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feat: stateless streamable http client #233

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Merged
merged 1 commit into from
May 28, 2025
Merged

feat: stateless streamable http client #233

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36 changes: 36 additions & 0 deletions crates/rmcp/src/transport/common/client_side_sse.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -76,6 +76,28 @@ impl SseRetryPolicy for ExponentialBackoff {
}
}

#[derive(Debug, Clone, Copy, Default)]
pub struct NeverRetry;

impl SseRetryPolicy for NeverRetry {
fn retry(&self, _current_times: usize) -> Option<Duration> {
None
}
}

#[derive(Debug, Default)]
pub struct NeverReconnect<E> {
error: Option<E>,
}

impl<E: std::error::Error + Send> SseStreamReconnect for NeverReconnect<E> {
type Error = E;
type Future = futures::future::Ready<Result<BoxedSseResponse, Self::Error>>;
fn retry_connection(&mut self, _last_event_id: Option<&str>) -> Self::Future {
futures::future::ready(Err(self.error.take().expect("should not be called again")))
}
}

pub(crate) trait SseStreamReconnect {
type Error: std::error::Error;
type Future: Future<Output = Result<BoxedSseResponse, Self::Error>> + Send;
Expand Down Expand Up @@ -111,6 +133,20 @@ impl<R: SseStreamReconnect> SseAutoReconnectStream<R> {
}
}

impl<E: std::error::Error + Send> SseAutoReconnectStream<NeverReconnect<E>> {
pub fn never_reconnect(stream: BoxedSseResponse, error_when_reconnect: E) -> Self {
Self {
retry_policy: Arc::new(NeverRetry),
last_event_id: None,
server_retry_interval: None,
connector: NeverReconnect {
error: Some(error_when_reconnect),
},
state: SseAutoReconnectStreamState::Connected { stream },
}
}
}

pin_project_lite::pin_project! {
#[project = SseAutoReconnectStreamStateProj]
pub enum SseAutoReconnectStreamState<F> {
Expand Down
141 changes: 81 additions & 60 deletions crates/rmcp/src/transport/streamable_http_client.rs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
use std::{borrow::Cow, sync::Arc, time::Duration};

use futures::{StreamExt, future::BoxFuture, stream::BoxStream};
use futures::{Stream, StreamExt, future::BoxFuture, stream::BoxStream};
pub use sse_stream::Error as SseError;
use sse_stream::Sse;
use thiserror::Error;
Expand Down Expand Up @@ -193,8 +193,7 @@ impl<C: StreamableHttpClient + Default> StreamableHttpClientWorker<C> {
client: C::default(),
config: StreamableHttpClientTransportConfig {
uri: url.into(),
retry_config: Arc::new(ExponentialBackoff::default()),
channel_buffer_capacity: 16,
..Default::default()
},
}
}
Expand All @@ -208,7 +207,9 @@ impl<C: StreamableHttpClient> StreamableHttpClientWorker<C> {

impl<C: StreamableHttpClient> StreamableHttpClientWorker<C> {
async fn execute_sse_stream(
sse_stream: SseAutoReconnectStream<StreamableHttpClientReconnect<C>>,
sse_stream: impl Stream<Item = Result<ServerJsonRpcMessage, StreamableHttpError<C::Error>>>
+ Send
+ 'static,
sse_worker_tx: tokio::sync::mpsc::Sender<ServerJsonRpcMessage>,
ct: CancellationToken,
) -> Result<(), StreamableHttpError<C::Error>> {
Expand Down Expand Up @@ -277,16 +278,19 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
.map_err(WorkerQuitReason::fatal_context(
"process initialize response",
))?;
let Some(session_id) = session_id else {
return Err(WorkerQuitReason::fatal(
"missing session id in initialize response",
"process initialize response",
));
let session_id: Option<Arc<str>> = if let Some(session_id) = session_id {
Some(session_id.into())
} else {
if !self.config.allow_stateless {
return Err(WorkerQuitReason::fatal(
"missing session id in initialize response",
"process initialize response",
));
}
None
};
let session_id: Arc<str> = session_id.into();

