsResult<System.Net.MxRecord> ResolveMx(string name) { throw null; }
 public System.Net.DnsResult<System.Net.TxtRecord> ResolveTxt(string name) { throw null; }
 public System.Net.DnsResult<System.Net.CNameRecord> ResolveCName(string name) { throw null; }
 public System.Net.DnsResult<System.Net.PtrRecord> ResolvePtr(string name) { throw null; }
 public System.Net.DnsResult<System.Net.NsRecord> ResolveNs(string name) { throw null; }
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Suggested change

publicSystem.Net.DnsResult<System.Net.AddressRecord>ResolveAddresses(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.AddressRecord>ResolveAddresses(stringname,System.Net.Sockets.AddressFamilyaddressFamily){thrownull;}
publicSystem.Net.DnsResult<System.Net.SrvRecord>ResolveSrv(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.MxRecord>ResolveMx(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.TxtRecord>ResolveTxt(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.CNameRecord>ResolveCName(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.PtrRecord>ResolvePtr(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.NsRecord>ResolveNs(stringname){thrownull;}
I think we should talk about this with the team :)
My stance continues to be that exposing sync APIs here is a mistake, especially if we have real plans to eventually add support for resolution over HTTPS/QUIC.

The fact that e.g. Resolve silently has 2x the latency compared to the async variant makes the argument that we need sync APIs for perf wrong IMO.
@rzikmrzikmJun 17, 2026

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I am also not entirely happy with having synchronous versions as well, we can bring it in a team discussion and push back if more of us feel strongly about this :)
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Pull request overview
Copilot reviewed 21 out of 21 changed files in this pull request and generated 4 comments.
Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/LoopbackDnsServer.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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I've worked with DNS apis here before so here's what I wanted to note:
  • This needs to account for this pre Windows 11 bug and fallback to DnsQueryW for affected cases (it's only when DnsQueryEx would return synchronously).
  • IIRC DnsQueryEx is also broken under impersonization, so this needs identical handling like the GetAddrInfoW handling today has.
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Pull request overview
Copilot reviewed 21 out of 21 changed files in this pull request and generated 6 comments.
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsTypes.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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 [OuterLoop("Binds the loopback DNS port 53 and issues real DnsQueryEx calls.")]
 [Collection(nameof(DisableParallelization))]
 [PlatformSpecific(TestPlatforms.Windows)]
 public class DnsResolverLoopbackTest : IClassFixture<WindowsLoopbackServer>
 {
 private static DnsResolver CreateResolver(LoopbackDnsServer server)
 => new DnsResolver(new DnsResolverOptions { Servers = { server.EndPoint } });
Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs
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Copilot wasn't able to review any files in this pull request.
@rzikmrzikm
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@rzikm
Implement DnsResolver for Windows (#129845)
e6e4d8d
Replacement for #129302 (thanks,
`gh stack submit` 😠)
Implements the API approved in
#19443:
New Dns.Resolve*[Async] static methods for
A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
New DnsResolver / DnsResolverOptions for instance-based resolution with
optional custom DNS servers.
Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord,
PtrRecord, NsRecord.
DnsResponseCode enum and DnsResult envelope carrying ResponseCode,
Records, and NegativeCacheTtl.
Windows implementation uses DnsQueryEx. Non-Windows platforms get
PlatformNotSupportedException stubs pending follow-up implementations
(splitting to multiple stacked PRs for easier review).
---------
Co-authored-by: rzikm <rzikm@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
@MihuBotMihuBot
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@rzikm
@eiriktsarpalis
Implement DnsResolver for Windows (#129845)
1afd7a2
Replacement for #129302 (thanks,
`gh stack submit` 😠)
Implements the API approved in
#19443:
New Dns.Resolve*[Async] static methods for
A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
New DnsResolver / DnsResolverOptions for instance-based resolution with
optional custom DNS servers.
Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord,
PtrRecord, NsRecord.
DnsResponseCode enum and DnsResult envelope carrying ResponseCode,
Records, and NegativeCacheTtl.
Windows implementation uses DnsQueryEx. Non-Windows platforms get
PlatformNotSupportedException stubs pending follow-up implementations
(splitting to multiple stacked PRs for easier review).
---------
Co-authored-by: rzikm <rzikm@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
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var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',
'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',
'ref', 'ref_src', 'source', 'medium', 'campaign'];
function cleanUrl(url) {
try {
var u = new URL(url, window.location.origin);
var changed = false;
trackingParams.forEach(function(p) {
if (u.searchParams.has(p)) {
u.searchParams.delete(p);
changed = true;
}
});
return changed ? u.toString() : url;
} catch (e) {
return url;
}
}
function cleanLinks() {
document.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
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m.addedNodes.forEach(function(node) {
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if (node.tagName === 'A') cleanLinks();
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var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
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observer.observe(document.body, { childList: true, subtree: true });
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} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
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try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

