Skip to content

fix: conservatively retry legacy server initialization #1045

New issue

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

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Draft
tsarlandie-oai wants to merge 1 commit into
base: main
Choose a base branch
from
Draft

fix: conservatively retry legacy server initialization #1045

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
625 changes: 598 additions & 27 deletions crates/rmcp/src/service/client.rs
View file
Open in desktop

Large diffs are not rendered by default.

40 changes: 35 additions & 5 deletions crates/rmcp/src/transport/common/reqwest/streamable_http_client.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -165,6 +165,11 @@ impl StreamableHttpClient for reqwest::Client {
custom_headers: HashMap<HeaderName, HeaderValue>,
max_sse_event_size: usize,
) -> Result<StreamableHttpPostResponse, StreamableHttpError<Self::Error>> {
let is_discover_request = matches!(
&message,
ClientJsonRpcMessage::Request(request)
if matches!(&request.request, crate::model::ClientRequest::DiscoverRequest(_))
);
let mut request = self
.post(uri.as_ref())
.header(ACCEPT, [EVENT_STREAM_MIME_TYPE, JSON_MIME_TYPE].join(", "));
Expand Down Expand Up @@ -219,6 +224,21 @@ impl StreamableHttpClient for reqwest::Client {
if status == reqwest::StatusCode::NOT_FOUND && session_was_attached {
return Err(StreamableHttpError::SessionExpired);
}
if matches!(
status,
reqwest::StatusCode::UNAUTHORIZED
| reqwest::StatusCode::FORBIDDEN
| reqwest::StatusCode::NOT_FOUND
| reqwest::StatusCode::METHOD_NOT_ALLOWED
) {
let body = response
.text()
.await
.unwrap_or_else(|_| "<failed to read response body>".to_owned());
return Err(StreamableHttpError::UnexpectedHttpStatus(
HttpStatusError::new(status.as_u16(), body),
));
}
let content_type = response
.headers()
.get(reqwest::header::CONTENT_TYPE)
Expand Down Expand Up @@ -249,6 +269,11 @@ impl StreamableHttpClient for reqwest::Client {
.text()
.await
.unwrap_or_else(|_| "<failed to read response body>".to_owned());
if is_discover_request {
return Err(StreamableHttpError::UnexpectedHttpStatus(
HttpStatusError::new(status.as_u16(), body),
));
}
if content_type
.as_deref()
.is_some_and(|ct| ct.as_bytes().starts_with(JSON_MIME_TYPE.as_bytes()))
Expand All @@ -262,9 +287,9 @@ impl StreamableHttpClient for reqwest::Client {
),
}
}
return Err(StreamableHttpError::UnexpectedServerResponse(Cow::Owned(
format!("HTTP {status}: {body}"),
)));
return Err(StreamableHttpError::UnexpectedHttpStatus(
HttpStatusError::new(status.as_u16(), body),
));
}
match content_type.as_deref() {
Some(ct) if ct.as_bytes().starts_with(EVENT_STREAM_MIME_TYPE.as_bytes()) => {
Expand Down Expand Up @@ -472,7 +497,9 @@ mod tests {
use tokio::sync::Mutex;

use super::StreamableHttpClientTransport;
use crate::transport::streamable_http_client::{StreamableHttpClient, StreamableHttpError};
use crate::transport::streamable_http_client::{
HttpStatusError, StreamableHttpClient, StreamableHttpError,
};