// delete session when drop guard is dropped
{
if let Some(session_id) = &session_id {
let ct = transport_task_ct.clone();
let client = self.client.clone();
let session_id = session_id.clone();
Expand Down Expand Up @@ -322,7 +326,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
.post_message(
config.uri.clone(),
initialized_notification.message,
Some(session_id.clone()),
session_id.clone(),
None,
)
.await
Expand All @@ -340,38 +344,40 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
StreamResult(Result<(), StreamableHttpError<E>>),
}
let mut streams = tokio::task::JoinSet::new();
match self
.client
.get_stream(config.uri.clone(), session_id.clone(), None, None)
.await
{
Ok(stream) => {
let sse_stream = SseAutoReconnectStream::new(
stream,
StreamableHttpClientReconnect {
client: self.client.clone(),
session_id: session_id.clone(),
uri: config.uri.clone(),
},
self.config.retry_config.clone(),
);
streams.spawn(Self::execute_sse_stream(
sse_stream,
sse_worker_tx.clone(),
transport_task_ct.child_token(),
));
tracing::debug!("got common stream");
}
Err(StreamableHttpError::SeverDoesNotSupportSse) => {
tracing::debug!("server doesn't support sse, skip common stream");
}
Err(e) => {
// fail to get common stream
tracing::error!("fail to get common stream: {e}");
return Err(WorkerQuitReason::fatal(
"fail to get general purpose event stream",
"get general purpose event stream",
));
if let Some(session_id) = &session_id {
match self
.client
.get_stream(config.uri.clone(), session_id.clone(), None, None)
.await
{
Ok(stream) => {
let sse_stream = SseAutoReconnectStream::new(
stream,
StreamableHttpClientReconnect {
client: self.client.clone(),
session_id: session_id.clone(),
uri: config.uri.clone(),
},
self.config.retry_config.clone(),
);
streams.spawn(Self::execute_sse_stream(
sse_stream,
sse_worker_tx.clone(),
transport_task_ct.child_token(),
));
tracing::debug!("got common stream");
}
Err(StreamableHttpError::SeverDoesNotSupportSse) => {
tracing::debug!("server doesn't support sse, skip common stream");
}
Err(e) => {
// fail to get common stream
tracing::error!("fail to get common stream: {e}");
return Err(WorkerQuitReason::fatal(
"fail to get general purpose event stream",
"get general purpose event stream",
));
}
}
}
loop {
Expand Down Expand Up @@ -407,7 +413,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
let WorkerSendRequest { message, responder } = send_request;
let response = self
.client
.post_message(config.uri.clone(), message, Some(session_id.clone()), None)
.post_message(config.uri.clone(), message, session_id.clone(), None)
.await;
let send_result = match response {
Err(e) => Err(e),
Expand All @@ -420,20 +426,32 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
Ok(())
}
Ok(StreamableHttpPostResponse::Sse(stream, ..)) => {
let sse_stream = SseAutoReconnectStream::new(
stream,
StreamableHttpClientReconnect {
client: self.client.clone(),
session_id: session_id.clone(),
uri: config.uri.clone(),
},
self.config.retry_config.clone(),
);
streams.spawn(Self::execute_sse_stream(
sse_stream,
sse_worker_tx.clone(),
transport_task_ct.child_token(),
));
if let Some(session_id) = &session_id {
let sse_stream = SseAutoReconnectStream::new(
stream,
StreamableHttpClientReconnect {
client: self.client.clone(),
session_id: session_id.clone(),
uri: config.uri.clone(),
},
self.config.retry_config.clone(),
);
streams.spawn(Self::execute_sse_stream(
sse_stream,
sse_worker_tx.clone(),
transport_task_ct.child_token(),
));
} else {
let sse_stream = SseAutoReconnectStream::never_reconnect(
stream,
StreamableHttpError::<C::Error>::UnexpectedEndOfStream,
);
streams.spawn(Self::execute_sse_stream(
sse_stream,
sse_worker_tx.clone(),
transport_task_ct.child_token(),
));
}
tracing::trace!("got new sse stream");
Ok(())
}
Expand Down Expand Up @@ -470,6 +488,8 @@ pub struct StreamableHttpClientTransportConfig {
pub uri: Arc<str>,
pub retry_config: Arc<dyn SseRetryPolicy>,
pub channel_buffer_capacity: usize,
/// if true, the transport will not require a session to be established
pub allow_stateless: bool,
}

impl StreamableHttpClientTransportConfig {
Expand All @@ -487,6 +507,7 @@ impl Default for StreamableHttpClientTransportConfig {
uri: "localhost".into(),
retry_config: Arc::new(ExponentialBackoff::default()),
channel_buffer_capacity: 16,
allow_stateless: true,
}
}
}