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Implement DnsResolver for Windows - #129302
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Implement DnsResolver for Windows#129302
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Implements the API approved in #19443:
  • New Dns.Resolve*[Async] static methods for A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
  • New DnsResolver / DnsResolverOptions for instance-based resolution with optional custom DNS servers.
  • Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord, PtrRecord, NsRecord.
  • DnsResponseCode enum and DnsResult envelope carrying ResponseCode, Records, and NegativeCacheTtl.
Windows implementation uses DnsQueryEx. Non-Windows platforms get PlatformNotSupportedException stubs pending follow-up implementations (splitting to multiple stacked PRs for easier review).
CopilotAI
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June 11, 2026 16:57
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Tagging subscribers to this area: @karelz, @dotnet/ncl

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Pull request overview
This PR adds a new DNS query API surface area to System.Net.NameResolution (new Dns.Resolve* static entry points plus an instance-based DnsResolver), and implements the Windows PAL using DnsQueryEx. It also introduces functional tests, including deterministic loopback-server-driven tests for record parsing/handling.
Changes:
  • Adds new public APIs: Dns.Resolve* (A/AAAA/SRV/MX/TXT/CNAME/PTR/NS), DnsResolver, DnsResolverOptions, record structs, DnsResult<T>, and DnsResponseCode.
  • Implements Windows DNS querying/parsing via DnsQueryEx (sync + async paths), plus non-Windows PNSE stubs.
  • Adds functional tests (outer-loop network tests + loopback DNS server tests) and extends NameResolution telemetry to handle string[] answers.
Reviewed changes
Copilot reviewed 21 out of 21 changed files in this pull request and generated 18 comments.
Show a summary per file
FileDescription
src/libraries/System.Net.NameResolution/tests/FunctionalTests/System.Net.NameResolution.Functional.Tests.csprojAdds new functional test sources to the project
src/libraries/System.Net.NameResolution/tests/FunctionalTests/LoopbackDnsServer.csAdds an in-process UDP/TCP loopback DNS server for deterministic tests
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResponseBuilder.csAdds a fluent builder for DNS response bytes used by loopback tests
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverTest.csAdds outer-loop functional tests for the new APIs (real DNS)
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.csAdds deterministic loopback-server-driven tests for parsing/behavior/metrics
src/libraries/System.Net.NameResolution/src/System/Net/NameResolutionTelemetry.csExtends telemetry answer handling to support string[]
src/libraries/System.Net.NameResolution/src/System/Net/DnsResult.csIntroduces DnsResult<T> envelope type
src/libraries/System.Net.NameResolution/src/System/Net/DnsResponseCode.csIntroduces DnsResponseCode enum
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.csImplements Windows PAL via DnsQueryEx, record parsing, cancellation, glue, TTL extraction
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Unsupported.csAdds non-Windows PNSE PAL stubs
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverOptions.csAdds options type for custom server selection
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.csAdds instance-based resolver API + telemetry wrapping
src/libraries/System.Net.NameResolution/src/System/Net/DnsRecords.csAdds record structs (Address/Srv/Mx/Txt/CName/Ptr/Ns)
src/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.csAdds new static Dns.Resolve* APIs backed by a default resolver
src/libraries/System.Net.NameResolution/src/System/Net/Dns.csMakes Dns partial to host the new Dns.Resolve* partial
src/libraries/System.Net.NameResolution/src/System.Net.NameResolution.csprojWires new sources and Windows Dnsapi interop into the build
src/libraries/System.Net.NameResolution/src/Resources/Strings.resxAdds SR string for unsupported custom DNS ports
src/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.csAdds new public API contract entries
src/libraries/Common/src/Interop/Windows/Interop.Libraries.csAdds Libraries.Dnsapi constant
src/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsTypes.csAdds DnsQueryEx/DNS_RECORD-related structs/constants
src/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsApi.csAdds LibraryImport declarations for DnsQueryEx/DnsCancelQuery/DnsFree
Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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Comment threadsrc/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsApi.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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First pass through.
Just curious, will there be a way to opt-in to using the managed implementation even on Windows, or would there be no reason to want to do that anyway?
Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs
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 public System.Net.DnsResult<System.Net.AddressRecord> ResolveAddresses(string name) { throw null; }
 public System.Net.DnsResult<System.Net.AddressRecord> ResolveAddresses(string name, System.Net.Sockets.AddressFamily addressFamily) { throw null; }
 public System.Net.DnsResult<System.Net.SrvRecord> ResolveSrv(string name) { throw null; }
 public System.Net.DnsResult<System.Net.MxRecord> ResolveMx(string name) { throw null; }
 public System.Net.DnsResult<System.Net.TxtRecord> ResolveTxt(string name) { throw null; }
 public System.Net.DnsResult<System.Net.CNameRecord> ResolveCName(string name) { throw null; }
 public System.Net.DnsResult<System.Net.PtrRecord> ResolvePtr(string name) { throw null; }
 public System.Net.DnsResult<System.Net.NsRecord> ResolveNs(string name) { throw null; }
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publicSystem.Net.DnsResult<System.Net.AddressRecord>ResolveAddresses(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.AddressRecord>ResolveAddresses(stringname,System.Net.Sockets.AddressFamilyaddressFamily){thrownull;}
publicSystem.Net.DnsResult<System.Net.SrvRecord>ResolveSrv(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.MxRecord>ResolveMx(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.TxtRecord>ResolveTxt(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.CNameRecord>ResolveCName(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.PtrRecord>ResolvePtr(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.NsRecord>ResolveNs(stringname){thrownull;}
I think we should talk about this with the team :)
My stance continues to be that exposing sync APIs here is a mistake, especially if we have real plans to eventually add support for resolution over HTTPS/QUIC.

