fix(streamable-http): preserve progress in JSON mode#990

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Merged
alexhancock merged 1 commit into from
Jul 14, 2026
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fix(streamable-http): preserve progress in JSON mode #990

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61 changes: 39 additions & 22 deletions crates/rmcp/src/transport/streamable_http_server/tower.rs
View file
Open in desktop
Original file line numberDiff line numberDiff line change
Expand Up@@ -19,6 +19,7 @@ use crate::{
ClientCapabilities, ClientJsonRpcMessage, ClientNotification, ClientRequest, ErrorData,
GetExtensions, Implementation, InitializeRequest, InitializeRequestParams,
InitializedNotification, JsonObject, JsonRpcError, ProtocolVersion, RequestId,
ServerJsonRpcMessage,
},
serve_server,
service::serve_directly,
Expand DownExpand Up@@ -48,10 +49,10 @@ pub struct StreamableHttpServerConfig {
/// If true, the server will create a session for each request and keep it alive.
/// When enabled, SSE priming events are sent to enable client reconnection.
pub stateful_mode: bool,
/// When true and `stateful_mode` is false, the server returns
/// `Content-Type: application/json` directly instead of `text/event-stream`.
/// This eliminates SSE framing overhead for simple request-response tools,
/// allowed by the MCP Streamable HTTP spec (2025-06-18).
/// When true and `stateful_mode` is false, the server prefers
/// `Content-Type: application/json` for simple request-response tools.
/// If the handler emits a notification or request before the final response,
/// the server falls back to `text/event-stream` so no message is lost.
pub json_response: bool,
/// Cancellation token for the Streamable HTTP server.
///
Expand DownExpand Up@@ -1352,31 +1353,47 @@ where
let _ = service.waiting().await;
});
if self.config.json_response {
// JSON-direct mode: await the single response and return as
// application/json, eliminating SSE framing overhead.
// Allowed by MCP Streamable HTTP spec (2025-06-18).
// Prefer JSON for a terminal first message. If the handler
// emits an intermediate notification or request, preserve
// the complete message sequence by falling back to SSE.
let cancel = self.config.cancellation_token.child_token();
match tokio::select! {
let Some(message) = (tokio::select! {
res = receiver.recv() => res,
_ = cancel.cancelled() => None,
} {
Some(message) => {
tracing::trace!(?message);
let body = serde_json::to_vec(&message).map_err(|e| {
internal_error_response("serialize json response")(e)
})?;
Ok(Response::builder()
.status(http::StatusCode::OK)
.header(http::header::CONTENT_TYPE, JSON_MIME_TYPE)
.body(Full::new(Bytes::from(body)).boxed())
.expect("valid response"))
}
None => Err(internal_error_response("empty response")(
}) else {
return Err(internal_error_response("empty response")(
std::io::Error::new(
std::io::ErrorKind::UnexpectedEof,
"no response message received from handler",
),
)),
));
};
tracing::trace!(?message);
if matches!(
message,
ServerJsonRpcMessage::Response(_) | ServerJsonRpcMessage::Error(_)
) {
let body = serde_json::to_vec(&message).map_err(|e| {
internal_error_response("serialize json response")(e)
})?;
Ok(Response::builder()
.status(http::StatusCode::OK)
.header(http::header::CONTENT_TYPE, JSON_MIME_TYPE)
.body(Full::new(Bytes::from(body)).boxed())
.expect("valid response"))
} else {
let first = futures::stream::once(async move {
ServerSseMessage::from_message(message)
});
let remaining = ReceiverStream::new(receiver).map(|message| {
tracing::trace!(?message);
ServerSseMessage::from_message(message)
});
Ok(sse_stream_response(
first.chain(remaining),
self.config.sse_keep_alive,
self.config.cancellation_token.child_token(),
))
}
} else {
// SSE mode (default): original behaviour preserved unchanged
Expand Down
120 changes: 118 additions & 2 deletions crates/rmcp/tests/test_streamable_http_json_response.rs
View file
Open in desktop
Original file line numberDiff line numberDiff line change
@@ -1,13 +1,52 @@
#![cfg(not(feature = "local"))]
use rmcp::transport::streamable_http_server::{
StreamableHttpServerConfig, StreamableHttpService, session::local::LocalSessionManager,
use rmcp::{
ErrorData, ServerHandler,
model::{
CallToolRequestParams, CallToolResponse, CallToolResult, ContentBlock,
ProgressNotificationParam, ServerCapabilities, ServerInfo,
},
service::RequestContext,
transport::streamable_http_server::{
StreamableHttpServerConfig, StreamableHttpService, session::local::LocalSessionManager,
},
};
use tokio_util::sync::CancellationToken;

