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Merged
DaleSeo merged 3 commits into from
Jun 17, 2026
Merged

feat: standardize resource-not-found error code (SEP-2164) #899

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ceffe06
feat: implement SEP-2164 resource not found errors
michaelneale Jun 5, 2026
ebaaa46
test: update protocol version utility expectations
michaelneale Jun 7, 2026
8a26837
feat: gate not-found code at server boundary
DaleSeo Jun 10, 2026
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2 changes: 1 addition & 1 deletion conformance/src/bin/server.rs
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Original file line numberDiff line numberDiff line change
Expand Up@@ -615,7 +615,7 @@ impl ServerHandler for ConformanceServer {
} else {
Err(ErrorData::resource_not_found(
format!("Resource not found: {}", uri),
None,
Some(json!({ "uri": uri })),
))
}
}
Expand Down
17 changes: 15 additions & 2 deletions crates/rmcp/src/handler/server.rs
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Original file line numberDiff line numberDiff line change
Expand Up@@ -22,7 +22,9 @@ impl<H: ServerHandler> Service<RoleServer> for H {
request: <RoleServer as ServiceRole>::PeerReq,
context: RequestContext<RoleServer>,
) -> Result<<RoleServer as ServiceRole>::Resp, McpError> {
match request {
// `context` is moved into the dispatch below, so read the negotiated version first.
let protocol_version = context.protocol_version();
let result = match request {
ClientRequest::InitializeRequest(request) => self
.initialize(request.params, context)
.await
Expand DownExpand Up@@ -127,7 +129,18 @@ impl<H: ServerHandler> Service<RoleServer> for H {
.cancel_task(request.params, context)
.await
.map(ServerResult::CancelTaskResult),
}
};
// SEP-2164: peers negotiating 2026-07-28+ get the standard INVALID_PARAMS code for
// resource-not-found; older peers keep RESOURCE_NOT_FOUND. ISO `YYYY-MM-DD` versions
// compare lexically the same as chronologically.
let use_invalid_params =
protocol_version.is_some_and(|v| v.as_str() >= ProtocolVersion::V_2026_07_28.as_str());
result.map_err(|mut error| {
if use_invalid_params && error.code == ErrorCode::RESOURCE_NOT_FOUND {
error.code = ErrorCode::INVALID_PARAMS;
}
error
})
}

async fn handle_notification(
Expand Down
6 changes: 6 additions & 0 deletions crates/rmcp/src/model.rs
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Original file line numberDiff line numberDiff line change
Expand Up@@ -152,6 +152,7 @@ impl std::fmt::Display for ProtocolVersion {
}

impl ProtocolVersion {
pub const V_2026_07_28: Self = Self(Cow::Borrowed("2026-07-28"));
pub const V_2025_11_25: Self = Self(Cow::Borrowed("2025-11-25"));
pub const V_2025_06_18: Self = Self(Cow::Borrowed("2025-06-18"));
pub const V_2025_03_26: Self = Self(Cow::Borrowed("2025-03-26"));
Expand All@@ -164,6 +165,7 @@ impl ProtocolVersion {
Self::V_2025_03_26,
Self::V_2025_06_18,
Self::V_2025_11_25,
Self::V_2026_07_28,
];

/// Returns the string representation of this protocol version.
Expand DownExpand Up@@ -193,6 +195,7 @@ impl<'de> Deserialize<'de> for ProtocolVersion {
"2025-03-26" => return Ok(ProtocolVersion::V_2025_03_26),
"2025-06-18" => return Ok(ProtocolVersion::V_2025_06_18),
"2025-11-25" => return Ok(ProtocolVersion::V_2025_11_25),
"2026-07-28" => return Ok(ProtocolVersion::V_2026_07_28),
_ => {}
}
Ok(ProtocolVersion(Cow::Owned(s)))
Expand DownExpand Up@@ -541,9 +544,12 @@ impl ErrorData {
data,
}
}
/// Resource-not-found error (`-32002`). The server upgrades this to `INVALID_PARAMS`
/// (`-32602`) for peers negotiating protocol `2026-07-28` or newer (SEP-2164).
pub fn resource_not_found(message: impl Into<Cow<'static, str>>, data: Option<Value>) -> Self {
Self::new(ErrorCode::RESOURCE_NOT_FOUND, message, data)
}

pub fn parse_error(message: impl Into<Cow<'static, str>>, data: Option<Value>) -> Self {
Self::new(ErrorCode::PARSE_ERROR, message, data)
}
Expand Down
10 changes: 10 additions & 0 deletions crates/rmcp/src/service.rs
View file
Open in desktop
Original file line numberDiff line numberDiff line change
Expand Up@@ -674,6 +674,16 @@ impl<R: ServiceRole> RequestContext<R> {
}
}

#[cfg(feature = "server")]
impl RequestContext<RoleServer> {
/// The protocol version the client negotiated, or `None` before peer info is recorded.
pub fn protocol_version(&self) -> Option<crate::model::ProtocolVersion> {
self.peer
.peer_info()
.map(|info| info.protocol_version.clone())
}
}

/// Request execution context
#[derive(Debug, Clone)]
#[non_exhaustive]
Expand Down
4 changes: 3 additions & 1 deletion crates/rmcp/tests/test_custom_headers.rs
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Original file line numberDiff line numberDiff line change
Expand Up@@ -866,16 +866,18 @@ async fn test_server_rejects_unsupported_protocol_version() {
fn test_protocol_version_utilities() {
use rmcp::model::ProtocolVersion;

assert_eq!(ProtocolVersion::V_2026_07_28.as_str(), "2026-07-28");
assert_eq!(ProtocolVersion::V_2025_11_25.as_str(), "2025-11-25");
assert_eq!(ProtocolVersion::V_2025_06_18.as_str(), "2025-06-18");
assert_eq!(ProtocolVersion::V_2025_03_26.as_str(), "2025-03-26");
assert_eq!(ProtocolVersion::V_2024_11_05.as_str(), "2024-11-05");

assert_eq!(ProtocolVersion::KNOWN_VERSIONS.len(), 4);
assert_eq!(ProtocolVersion::KNOWN_VERSIONS.len(), 5);
assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2024_11_05));
assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_03_26));
assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_06_18));
assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_11_25));
assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2026_07_28));
}

/// Integration test: Verify server validates only the Host header for DNS rebinding protection
Expand Down
91 changes: 91 additions & 0 deletions crates/rmcp/tests/test_resource_not_found_version.rs
View file
Open in desktop
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,91 @@
//! SEP-2164: the resource-not-found error code follows the negotiated protocol version.
//!
//! `2026-07-28` and newer get the standard `INVALID_PARAMS` (-32602); older versions
//! keep the legacy `RESOURCE_NOT_FOUND` (-32002).
#![cfg(not(feature = "local"))]
#![cfg(feature = "client")]

use rmcp::{
ClientHandler, RoleServer, ServerHandler, ServiceError, ServiceExt,
model::{
ClientInfo, ErrorCode, ErrorData, ProtocolVersion, ReadResourceRequestParams,
ReadResourceResult,
},
service::RequestContext,
};

#[derive(Debug, Clone, Default)]
struct ResourceServer;

impl ServerHandler for ResourceServer {
async fn read_resource(
&self,
_request: ReadResourceRequestParams,
_context: RequestContext<RoleServer>,
) -> Result<ReadResourceResult, ErrorData> {
Err(ErrorData::resource_not_found("resource not found", None))
}
}

#[derive(Debug, Clone)]
struct VersionedClient {
protocol_version: ProtocolVersion,
}

impl ClientHandler for VersionedClient {
fn get_info(&self) -> ClientInfo {
let mut info = ClientInfo::default();
info.protocol_version = self.protocol_version.clone();
info
}
}

async fn not_found_code(client_version: ProtocolVersion) -> ErrorCode {
let (server_transport, client_transport) = tokio::io::duplex(4096);

let server_handle = tokio::spawn(async move {
ResourceServer
.serve(server_transport)
.await?
.waiting()
.await?;
anyhow::Ok(())
});

let client = VersionedClient {
protocol_version: client_version,
}
.serve(client_transport)
.await
.expect("client should connect");

let error = client
.read_resource(ReadResourceRequestParams::new("missing://resource"))
.await
.expect_err("missing resource should error");

let code = match error {
ServiceError::McpError(data) => data.code,
other => panic!("expected McpError, got: {other:?}"),
};

client.cancel().await.expect("client should cancel");
server_handle.await.expect("server task").expect("server");
code
}

#[tokio::test]
async fn legacy_version_gets_resource_not_found_code() {
assert_eq!(
not_found_code(ProtocolVersion::V_2025_11_25).await,
ErrorCode::RESOURCE_NOT_FOUND,
);
}

#[tokio::test]
async fn sep_2164_version_gets_invalid_params_code() {
assert_eq!(
not_found_code(ProtocolVersion::V_2026_07_28).await,
ErrorCode::INVALID_PARAMS,
);
}
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feat: standardize resource-not-found error code (SEP-2164) by DaleSeo · Pull Request #899 · modelcontextprotocol/rust-sdk · GitHub
Skip to content
feat: standardize resource-not-found error code (SEP-2164)#899

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to your account

 Merged

DaleSeo
merged 3 commits into

from

Jun 17, 2026
 Merged


feat: standardize resource-not-found error code (SEP-2164)
#899
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ceffe06

feat: implement SEP-2164 resource not found errors


michaelneale Jun 5, 2026
ebaaa46

test: update protocol version utility expectations


michaelneale Jun 7, 2026
8a26837

feat: gate not-found code at server boundary


DaleSeo Jun 10, 2026

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2 changes: 1 addition & 1 deletion
conformance/src/bin/server.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -615,7 +615,7 @@ impl ServerHandler for ConformanceServer {
 } else {
 Err(ErrorData::resource_not_found(
 format!("Resource not found: {}", uri),
None,
Some(json!({ "uri": uri })),
 ))
 }
 }
Expand Down

