Expand Windows DNS sync-query detection for inline-completing names by Copilot · Pull Request #130411 · dotnet/runtime

Copilot · 2026-07-09T14:20:05Z

This broadens the Windows DnsResolver workaround for pre-22000 DnsQueryEx inline completion so it covers the full set of names the OS team identified as synchronously completing, not just localhost. The change keeps the existing async path for all other names and avoids the extra DNS_QUERY_NO_WIRE_QUERY probe.

Behavior
- Route these names directly through the synchronous path on affected Windows versions:
  - IP literals
  - machine hostname
  - loopback
  - localhost
  - ..DnsServers
  - ..localmachine
Implementation
- Replace the localhost-only check with a broader predicate for synchronously completing names.
- Use IPAddress.IsValid(...) for allocation-free IP literal detection.
- Compare against the current hostname without process-wide caching.
- If hostname lookup fails, fall back to the normal async path rather than introducing a new failure mode.
Regression coverage
- Expand the existing Windows regression test to cover the added synchronous-completion cases through both sync and async entry points.

if(IPAddress.IsValid(name)){returntrue;}

dotnet-policy-service · 2026-07-09T14:39:16Z

Tagging subscribers to this area: @dotnet/runtime-infrastructure
See info in area-owners.md if you want to be subscribed.

Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

Copilot

Pull request overview

This PR updates the Windows System.Net.NameResolution DnsQueryEx workaround by expanding the set of query names treated as “known to complete synchronously” on affected Windows versions, and extends the existing regression test to exercise those names through both sync/async resolver entry points.

Changes:

Replace the localhost-only fast-path with IsSynchronouslyCompletingQueryName, including IP literal detection and additional special-case names.
Route those names directly through the synchronous DnsQueryEx path when running async on pre-22000 Windows versions.
Expand the Windows regression test to cover the additional “synchronously completing” names.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs	Broaden the pre-22000 async inline-completion workaround to a wider set of names via a new predicate.
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverTest.cs	Expand the existing Windows regression test to cover the broader set of synchronously-completing names.

MichalPetryka

Should we add an assert that we never got null and a memory leak here?

…n true on hostname failure, fix test data Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

…tion test Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

rzikm · 2026-07-13T15:53:37Z

/ba-g System.Text.Json failures are unrelated

…130411)  This broadens the Windows `DnsResolver` workaround for pre-22000 `DnsQueryEx` inline completion so it covers the full set of names the OS team identified as synchronously completing, not just `localhost`. The change keeps the existing async path for all other names and avoids the extra `DNS_QUERY_NO_WIRE_QUERY` probe. - **Behavior** - Route these names directly through the synchronous path on affected Windows versions: - IP literals - machine hostname - `loopback` - `localhost` - `..DnsServers` - `..localmachine` - **Implementation** - Replace the `localhost`-only check with a broader predicate for synchronously completing names. - Use `IPAddress.IsValid(...)` for allocation-free IP literal detection. - Compare against the current hostname without process-wide caching. - If hostname lookup fails, fall back to the normal async path rather than introducing a new failure mode. - **Regression coverage** - Expand the existing Windows regression test to cover the added synchronous-completion cases through both sync and async entry points. ```csharp if (IPAddress.IsValid(name)) { return true; } ``` --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

Copilot · 2026-07-09T14:20:05Z

This broadens the Windows DnsResolver workaround for pre-22000 DnsQueryEx inline completion so it covers the full set of names the OS team identified as synchronously completing, not just localhost. The change keeps the existing async path for all other names and avoids the extra DNS_QUERY_NO_WIRE_QUERY probe.

Behavior
- Route these names directly through the synchronous path on affected Windows versions:
  - IP literals
  - machine hostname
  - loopback
  - localhost
  - ..DnsServers
  - ..localmachine
Implementation
- Replace the localhost-only check with a broader predicate for synchronously completing names.
- Use IPAddress.IsValid(...) for allocation-free IP literal detection.
- Compare against the current hostname without process-wide caching.
- If hostname lookup fails, fall back to the normal async path rather than introducing a new failure mode.
Regression coverage
- Expand the existing Windows regression test to cover the added synchronous-completion cases through both sync and async entry points.

if(IPAddress.IsValid(name)){returntrue;}

dotnet-policy-service · 2026-07-09T14:39:16Z

Tagging subscribers to this area: @dotnet/runtime-infrastructure
See info in area-owners.md if you want to be subscribed.

Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

Copilot

Pull request overview

This PR updates the Windows System.Net.NameResolution DnsQueryEx workaround by expanding the set of query names treated as “known to complete synchronously” on affected Windows versions, and extends the existing regression test to exercise those names through both sync/async resolver entry points.

Changes:

Replace the localhost-only fast-path with IsSynchronouslyCompletingQueryName, including IP literal detection and additional special-case names.
Route those names directly through the synchronous DnsQueryEx path when running async on pre-22000 Windows versions.
Expand the Windows regression test to cover the additional “synchronously completing” names.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs	Broaden the pre-22000 async inline-completion workaround to a wider set of names via a new predicate.
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverTest.cs	Expand the existing Windows regression test to cover the broader set of synchronously-completing names.

MichalPetryka

Should we add an assert that we never got null and a memory leak here?

…n true on hostname failure, fix test data Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

…tion test Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

rzikm · 2026-07-13T15:53:37Z

/ba-g System.Text.Json failures are unrelated

…130411)  This broadens the Windows `DnsResolver` workaround for pre-22000 `DnsQueryEx` inline completion so it covers the full set of names the OS team identified as synchronously completing, not just `localhost`. The change keeps the existing async path for all other names and avoids the extra `DNS_QUERY_NO_WIRE_QUERY` probe. - **Behavior** - Route these names directly through the synchronous path on affected Windows versions: - IP literals - machine hostname - `loopback` - `localhost` - `..DnsServers` - `..localmachine` - **Implementation** - Replace the `localhost`-only check with a broader predicate for synchronously completing names. - Use `IPAddress.IsValid(...)` for allocation-free IP literal detection. - Compare against the current hostname without process-wide caching. - If hostname lookup fails, fall back to the normal async path rather than introducing a new failure mode. - **Regression coverage** - Expand the existing Windows regression test to cover the added synchronous-completion cases through both sync and async entry points. ```csharp if (IPAddress.IsValid(name)) { return true; } ``` --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

Copilot · 2026-07-09T14:20:05Z

This broadens the Windows DnsResolver workaround for pre-22000 DnsQueryEx inline completion so it covers the full set of names the OS team identified as synchronously completing, not just localhost. The change keeps the existing async path for all other names and avoids the extra DNS_QUERY_NO_WIRE_QUERY probe.

Behavior
- Route these names directly through the synchronous path on affected Windows versions:
  - IP literals
  - machine hostname
  - loopback
  - localhost
  - ..DnsServers
  - ..localmachine
Implementation
- Replace the localhost-only check with a broader predicate for synchronously completing names.
- Use IPAddress.IsValid(...) for allocation-free IP literal detection.
- Compare against the current hostname without process-wide caching.
- If hostname lookup fails, fall back to the normal async path rather than introducing a new failure mode.
Regression coverage
- Expand the existing Windows regression test to cover the added synchronous-completion cases through both sync and async entry points.

if(IPAddress.IsValid(name)){returntrue;}

dotnet-policy-service · 2026-07-09T14:39:16Z

Tagging subscribers to this area: @dotnet/runtime-infrastructure
See info in area-owners.md if you want to be subscribed.

Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

Copilot

Pull request overview

This PR updates the Windows System.Net.NameResolution DnsQueryEx workaround by expanding the set of query names treated as “known to complete synchronously” on affected Windows versions, and extends the existing regression test to exercise those names through both sync/async resolver entry points.

Changes:

Replace the localhost-only fast-path with IsSynchronouslyCompletingQueryName, including IP literal detection and additional special-case names.
Route those names directly through the synchronous DnsQueryEx path when running async on pre-22000 Windows versions.
Expand the Windows regression test to cover the additional “synchronously completing” names.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs	Broaden the pre-22000 async inline-completion workaround to a wider set of names via a new predicate.
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverTest.cs	Expand the existing Windows regression test to cover the broader set of synchronously-completing names.