The fact that e.g. Resolve silently has 2x the latency compared to the async variant makes the argument that we need sync APIs for perf wrong IMO.
@rzikmrzikmJun 17, 2026

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I am also not entirely happy with having synchronous versions as well, we can bring it in a team discussion and push back if more of us feel strongly about this :)
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Pull request overview
Copilot reviewed 21 out of 21 changed files in this pull request and generated 4 comments.
Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/LoopbackDnsServer.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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I've worked with DNS apis here before so here's what I wanted to note:
  • This needs to account for this pre Windows 11 bug and fallback to DnsQueryW for affected cases (it's only when DnsQueryEx would return synchronously).
  • IIRC DnsQueryEx is also broken under impersonization, so this needs identical handling like the GetAddrInfoW handling today has.
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Pull request overview
Copilot reviewed 21 out of 21 changed files in this pull request and generated 6 comments.
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsTypes.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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 [OuterLoop("Binds the loopback DNS port 53 and issues real DnsQueryEx calls.")]
 [Collection(nameof(DisableParallelization))]
 [PlatformSpecific(TestPlatforms.Windows)]
 public class DnsResolverLoopbackTest : IClassFixture<WindowsLoopbackServer>
 {
 private static DnsResolver CreateResolver(LoopbackDnsServer server)
 => new DnsResolver(new DnsResolverOptions { Servers = { server.EndPoint } });
Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs
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@rzikmrzikm
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@rzikm
Implement DnsResolver for Windows (#129845)
e6e4d8d
Replacement for #129302 (thanks,
`gh stack submit` 😠)
Implements the API approved in
#19443:
New Dns.Resolve*[Async] static methods for
A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
New DnsResolver / DnsResolverOptions for instance-based resolution with
optional custom DNS servers.
Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord,
PtrRecord, NsRecord.
DnsResponseCode enum and DnsResult envelope carrying ResponseCode,
Records, and NegativeCacheTtl.
Windows implementation uses DnsQueryEx. Non-Windows platforms get
PlatformNotSupportedException stubs pending follow-up implementations
(splitting to multiple stacked PRs for easier review).
---------
Co-authored-by: rzikm <rzikm@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
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@rzikm
@eiriktsarpalis
Implement DnsResolver for Windows (#129845)
1afd7a2
Replacement for #129302 (thanks,
`gh stack submit` 😠)
Implements the API approved in
#19443:
New Dns.Resolve*[Async] static methods for
A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
New DnsResolver / DnsResolverOptions for instance-based resolution with
optional custom DNS servers.
Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord,
PtrRecord, NsRecord.
DnsResponseCode enum and DnsResult envelope carrying ResponseCode,
Records, and NegativeCacheTtl.
Windows implementation uses DnsQueryEx. Non-Windows platforms get
PlatformNotSupportedException stubs pending follow-up implementations
(splitting to multiple stacked PRs for easier review).
---------
Co-authored-by: rzikm <rzikm@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
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// Auto-enable theater mode on YouTube
(function() {
function tryTheater() {
var btn = document.querySelector('button[aria-label="Theater mode"], ytd-player #player button[title="Theater mode"]');
if (btn && !btn.classList.contains('activated')) {
btn.click();
}
}
// Try immediately
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if (location.href !== lastUrl) {
lastUrl = location.href;
setTimeout(tryTheater, 500);
}
}, 1000);
// Also try on player load
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observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

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Implement DnsResolver for Windows - #129302
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Implements the API approved in #19443:
  • New Dns.Resolve*[Async] static methods for A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
  • New DnsResolver / DnsResolverOptions for instance-based resolution with optional custom DNS servers.
  • Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord, PtrRecord, NsRecord.
  • DnsResponseCode enum and DnsResult envelope carrying ResponseCode, Records, and NegativeCacheTtl.
Windows implementation uses DnsQueryEx. Non-Windows platforms get PlatformNotSupportedException stubs pending follow-up implementations (splitting to multiple stacked PRs for easier review).
CopilotAI
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Tagging subscribers to this area: @karelz, @dotnet/ncl