17 changes: 15 additions & 2 deletions
crates/rmcp/src/handler/server.rs

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -22,7 +22,9 @@ impl<H: ServerHandler> Service<RoleServer> for H {
 request: <RoleServer as ServiceRole>::PeerReq,
 context: RequestContext<RoleServer>,
 ) -> Result<<RoleServer as ServiceRole>::Resp, McpError> {
 match request {
 // `context` is moved into the dispatch below, so read the negotiated version first.
 let protocol_version = context.protocol_version();
 let result = match request {
 ClientRequest::InitializeRequest(request) => self
 .initialize(request.params, context)
 .await
Expand DownExpand Up@@ -127,7 +129,18 @@ impl<H: ServerHandler> Service<RoleServer> for H {
 .cancel_task(request.params, context)
 .await
 .map(ServerResult::CancelTaskResult),
 }
 };
 // SEP-2164: peers negotiating 2026-07-28+ get the standard INVALID_PARAMS code for
 // resource-not-found; older peers keep RESOURCE_NOT_FOUND. ISO `YYYY-MM-DD` versions
 // compare lexically the same as chronologically.
 let use_invalid_params =
 protocol_version.is_some_and(|v| v.as_str() >= ProtocolVersion::V_2026_07_28.as_str());
 result.map_err(|mut error| {
 if use_invalid_params && error.code == ErrorCode::RESOURCE_NOT_FOUND {
 error.code = ErrorCode::INVALID_PARAMS;
 }
 error
 })
 }

 async fn handle_notification(
Expand Down

6 changes: 6 additions & 0 deletions
crates/rmcp/src/model.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -152,6 +152,7 @@ impl std::fmt::Display for ProtocolVersion {
}

impl ProtocolVersion {
 pub const V_2026_07_28: Self = Self(Cow::Borrowed("2026-07-28"));
 pub const V_2025_11_25: Self = Self(Cow::Borrowed("2025-11-25"));
 pub const V_2025_06_18: Self = Self(Cow::Borrowed("2025-06-18"));
 pub const V_2025_03_26: Self = Self(Cow::Borrowed("2025-03-26"));
Expand All@@ -164,6 +165,7 @@ impl ProtocolVersion {
 Self::V_2025_03_26,
 Self::V_2025_06_18,
 Self::V_2025_11_25,
 Self::V_2026_07_28,
 ];

 /// Returns the string representation of this protocol version.
Expand DownExpand Up@@ -193,6 +195,7 @@ impl<'de> Deserialize<'de> for ProtocolVersion {
 "2025-03-26" => return Ok(ProtocolVersion::V_2025_03_26),
 "2025-06-18" => return Ok(ProtocolVersion::V_2025_06_18),
 "2025-11-25" => return Ok(ProtocolVersion::V_2025_11_25),
 "2026-07-28" => return Ok(ProtocolVersion::V_2026_07_28),
 _ => {}
 }
 Ok(ProtocolVersion(Cow::Owned(s)))
Expand DownExpand Up@@ -541,9 +544,12 @@ impl ErrorData {
 data,
 }
 }
 /// Resource-not-found error (`-32002`). The server upgrades this to `INVALID_PARAMS`
 /// (`-32602`) for peers negotiating protocol `2026-07-28` or newer (SEP-2164).
 pub fn resource_not_found(message: impl Into<Cow<'static, str>>, data: Option<Value>) -> Self {
 Self::new(ErrorCode::RESOURCE_NOT_FOUND, message, data)
 }

 pub fn parse_error(message: impl Into<Cow<'static, str>>, data: Option<Value>) -> Self {
 Self::new(ErrorCode::PARSE_ERROR, message, data)
 }
Expand Down

10 changes: 10 additions & 0 deletions
crates/rmcp/src/service.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -674,6 +674,16 @@ impl<R: ServiceRole> RequestContext<R> {
 }
}

#[cfg(feature = "server")]
impl RequestContext<RoleServer> {
 /// The protocol version the client negotiated, or `None` before peer info is recorded.
 pub fn protocol_version(&self) -> Option<crate::model::ProtocolVersion> {
 self.peer
 .peer_info()
 .map(|info| info.protocol_version.clone())
 }
}

/// Request execution context
#[derive(Debug, Clone)]
#[non_exhaustive]
Expand Down

4 changes: 3 additions & 1 deletion
crates/rmcp/tests/test_custom_headers.rs

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -866,16 +866,18 @@ async fn test_server_rejects_unsupported_protocol_version() {
fn test_protocol_version_utilities() {
 use rmcp::model::ProtocolVersion;

 assert_eq!(ProtocolVersion::V_2026_07_28.as_str(), "2026-07-28");
 assert_eq!(ProtocolVersion::V_2025_11_25.as_str(), "2025-11-25");
 assert_eq!(ProtocolVersion::V_2025_06_18.as_str(), "2025-06-18");
 assert_eq!(ProtocolVersion::V_2025_03_26.as_str(), "2025-03-26");
 assert_eq!(ProtocolVersion::V_2024_11_05.as_str(), "2024-11-05");

 assert_eq!(ProtocolVersion::KNOWN_VERSIONS.len(), 4);
 assert_eq!(ProtocolVersion::KNOWN_VERSIONS.len(), 5);
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2024_11_05));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_03_26));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_06_18));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_11_25));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2026_07_28));
}

/// Integration test: Verify server validates only the Host header for DNS rebinding protection
Expand Down

91 changes: 91 additions & 0 deletions
crates/rmcp/tests/test_resource_not_found_version.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -0,0 +1,91 @@
//! SEP-2164: the resource-not-found error code follows the negotiated protocol version.
//!
//! `2026-07-28` and newer get the standard `INVALID_PARAMS` (-32602); older versions
//! keep the legacy `RESOURCE_NOT_FOUND` (-32002).
#![cfg(not(feature = "local"))]
#![cfg(feature = "client")]

use rmcp::{
 ClientHandler, RoleServer, ServerHandler, ServiceError, ServiceExt,
 model::{
 ClientInfo, ErrorCode, ErrorData, ProtocolVersion, ReadResourceRequestParams,
 ReadResourceResult,
 },
 service::RequestContext,
};

#[derive(Debug, Clone, Default)]
struct ResourceServer;

impl ServerHandler for ResourceServer {
 async fn read_resource(
 &self,
 _request: ReadResourceRequestParams,
 _context: RequestContext<RoleServer>,
 ) -> Result<ReadResourceResult, ErrorData> {
 Err(ErrorData::resource_not_found("resource not found", None))
 }
}

#[derive(Debug, Clone)]
struct VersionedClient {
 protocol_version: ProtocolVersion,
}

impl ClientHandler for VersionedClient {
 fn get_info(&self) -> ClientInfo {
 let mut info = ClientInfo::default();
 info.protocol_version = self.protocol_version.clone();
 info
 }
}

async fn not_found_code(client_version: ProtocolVersion) -> ErrorCode {
 let (server_transport, client_transport) = tokio::io::duplex(4096);

 let server_handle = tokio::spawn(async move {
 ResourceServer
 .serve(server_transport)
 .await?
 .waiting()
 .await?;
 anyhow::Ok(())
 });

 let client = VersionedClient {
 protocol_version: client_version,
 }
 .serve(client_transport)
 .await
 .expect("client should connect");

 let error = client
 .read_resource(ReadResourceRequestParams::new("missing://resource"))
 .await
 .expect_err("missing resource should error");

 let code = match error {
 ServiceError::McpError(data) => data.code,
 other => panic!("expected McpError, got: {other:?}"),
 };

 client.cancel().await.expect("client should cancel");
 server_handle.await.expect("server task").expect("server");
 code
}

#[tokio::test]
async fn legacy_version_gets_resource_not_found_code() {
 assert_eq!(
 not_found_code(ProtocolVersion::V_2025_11_25).await,
 ErrorCode::RESOURCE_NOT_FOUND,
 );
}

#[tokio::test]
async fn sep_2164_version_gets_invalid_params_code() {
 assert_eq!(
 not_found_code(ProtocolVersion::V_2026_07_28).await,
 ErrorCode::INVALID_PARAMS,
 );
}

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Force GitHub README to respect dark mode
(function() {
var style = document.createElement('style');
style.textContent = '
.markdown-body {
color-scheme: dark light;
}
.markdown-body pre { background: #161b22 !important; }
.markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }
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';
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})();
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
feat: standardize resource-not-found error code (SEP-2164) by DaleSeo · Pull Request #899 · modelcontextprotocol/rust-sdk · GitHub
Skip to content
feat: standardize resource-not-found error code (SEP-2164)#899

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Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

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Already on GitHub?
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 Merged

DaleSeo
merged 3 commits into

from

Jun 17, 2026
 Merged


feat: standardize resource-not-found error code (SEP-2164)
#899
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ceffe06

feat: implement SEP-2164 resource not found errors


michaelneale Jun 5, 2026
ebaaa46

test: update protocol version utility expectations


michaelneale Jun 7, 2026
8a26837

feat: gate not-found code at server boundary


DaleSeo Jun 10, 2026

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2 changes: 1 addition & 1 deletion
conformance/src/bin/server.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -615,7 +615,7 @@ impl ServerHandler for ConformanceServer {
 } else {
 Err(ErrorData::resource_not_found(
 format!("Resource not found: {}", uri),
None,
Some(json!({ "uri": uri })),
 ))
 }
 }
Expand Down