MichalPetryka

Should we add an assert that we never got null and a memory leak here?

…n true on hostname failure, fix test data Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

…tion test Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

rzikm · 2026-07-13T15:53:37Z

/ba-g System.Text.Json failures are unrelated

…130411)  This broadens the Windows `DnsResolver` workaround for pre-22000 `DnsQueryEx` inline completion so it covers the full set of names the OS team identified as synchronously completing, not just `localhost`. The change keeps the existing async path for all other names and avoids the extra `DNS_QUERY_NO_WIRE_QUERY` probe. - **Behavior** - Route these names directly through the synchronous path on affected Windows versions: - IP literals - machine hostname - `loopback` - `localhost` - `..DnsServers` - `..localmachine` - **Implementation** - Replace the `localhost`-only check with a broader predicate for synchronously completing names. - Use `IPAddress.IsValid(...)` for allocation-free IP literal detection. - Compare against the current hostname without process-wide caching. - If hostname lookup fails, fall back to the normal async path rather than introducing a new failure mode. - **Regression coverage** - Expand the existing Windows regression test to cover the added synchronous-completion cases through both sync and async entry points. ```csharp if (IPAddress.IsValid(name)) { return true; } ``` --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

Copilot · 2026-07-09T14:20:05Z

This broadens the Windows DnsResolver workaround for pre-22000 DnsQueryEx inline completion so it covers the full set of names the OS team identified as synchronously completing, not just localhost. The change keeps the existing async path for all other names and avoids the extra DNS_QUERY_NO_WIRE_QUERY probe.

Behavior
- Route these names directly through the synchronous path on affected Windows versions:
  - IP literals
  - machine hostname
  - loopback
  - localhost
  - ..DnsServers
  - ..localmachine
Implementation
- Replace the localhost-only check with a broader predicate for synchronously completing names.
- Use IPAddress.IsValid(...) for allocation-free IP literal detection.
- Compare against the current hostname without process-wide caching.
- If hostname lookup fails, fall back to the normal async path rather than introducing a new failure mode.
Regression coverage
- Expand the existing Windows regression test to cover the added synchronous-completion cases through both sync and async entry points.

if(IPAddress.IsValid(name)){returntrue;}

dotnet-policy-service · 2026-07-09T14:39:16Z

Tagging subscribers to this area: @dotnet/runtime-infrastructure
See info in area-owners.md if you want to be subscribed.

Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

Copilot

Pull request overview

This PR updates the Windows System.Net.NameResolution DnsQueryEx workaround by expanding the set of query names treated as “known to complete synchronously” on affected Windows versions, and extends the existing regression test to exercise those names through both sync/async resolver entry points.

Changes:

Replace the localhost-only fast-path with IsSynchronouslyCompletingQueryName, including IP literal detection and additional special-case names.
Route those names directly through the synchronous DnsQueryEx path when running async on pre-22000 Windows versions.
Expand the Windows regression test to cover the additional “synchronously completing” names.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs	Broaden the pre-22000 async inline-completion workaround to a wider set of names via a new predicate.
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverTest.cs	Expand the existing Windows regression test to cover the broader set of synchronously-completing names.

MichalPetryka

Should we add an assert that we never got null and a memory leak here?

…n true on hostname failure, fix test data Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

…tion test Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

rzikm · 2026-07-13T15:53:37Z

/ba-g System.Text.Json failures are unrelated

…130411)  This broadens the Windows `DnsResolver` workaround for pre-22000 `DnsQueryEx` inline completion so it covers the full set of names the OS team identified as synchronously completing, not just `localhost`. The change keeps the existing async path for all other names and avoids the extra `DNS_QUERY_NO_WIRE_QUERY` probe. - **Behavior** - Route these names directly through the synchronous path on affected Windows versions: - IP literals - machine hostname - `loopback` - `localhost` - `..DnsServers` - `..localmachine` - **Implementation** - Replace the `localhost`-only check with a broader predicate for synchronously completing names. - Use `IPAddress.IsValid(...)` for allocation-free IP literal detection. - Compare against the current hostname without process-wide caching. - If hostname lookup fails, fall back to the normal async path rather than introducing a new failure mode. - **Regression coverage** - Expand the existing Windows regression test to cover the added synchronous-completion cases through both sync and async entry points. ```csharp if (IPAddress.IsValid(name)) { return true; } ``` --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

Copilot · 2026-07-09T14:20:05Z

This broadens the Windows DnsResolver workaround for pre-22000 DnsQueryEx inline completion so it covers the full set of names the OS team identified as synchronously completing, not just localhost. The change keeps the existing async path for all other names and avoids the extra DNS_QUERY_NO_WIRE_QUERY probe.