See info in area-owners.md if you want to be subscribed.
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Pull request overview
This PR adds a new DNS query API surface area to System.Net.NameResolution (new Dns.Resolve* static entry points plus an instance-based DnsResolver), and implements the Windows PAL using DnsQueryEx. It also introduces functional tests, including deterministic loopback-server-driven tests for record parsing/handling.
Changes:
  • Adds new public APIs: Dns.Resolve* (A/AAAA/SRV/MX/TXT/CNAME/PTR/NS), DnsResolver, DnsResolverOptions, record structs, DnsResult<T>, and DnsResponseCode.
  • Implements Windows DNS querying/parsing via DnsQueryEx (sync + async paths), plus non-Windows PNSE stubs.
  • Adds functional tests (outer-loop network tests + loopback DNS server tests) and extends NameResolution telemetry to handle string[] answers.
Reviewed changes
Copilot reviewed 21 out of 21 changed files in this pull request and generated 18 comments.
Show a summary per file
FileDescription
src/libraries/System.Net.NameResolution/tests/FunctionalTests/System.Net.NameResolution.Functional.Tests.csprojAdds new functional test sources to the project
src/libraries/System.Net.NameResolution/tests/FunctionalTests/LoopbackDnsServer.csAdds an in-process UDP/TCP loopback DNS server for deterministic tests
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResponseBuilder.csAdds a fluent builder for DNS response bytes used by loopback tests
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverTest.csAdds outer-loop functional tests for the new APIs (real DNS)
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.csAdds deterministic loopback-server-driven tests for parsing/behavior/metrics
src/libraries/System.Net.NameResolution/src/System/Net/NameResolutionTelemetry.csExtends telemetry answer handling to support string[]
src/libraries/System.Net.NameResolution/src/System/Net/DnsResult.csIntroduces DnsResult<T> envelope type
src/libraries/System.Net.NameResolution/src/System/Net/DnsResponseCode.csIntroduces DnsResponseCode enum
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.csImplements Windows PAL via DnsQueryEx, record parsing, cancellation, glue, TTL extraction
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Unsupported.csAdds non-Windows PNSE PAL stubs
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverOptions.csAdds options type for custom server selection
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.csAdds instance-based resolver API + telemetry wrapping
src/libraries/System.Net.NameResolution/src/System/Net/DnsRecords.csAdds record structs (Address/Srv/Mx/Txt/CName/Ptr/Ns)
src/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.csAdds new static Dns.Resolve* APIs backed by a default resolver
src/libraries/System.Net.NameResolution/src/System/Net/Dns.csMakes Dns partial to host the new Dns.Resolve* partial
src/libraries/System.Net.NameResolution/src/System.Net.NameResolution.csprojWires new sources and Windows Dnsapi interop into the build
src/libraries/System.Net.NameResolution/src/Resources/Strings.resxAdds SR string for unsupported custom DNS ports
src/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.csAdds new public API contract entries
src/libraries/Common/src/Interop/Windows/Interop.Libraries.csAdds Libraries.Dnsapi constant
src/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsTypes.csAdds DnsQueryEx/DNS_RECORD-related structs/constants
src/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsApi.csAdds LibraryImport declarations for DnsQueryEx/DnsCancelQuery/DnsFree
Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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Comment threadsrc/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsApi.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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First pass through.
Just curious, will there be a way to opt-in to using the managed implementation even on Windows, or would there be no reason to want to do that anyway?
Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs
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 public System.Net.DnsResult<System.Net.AddressRecord> ResolveAddresses(string name) { throw null; }
 public System.Net.DnsResult<System.Net.AddressRecord> ResolveAddresses(string name, System.Net.Sockets.AddressFamily addressFamily) { throw null; }
 public System.Net.DnsResult<System.Net.SrvRecord> ResolveSrv(string name) { throw null; }
 public System.Net.DnsResult<System.Net.MxRecord> ResolveMx(string name) { throw null; }
 public System.Net.DnsResult<System.Net.TxtRecord> ResolveTxt(string name) { throw null; }
 public System.Net.DnsResult<System.Net.CNameRecord> ResolveCName(string name) { throw null; }
 public System.Net.DnsResult<System.Net.PtrRecord> ResolvePtr(string name) { throw null; }
 public System.Net.DnsResult<System.Net.NsRecord> ResolveNs(string name) { throw null; }
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Suggested change

publicSystem.Net.DnsResult<System.Net.AddressRecord>ResolveAddresses(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.AddressRecord>ResolveAddresses(stringname,System.Net.Sockets.AddressFamilyaddressFamily){thrownull;}
publicSystem.Net.DnsResult<System.Net.SrvRecord>ResolveSrv(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.MxRecord>ResolveMx(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.TxtRecord>ResolveTxt(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.CNameRecord>ResolveCName(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.PtrRecord>ResolvePtr(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.NsRecord>ResolveNs(stringname){thrownull;}
I think we should talk about this with the team :)
My stance continues to be that exposing sync APIs here is a mistake, especially if we have real plans to eventually add support for resolution over HTTPS/QUIC.

The fact that e.g. Resolve silently has 2x the latency compared to the async variant makes the argument that we need sync APIs for perf wrong IMO.
@rzikmrzikmJun 17, 2026

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I am also not entirely happy with having synchronous versions as well, we can bring it in a team discussion and push back if more of us feel strongly about this :)
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Pull request overview
Copilot reviewed 21 out of 21 changed files in this pull request and generated 4 comments.
Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/LoopbackDnsServer.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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@MichalPetryka
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I've worked with DNS apis here before so here's what I wanted to note:
  • This needs to account for this pre Windows 11 bug and fallback to DnsQueryW for affected cases (it's only when DnsQueryEx would return synchronously).
  • IIRC DnsQueryEx is also broken under impersonization, so this needs identical handling like the GetAddrInfoW handling today has.
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Pull request overview
Copilot reviewed 21 out of 21 changed files in this pull request and generated 6 comments.
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsTypes.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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Comment on lines