17 changes: 15 additions & 2 deletions
crates/rmcp/src/handler/server.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -22,7 +22,9 @@ impl<H: ServerHandler> Service<RoleServer> for H {
 request: <RoleServer as ServiceRole>::PeerReq,
 context: RequestContext<RoleServer>,
 ) -> Result<<RoleServer as ServiceRole>::Resp, McpError> {
 match request {
 // `context` is moved into the dispatch below, so read the negotiated version first.
 let protocol_version = context.protocol_version();
 let result = match request {
 ClientRequest::InitializeRequest(request) => self
 .initialize(request.params, context)
 .await
Expand DownExpand Up@@ -127,7 +129,18 @@ impl<H: ServerHandler> Service<RoleServer> for H {
 .cancel_task(request.params, context)
 .await
 .map(ServerResult::CancelTaskResult),
 }
 };
 // SEP-2164: peers negotiating 2026-07-28+ get the standard INVALID_PARAMS code for
 // resource-not-found; older peers keep RESOURCE_NOT_FOUND. ISO `YYYY-MM-DD` versions
 // compare lexically the same as chronologically.
 let use_invalid_params =
 protocol_version.is_some_and(|v| v.as_str() >= ProtocolVersion::V_2026_07_28.as_str());
 result.map_err(|mut error| {
 if use_invalid_params && error.code == ErrorCode::RESOURCE_NOT_FOUND {
 error.code = ErrorCode::INVALID_PARAMS;
 }
 error
 })
 }

 async fn handle_notification(
Expand Down

6 changes: 6 additions & 0 deletions
crates/rmcp/src/model.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -152,6 +152,7 @@ impl std::fmt::Display for ProtocolVersion {
}

impl ProtocolVersion {
 pub const V_2026_07_28: Self = Self(Cow::Borrowed("2026-07-28"));
 pub const V_2025_11_25: Self = Self(Cow::Borrowed("2025-11-25"));
 pub const V_2025_06_18: Self = Self(Cow::Borrowed("2025-06-18"));
 pub const V_2025_03_26: Self = Self(Cow::Borrowed("2025-03-26"));
Expand All@@ -164,6 +165,7 @@ impl ProtocolVersion {
 Self::V_2025_03_26,
 Self::V_2025_06_18,
 Self::V_2025_11_25,
 Self::V_2026_07_28,
 ];

 /// Returns the string representation of this protocol version.
Expand DownExpand Up@@ -193,6 +195,7 @@ impl<'de> Deserialize<'de> for ProtocolVersion {
 "2025-03-26" => return Ok(ProtocolVersion::V_2025_03_26),
 "2025-06-18" => return Ok(ProtocolVersion::V_2025_06_18),
 "2025-11-25" => return Ok(ProtocolVersion::V_2025_11_25),
 "2026-07-28" => return Ok(ProtocolVersion::V_2026_07_28),
 _ => {}
 }
 Ok(ProtocolVersion(Cow::Owned(s)))
Expand DownExpand Up@@ -541,9 +544,12 @@ impl ErrorData {
 data,
 }
 }
 /// Resource-not-found error (`-32002`). The server upgrades this to `INVALID_PARAMS`
 /// (`-32602`) for peers negotiating protocol `2026-07-28` or newer (SEP-2164).
 pub fn resource_not_found(message: impl Into<Cow<'static, str>>, data: Option<Value>) -> Self {
 Self::new(ErrorCode::RESOURCE_NOT_FOUND, message, data)
 }

 pub fn parse_error(message: impl Into<Cow<'static, str>>, data: Option<Value>) -> Self {
 Self::new(ErrorCode::PARSE_ERROR, message, data)
 }
Expand Down

10 changes: 10 additions & 0 deletions
crates/rmcp/src/service.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -674,6 +674,16 @@ impl<R: ServiceRole> RequestContext<R> {
 }
}

#[cfg(feature = "server")]
impl RequestContext<RoleServer> {
 /// The protocol version the client negotiated, or `None` before peer info is recorded.
 pub fn protocol_version(&self) -> Option<crate::model::ProtocolVersion> {
 self.peer
 .peer_info()
 .map(|info| info.protocol_version.clone())
 }
}

/// Request execution context
#[derive(Debug, Clone)]
#[non_exhaustive]
Expand Down

4 changes: 3 additions & 1 deletion
crates/rmcp/tests/test_custom_headers.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -866,16 +866,18 @@ async fn test_server_rejects_unsupported_protocol_version() {
fn test_protocol_version_utilities() {
 use rmcp::model::ProtocolVersion;

 assert_eq!(ProtocolVersion::V_2026_07_28.as_str(), "2026-07-28");
 assert_eq!(ProtocolVersion::V_2025_11_25.as_str(), "2025-11-25");
 assert_eq!(ProtocolVersion::V_2025_06_18.as_str(), "2025-06-18");
 assert_eq!(ProtocolVersion::V_2025_03_26.as_str(), "2025-03-26");
 assert_eq!(ProtocolVersion::V_2024_11_05.as_str(), "2024-11-05");

 assert_eq!(ProtocolVersion::KNOWN_VERSIONS.len(), 4);
 assert_eq!(ProtocolVersion::KNOWN_VERSIONS.len(), 5);
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2024_11_05));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_03_26));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_06_18));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_11_25));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2026_07_28));
}

/// Integration test: Verify server validates only the Host header for DNS rebinding protection
Expand Down

91 changes: 91 additions & 0 deletions
crates/rmcp/tests/test_resource_not_found_version.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -0,0 +1,91 @@
//! SEP-2164: the resource-not-found error code follows the negotiated protocol version.
//!
//! `2026-07-28` and newer get the standard `INVALID_PARAMS` (-32602); older versions
//! keep the legacy `RESOURCE_NOT_FOUND` (-32002).
#![cfg(not(feature = "local"))]
#![cfg(feature = "client")]

use rmcp::{
 ClientHandler, RoleServer, ServerHandler, ServiceError, ServiceExt,
 model::{
 ClientInfo, ErrorCode, ErrorData, ProtocolVersion, ReadResourceRequestParams,
 ReadResourceResult,
 },
 service::RequestContext,
};

#[derive(Debug, Clone, Default)]
struct ResourceServer;

impl ServerHandler for ResourceServer {
 async fn read_resource(
 &self,
 _request: ReadResourceRequestParams,
 _context: RequestContext<RoleServer>,
 ) -> Result<ReadResourceResult, ErrorData> {
 Err(ErrorData::resource_not_found("resource not found", None))
 }
}

#[derive(Debug, Clone)]
struct VersionedClient {
 protocol_version: ProtocolVersion,
}

impl ClientHandler for VersionedClient {
 fn get_info(&self) -> ClientInfo {
 let mut info = ClientInfo::default();
 info.protocol_version = self.protocol_version.clone();
 info
 }
}

async fn not_found_code(client_version: ProtocolVersion) -> ErrorCode {
 let (server_transport, client_transport) = tokio::io::duplex(4096);

 let server_handle = tokio::spawn(async move {
 ResourceServer
 .serve(server_transport)
 .await?
 .waiting()
 .await?;
 anyhow::Ok(())
 });

 let client = VersionedClient {
 protocol_version: client_version,
 }
 .serve(client_transport)
 .await
 .expect("client should connect");

 let error = client
 .read_resource(ReadResourceRequestParams::new("missing://resource"))
 .await
 .expect_err("missing resource should error");

 let code = match error {
 ServiceError::McpError(data) => data.code,
 other => panic!("expected McpError, got: {other:?}"),
 };

 client.cancel().await.expect("client should cancel");
 server_handle.await.expect("server task").expect("server");
 code
}

#[tokio::test]
async fn legacy_version_gets_resource_not_found_code() {
 assert_eq!(
 not_found_code(ProtocolVersion::V_2025_11_25).await,
 ErrorCode::RESOURCE_NOT_FOUND,
 );
}

#[tokio::test]
async fn sep_2164_version_gets_invalid_params_code() {
 assert_eq!(
 not_found_code(ProtocolVersion::V_2026_07_28).await,
 ErrorCode::INVALID_PARAMS,
 );
}

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Highlight search terms from Google/DuckDuckGo/Bing referrer
(function() {
var ref = document.referrer;
var terms = [];
if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {
var url = new URL(ref);
var q = url.searchParams.get('q') || url.searchParams.get('p');
if (q) {
terms = q.split(/\s+/).filter(function(t) { return t.length > 2; });
}
}
if (terms.length === 0) return;
var style = document.createElement('style');
style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';
document.head.appendChild(style);
function highlight(node) {
if (node.nodeType === 3) { // text node
var text = node.textContent;
var found = false;
terms.forEach(function(term) {
var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\]\\]/g, '\\') + ')', 'gi');
if (regex.test(text)) {
found = true;
var frag = document.createDocumentFragment();
var parts = text.split(regex);
parts.forEach(function(part, i) {
if (i % 2 === 0) {
frag.appendChild(document.createTextNode(part));
} else {
var span = document.createElement('span');
span.className = 'userscript-highlight';
span.textContent = part;
frag.appendChild(span);
}
});
node.parentNode.replaceChild(frag, node);
}
});
} else if (node.nodeType === 1 && node.childNodes) { // element
var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];
if (!skipTags.includes(node.tagName)) {
Array.from(node.childNodes).forEach(highlight);
}
}
}
highlight(document.body);
// Re-highlight on dynamic content
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(m) {
m.addedNodes.forEach(function(node) {
if (node.nodeType === 1 || node.nodeType === 3) highlight(node);
});
});
});
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
feat: standardize resource-not-found error code (SEP-2164) by DaleSeo · Pull Request #899 · modelcontextprotocol/rust-sdk · GitHub
Skip to content
feat: standardize resource-not-found error code (SEP-2164)#899