Behavior
- Route these names directly through the synchronous path on affected Windows versions:
  - IP literals
  - machine hostname
  - loopback
  - localhost
  - ..DnsServers
  - ..localmachine
Implementation
- Replace the localhost-only check with a broader predicate for synchronously completing names.
- Use IPAddress.IsValid(...) for allocation-free IP literal detection.
- Compare against the current hostname without process-wide caching.
- If hostname lookup fails, fall back to the normal async path rather than introducing a new failure mode.
Regression coverage
- Expand the existing Windows regression test to cover the added synchronous-completion cases through both sync and async entry points.

if(IPAddress.IsValid(name)){returntrue;}

dotnet-policy-service · 2026-07-09T14:39:16Z

Tagging subscribers to this area: @dotnet/runtime-infrastructure
See info in area-owners.md if you want to be subscribed.

Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

Copilot

Pull request overview

This PR updates the Windows System.Net.NameResolution DnsQueryEx workaround by expanding the set of query names treated as “known to complete synchronously” on affected Windows versions, and extends the existing regression test to exercise those names through both sync/async resolver entry points.

Changes:

Replace the localhost-only fast-path with IsSynchronouslyCompletingQueryName, including IP literal detection and additional special-case names.
Route those names directly through the synchronous DnsQueryEx path when running async on pre-22000 Windows versions.
Expand the Windows regression test to cover the additional “synchronously completing” names.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs	Broaden the pre-22000 async inline-completion workaround to a wider set of names via a new predicate.
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverTest.cs	Expand the existing Windows regression test to cover the broader set of synchronously-completing names.

MichalPetryka

Should we add an assert that we never got null and a memory leak here?

…n true on hostname failure, fix test data Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

…tion test Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

rzikm · 2026-07-13T15:53:37Z

/ba-g System.Text.Json failures are unrelated

…130411)  This broadens the Windows `DnsResolver` workaround for pre-22000 `DnsQueryEx` inline completion so it covers the full set of names the OS team identified as synchronously completing, not just `localhost`. The change keeps the existing async path for all other names and avoids the extra `DNS_QUERY_NO_WIRE_QUERY` probe. - **Behavior** - Route these names directly through the synchronous path on affected Windows versions: - IP literals - machine hostname - `loopback` - `localhost` - `..DnsServers` - `..localmachine` - **Implementation** - Replace the `localhost`-only check with a broader predicate for synchronously completing names. - Use `IPAddress.IsValid(...)` for allocation-free IP literal detection. - Compare against the current hostname without process-wide caching. - If hostname lookup fails, fall back to the normal async path rather than introducing a new failure mode. - **Regression coverage** - Expand the existing Windows regression test to cover the added synchronous-completion cases through both sync and async entry points. ```csharp if (IPAddress.IsValid(name)) { return true; } ``` --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

Copilot · 2026-07-09T14:20:05Z

This broadens the Windows DnsResolver workaround for pre-22000 DnsQueryEx inline completion so it covers the full set of names the OS team identified as synchronously completing, not just localhost. The change keeps the existing async path for all other names and avoids the extra DNS_QUERY_NO_WIRE_QUERY probe.

Behavior
- Route these names directly through the synchronous path on affected Windows versions:
  - IP literals
  - machine hostname
  - loopback
  - localhost
  - ..DnsServers
  - ..localmachine
Implementation
- Replace the localhost-only check with a broader predicate for synchronously completing names.
- Use IPAddress.IsValid(...) for allocation-free IP literal detection.
- Compare against the current hostname without process-wide caching.
- If hostname lookup fails, fall back to the normal async path rather than introducing a new failure mode.
Regression coverage
- Expand the existing Windows regression test to cover the added synchronous-completion cases through both sync and async entry points.

if(IPAddress.IsValid(name)){returntrue;}

dotnet-policy-service · 2026-07-09T14:39:16Z

Tagging subscribers to this area: @dotnet/runtime-infrastructure
See info in area-owners.md if you want to be subscribed.

Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

Copilot

Pull request overview

This PR updates the Windows System.Net.NameResolution DnsQueryEx workaround by expanding the set of query names treated as “known to complete synchronously” on affected Windows versions, and extends the existing regression test to exercise those names through both sync/async resolver entry points.

Changes:

Replace the localhost-only fast-path with IsSynchronouslyCompletingQueryName, including IP literal detection and additional special-case names.
Route those names directly through the synchronous DnsQueryEx path when running async on pre-22000 Windows versions.
Expand the Windows regression test to cover the additional “synchronously completing” names.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs	Broaden the pre-22000 async inline-completion workaround to a wider set of names via a new predicate.
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverTest.cs	Expand the existing Windows regression test to cover the broader set of synchronously-completing names.

MichalPetryka

Should we add an assert that we never got null and a memory leak here?

…n true on hostname failure, fix test data Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

…tion test Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

rzikm · 2026-07-13T15:53:37Z

/ba-g System.Text.Json failures are unrelated

…130411)  This broadens the Windows `DnsResolver` workaround for pre-22000 `DnsQueryEx` inline completion so it covers the full set of names the OS team identified as synchronously completing, not just `localhost`. The change keeps the existing async path for all other names and avoids the extra `DNS_QUERY_NO_WIRE_QUERY` probe. - **Behavior** - Route these names directly through the synchronous path on affected Windows versions: - IP literals - machine hostname - `loopback` - `localhost` - `..DnsServers` - `..localmachine` - **Implementation** - Replace the `localhost`-only check with a broader predicate for synchronously completing names. - Use `IPAddress.IsValid(...)` for allocation-free IP literal detection. - Compare against the current hostname without process-wide caching. - If hostname lookup fails, fall back to the normal async path rather than introducing a new failure mode. - **Regression coverage** - Expand the existing Windows regression test to cover the added synchronous-completion cases through both sync and async entry points. ```csharp if (IPAddress.IsValid(name)) { return true; } ``` --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

Copilot · 2026-07-09T14:20:05Z

This broadens the Windows DnsResolver workaround for pre-22000 DnsQueryEx inline completion so it covers the full set of names the OS team identified as synchronously completing, not just localhost. The change keeps the existing async path for all other names and avoids the extra DNS_QUERY_NO_WIRE_QUERY probe.

Behavior
- Route these names directly through the synchronous path on affected Windows versions:
  - IP literals
  - machine hostname
  - loopback
  - localhost
  - ..DnsServers
  - ..localmachine
Implementation
- Replace the localhost-only check with a broader predicate for synchronously completing names.
- Use IPAddress.IsValid(...) for allocation-free IP literal detection.
- Compare against the current hostname without process-wide caching.
- If hostname lookup fails, fall back to the normal async path rather than introducing a new failure mode.
Regression coverage
- Expand the existing Windows regression test to cover the added synchronous-completion cases through both sync and async entry points.

if(IPAddress.IsValid(name)){returntrue;}

dotnet-policy-service · 2026-07-09T14:39:16Z

Tagging subscribers to this area: @dotnet/runtime-infrastructure
See info in area-owners.md if you want to be subscribed.

Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

Copilot

Pull request overview

This PR updates the Windows System.Net.NameResolution DnsQueryEx workaround by expanding the set of query names treated as “known to complete synchronously” on affected Windows versions, and extends the existing regression test to exercise those names through both sync/async resolver entry points.

Changes:

Replace the localhost-only fast-path with IsSynchronouslyCompletingQueryName, including IP literal detection and additional special-case names.
Route those names directly through the synchronous DnsQueryEx path when running async on pre-22000 Windows versions.
Expand the Windows regression test to cover the additional “synchronously completing” names.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs	Broaden the pre-22000 async inline-completion workaround to a wider set of names via a new predicate.
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverTest.cs	Expand the existing Windows regression test to cover the broader set of synchronously-completing names.