mod common;
use common::calculator::Calculator;

const INIT_BODY: &str = r#"{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-03-26","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}"#;
const CALL_WITH_PROGRESS_BODY: &str = r#"{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"progress","arguments":{},"_meta":{"progressToken":"progress-test-1"}}}"#;

#[derive(Clone)]
struct ProgressServer;

impl ServerHandler for ProgressServer {
fn get_info(&self) -> ServerInfo {
ServerInfo::new(ServerCapabilities::builder().enable_tools().build())
}

async fn call_tool(
&self,
_request: CallToolRequestParams,
context: RequestContext<rmcp::RoleServer>,
) -> Result<CallToolResponse, ErrorData> {
let progress_token = context
.meta
.get_progress_token()
.expect("request includes progressToken");
context
.peer
.notify_progress(
ProgressNotificationParam::new(progress_token, 50.0)
.with_total(100.0)
.with_message("working"),
)
.await
.expect("progress notification is delivered");
Ok(CallToolResult::success(vec![ContentBlock::text("done")]).into())
}
}

async fn spawn_server(
config: StreamableHttpServerConfig,
Expand All@@ -34,6 +73,31 @@ async fn spawn_server(
(client, base_url, ct)
}

async fn spawn_progress_server(
config: StreamableHttpServerConfig,
) -> (reqwest::Client, String, CancellationToken) {
let ct = config.cancellation_token.clone();
let service: StreamableHttpService<ProgressServer, LocalSessionManager> =
StreamableHttpService::new(|| Ok(ProgressServer), Default::default(), config);

let router = axum::Router::new().nest_service("/mcp", service);
let tcp_listener = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
let addr = tcp_listener.local_addr().unwrap();

tokio::spawn({
let ct = ct.clone();
async move {
let _ = axum::serve(tcp_listener, router)
.with_graceful_shutdown(async move { ct.cancelled_owned().await })
.await;
}
});

let client = reqwest::Client::new();
let base_url = format!("http://{addr}/mcp");
(client, base_url, ct)
}

#[tokio::test]
async fn stateless_json_response_returns_application_json() -> anyhow::Result<()> {
let ct = CancellationToken::new();
Expand DownExpand Up@@ -76,6 +140,58 @@ async fn stateless_json_response_returns_application_json() -> anyhow::Result<()
Ok(())
}

#[tokio::test]
async fn stateless_json_response_falls_back_to_sse_for_progress() -> anyhow::Result<()> {
let ct = CancellationToken::new();
let (client, url, ct) = spawn_progress_server(
StreamableHttpServerConfig::default()
.with_stateful_mode(false)
.with_json_response(true)
.with_sse_keep_alive(None)
.with_cancellation_token(ct.child_token()),
)
.await;

let response = client
.post(&url)
.header("Content-Type", "application/json")
.header("Accept", "application/json, text/event-stream")
.body(CALL_WITH_PROGRESS_BODY)
.send()
.await?;

assert_eq!(response.status(), 200);

let content_type = response
.headers()
.get("content-type")
.and_then(|value| value.to_str().ok())
.unwrap_or("");
assert!(
content_type.contains("text/event-stream"),
"Expected SSE fallback, got: {content_type}"
);

let body = response.text().await?;
let messages: Vec<serde_json::Value> = body
.lines()
.filter_map(|line| line.strip_prefix("data:"))
.map(str::trim)
.filter(|data| !data.is_empty())
.map(serde_json::from_str)
.collect::<Result<_, _>>()?;
assert_eq!(messages.len(), 2, "Expected progress and result: {body}");
assert_eq!(messages[0]["method"], "notifications/progress");
assert_eq!(messages[1]["id"], 2);
assert!(
messages[1]["result"].is_object(),
"Expected result object: {body}"
);