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 Merged

DaleSeo
merged 3 commits into

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Jun 17, 2026
 Merged


feat: standardize resource-not-found error code (SEP-2164)
#899
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ceffe06

feat: implement SEP-2164 resource not found errors


michaelneale Jun 5, 2026
ebaaa46

test: update protocol version utility expectations


michaelneale Jun 7, 2026
8a26837

feat: gate not-found code at server boundary


DaleSeo Jun 10, 2026

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2 changes: 1 addition & 1 deletion
conformance/src/bin/server.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -615,7 +615,7 @@ impl ServerHandler for ConformanceServer {
 } else {
 Err(ErrorData::resource_not_found(
 format!("Resource not found: {}", uri),
None,
Some(json!({ "uri": uri })),
 ))
 }
 }
Expand Down

17 changes: 15 additions & 2 deletions
crates/rmcp/src/handler/server.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -22,7 +22,9 @@ impl<H: ServerHandler> Service<RoleServer> for H {
 request: <RoleServer as ServiceRole>::PeerReq,
 context: RequestContext<RoleServer>,
 ) -> Result<<RoleServer as ServiceRole>::Resp, McpError> {
 match request {
 // `context` is moved into the dispatch below, so read the negotiated version first.
 let protocol_version = context.protocol_version();
 let result = match request {
 ClientRequest::InitializeRequest(request) => self
 .initialize(request.params, context)
 .await
Expand DownExpand Up@@ -127,7 +129,18 @@ impl<H: ServerHandler> Service<RoleServer> for H {
 .cancel_task(request.params, context)
 .await
 .map(ServerResult::CancelTaskResult),
 }
 };
 // SEP-2164: peers negotiating 2026-07-28+ get the standard INVALID_PARAMS code for
 // resource-not-found; older peers keep RESOURCE_NOT_FOUND. ISO `YYYY-MM-DD` versions
 // compare lexically the same as chronologically.
 let use_invalid_params =
 protocol_version.is_some_and(|v| v.as_str() >= ProtocolVersion::V_2026_07_28.as_str());
 result.map_err(|mut error| {
 if use_invalid_params && error.code == ErrorCode::RESOURCE_NOT_FOUND {
 error.code = ErrorCode::INVALID_PARAMS;
 }
 error
 })
 }

 async fn handle_notification(
Expand Down

6 changes: 6 additions & 0 deletions
crates/rmcp/src/model.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -152,6 +152,7 @@ impl std::fmt::Display for ProtocolVersion {
}

impl ProtocolVersion {
 pub const V_2026_07_28: Self = Self(Cow::Borrowed("2026-07-28"));
 pub const V_2025_11_25: Self = Self(Cow::Borrowed("2025-11-25"));
 pub const V_2025_06_18: Self = Self(Cow::Borrowed("2025-06-18"));
 pub const V_2025_03_26: Self = Self(Cow::Borrowed("2025-03-26"));
Expand All@@ -164,6 +165,7 @@ impl ProtocolVersion {
 Self::V_2025_03_26,
 Self::V_2025_06_18,
 Self::V_2025_11_25,
 Self::V_2026_07_28,
 ];

 /// Returns the string representation of this protocol version.
Expand DownExpand Up@@ -193,6 +195,7 @@ impl<'de> Deserialize<'de> for ProtocolVersion {
 "2025-03-26" => return Ok(ProtocolVersion::V_2025_03_26),
 "2025-06-18" => return Ok(ProtocolVersion::V_2025_06_18),
 "2025-11-25" => return Ok(ProtocolVersion::V_2025_11_25),
 "2026-07-28" => return Ok(ProtocolVersion::V_2026_07_28),
 _ => {}
 }
 Ok(ProtocolVersion(Cow::Owned(s)))
Expand DownExpand Up@@ -541,9 +544,12 @@ impl ErrorData {
 data,
 }
 }
 /// Resource-not-found error (`-32002`). The server upgrades this to `INVALID_PARAMS`
 /// (`-32602`) for peers negotiating protocol `2026-07-28` or newer (SEP-2164).
 pub fn resource_not_found(message: impl Into<Cow<'static, str>>, data: Option<Value>) -> Self {
 Self::new(ErrorCode::RESOURCE_NOT_FOUND, message, data)
 }

 pub fn parse_error(message: impl Into<Cow<'static, str>>, data: Option<Value>) -> Self {
 Self::new(ErrorCode::PARSE_ERROR, message, data)
 }
Expand Down

10 changes: 10 additions & 0 deletions
crates/rmcp/src/service.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -674,6 +674,16 @@ impl<R: ServiceRole> RequestContext<R> {
 }
}

#[cfg(feature = "server")]
impl RequestContext<RoleServer> {
 /// The protocol version the client negotiated, or `None` before peer info is recorded.
 pub fn protocol_version(&self) -> Option<crate::model::ProtocolVersion> {
 self.peer
 .peer_info()
 .map(|info| info.protocol_version.clone())
 }
}

/// Request execution context
#[derive(Debug, Clone)]
#[non_exhaustive]
Expand Down

4 changes: 3 additions & 1 deletion
crates/rmcp/tests/test_custom_headers.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -866,16 +866,18 @@ async fn test_server_rejects_unsupported_protocol_version() {
fn test_protocol_version_utilities() {
 use rmcp::model::ProtocolVersion;

 assert_eq!(ProtocolVersion::V_2026_07_28.as_str(), "2026-07-28");
 assert_eq!(ProtocolVersion::V_2025_11_25.as_str(), "2025-11-25");
 assert_eq!(ProtocolVersion::V_2025_06_18.as_str(), "2025-06-18");
 assert_eq!(ProtocolVersion::V_2025_03_26.as_str(), "2025-03-26");
 assert_eq!(ProtocolVersion::V_2024_11_05.as_str(), "2024-11-05");

 assert_eq!(ProtocolVersion::KNOWN_VERSIONS.len(), 4);
 assert_eq!(ProtocolVersion::KNOWN_VERSIONS.len(), 5);
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2024_11_05));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_03_26));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_06_18));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_11_25));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2026_07_28));
}

/// Integration test: Verify server validates only the Host header for DNS rebinding protection
Expand Down

91 changes: 91 additions & 0 deletions
crates/rmcp/tests/test_resource_not_found_version.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -0,0 +1,91 @@
//! SEP-2164: the resource-not-found error code follows the negotiated protocol version.
//!
//! `2026-07-28` and newer get the standard `INVALID_PARAMS` (-32602); older versions
//! keep the legacy `RESOURCE_NOT_FOUND` (-32002).
#![cfg(not(feature = "local"))]
#![cfg(feature = "client")]

use rmcp::{
 ClientHandler, RoleServer, ServerHandler, ServiceError, ServiceExt,
 model::{
 ClientInfo, ErrorCode, ErrorData, ProtocolVersion, ReadResourceRequestParams,
 ReadResourceResult,
 },
 service::RequestContext,
};

#[derive(Debug, Clone, Default)]
struct ResourceServer;

impl ServerHandler for ResourceServer {
 async fn read_resource(
 &self,
 _request: ReadResourceRequestParams,
 _context: RequestContext<RoleServer>,
 ) -> Result<ReadResourceResult, ErrorData> {
 Err(ErrorData::resource_not_found("resource not found", None))
 }
}

#[derive(Debug, Clone)]
struct VersionedClient {
 protocol_version: ProtocolVersion,
}

impl ClientHandler for VersionedClient {
 fn get_info(&self) -> ClientInfo {
 let mut info = ClientInfo::default();
 info.protocol_version = self.protocol_version.clone();
 info
 }
}

async fn not_found_code(client_version: ProtocolVersion) -> ErrorCode {
 let (server_transport, client_transport) = tokio::io::duplex(4096);

 let server_handle = tokio::spawn(async move {
 ResourceServer
 .serve(server_transport)
 .await?
 .waiting()
 .await?;
 anyhow::Ok(())
 });

 let client = VersionedClient {
 protocol_version: client_version,
 }
 .serve(client_transport)
 .await
 .expect("client should connect");

 let error = client
 .read_resource(ReadResourceRequestParams::new("missing://resource"))
 .await
 .expect_err("missing resource should error");

 let code = match error {
 ServiceError::McpError(data) => data.code,
 other => panic!("expected McpError, got: {other:?}"),
 };

 client.cancel().await.expect("client should cancel");
 server_handle.await.expect("server task").expect("server");
 code
}

#[tokio::test]
async fn legacy_version_gets_resource_not_found_code() {
 assert_eq!(
 not_found_code(ProtocolVersion::V_2025_11_25).await,
 ErrorCode::RESOURCE_NOT_FOUND,
 );
}

#[tokio::test]
async fn sep_2164_version_gets_invalid_params_code() {
 assert_eq!(
 not_found_code(ProtocolVersion::V_2026_07_28).await,
 ErrorCode::INVALID_PARAMS,
 );
}

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Strip utm_, fbclid, gclid, etc. from all links on page
(function() {
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);
if (clean !== a.href) a.href = clean;
});
}
cleanLinks();
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(m) {
m.addedNodes.forEach(function(node) {
if (node.nodeType === 1) {
if (node.tagName === 'A') cleanLinks();
node.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
});
});
});
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '
feat: standardize resource-not-found error code (SEP-2164) by DaleSeo · Pull Request #899 · modelcontextprotocol/rust-sdk · GitHub
Skip to content
feat: standardize resource-not-found error code (SEP-2164)#899

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Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