MichalPetryka

Should we add an assert that we never got null and a memory leak here?

…n true on hostname failure, fix test data Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

…tion test Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

rzikm · 2026-07-13T15:53:37Z

/ba-g System.Text.Json failures are unrelated

…130411)  This broadens the Windows `DnsResolver` workaround for pre-22000 `DnsQueryEx` inline completion so it covers the full set of names the OS team identified as synchronously completing, not just `localhost`. The change keeps the existing async path for all other names and avoids the extra `DNS_QUERY_NO_WIRE_QUERY` probe. - **Behavior** - Route these names directly through the synchronous path on affected Windows versions: - IP literals - machine hostname - `loopback` - `localhost` - `..DnsServers` - `..localmachine` - **Implementation** - Replace the `localhost`-only check with a broader predicate for synchronously completing names. - Use `IPAddress.IsValid(...)` for allocation-free IP literal detection. - Compare against the current hostname without process-wide caching. - If hostname lookup fails, fall back to the normal async path rather than introducing a new failure mode. - **Regression coverage** - Expand the existing Windows regression test to cover the added synchronous-completion cases through both sync and async entry points. ```csharp if (IPAddress.IsValid(name)) { return true; } ``` --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

Copilot · 2026-07-09T14:20:05Z

This broadens the Windows DnsResolver workaround for pre-22000 DnsQueryEx inline completion so it covers the full set of names the OS team identified as synchronously completing, not just localhost. The change keeps the existing async path for all other names and avoids the extra DNS_QUERY_NO_WIRE_QUERY probe.

Behavior
- Route these names directly through the synchronous path on affected Windows versions:
  - IP literals
  - machine hostname
  - loopback
  - localhost
  - ..DnsServers
  - ..localmachine
Implementation
- Replace the localhost-only check with a broader predicate for synchronously completing names.
- Use IPAddress.IsValid(...) for allocation-free IP literal detection.
- Compare against the current hostname without process-wide caching.
- If hostname lookup fails, fall back to the normal async path rather than introducing a new failure mode.
Regression coverage
- Expand the existing Windows regression test to cover the added synchronous-completion cases through both sync and async entry points.

if(IPAddress.IsValid(name)){returntrue;}

dotnet-policy-service · 2026-07-09T14:39:16Z

Tagging subscribers to this area: @dotnet/runtime-infrastructure
See info in area-owners.md if you want to be subscribed.

Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

Copilot

Pull request overview

This PR updates the Windows System.Net.NameResolution DnsQueryEx workaround by expanding the set of query names treated as “known to complete synchronously” on affected Windows versions, and extends the existing regression test to exercise those names through both sync/async resolver entry points.

Changes:

Replace the localhost-only fast-path with IsSynchronouslyCompletingQueryName, including IP literal detection and additional special-case names.
Route those names directly through the synchronous DnsQueryEx path when running async on pre-22000 Windows versions.
Expand the Windows regression test to cover the additional “synchronously completing” names.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs	Broaden the pre-22000 async inline-completion workaround to a wider set of names via a new predicate.
src/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverTest.cs	Expand the existing Windows regression test to cover the broader set of synchronously-completing names.

MichalPetryka

Should we add an assert that we never got null and a memory leak here?

…n true on hostname failure, fix test data Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

…tion test Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

rzikm · 2026-07-13T15:53:37Z

/ba-g System.Text.Json failures are unrelated

…130411)  This broadens the Windows `DnsResolver` workaround for pre-22000 `DnsQueryEx` inline completion so it covers the full set of names the OS team identified as synchronously completing, not just `localhost`. The change keeps the existing async path for all other names and avoids the extra `DNS_QUERY_NO_WIRE_QUERY` probe. - **Behavior** - Route these names directly through the synchronous path on affected Windows versions: - IP literals - machine hostname - `loopback` - `localhost` - `..DnsServers` - `..localmachine` - **Implementation** - Replace the `localhost`-only check with a broader predicate for synchronously completing names. - Use `IPAddress.IsValid(...)` for allocation-free IP literal detection. - Compare against the current hostname without process-wide caching. - If hostname lookup fails, fall back to the normal async path rather than introducing a new failure mode. - **Regression coverage** - Expand the existing Windows regression test to cover the added synchronous-completion cases through both sync and async entry points. ```csharp if (IPAddress.IsValid(name)) { return true; } ``` --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