+48
 to 
+54

 [OuterLoop("Binds the loopback DNS port 53 and issues real DnsQueryEx calls.")]
 [Collection(nameof(DisableParallelization))]
 [PlatformSpecific(TestPlatforms.Windows)]
 public class DnsResolverLoopbackTest : IClassFixture<WindowsLoopbackServer>
 {
 private static DnsResolver CreateResolver(LoopbackDnsServer server)
 => new DnsResolver(new DnsResolverOptions { Servers = { server.EndPoint } });
Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs
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Copilot wasn't able to review any files in this pull request.
@rzikmrzikm
mentioned this pull request
Jun 25, 2026
 Merged

rzikm added a commit
that referenced
this pull request
Jul 8, 2026
@rzikm
Implement DnsResolver for Windows (#129845)
e6e4d8d
Replacement for #129302 (thanks,
`gh stack submit` 😠)
Implements the API approved in
#19443:
New Dns.Resolve*[Async] static methods for
A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
New DnsResolver / DnsResolverOptions for instance-based resolution with
optional custom DNS servers.
Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord,
PtrRecord, NsRecord.
DnsResponseCode enum and DnsResult envelope carrying ResponseCode,
Records, and NegativeCacheTtl.
Windows implementation uses DnsQueryEx. Non-Windows platforms get
PlatformNotSupportedException stubs pending follow-up implementations
(splitting to multiple stacked PRs for easier review).
---------
Co-authored-by: rzikm <rzikm@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
@MihuBotMihuBot
mentioned this pull request
Jul 14, 2026

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eiriktsarpalis pushed a commit
that referenced
this pull request
Jul 15, 2026
@rzikm
@eiriktsarpalis
Implement DnsResolver for Windows (#129845)
1afd7a2
Replacement for #129302 (thanks,
`gh stack submit` 😠)
Implements the API approved in
#19443:
New Dns.Resolve*[Async] static methods for
A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
New DnsResolver / DnsResolverOptions for instance-based resolution with
optional custom DNS servers.
Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord,
PtrRecord, NsRecord.
DnsResponseCode enum and DnsResult envelope carrying ResponseCode,
Records, and NegativeCacheTtl.
Windows implementation uses DnsQueryEx. Non-Windows platforms get
PlatformNotSupportedException stubs pending follow-up implementations
(splitting to multiple stacked PRs for easier review).
---------
Co-authored-by: rzikm <rzikm@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
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Implement DnsResolver for Windows - #129302
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Implements the API approved in #19443:
  • New Dns.Resolve*[Async] static methods for A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
  • New DnsResolver / DnsResolverOptions for instance-based resolution with optional custom DNS servers.
  • Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord, PtrRecord, NsRecord.
  • DnsResponseCode enum and DnsResult envelope carrying ResponseCode, Records, and NegativeCacheTtl.
Windows implementation uses DnsQueryEx. Non-Windows platforms get PlatformNotSupportedException stubs pending follow-up implementations (splitting to multiple stacked PRs for easier review).
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Pull request overview
This PR adds a new DNS query API surface area to System.Net.NameResolution (new Dns.Resolve* static entry points plus an instance-based DnsResolver), and implements the Windows PAL using DnsQueryEx. It also introduces functional tests, including deterministic loopback-server-driven tests for record parsing/handling.
Changes:
  • Adds new public APIs: Dns.Resolve* (A/AAAA/SRV/MX/TXT/CNAME/PTR/NS), DnsResolver, DnsResolverOptions, record structs, DnsResult<T>, and DnsResponseCode.
  • Implements Windows DNS querying/parsing via DnsQueryEx (sync + async paths), plus non-Windows PNSE stubs.
  • Adds functional tests (outer-loop network tests + loopback DNS server tests) and extends NameResolution telemetry to handle string[] answers.
Reviewed changes
Copilot reviewed 21 out of 21 changed files in this pull request and generated 18 comments.
Show a summary per file
FileDescription
src/libraries/System.Net.NameResolution/tests/FunctionalTests/System.Net.NameResolution.Functional.Tests.csprojAdds new functional test sources to the project
src/libraries/System.Net.NameResolution/tests/FunctionalTests/LoopbackDnsServer.csAdds an in-process UDP/TCP loopback DNS server for deterministic tests
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResponseBuilder.csAdds a fluent builder for DNS response bytes used by loopback tests
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverTest.csAdds outer-loop functional tests for the new APIs (real DNS)
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.csAdds deterministic loopback-server-driven tests for parsing/behavior/metrics
src/libraries/System.Net.NameResolution/src/System/Net/NameResolutionTelemetry.csExtends telemetry answer handling to support string[]
src/libraries/System.Net.NameResolution/src/System/Net/DnsResult.csIntroduces DnsResult<T> envelope type
src/libraries/System.Net.NameResolution/src/System/Net/DnsResponseCode.csIntroduces DnsResponseCode enum
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.csImplements Windows PAL via DnsQueryEx, record parsing, cancellation, glue, TTL extraction
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Unsupported.csAdds non-Windows PNSE PAL stubs
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverOptions.csAdds options type for custom server selection
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.csAdds instance-based resolver API + telemetry wrapping
src/libraries/System.Net.NameResolution/src/System/Net/DnsRecords.csAdds record structs (Address/Srv/Mx/Txt/CName/Ptr/Ns)
src/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.csAdds new static Dns.Resolve* APIs backed by a default resolver
src/libraries/System.Net.NameResolution/src/System/Net/Dns.csMakes Dns partial to host the new Dns.Resolve* partial
src/libraries/System.Net.NameResolution/src/System.Net.NameResolution.csprojWires new sources and Windows Dnsapi interop into the build
src/libraries/System.Net.NameResolution/src/Resources/Strings.resxAdds SR string for unsupported custom DNS ports
src/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.csAdds new public API contract entries
src/libraries/Common/src/Interop/Windows/Interop.Libraries.csAdds Libraries.Dnsapi constant
src/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsTypes.csAdds DnsQueryEx/DNS_RECORD-related structs/constants
src/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsApi.csAdds LibraryImport declarations for DnsQueryEx/DnsCancelQuery/DnsFree
Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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Comment threadsrc/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsApi.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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First pass through.
Just curious, will there be a way to opt-in to using the managed implementation even on Windows, or would there be no reason to want to do that anyway?
Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs
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 public System.Net.DnsResult<System.Net.AddressRecord> ResolveAddresses(string name) { throw null; }
 public System.Net.DnsResult<System.Net.AddressRecord> ResolveAddresses(string name, System.Net.Sockets.AddressFamily addressFamily) { throw null; }
 public System.Net.DnsResult<System.Net.SrvRecord> ResolveSrv(string name) { throw null; }
 public System.Net.DnsResult<System.Net.MxRecord> ResolveMx(string name) { throw null; }
 public System.Net.DnsResult<System.Net.TxtRecord> ResolveTxt(string name) { throw null; }
 public System.Net.DnsResult<System.Net.CNameRecord> ResolveCName(string name) { throw null; }
 public System.Net.DnsResult<System.Net.PtrRecord> ResolvePtr(string name) { throw null; }
 public System.Net.DnsResult<System.Net.NsRecord> ResolveNs(string name) { throw null; }
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Suggested change