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to your account

 Merged

DaleSeo
merged 3 commits into

from

Jun 17, 2026
 Merged


feat: standardize resource-not-found error code (SEP-2164)
#899
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ceffe06

feat: implement SEP-2164 resource not found errors


michaelneale Jun 5, 2026
ebaaa46

test: update protocol version utility expectations


michaelneale Jun 7, 2026
8a26837

feat: gate not-found code at server boundary


DaleSeo Jun 10, 2026

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2 changes: 1 addition & 1 deletion
conformance/src/bin/server.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -615,7 +615,7 @@ impl ServerHandler for ConformanceServer {
 } else {
 Err(ErrorData::resource_not_found(
 format!("Resource not found: {}", uri),
None,
Some(json!({ "uri": uri })),
 ))
 }
 }
Expand Down

17 changes: 15 additions & 2 deletions
crates/rmcp/src/handler/server.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -22,7 +22,9 @@ impl<H: ServerHandler> Service<RoleServer> for H {
 request: <RoleServer as ServiceRole>::PeerReq,
 context: RequestContext<RoleServer>,
 ) -> Result<<RoleServer as ServiceRole>::Resp, McpError> {
 match request {
 // `context` is moved into the dispatch below, so read the negotiated version first.
 let protocol_version = context.protocol_version();
 let result = match request {
 ClientRequest::InitializeRequest(request) => self
 .initialize(request.params, context)
 .await
Expand DownExpand Up@@ -127,7 +129,18 @@ impl<H: ServerHandler> Service<RoleServer> for H {
 .cancel_task(request.params, context)
 .await
 .map(ServerResult::CancelTaskResult),
 }
 };
 // SEP-2164: peers negotiating 2026-07-28+ get the standard INVALID_PARAMS code for
 // resource-not-found; older peers keep RESOURCE_NOT_FOUND. ISO `YYYY-MM-DD` versions
 // compare lexically the same as chronologically.
 let use_invalid_params =
 protocol_version.is_some_and(|v| v.as_str() >= ProtocolVersion::V_2026_07_28.as_str());
 result.map_err(|mut error| {
 if use_invalid_params && error.code == ErrorCode::RESOURCE_NOT_FOUND {
 error.code = ErrorCode::INVALID_PARAMS;
 }
 error
 })
 }

 async fn handle_notification(
Expand Down

6 changes: 6 additions & 0 deletions
crates/rmcp/src/model.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -152,6 +152,7 @@ impl std::fmt::Display for ProtocolVersion {
}

impl ProtocolVersion {
 pub const V_2026_07_28: Self = Self(Cow::Borrowed("2026-07-28"));
 pub const V_2025_11_25: Self = Self(Cow::Borrowed("2025-11-25"));
 pub const V_2025_06_18: Self = Self(Cow::Borrowed("2025-06-18"));
 pub const V_2025_03_26: Self = Self(Cow::Borrowed("2025-03-26"));
Expand All@@ -164,6 +165,7 @@ impl ProtocolVersion {
 Self::V_2025_03_26,
 Self::V_2025_06_18,
 Self::V_2025_11_25,
 Self::V_2026_07_28,
 ];

 /// Returns the string representation of this protocol version.
Expand DownExpand Up@@ -193,6 +195,7 @@ impl<'de> Deserialize<'de> for ProtocolVersion {
 "2025-03-26" => return Ok(ProtocolVersion::V_2025_03_26),
 "2025-06-18" => return Ok(ProtocolVersion::V_2025_06_18),
 "2025-11-25" => return Ok(ProtocolVersion::V_2025_11_25),
 "2026-07-28" => return Ok(ProtocolVersion::V_2026_07_28),
 _ => {}
 }
 Ok(ProtocolVersion(Cow::Owned(s)))
Expand DownExpand Up@@ -541,9 +544,12 @@ impl ErrorData {
 data,
 }
 }
 /// Resource-not-found error (`-32002`). The server upgrades this to `INVALID_PARAMS`
 /// (`-32602`) for peers negotiating protocol `2026-07-28` or newer (SEP-2164).
 pub fn resource_not_found(message: impl Into<Cow<'static, str>>, data: Option<Value>) -> Self {
 Self::new(ErrorCode::RESOURCE_NOT_FOUND, message, data)
 }

 pub fn parse_error(message: impl Into<Cow<'static, str>>, data: Option<Value>) -> Self {
 Self::new(ErrorCode::PARSE_ERROR, message, data)
 }
Expand Down

10 changes: 10 additions & 0 deletions
crates/rmcp/src/service.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -674,6 +674,16 @@ impl<R: ServiceRole> RequestContext<R> {
 }
}

#[cfg(feature = "server")]
impl RequestContext<RoleServer> {
 /// The protocol version the client negotiated, or `None` before peer info is recorded.
 pub fn protocol_version(&self) -> Option<crate::model::ProtocolVersion> {
 self.peer
 .peer_info()
 .map(|info| info.protocol_version.clone())
 }
}

/// Request execution context
#[derive(Debug, Clone)]
#[non_exhaustive]
Expand Down

4 changes: 3 additions & 1 deletion
crates/rmcp/tests/test_custom_headers.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -866,16 +866,18 @@ async fn test_server_rejects_unsupported_protocol_version() {
fn test_protocol_version_utilities() {
 use rmcp::model::ProtocolVersion;

 assert_eq!(ProtocolVersion::V_2026_07_28.as_str(), "2026-07-28");
 assert_eq!(ProtocolVersion::V_2025_11_25.as_str(), "2025-11-25");
 assert_eq!(ProtocolVersion::V_2025_06_18.as_str(), "2025-06-18");
 assert_eq!(ProtocolVersion::V_2025_03_26.as_str(), "2025-03-26");
 assert_eq!(ProtocolVersion::V_2024_11_05.as_str(), "2024-11-05");

 assert_eq!(ProtocolVersion::KNOWN_VERSIONS.len(), 4);
 assert_eq!(ProtocolVersion::KNOWN_VERSIONS.len(), 5);
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2024_11_05));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_03_26));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_06_18));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_11_25));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2026_07_28));
}

/// Integration test: Verify server validates only the Host header for DNS rebinding protection
Expand Down

91 changes: 91 additions & 0 deletions
crates/rmcp/tests/test_resource_not_found_version.rs

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,91 @@
//! SEP-2164: the resource-not-found error code follows the negotiated protocol version.
//!
//! `2026-07-28` and newer get the standard `INVALID_PARAMS` (-32602); older versions
//! keep the legacy `RESOURCE_NOT_FOUND` (-32002).
#![cfg(not(feature = "local"))]
#![cfg(feature = "client")]

use rmcp::{
 ClientHandler, RoleServer, ServerHandler, ServiceError, ServiceExt,
 model::{
 ClientInfo, ErrorCode, ErrorData, ProtocolVersion, ReadResourceRequestParams,
 ReadResourceResult,
 },
 service::RequestContext,
};

#[derive(Debug, Clone, Default)]
struct ResourceServer;

impl ServerHandler for ResourceServer {
 async fn read_resource(
 &self,
 _request: ReadResourceRequestParams,
 _context: RequestContext<RoleServer>,
 ) -> Result<ReadResourceResult, ErrorData> {
 Err(ErrorData::resource_not_found("resource not found", None))
 }
}

#[derive(Debug, Clone)]
struct VersionedClient {
 protocol_version: ProtocolVersion,
}

impl ClientHandler for VersionedClient {
 fn get_info(&self) -> ClientInfo {
 let mut info = ClientInfo::default();
 info.protocol_version = self.protocol_version.clone();
 info
 }
}

async fn not_found_code(client_version: ProtocolVersion) -> ErrorCode {
 let (server_transport, client_transport) = tokio::io::duplex(4096);

 let server_handle = tokio::spawn(async move {
 ResourceServer
 .serve(server_transport)
 .await?
 .waiting()
 .await?;
 anyhow::Ok(())
 });

 let client = VersionedClient {
 protocol_version: client_version,
 }
 .serve(client_transport)
 .await
 .expect("client should connect");

 let error = client
 .read_resource(ReadResourceRequestParams::new("missing://resource"))
 .await
 .expect_err("missing resource should error");

 let code = match error {
 ServiceError::McpError(data) => data.code,
 other => panic!("expected McpError, got: {other:?}"),
 };

 client.cancel().await.expect("client should cancel");
 server_handle.await.expect("server task").expect("server");
 code
}

#[tokio::test]
async fn legacy_version_gets_resource_not_found_code() {
 assert_eq!(
 not_found_code(ProtocolVersion::V_2025_11_25).await,
 ErrorCode::RESOURCE_NOT_FOUND,
 );
}

#[tokio::test]
async fn sep_2164_version_gets_invalid_params_code() {
 assert_eq!(
 not_found_code(ProtocolVersion::V_2026_07_28).await,
 ErrorCode::INVALID_PARAMS,
 );
}

, 'i');
if (__m === '*' || __re.test(location.href)) {
// 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
tryTheater();
// Try after navigation (SPA)
var lastUrl = location.href;
setInterval(function() {
if (location.href !== lastUrl) {
lastUrl = location.href;
setTimeout(tryTheater, 500);
}
}, 1000);
// Also try on player load
var observer = new MutationObserver(tryTheater);
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('^' + ".*" + '
feat: standardize resource-not-found error code (SEP-2164) by DaleSeo · Pull Request #899 · modelcontextprotocol/rust-sdk · GitHub
Skip to content
feat: standardize resource-not-found error code (SEP-2164)#899