Initial plan
35ee464

CopilotAI self-assigned this Jul 9, 2026

CopilotAI review requested due to automatic review settings July 9, 2026 14:20

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CopilotAI removed the request for review from Copilot July 9, 2026 14:20

Copilotstarted work on behalf of rzikm July 9, 2026 14:20 View session

CopilotAI linked an issue Jul 9, 2026 that may be closed by this pull request
DnsResolver Windows 10/Server 2019 memory leak #130374
Closed

github-actionsBot added the area-Infrastructure label Jul 9, 2026

github-project-automationBot added this to Runtime Infra Jul 9, 2026

Handle more synchronous Windows DNS names
3a37bf1
Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

CopilotAI requested review from Copilot and removed request for Copilot July 9, 2026 14:54

Refine Windows DNS sync-name detection
db2443f
Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

CopilotAI requested review from Copilot and removed request for Copilot July 9, 2026 15:08

CopilotAI changed the title ~~[WIP] Fix memory leak in DnsResolver for Windows 10/Server 2019~~Expand Windows DNS sync-query detection for inline-completing namesJul 9, 2026

Copilotfinished work on behalf of rzikm July 9, 2026 15:10

CopilotAI requested a review from rzikm July 9, 2026 15:10

rzikm marked this pull request as ready for review July 9, 2026 15:22

CopilotAI review requested due to automatic review settings July 9, 2026 15:22

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rzikm approved these changes Jul 9, 2026
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Comment threadsrc/libraries/System.Net.NameResolution/src/System/Net/DnsResolverPal.Windows.cs Outdated
Comment threadsrc/libraries/System.Net.NameResolution/tests/FunctionalTests/DnsResolverTest.cs Outdated

MichalPetryka reviewed Jul 9, 2026
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This was referenced Jul 9, 2026
slow macOS - "##[error]The job running on agent Azure Pipelines 9 ran longer than the maximum time of 60 minutes." dotnet/dnceng#1883
Open
The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#3008
Open

Copilotstarted work on behalf of rzikm July 13, 2026 09:56 View session

Address code review comments: cache hostname, use TrimEnd('.'), retur…
2452675
…n true on hostname failure, fix test data Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

CopilotAI requested review from Copilot and removed request for Copilot July 13, 2026 10:07

Copilotfinished work on behalf of rzikm July 13, 2026 10:08

CopilotAI requested a review from rzikm July 13, 2026 10:08

Copilotstarted work on behalf of rzikm July 13, 2026 10:14 View session

Test: assert NotEmpty records when response is NoError in sync-comple…
88af758
…tion test Co-authored-by: rzikm <32671551+rzikm@users.noreply.github.com>

CopilotAI requested review from Copilot and removed request for Copilot July 13, 2026 10:21

Copilotfinished work on behalf of rzikm July 13, 2026 10:22

Copilotfinished work on behalf of rzikm July 13, 2026 13:21

rzikm requested a review from a teamJuly 13, 2026 14:13

MihaZupan approved these changes Jul 13, 2026
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MihuBot mentioned this pull request Jul 14, 2026
[✨ Triage] dotnet/runtime#130374 by MichalPetryka - DnsResolver Windows 10/Server 2019 memory leak MihuBot/dotnet-triage#210
Open

rzikm merged commit 46178ac into mainJul 14, 2026
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rzikm deleted the copilot/dotnetruntime-130374-fix-dns-resolver-memory-leak branch July 14, 2026 10:35

github-project-automationBot moved this to Done in Runtime Infra Jul 14, 2026

dotnet-maestroBot mentioned this pull request Jul 15, 2026
[main] Source code updates from dotnet/runtime dotnet/dotnet#7749
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dotnet-maestroBot mentioned this pull request Jul 15, 2026
[main] Source code updates from dotnet/runtime dotnet/dotnet#7752
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dotnet-milestone-botBot added this to the 11.0-preview7 milestone Jul 15, 2026

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