publicSystem.Net.DnsResult<System.Net.AddressRecord>ResolveAddresses(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.AddressRecord>ResolveAddresses(stringname,System.Net.Sockets.AddressFamilyaddressFamily){thrownull;}
publicSystem.Net.DnsResult<System.Net.SrvRecord>ResolveSrv(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.MxRecord>ResolveMx(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.TxtRecord>ResolveTxt(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.CNameRecord>ResolveCName(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.PtrRecord>ResolvePtr(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.NsRecord>ResolveNs(stringname){thrownull;}
I think we should talk about this with the team :)
My stance continues to be that exposing sync APIs here is a mistake, especially if we have real plans to eventually add support for resolution over HTTPS/QUIC.

The fact that e.g. Resolve silently has 2x the latency compared to the async variant makes the argument that we need sync APIs for perf wrong IMO.
@rzikmrzikmJun 17, 2026

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I am also not entirely happy with having synchronous versions as well, we can bring it in a team discussion and push back if more of us feel strongly about this :)
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Pull request overview
Copilot reviewed 21 out of 21 changed files in this pull request and generated 4 comments.
Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/LoopbackDnsServer.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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I've worked with DNS apis here before so here's what I wanted to note:
  • This needs to account for this pre Windows 11 bug and fallback to DnsQueryW for affected cases (it's only when DnsQueryEx would return synchronously).
  • IIRC DnsQueryEx is also broken under impersonization, so this needs identical handling like the GetAddrInfoW handling today has.
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Pull request overview
Copilot reviewed 21 out of 21 changed files in this pull request and generated 6 comments.
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsTypes.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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 [OuterLoop("Binds the loopback DNS port 53 and issues real DnsQueryEx calls.")]
 [Collection(nameof(DisableParallelization))]
 [PlatformSpecific(TestPlatforms.Windows)]
 public class DnsResolverLoopbackTest : IClassFixture<WindowsLoopbackServer>
 {
 private static DnsResolver CreateResolver(LoopbackDnsServer server)
 => new DnsResolver(new DnsResolverOptions { Servers = { server.EndPoint } });
Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs
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Copilot wasn't able to review any files in this pull request.
@rzikmrzikm
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@rzikm
Implement DnsResolver for Windows (#129845)
e6e4d8d
Replacement for #129302 (thanks,
`gh stack submit` 😠)
Implements the API approved in
#19443:
New Dns.Resolve*[Async] static methods for
A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
New DnsResolver / DnsResolverOptions for instance-based resolution with
optional custom DNS servers.
Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord,
PtrRecord, NsRecord.
DnsResponseCode enum and DnsResult envelope carrying ResponseCode,
Records, and NegativeCacheTtl.
Windows implementation uses DnsQueryEx. Non-Windows platforms get
PlatformNotSupportedException stubs pending follow-up implementations
(splitting to multiple stacked PRs for easier review).
---------
Co-authored-by: rzikm <rzikm@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
@MihuBotMihuBot
mentioned this pull request
Jul 14, 2026