const API_KEY_HEADER: &str = "x-api-key";
const API_KEY_VALUE: &str = "secret";
Expand Down Expand Up @@ -575,7 +602,10 @@ mod tests {
assert!(
matches!(
result,
Err(StreamableHttpError::UnexpectedServerResponse(_))
Err(StreamableHttpError::UnexpectedHttpStatus(HttpStatusError {
status: 307,
..
}))
),
"redirect response should be returned to the transport, got {result:?}"
);
Expand Down
6 changes: 3 additions & 3 deletions crates/rmcp/src/transport/common/unix_socket.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -274,9 +274,9 @@ impl StreamableHttpClient for UnixSocketHttpClient {
.await
.map(|c| String::from_utf8_lossy(&c.to_bytes()).into_owned())
.unwrap_or_else(|_| "<failed to read response body>".to_owned());
return Err(StreamableHttpError::UnexpectedServerResponse(Cow::Owned(
format!("HTTP {status}: {body}"),
)));
return Err(StreamableHttpError::UnexpectedHttpStatus(
HttpStatusError::new(status.as_u16(), body),
));
}

let content_type = response.headers().get(http::header::CONTENT_TYPE).cloned();
Expand Down
175 changes: 129 additions & 46 deletions crates/rmcp/src/transport/streamable_http_client.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -20,8 +20,8 @@ use crate::{
RoleClient,
model::{
ClientJsonRpcMessage, ClientNotification, ClientRequest, ErrorData, GetMeta,
InitializedNotification, JsonObject, ProtocolVersion, RequestId, ServerJsonRpcMessage,
ServerResult,
InitializedNotification, JsonObject, JsonRpcMessage, ProtocolVersion, RequestId,
ServerJsonRpcMessage, ServerResult,
},
transport::{
common::{client_side_sse::SseAutoReconnectStream, mcp_headers},
Expand Down Expand Up @@ -168,6 +168,35 @@ impl InsufficientScopeError {
}
}

/// A non-success HTTP response, including the status and response body.
///
/// Keeping this error independent of the HTTP client implementation lets
/// lifecycle negotiation inspect the response consistently for reqwest,
/// custom [`StreamableHttpClient`] implementations, and Unix-socket clients.
#[derive(Error, Debug)]
#[error("unexpected HTTP status {status}: {body}")]
#[non_exhaustive]
pub struct HttpStatusError {
pub status: u16,
pub body: Cow<'static, str>,
}

impl HttpStatusError {
pub fn new(status: u16, body: impl Into<Cow<'static, str>>) -> Self {
Self {
status,
body: body.into(),
}
}

fn json_rpc_error(&self) -> Option<ServerJsonRpcMessage> {
match serde_json::from_str::<ServerJsonRpcMessage>(&self.body) {
Ok(message @ JsonRpcMessage::Error(_)) => Some(message),
_ => None,
}
}
}