ct.cancel();
Ok(())
}

#[tokio::test]
async fn stateless_sse_mode_default_unchanged() -> anyhow::Result<()> {
let ct = CancellationToken::new();
Expand Down
, 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Add copy buttons to all 
 blocks\n(function() {\n function addCopyButtons() {\n document.querySelectorAll('pre code').forEach(function(codeBlock) {\n if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;\n codeBlock.parentElement.setAttribute('data-copy-added', 'true');\n \n var btn = document.createElement('button');\n btn.textContent = 'Copy';\n btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';\n btn.onmouseover = function() { this.style.opacity = '1'; };\n btn.onmouseout = function() { this.style.opacity = '0.7'; };\n btn.onclick = function() {\n navigator.clipboard.writeText(codeBlock.textContent).then(function() {\n btn.textContent = 'Copied!';\n setTimeout(function() { btn.textContent = 'Copy'; }, 1500);\n });\n };\n codeBlock.parentElement.style.position = 'relative';\n codeBlock.parentElement.appendChild(btn);\n });\n }\n \n addCopyButtons();\n \n // Re-run on dynamic content\n var observer = new MutationObserver(addCopyButtons);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Add Copy Buttons to Code Blocks");
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

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fix(streamable-http): preserve progress in JSON mode#990

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to your account

 Merged

alexhancock
merged 1 commit into

from

Jul 14, 2026
 Merged


fix(streamable-http): preserve progress in JSON mode
#990
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61 changes: 39 additions & 22 deletions
crates/rmcp/src/transport/streamable_http_server/tower.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -19,6 +19,7 @@ use crate::{
 ClientCapabilities, ClientJsonRpcMessage, ClientNotification, ClientRequest, ErrorData,
 GetExtensions, Implementation, InitializeRequest, InitializeRequestParams,
 InitializedNotification, JsonObject, JsonRpcError, ProtocolVersion, RequestId,
 ServerJsonRpcMessage,
 },
 serve_server,
 service::serve_directly,
Expand DownExpand Up@@ -48,10 +49,10 @@ pub struct StreamableHttpServerConfig {
 /// If true, the server will create a session for each request and keep it alive.
 /// When enabled, SSE priming events are sent to enable client reconnection.
 pub stateful_mode: bool,
 /// When true and `stateful_mode` is false, the server returns
 /// `Content-Type: application/json` directly instead of `text/event-stream`.
 /// This eliminates SSE framing overhead for simple request-response tools,
 /// allowed by the MCP Streamable HTTP spec (2025-06-18).
 /// When true and `stateful_mode` is false, the server prefers
 /// `Content-Type: application/json` for simple request-response tools.
 /// If the handler emits a notification or request before the final response,
 /// the server falls back to `text/event-stream` so no message is lost.
 pub json_response: bool,
 /// Cancellation token for the Streamable HTTP server.
 ///
Expand DownExpand Up@@ -1352,31 +1353,47 @@ where
 let _ = service.waiting().await;
 });
 if self.config.json_response {
 // JSON-direct mode: await the single response and return as
 // application/json, eliminating SSE framing overhead.
 // Allowed by MCP Streamable HTTP spec (2025-06-18).
 // Prefer JSON for a terminal first message. If the handler
 // emits an intermediate notification or request, preserve
 // the complete message sequence by falling back to SSE.
 let cancel = self.config.cancellation_token.child_token();
match tokio::select! {
let Some(message) = (tokio::select! {
 res = receiver.recv() => res,
 _ = cancel.cancelled() => None,
 } {
 Some(message) => {
 tracing::trace!(?message);
 let body = serde_json::to_vec(&message).map_err(|e| {
 internal_error_response("serialize json response")(e)
 })?;
 Ok(Response::builder()
 .status(http::StatusCode::OK)
 .header(http::header::CONTENT_TYPE, JSON_MIME_TYPE)
 .body(Full::new(Bytes::from(body)).boxed())
 .expect("valid response"))
 }
 None => Err(internal_error_response("empty response")(
 }) else {
 return Err(internal_error_response("empty response")(
 std::io::Error::new(
 std::io::ErrorKind::UnexpectedEof,
 "no response message received from handler",
 ),
 )),
 ));
 };
 tracing::trace!(?message);
 if matches!(
 message,
 ServerJsonRpcMessage::Response(_) | ServerJsonRpcMessage::Error(_)
 ) {
 let body = serde_json::to_vec(&message).map_err(|e| {
 internal_error_response("serialize json response")(e)
 })?;
 Ok(Response::builder()
 .status(http::StatusCode::OK)
 .header(http::header::CONTENT_TYPE, JSON_MIME_TYPE)
 .body(Full::new(Bytes::from(body)).boxed())
 .expect("valid response"))
 } else {
 let first = futures::stream::once(async move {
 ServerSseMessage::from_message(message)
 });
 let remaining = ReceiverStream::new(receiver).map(|message| {
 tracing::trace!(?message);
 ServerSseMessage::from_message(message)
 });
 Ok(sse_stream_response(
 first.chain(remaining),
 self.config.sse_keep_alive,
 self.config.cancellation_token.child_token(),
 ))
 }
 } else {
 // SSE mode (default): original behaviour preserved unchanged
Expand Down