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eiriktsarpalis pushed a commit
that referenced
this pull request
Jul 15, 2026
@rzikm
@eiriktsarpalis
Implement DnsResolver for Windows (#129845)
1afd7a2
Replacement for #129302 (thanks,
`gh stack submit` 😠)
Implements the API approved in
#19443:
New Dns.Resolve*[Async] static methods for
A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
New DnsResolver / DnsResolverOptions for instance-based resolution with
optional custom DNS servers.
Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord,
PtrRecord, NsRecord.
DnsResponseCode enum and DnsResult envelope carrying ResponseCode,
Records, and NegativeCacheTtl.
Windows implementation uses DnsQueryEx. Non-Windows platforms get
PlatformNotSupportedException stubs pending follow-up implementations
(splitting to multiple stacked PRs for easier review).
---------
Co-authored-by: rzikm <rzikm@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
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Implement DnsResolver for Windows - #129302
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Implements the API approved in #19443:
  • New Dns.Resolve*[Async] static methods for A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
  • New DnsResolver / DnsResolverOptions for instance-based resolution with optional custom DNS servers.
  • Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord, PtrRecord, NsRecord.
  • DnsResponseCode enum and DnsResult envelope carrying ResponseCode, Records, and NegativeCacheTtl.
Windows implementation uses DnsQueryEx. Non-Windows platforms get PlatformNotSupportedException stubs pending follow-up implementations (splitting to multiple stacked PRs for easier review).
CopilotAI
review requested due to automatic review settings
June 11, 2026 16:57
@rzikm
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Tagging subscribers to this area: @karelz, @dotnet/ncl

See info in area-owners.md if you want to be subscribed.
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Pull request overview
This PR adds a new DNS query API surface area to System.Net.NameResolution (new Dns.Resolve* static entry points plus an instance-based DnsResolver), and implements the Windows PAL using DnsQueryEx. It also introduces functional tests, including deterministic loopback-server-driven tests for record parsing/handling.
Changes:
  • Adds new public APIs: Dns.Resolve* (A/AAAA/SRV/MX/TXT/CNAME/PTR/NS), DnsResolver, DnsResolverOptions, record structs, DnsResult<T>, and DnsResponseCode.
  • Implements Windows DNS querying/parsing via DnsQueryEx (sync + async paths), plus non-Windows PNSE stubs.
  • Adds functional tests (outer-loop network tests + loopback DNS server tests) and extends NameResolution telemetry to handle string[] answers.
Reviewed changes
Copilot reviewed 21 out of 21 changed files in this pull request and generated 18 comments.
Show a summary per file
FileDescription
src/libraries/System.Net.NameResolution/tests/FunctionalTests/System.Net.NameResolution.Functional.Tests.csprojAdds new functional test sources to the project
src/libraries/System.Net.NameResolution/tests/FunctionalTests/LoopbackDnsServer.csAdds an in-process UDP/TCP loopback DNS server for deterministic tests
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResponseBuilder.csAdds a fluent builder for DNS response bytes used by loopback tests
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverTest.csAdds outer-loop functional tests for the new APIs (real DNS)
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.csAdds deterministic loopback-server-driven tests for parsing/behavior/metrics
src/libraries/System.Net.NameResolution/src/System/Net/NameResolutionTelemetry.csExtends telemetry answer handling to support string[]
src/libraries/System.Net.NameResolution/src/System/Net/DnsResult.csIntroduces DnsResult<T> envelope type
src/libraries/System.Net.NameResolution/src/System/Net/DnsResponseCode.csIntroduces DnsResponseCode enum
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.csImplements Windows PAL via DnsQueryEx, record parsing, cancellation, glue, TTL extraction
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Unsupported.csAdds non-Windows PNSE PAL stubs
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverOptions.csAdds options type for custom server selection
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.csAdds instance-based resolver API + telemetry wrapping
src/libraries/System.Net.NameResolution/src/System/Net/DnsRecords.csAdds record structs (Address/Srv/Mx/Txt/CName/Ptr/Ns)
src/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.csAdds new static Dns.Resolve* APIs backed by a default resolver
src/libraries/System.Net.NameResolution/src/System/Net/Dns.csMakes Dns partial to host the new Dns.Resolve* partial
src/libraries/System.Net.NameResolution/src/System.Net.NameResolution.csprojWires new sources and Windows Dnsapi interop into the build
src/libraries/System.Net.NameResolution/src/Resources/Strings.resxAdds SR string for unsupported custom DNS ports
src/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.csAdds new public API contract entries
src/libraries/Common/src/Interop/Windows/Interop.Libraries.csAdds Libraries.Dnsapi constant
src/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsTypes.csAdds DnsQueryEx/DNS_RECORD-related structs/constants
src/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsApi.csAdds LibraryImport declarations for DnsQueryEx/DnsCancelQuery/DnsFree
Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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Comment threadsrc/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsApi.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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MihaZupan
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First pass through.
Just curious, will there be a way to opt-in to using the managed implementation even on Windows, or would there be no reason to want to do that anyway?
Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs
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 public System.Net.DnsResult<System.Net.AddressRecord> ResolveAddresses(string name) { throw null; }
 public System.Net.DnsResult<System.Net.AddressRecord> ResolveAddresses(string name, System.Net.Sockets.AddressFamily addressFamily) { throw null; }
 public System.Net.DnsResult<System.Net.SrvRecord> ResolveSrv(string name) { throw null; }
 public System.Net.DnsResult<System.Net.MxRecord> ResolveMx(string name) { throw null; }
 public System.Net.DnsResult<System.Net.TxtRecord> ResolveTxt(string name) { throw null; }
 public System.Net.DnsResult<System.Net.CNameRecord> ResolveCName(string name) { throw null; }
 public System.Net.DnsResult<System.Net.PtrRecord> ResolvePtr(string name) { throw null; }
 public System.Net.DnsResult<System.Net.NsRecord> ResolveNs(string name) { throw null; }
@MihaZupanMihaZupanJun 11, 2026