#[derive(Error, Debug)]
#[non_exhaustive]
pub enum StreamableHttpError<E: std::error::Error + Send + Sync + 'static> {
Expand All @@ -181,6 +210,8 @@ pub enum StreamableHttpError<E: std::error::Error + Send + Sync + 'static> {
UnexpectedEndOfStream,
#[error("unexpected server response: {0}")]
UnexpectedServerResponse(Cow<'static, str>),
#[error("{0}")]
UnexpectedHttpStatus(#[source] HttpStatusError),
#[error("Unexpected content type: {0:?}")]
UnexpectedContentType(Option<String>),
#[error("Server does not support SSE")]
Expand Down Expand Up @@ -324,6 +355,12 @@ impl StreamableHttpPostResponse {
/// [`Self::post_message_with_max_sse_event_size`] and
/// [`Self::get_stream_with_max_sse_event_size`] to enforce the transport's
/// configured event-size limit.
///
/// For a non-success response to an initial `server/discover` request,
/// implementations should return
/// [`StreamableHttpError::UnexpectedHttpStatus`] with the original status and
/// body. [`ClientLifecycleMode::Auto`](crate::service::ClientLifecycleMode::Auto)
/// uses that typed response to decide whether a legacy retry is safe.
pub trait StreamableHttpClient: Clone + Send + 'static {
type Error: std::error::Error + Send + Sync + 'static;
fn post_message(
Expand Down Expand Up @@ -833,54 +870,100 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
let config = self.config.clone();
let transport_task_ct = context.cancellation_token.clone();
let _drop_guard = transport_task_ct.clone().drop_guard();
let WorkerSendRequest {
responder,
message: startup_request,
} = context.recv_from_handler().await?;
let is_legacy_startup = matches!(
&startup_request,
ClientJsonRpcMessage::Request(request)
if matches!(&request.request, ClientRequest::InitializeRequest(_))
);
let mut saved_init_request = is_legacy_startup.then(|| startup_request.clone());
let empty_tool_cache = HashMap::new();
let (bootstrap_version, bootstrap_headers) = if is_legacy_startup {
(ProtocolVersion::default(), config.custom_headers.clone())
} else {
request_version_headers(
&config.custom_headers,
let (
startup_request,
is_legacy_startup,
bootstrap_version,
bootstrap_headers,
message,
session_id,
) = loop {
let WorkerSendRequest {
responder,
message: startup_request,
} = context.recv_from_handler().await?;
let is_legacy_startup = matches!(
&startup_request,
&ProtocolVersion::default(),
&empty_tool_cache,
)
};
let (message, session_id) = match self
.client
.post_message_with_max_sse_event_size(
config.uri.clone(),
startup_request,
None,
config.auth_header.clone(),
bootstrap_headers.clone(),
config.max_sse_event_size,
)
.await
{
Ok(res) => {
let _ = responder.send(Ok(()));
res.expect_initialized::<C::Error>().await.map_err(
WorkerQuitReason::fatal_context("process initialize response"),
)?
}
Err(err) => {
let msg = format!("{:?}", err);
let _ = responder.send(Err(err));
return Err(WorkerQuitReason::fatal(
StreamableHttpError::TransportChannelClosed,
msg,
));
ClientJsonRpcMessage::Request(request)
if matches!(&request.request, ClientRequest::InitializeRequest(_))
);
let is_discover_startup = matches!(
&startup_request,
ClientJsonRpcMessage::Request(request)
if matches!(&request.request, ClientRequest::DiscoverRequest(_))
);
let (bootstrap_version, bootstrap_headers) = if is_legacy_startup {
(ProtocolVersion::default(), config.custom_headers.clone())
} else {
request_version_headers(
&config.custom_headers,
&startup_request,
&ProtocolVersion::default(),
&empty_tool_cache,
)
};
match self
.client
.post_message_with_max_sse_event_size(
config.uri.clone(),
startup_request.clone(),
None,
config.auth_header.clone(),
bootstrap_headers.clone(),
config.max_sse_event_size,
)
.await
{
Ok(response) => {
let _ = responder.send(Ok(()));
let (message, session_id) =
response.expect_initialized::<C::Error>().await.map_err(
WorkerQuitReason::fatal_context("process initialize response"),
)?;
break (
startup_request,
is_legacy_startup,
bootstrap_version,
bootstrap_headers,
message,
session_id,
);
}
Err(StreamableHttpError::UnexpectedHttpStatus(error)) if is_discover_startup => {
if error.status == 400
&& let Some(message) = error.json_rpc_error()
{
// An HTTP 400 can still carry a valid JSON-RPC
// discovery error. Route it through normal negotiation
// so a correlated unsupported-version response can
// select or retry another modern version.
let _ = responder.send(Ok(()));
break (
startup_request,
is_legacy_startup,
bootstrap_version,
bootstrap_headers,
message,
None,
);
}

// Surface raw prevalidation failures to Auto mode but keep
// the worker available for a possible legacy initialize.
let _ = responder.send(Err(StreamableHttpError::UnexpectedHttpStatus(error)));
}
Err(error) => {
let message = format!("{error:?}");
let _ = responder.send(Err(error));
return Err(WorkerQuitReason::fatal(
StreamableHttpError::TransportChannelClosed,
message,
));
}
}
};
let mut saved_init_request = is_legacy_startup.then(|| startup_request.clone());
let mut uses_modern_http = !is_legacy_startup;
let mut session_id: Option<Arc<str>> = if uses_modern_http {
None
Expand Down
Loading