120 changes: 118 additions & 2 deletions
crates/rmcp/tests/test_streamable_http_json_response.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -1,13 +1,52 @@
#![cfg(not(feature = "local"))]
use rmcp::transport::streamable_http_server::{
 StreamableHttpServerConfig, StreamableHttpService, session::local::LocalSessionManager,
use rmcp::{
 ErrorData, ServerHandler,
 model::{
 CallToolRequestParams, CallToolResponse, CallToolResult, ContentBlock,
 ProgressNotificationParam, ServerCapabilities, ServerInfo,
 },
 service::RequestContext,
 transport::streamable_http_server::{
 StreamableHttpServerConfig, StreamableHttpService, session::local::LocalSessionManager,
 },
};
use tokio_util::sync::CancellationToken;

mod common;
use common::calculator::Calculator;

const INIT_BODY: &str = r#"{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-03-26","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}"#;
const CALL_WITH_PROGRESS_BODY: &str = r#"{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"progress","arguments":{},"_meta":{"progressToken":"progress-test-1"}}}"#;

#[derive(Clone)]
struct ProgressServer;

impl ServerHandler for ProgressServer {
 fn get_info(&self) -> ServerInfo {
 ServerInfo::new(ServerCapabilities::builder().enable_tools().build())
 }

 async fn call_tool(
 &self,
 _request: CallToolRequestParams,
 context: RequestContext<rmcp::RoleServer>,
 ) -> Result<CallToolResponse, ErrorData> {
 let progress_token = context
 .meta
 .get_progress_token()
 .expect("request includes progressToken");
 context
 .peer
 .notify_progress(
 ProgressNotificationParam::new(progress_token, 50.0)
 .with_total(100.0)
 .with_message("working"),
 )
 .await
 .expect("progress notification is delivered");
 Ok(CallToolResult::success(vec![ContentBlock::text("done")]).into())
 }
}

async fn spawn_server(
 config: StreamableHttpServerConfig,
Expand All@@ -34,6 +73,31 @@ async fn spawn_server(
 (client, base_url, ct)
}

async fn spawn_progress_server(
 config: StreamableHttpServerConfig,
) -> (reqwest::Client, String, CancellationToken) {
 let ct = config.cancellation_token.clone();
 let service: StreamableHttpService<ProgressServer, LocalSessionManager> =
 StreamableHttpService::new(|| Ok(ProgressServer), Default::default(), config);

 let router = axum::Router::new().nest_service("/mcp", service);
 let tcp_listener = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
 let addr = tcp_listener.local_addr().unwrap();

 tokio::spawn({
 let ct = ct.clone();
 async move {
 let _ = axum::serve(tcp_listener, router)
 .with_graceful_shutdown(async move { ct.cancelled_owned().await })
 .await;
 }
 });

 let client = reqwest::Client::new();
 let base_url = format!("http://{addr}/mcp");
 (client, base_url, ct)
}