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 Merged

DaleSeo
merged 3 commits into

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Jun 17, 2026
 Merged


feat: standardize resource-not-found error code (SEP-2164)
#899
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ceffe06

feat: implement SEP-2164 resource not found errors


michaelneale Jun 5, 2026
ebaaa46

test: update protocol version utility expectations


michaelneale Jun 7, 2026
8a26837

feat: gate not-found code at server boundary


DaleSeo Jun 10, 2026

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2 changes: 1 addition & 1 deletion
conformance/src/bin/server.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -615,7 +615,7 @@ impl ServerHandler for ConformanceServer {
 } else {
 Err(ErrorData::resource_not_found(
 format!("Resource not found: {}", uri),
None,
Some(json!({ "uri": uri })),
 ))
 }
 }
Expand Down

17 changes: 15 additions & 2 deletions
crates/rmcp/src/handler/server.rs

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -22,7 +22,9 @@ impl<H: ServerHandler> Service<RoleServer> for H {
 request: <RoleServer as ServiceRole>::PeerReq,
 context: RequestContext<RoleServer>,
 ) -> Result<<RoleServer as ServiceRole>::Resp, McpError> {
 match request {
 // `context` is moved into the dispatch below, so read the negotiated version first.
 let protocol_version = context.protocol_version();
 let result = match request {
 ClientRequest::InitializeRequest(request) => self
 .initialize(request.params, context)
 .await
Expand DownExpand Up@@ -127,7 +129,18 @@ impl<H: ServerHandler> Service<RoleServer> for H {
 .cancel_task(request.params, context)
 .await
 .map(ServerResult::CancelTaskResult),
 }
 };
 // SEP-2164: peers negotiating 2026-07-28+ get the standard INVALID_PARAMS code for
 // resource-not-found; older peers keep RESOURCE_NOT_FOUND. ISO `YYYY-MM-DD` versions
 // compare lexically the same as chronologically.
 let use_invalid_params =
 protocol_version.is_some_and(|v| v.as_str() >= ProtocolVersion::V_2026_07_28.as_str());
 result.map_err(|mut error| {
 if use_invalid_params && error.code == ErrorCode::RESOURCE_NOT_FOUND {
 error.code = ErrorCode::INVALID_PARAMS;
 }
 error
 })
 }

 async fn handle_notification(
Expand Down

6 changes: 6 additions & 0 deletions
crates/rmcp/src/model.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -152,6 +152,7 @@ impl std::fmt::Display for ProtocolVersion {
}

impl ProtocolVersion {
 pub const V_2026_07_28: Self = Self(Cow::Borrowed("2026-07-28"));
 pub const V_2025_11_25: Self = Self(Cow::Borrowed("2025-11-25"));
 pub const V_2025_06_18: Self = Self(Cow::Borrowed("2025-06-18"));
 pub const V_2025_03_26: Self = Self(Cow::Borrowed("2025-03-26"));
Expand All@@ -164,6 +165,7 @@ impl ProtocolVersion {
 Self::V_2025_03_26,
 Self::V_2025_06_18,
 Self::V_2025_11_25,
 Self::V_2026_07_28,
 ];

 /// Returns the string representation of this protocol version.
Expand DownExpand Up@@ -193,6 +195,7 @@ impl<'de> Deserialize<'de> for ProtocolVersion {
 "2025-03-26" => return Ok(ProtocolVersion::V_2025_03_26),
 "2025-06-18" => return Ok(ProtocolVersion::V_2025_06_18),
 "2025-11-25" => return Ok(ProtocolVersion::V_2025_11_25),
 "2026-07-28" => return Ok(ProtocolVersion::V_2026_07_28),
 _ => {}
 }
 Ok(ProtocolVersion(Cow::Owned(s)))
Expand DownExpand Up@@ -541,9 +544,12 @@ impl ErrorData {
 data,
 }
 }
 /// Resource-not-found error (`-32002`). The server upgrades this to `INVALID_PARAMS`
 /// (`-32602`) for peers negotiating protocol `2026-07-28` or newer (SEP-2164).
 pub fn resource_not_found(message: impl Into<Cow<'static, str>>, data: Option<Value>) -> Self {
 Self::new(ErrorCode::RESOURCE_NOT_FOUND, message, data)
 }

 pub fn parse_error(message: impl Into<Cow<'static, str>>, data: Option<Value>) -> Self {
 Self::new(ErrorCode::PARSE_ERROR, message, data)
 }
Expand Down

10 changes: 10 additions & 0 deletions
crates/rmcp/src/service.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -674,6 +674,16 @@ impl<R: ServiceRole> RequestContext<R> {
 }
}

#[cfg(feature = "server")]
impl RequestContext<RoleServer> {
 /// The protocol version the client negotiated, or `None` before peer info is recorded.
 pub fn protocol_version(&self) -> Option<crate::model::ProtocolVersion> {
 self.peer
 .peer_info()
 .map(|info| info.protocol_version.clone())
 }
}

/// Request execution context
#[derive(Debug, Clone)]
#[non_exhaustive]
Expand Down

4 changes: 3 additions & 1 deletion
crates/rmcp/tests/test_custom_headers.rs

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -866,16 +866,18 @@ async fn test_server_rejects_unsupported_protocol_version() {
fn test_protocol_version_utilities() {
 use rmcp::model::ProtocolVersion;

 assert_eq!(ProtocolVersion::V_2026_07_28.as_str(), "2026-07-28");
 assert_eq!(ProtocolVersion::V_2025_11_25.as_str(), "2025-11-25");
 assert_eq!(ProtocolVersion::V_2025_06_18.as_str(), "2025-06-18");
 assert_eq!(ProtocolVersion::V_2025_03_26.as_str(), "2025-03-26");
 assert_eq!(ProtocolVersion::V_2024_11_05.as_str(), "2024-11-05");

 assert_eq!(ProtocolVersion::KNOWN_VERSIONS.len(), 4);
 assert_eq!(ProtocolVersion::KNOWN_VERSIONS.len(), 5);
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2024_11_05));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_03_26));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_06_18));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_11_25));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2026_07_28));
}

/// Integration test: Verify server validates only the Host header for DNS rebinding protection
Expand Down

91 changes: 91 additions & 0 deletions
crates/rmcp/tests/test_resource_not_found_version.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -0,0 +1,91 @@
//! SEP-2164: the resource-not-found error code follows the negotiated protocol version.
//!
//! `2026-07-28` and newer get the standard `INVALID_PARAMS` (-32602); older versions
//! keep the legacy `RESOURCE_NOT_FOUND` (-32002).
#![cfg(not(feature = "local"))]
#![cfg(feature = "client")]

use rmcp::{
 ClientHandler, RoleServer, ServerHandler, ServiceError, ServiceExt,
 model::{
 ClientInfo, ErrorCode, ErrorData, ProtocolVersion, ReadResourceRequestParams,
 ReadResourceResult,
 },
 service::RequestContext,
};

#[derive(Debug, Clone, Default)]
struct ResourceServer;

impl ServerHandler for ResourceServer {
 async fn read_resource(
 &self,
 _request: ReadResourceRequestParams,
 _context: RequestContext<RoleServer>,
 ) -> Result<ReadResourceResult, ErrorData> {
 Err(ErrorData::resource_not_found("resource not found", None))
 }
}

#[derive(Debug, Clone)]
struct VersionedClient {
 protocol_version: ProtocolVersion,
}

impl ClientHandler for VersionedClient {
 fn get_info(&self) -> ClientInfo {
 let mut info = ClientInfo::default();
 info.protocol_version = self.protocol_version.clone();
 info
 }
}

async fn not_found_code(client_version: ProtocolVersion) -> ErrorCode {
 let (server_transport, client_transport) = tokio::io::duplex(4096);

 let server_handle = tokio::spawn(async move {
 ResourceServer
 .serve(server_transport)
 .await?
 .waiting()
 .await?;
 anyhow::Ok(())
 });

 let client = VersionedClient {
 protocol_version: client_version,
 }
 .serve(client_transport)
 .await
 .expect("client should connect");

 let error = client
 .read_resource(ReadResourceRequestParams::new("missing://resource"))
 .await
 .expect_err("missing resource should error");

 let code = match error {
 ServiceError::McpError(data) => data.code,
 other => panic!("expected McpError, got: {other:?}"),
 };

 client.cancel().await.expect("client should cancel");
 server_handle.await.expect("server task").expect("server");
 code
}

#[tokio::test]
async fn legacy_version_gets_resource_not_found_code() {
 assert_eq!(
 not_found_code(ProtocolVersion::V_2025_11_25).await,
 ErrorCode::RESOURCE_NOT_FOUND,
 );
}

#[tokio::test]
async fn sep_2164_version_gets_invalid_params_code() {
 assert_eq!(
 not_found_code(ProtocolVersion::V_2026_07_28).await,
 ErrorCode::INVALID_PARAMS,
 );
}

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Remove or un-stick sticky/fixed headers that block content
(function() {
function unstick() {
document.querySelectorAll('header, nav, [role="banner"], .header, .navbar, .sticky, .fixed-top, [style*="position: fixed"], [style*="position:sticky"]').forEach(function(el) {
if (el.style.position === 'fixed' || el.style.position === 'sticky' || getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {
el.style.position = 'static';
el.style.top = 'auto';
el.style.zIndex = 'auto';
}
});
}
unstick();
var observer = new MutationObserver(unstick);
observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });
})();
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
feat: standardize resource-not-found error code (SEP-2164) by DaleSeo · Pull Request #899 · modelcontextprotocol/rust-sdk · GitHub
Skip to content
feat: standardize resource-not-found error code (SEP-2164)#899