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Suggested change

publicSystem.Net.DnsResult<System.Net.AddressRecord>ResolveAddresses(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.AddressRecord>ResolveAddresses(stringname,System.Net.Sockets.AddressFamilyaddressFamily){thrownull;}
publicSystem.Net.DnsResult<System.Net.SrvRecord>ResolveSrv(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.MxRecord>ResolveMx(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.TxtRecord>ResolveTxt(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.CNameRecord>ResolveCName(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.PtrRecord>ResolvePtr(stringname){thrownull;}
publicSystem.Net.DnsResult<System.Net.NsRecord>ResolveNs(stringname){thrownull;}
I think we should talk about this with the team :)
My stance continues to be that exposing sync APIs here is a mistake, especially if we have real plans to eventually add support for resolution over HTTPS/QUIC.

The fact that e.g. Resolve silently has 2x the latency compared to the async variant makes the argument that we need sync APIs for perf wrong IMO.
@rzikmrzikmJun 17, 2026

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I am also not entirely happy with having synchronous versions as well, we can bring it in a team discussion and push back if more of us feel strongly about this :)
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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Pull request overview
Copilot reviewed 21 out of 21 changed files in this pull request and generated 4 comments.
Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/LoopbackDnsServer.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/Dns.Resolve.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolver.cs
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@MichalPetryka
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I've worked with DNS apis here before so here's what I wanted to note:
  • This needs to account for this pre Windows 11 bug and fallback to DnsQueryW for affected cases (it's only when DnsQueryEx would return synchronously).
  • IIRC DnsQueryEx is also broken under impersonization, so this needs identical handling like the GetAddrInfoW handling today has.
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Pull request overview
Copilot reviewed 21 out of 21 changed files in this pull request and generated 6 comments.
Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs
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Comment threadsrc/libraries/Common/src/Interop/Windows/Dnsapi/Interop.DnsTypes.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverLoopbackTest.cs
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 [OuterLoop("Binds the loopback DNS port 53 and issues real DnsQueryEx calls.")]
 [Collection(nameof(DisableParallelization))]
 [PlatformSpecific(TestPlatforms.Windows)]
 public class DnsResolverLoopbackTest : IClassFixture<WindowsLoopbackServer>
 {
 private static DnsResolver CreateResolver(LoopbackDnsServer server)
 => new DnsResolver(new DnsResolverOptions { Servers = { server.EndPoint } });
Comment threadsrc/libraries/System.Net.NameResolution/ref/System.Net.NameResolution.cs
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Copilot wasn't able to review any files in this pull request.
@rzikmrzikm
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Jun 25, 2026
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@rzikm
Implement DnsResolver for Windows (#129845)
e6e4d8d
Replacement for #129302 (thanks,
`gh stack submit` 😠)
Implements the API approved in
#19443:
New Dns.Resolve*[Async] static methods for
A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
New DnsResolver / DnsResolverOptions for instance-based resolution with
optional custom DNS servers.
Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord,
PtrRecord, NsRecord.
DnsResponseCode enum and DnsResult envelope carrying ResponseCode,
Records, and NegativeCacheTtl.
Windows implementation uses DnsQueryEx. Non-Windows platforms get
PlatformNotSupportedException stubs pending follow-up implementations
(splitting to multiple stacked PRs for easier review).
---------
Co-authored-by: rzikm <rzikm@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
@MihuBotMihuBot
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Jul 15, 2026
@rzikm
@eiriktsarpalis
Implement DnsResolver for Windows (#129845)
1afd7a2
Replacement for #129302 (thanks,
`gh stack submit` 😠)
Implements the API approved in
#19443:
New Dns.Resolve*[Async] static methods for
A/AAAA/SRV/MX/TXT/CNAME/PTR/NS records.
New DnsResolver / DnsResolverOptions for instance-based resolution with
optional custom DNS servers.
Record types AddressRecord, SrvRecord, MxRecord, TxtRecord, CNameRecord,
PtrRecord, NsRecord.
DnsResponseCode enum and DnsResult envelope carrying ResponseCode,
Records, and NegativeCacheTtl.
Windows implementation uses DnsQueryEx. Non-Windows platforms get
PlatformNotSupportedException stubs pending follow-up implementations
(splitting to multiple stacked PRs for easier review).
---------
Co-authored-by: rzikm <rzikm@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
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