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 Merged

DaleSeo
merged 3 commits into

from

Jun 17, 2026
 Merged


feat: standardize resource-not-found error code (SEP-2164)
#899
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ceffe06

feat: implement SEP-2164 resource not found errors


michaelneale Jun 5, 2026
ebaaa46

test: update protocol version utility expectations


michaelneale Jun 7, 2026
8a26837

feat: gate not-found code at server boundary


DaleSeo Jun 10, 2026

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2 changes: 1 addition & 1 deletion
conformance/src/bin/server.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -615,7 +615,7 @@ impl ServerHandler for ConformanceServer {
 } else {
 Err(ErrorData::resource_not_found(
 format!("Resource not found: {}", uri),
None,
Some(json!({ "uri": uri })),
 ))
 }
 }
Expand Down

17 changes: 15 additions & 2 deletions
crates/rmcp/src/handler/server.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -22,7 +22,9 @@ impl<H: ServerHandler> Service<RoleServer> for H {
 request: <RoleServer as ServiceRole>::PeerReq,
 context: RequestContext<RoleServer>,
 ) -> Result<<RoleServer as ServiceRole>::Resp, McpError> {
 match request {
 // `context` is moved into the dispatch below, so read the negotiated version first.
 let protocol_version = context.protocol_version();
 let result = match request {
 ClientRequest::InitializeRequest(request) => self
 .initialize(request.params, context)
 .await
Expand DownExpand Up@@ -127,7 +129,18 @@ impl<H: ServerHandler> Service<RoleServer> for H {
 .cancel_task(request.params, context)
 .await
 .map(ServerResult::CancelTaskResult),
 }
 };
 // SEP-2164: peers negotiating 2026-07-28+ get the standard INVALID_PARAMS code for
 // resource-not-found; older peers keep RESOURCE_NOT_FOUND. ISO `YYYY-MM-DD` versions
 // compare lexically the same as chronologically.
 let use_invalid_params =
 protocol_version.is_some_and(|v| v.as_str() >= ProtocolVersion::V_2026_07_28.as_str());
 result.map_err(|mut error| {
 if use_invalid_params && error.code == ErrorCode::RESOURCE_NOT_FOUND {
 error.code = ErrorCode::INVALID_PARAMS;
 }
 error
 })
 }

 async fn handle_notification(
Expand Down

6 changes: 6 additions & 0 deletions
crates/rmcp/src/model.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -152,6 +152,7 @@ impl std::fmt::Display for ProtocolVersion {
}

impl ProtocolVersion {
 pub const V_2026_07_28: Self = Self(Cow::Borrowed("2026-07-28"));
 pub const V_2025_11_25: Self = Self(Cow::Borrowed("2025-11-25"));
 pub const V_2025_06_18: Self = Self(Cow::Borrowed("2025-06-18"));
 pub const V_2025_03_26: Self = Self(Cow::Borrowed("2025-03-26"));
Expand All@@ -164,6 +165,7 @@ impl ProtocolVersion {
 Self::V_2025_03_26,
 Self::V_2025_06_18,
 Self::V_2025_11_25,
 Self::V_2026_07_28,
 ];

 /// Returns the string representation of this protocol version.
Expand DownExpand Up@@ -193,6 +195,7 @@ impl<'de> Deserialize<'de> for ProtocolVersion {
 "2025-03-26" => return Ok(ProtocolVersion::V_2025_03_26),
 "2025-06-18" => return Ok(ProtocolVersion::V_2025_06_18),
 "2025-11-25" => return Ok(ProtocolVersion::V_2025_11_25),
 "2026-07-28" => return Ok(ProtocolVersion::V_2026_07_28),
 _ => {}
 }
 Ok(ProtocolVersion(Cow::Owned(s)))
Expand DownExpand Up@@ -541,9 +544,12 @@ impl ErrorData {
 data,
 }
 }
 /// Resource-not-found error (`-32002`). The server upgrades this to `INVALID_PARAMS`
 /// (`-32602`) for peers negotiating protocol `2026-07-28` or newer (SEP-2164).
 pub fn resource_not_found(message: impl Into<Cow<'static, str>>, data: Option<Value>) -> Self {
 Self::new(ErrorCode::RESOURCE_NOT_FOUND, message, data)
 }

 pub fn parse_error(message: impl Into<Cow<'static, str>>, data: Option<Value>) -> Self {
 Self::new(ErrorCode::PARSE_ERROR, message, data)
 }
Expand Down

10 changes: 10 additions & 0 deletions
crates/rmcp/src/service.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -674,6 +674,16 @@ impl<R: ServiceRole> RequestContext<R> {
 }
}

#[cfg(feature = "server")]
impl RequestContext<RoleServer> {
 /// The protocol version the client negotiated, or `None` before peer info is recorded.
 pub fn protocol_version(&self) -> Option<crate::model::ProtocolVersion> {
 self.peer
 .peer_info()
 .map(|info| info.protocol_version.clone())
 }
}

/// Request execution context
#[derive(Debug, Clone)]
#[non_exhaustive]
Expand Down

4 changes: 3 additions & 1 deletion
crates/rmcp/tests/test_custom_headers.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -866,16 +866,18 @@ async fn test_server_rejects_unsupported_protocol_version() {
fn test_protocol_version_utilities() {
 use rmcp::model::ProtocolVersion;

 assert_eq!(ProtocolVersion::V_2026_07_28.as_str(), "2026-07-28");
 assert_eq!(ProtocolVersion::V_2025_11_25.as_str(), "2025-11-25");
 assert_eq!(ProtocolVersion::V_2025_06_18.as_str(), "2025-06-18");
 assert_eq!(ProtocolVersion::V_2025_03_26.as_str(), "2025-03-26");
 assert_eq!(ProtocolVersion::V_2024_11_05.as_str(), "2024-11-05");

 assert_eq!(ProtocolVersion::KNOWN_VERSIONS.len(), 4);
 assert_eq!(ProtocolVersion::KNOWN_VERSIONS.len(), 5);
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2024_11_05));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_03_26));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_06_18));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_11_25));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2026_07_28));
}

/// Integration test: Verify server validates only the Host header for DNS rebinding protection
Expand Down

91 changes: 91 additions & 0 deletions
crates/rmcp/tests/test_resource_not_found_version.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -0,0 +1,91 @@
//! SEP-2164: the resource-not-found error code follows the negotiated protocol version.
//!
//! `2026-07-28` and newer get the standard `INVALID_PARAMS` (-32602); older versions
//! keep the legacy `RESOURCE_NOT_FOUND` (-32002).
#![cfg(not(feature = "local"))]
#![cfg(feature = "client")]

use rmcp::{
 ClientHandler, RoleServer, ServerHandler, ServiceError, ServiceExt,
 model::{
 ClientInfo, ErrorCode, ErrorData, ProtocolVersion, ReadResourceRequestParams,
 ReadResourceResult,
 },
 service::RequestContext,
};

#[derive(Debug, Clone, Default)]
struct ResourceServer;

impl ServerHandler for ResourceServer {
 async fn read_resource(
 &self,
 _request: ReadResourceRequestParams,
 _context: RequestContext<RoleServer>,
 ) -> Result<ReadResourceResult, ErrorData> {
 Err(ErrorData::resource_not_found("resource not found", None))
 }
}

#[derive(Debug, Clone)]
struct VersionedClient {
 protocol_version: ProtocolVersion,
}

impl ClientHandler for VersionedClient {
 fn get_info(&self) -> ClientInfo {
 let mut info = ClientInfo::default();
 info.protocol_version = self.protocol_version.clone();
 info
 }
}

async fn not_found_code(client_version: ProtocolVersion) -> ErrorCode {
 let (server_transport, client_transport) = tokio::io::duplex(4096);

 let server_handle = tokio::spawn(async move {
 ResourceServer
 .serve(server_transport)
 .await?
 .waiting()
 .await?;
 anyhow::Ok(())
 });

 let client = VersionedClient {
 protocol_version: client_version,
 }
 .serve(client_transport)
 .await
 .expect("client should connect");

 let error = client
 .read_resource(ReadResourceRequestParams::new("missing://resource"))
 .await
 .expect_err("missing resource should error");

 let code = match error {
 ServiceError::McpError(data) => data.code,
 other => panic!("expected McpError, got: {other:?}"),
 };

 client.cancel().await.expect("client should cancel");
 server_handle.await.expect("server task").expect("server");
 code
}

#[tokio::test]
async fn legacy_version_gets_resource_not_found_code() {
 assert_eq!(
 not_found_code(ProtocolVersion::V_2025_11_25).await,
 ErrorCode::RESOURCE_NOT_FOUND,
 );
}

#[tokio::test]
async fn sep_2164_version_gets_invalid_params_code() {
 assert_eq!(
 not_found_code(ProtocolVersion::V_2026_07_28).await,
 ErrorCode::INVALID_PARAMS,
 );
}

, 'i');
if (__m === '*' || __re.test(location.href)) {
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if (!enabled) return;
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var style = document.getElementById('universal-dark-mode-style');
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style = document.createElement('style');
style.id = 'universal-dark-mode-style';
document.head.appendChild(style);
}
// Dark mode CSS - inverts colors but preserves images/video
style.textContent = '
/* Invert everything except media */
html {
filter: invert(1) hue-rotate(180deg) !important;
background: #1a1a2e !important;
}
/* Restore images, videos, iframes, canvas */
img, video, iframe, canvas, svg, picture, [style*="background-image"] {
filter: invert(1) hue-rotate(180deg) !important;
}
/* Preserve specific elements that should not be inverted */
.no-dark-mode, .no-dark-mode *,
[data-theme="light"], [data-theme="light"],
.ace_editor, .ace_editor *,
.CodeMirror, .CodeMirror *,
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.highlight, .highlight *,
pre code, pre code * {
filter: none !important;
}
/* Fix common UI elements */
.modal, .popup, .dropdown-menu, .tooltip, .popover {
filter: invert(1) hue-rotate(180deg) !important;
background: #2d2d44 !important;
border-color: #444 !important;
}
/* Scrollbars */
::-webkit-scrollbar { background: #1a1a2e !important; }
::-webkit-scrollbar-thumb { background: #444 !important; }
::-webkit-scrollbar-thumb:hover { background: #555 !important; }
/* Selection */
::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }
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';
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} else {
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}
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} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
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feat: standardize resource-not-found error code (SEP-2164) by DaleSeo · Pull Request #899 · modelcontextprotocol/rust-sdk · GitHub
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feat: standardize resource-not-found error code (SEP-2164)#899

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 Merged

DaleSeo
merged 3 commits into

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Jun 17, 2026
 Merged


feat: standardize resource-not-found error code (SEP-2164)
#899
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ceffe06

feat: implement SEP-2164 resource not found errors


michaelneale Jun 5, 2026
ebaaa46

test: update protocol version utility expectations


michaelneale Jun 7, 2026
8a26837

feat: gate not-found code at server boundary


DaleSeo Jun 10, 2026

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2 changes: 1 addition & 1 deletion
conformance/src/bin/server.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -615,7 +615,7 @@ impl ServerHandler for ConformanceServer {
 } else {
 Err(ErrorData::resource_not_found(
 format!("Resource not found: {}", uri),
None,
Some(json!({ "uri": uri })),
 ))
 }
 }
Expand Down

17 changes: 15 additions & 2 deletions
crates/rmcp/src/handler/server.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -22,7 +22,9 @@ impl<H: ServerHandler> Service<RoleServer> for H {
 request: <RoleServer as ServiceRole>::PeerReq,
 context: RequestContext<RoleServer>,
 ) -> Result<<RoleServer as ServiceRole>::Resp, McpError> {
 match request {
 // `context` is moved into the dispatch below, so read the negotiated version first.
 let protocol_version = context.protocol_version();
 let result = match request {
 ClientRequest::InitializeRequest(request) => self
 .initialize(request.params, context)
 .await
Expand DownExpand Up@@ -127,7 +129,18 @@ impl<H: ServerHandler> Service<RoleServer> for H {
 .cancel_task(request.params, context)
 .await
 .map(ServerResult::CancelTaskResult),
 }
 };
 // SEP-2164: peers negotiating 2026-07-28+ get the standard INVALID_PARAMS code for
 // resource-not-found; older peers keep RESOURCE_NOT_FOUND. ISO `YYYY-MM-DD` versions
 // compare lexically the same as chronologically.
 let use_invalid_params =
 protocol_version.is_some_and(|v| v.as_str() >= ProtocolVersion::V_2026_07_28.as_str());
 result.map_err(|mut error| {
 if use_invalid_params && error.code == ErrorCode::RESOURCE_NOT_FOUND {
 error.code = ErrorCode::INVALID_PARAMS;
 }
 error
 })
 }

 async fn handle_notification(
Expand Down

6 changes: 6 additions & 0 deletions
crates/rmcp/src/model.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -152,6 +152,7 @@ impl std::fmt::Display for ProtocolVersion {
}

impl ProtocolVersion {
 pub const V_2026_07_28: Self = Self(Cow::Borrowed("2026-07-28"));
 pub const V_2025_11_25: Self = Self(Cow::Borrowed("2025-11-25"));
 pub const V_2025_06_18: Self = Self(Cow::Borrowed("2025-06-18"));
 pub const V_2025_03_26: Self = Self(Cow::Borrowed("2025-03-26"));
Expand All@@ -164,6 +165,7 @@ impl ProtocolVersion {
 Self::V_2025_03_26,
 Self::V_2025_06_18,
 Self::V_2025_11_25,
 Self::V_2026_07_28,
 ];

 /// Returns the string representation of this protocol version.
Expand DownExpand Up@@ -193,6 +195,7 @@ impl<'de> Deserialize<'de> for ProtocolVersion {
 "2025-03-26" => return Ok(ProtocolVersion::V_2025_03_26),
 "2025-06-18" => return Ok(ProtocolVersion::V_2025_06_18),
 "2025-11-25" => return Ok(ProtocolVersion::V_2025_11_25),
 "2026-07-28" => return Ok(ProtocolVersion::V_2026_07_28),
 _ => {}
 }
 Ok(ProtocolVersion(Cow::Owned(s)))
Expand DownExpand Up@@ -541,9 +544,12 @@ impl ErrorData {
 data,
 }
 }
 /// Resource-not-found error (`-32002`). The server upgrades this to `INVALID_PARAMS`
 /// (`-32602`) for peers negotiating protocol `2026-07-28` or newer (SEP-2164).
 pub fn resource_not_found(message: impl Into<Cow<'static, str>>, data: Option<Value>) -> Self {
 Self::new(ErrorCode::RESOURCE_NOT_FOUND, message, data)
 }

 pub fn parse_error(message: impl Into<Cow<'static, str>>, data: Option<Value>) -> Self {
 Self::new(ErrorCode::PARSE_ERROR, message, data)
 }
Expand Down

10 changes: 10 additions & 0 deletions
crates/rmcp/src/service.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -674,6 +674,16 @@ impl<R: ServiceRole> RequestContext<R> {
 }
}

#[cfg(feature = "server")]
impl RequestContext<RoleServer> {
 /// The protocol version the client negotiated, or `None` before peer info is recorded.
 pub fn protocol_version(&self) -> Option<crate::model::ProtocolVersion> {
 self.peer
 .peer_info()
 .map(|info| info.protocol_version.clone())
 }
}

/// Request execution context
#[derive(Debug, Clone)]
#[non_exhaustive]
Expand Down

4 changes: 3 additions & 1 deletion
crates/rmcp/tests/test_custom_headers.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -866,16 +866,18 @@ async fn test_server_rejects_unsupported_protocol_version() {
fn test_protocol_version_utilities() {
 use rmcp::model::ProtocolVersion;

 assert_eq!(ProtocolVersion::V_2026_07_28.as_str(), "2026-07-28");
 assert_eq!(ProtocolVersion::V_2025_11_25.as_str(), "2025-11-25");
 assert_eq!(ProtocolVersion::V_2025_06_18.as_str(), "2025-06-18");
 assert_eq!(ProtocolVersion::V_2025_03_26.as_str(), "2025-03-26");
 assert_eq!(ProtocolVersion::V_2024_11_05.as_str(), "2024-11-05");

 assert_eq!(ProtocolVersion::KNOWN_VERSIONS.len(), 4);
 assert_eq!(ProtocolVersion::KNOWN_VERSIONS.len(), 5);
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2024_11_05));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_03_26));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_06_18));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2025_11_25));
 assert!(ProtocolVersion::KNOWN_VERSIONS.contains(&ProtocolVersion::V_2026_07_28));
}

/// Integration test: Verify server validates only the Host header for DNS rebinding protection
Expand Down

91 changes: 91 additions & 0 deletions
crates/rmcp/tests/test_resource_not_found_version.rs

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,91 @@
//! SEP-2164: the resource-not-found error code follows the negotiated protocol version.
//!
//! `2026-07-28` and newer get the standard `INVALID_PARAMS` (-32602); older versions
//! keep the legacy `RESOURCE_NOT_FOUND` (-32002).
#![cfg(not(feature = "local"))]
#![cfg(feature = "client")]

use rmcp::{
 ClientHandler, RoleServer, ServerHandler, ServiceError, ServiceExt,
 model::{
 ClientInfo, ErrorCode, ErrorData, ProtocolVersion, ReadResourceRequestParams,
 ReadResourceResult,
 },
 service::RequestContext,
};

#[derive(Debug, Clone, Default)]
struct ResourceServer;

impl ServerHandler for ResourceServer {
 async fn read_resource(
 &self,
 _request: ReadResourceRequestParams,
 _context: RequestContext<RoleServer>,
 ) -> Result<ReadResourceResult, ErrorData> {
 Err(ErrorData::resource_not_found("resource not found", None))
 }
}

#[derive(Debug, Clone)]
struct VersionedClient {
 protocol_version: ProtocolVersion,
}

impl ClientHandler for VersionedClient {
 fn get_info(&self) -> ClientInfo {
 let mut info = ClientInfo::default();
 info.protocol_version = self.protocol_version.clone();
 info
 }
}

async fn not_found_code(client_version: ProtocolVersion) -> ErrorCode {
 let (server_transport, client_transport) = tokio::io::duplex(4096);

 let server_handle = tokio::spawn(async move {
 ResourceServer
 .serve(server_transport)
 .await?
 .waiting()
 .await?;
 anyhow::Ok(())
 });

 let client = VersionedClient {
 protocol_version: client_version,
 }
 .serve(client_transport)
 .await
 .expect("client should connect");

 let error = client
 .read_resource(ReadResourceRequestParams::new("missing://resource"))
 .await
 .expect_err("missing resource should error");

 let code = match error {
 ServiceError::McpError(data) => data.code,
 other => panic!("expected McpError, got: {other:?}"),
 };

 client.cancel().await.expect("client should cancel");
 server_handle.await.expect("server task").expect("server");
 code
}

#[tokio::test]
async fn legacy_version_gets_resource_not_found_code() {
 assert_eq!(
 not_found_code(ProtocolVersion::V_2025_11_25).await,
 ErrorCode::RESOURCE_NOT_FOUND,
 );
}

#[tokio::test]
async fn sep_2164_version_gets_invalid_params_code() {
 assert_eq!(
 not_found_code(ProtocolVersion::V_2026_07_28).await,
 ErrorCode::INVALID_PARAMS,
 );
}