#[tokio::test]
async fn stateless_json_response_returns_application_json() -> anyhow::Result<()> {
 let ct = CancellationToken::new();
Expand DownExpand Up@@ -76,6 +140,58 @@ async fn stateless_json_response_returns_application_json() -> anyhow::Result<()
 Ok(())
}

#[tokio::test]
async fn stateless_json_response_falls_back_to_sse_for_progress() -> anyhow::Result<()> {
 let ct = CancellationToken::new();
 let (client, url, ct) = spawn_progress_server(
 StreamableHttpServerConfig::default()
 .with_stateful_mode(false)
 .with_json_response(true)
 .with_sse_keep_alive(None)
 .with_cancellation_token(ct.child_token()),
 )
 .await;

 let response = client
 .post(&url)
 .header("Content-Type", "application/json")
 .header("Accept", "application/json, text/event-stream")
 .body(CALL_WITH_PROGRESS_BODY)
 .send()
 .await?;

 assert_eq!(response.status(), 200);

 let content_type = response
 .headers()
 .get("content-type")
 .and_then(|value| value.to_str().ok())
 .unwrap_or("");
 assert!(
 content_type.contains("text/event-stream"),
 "Expected SSE fallback, got: {content_type}"
 );

 let body = response.text().await?;
 let messages: Vec<serde_json::Value> = body
 .lines()
 .filter_map(|line| line.strip_prefix("data:"))
 .map(str::trim)
 .filter(|data| !data.is_empty())
 .map(serde_json::from_str)
 .collect::<Result<_, _>>()?;
 assert_eq!(messages.len(), 2, "Expected progress and result: {body}");
 assert_eq!(messages[0]["method"], "notifications/progress");
 assert_eq!(messages[1]["id"], 2);
 assert!(
 messages[1]["result"].is_object(),
 "Expected result object: {body}"
 );

 ct.cancel();
 Ok(())
}

#[tokio::test]
async fn stateless_sse_mode_default_unchanged() -> anyhow::Result<()> {
 let ct = CancellationToken::new();
Expand Down

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Force GitHub README to respect dark mode\n(function() {\n var style = document.createElement('style');\n style.textContent = '\n .markdown-body {\n color-scheme: dark light;\n }\n .markdown-body pre { background: #161b22 !important; }\n .markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }\n .markdown-body table th, .markdown-body table td { border-color: #30363d !important; }\n .markdown-body img { background: #0d1117; }\n .markdown-body blockquote { border-left-color: #8b949e; }\n .markdown-body hr { border-color: #30363d; }\n ';\n document.head.appendChild(style);\n})();", "GitHub Dark Mode README Fix");
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
fix(streamable-http): preserve progress in JSON mode#990

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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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privacy statement. We’ll occasionally send you account related emails.

Already on GitHub?
Sign in
to your account

 Merged

alexhancock
merged 1 commit into

from

Jul 14, 2026
 Merged


fix(streamable-http): preserve progress in JSON mode
#990
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61 changes: 39 additions & 22 deletions
crates/rmcp/src/transport/streamable_http_server/tower.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -19,6 +19,7 @@ use crate::{
 ClientCapabilities, ClientJsonRpcMessage, ClientNotification, ClientRequest, ErrorData,
 GetExtensions, Implementation, InitializeRequest, InitializeRequestParams,
 InitializedNotification, JsonObject, JsonRpcError, ProtocolVersion, RequestId,
 ServerJsonRpcMessage,
 },
 serve_server,
 service::serve_directly,
Expand DownExpand Up@@ -48,10 +49,10 @@ pub struct StreamableHttpServerConfig {
 /// If true, the server will create a session for each request and keep it alive.
 /// When enabled, SSE priming events are sent to enable client reconnection.
 pub stateful_mode: bool,
 /// When true and `stateful_mode` is false, the server returns
 /// `Content-Type: application/json` directly instead of `text/event-stream`.
 /// This eliminates SSE framing overhead for simple request-response tools,
 /// allowed by the MCP Streamable HTTP spec (2025-06-18).
 /// When true and `stateful_mode` is false, the server prefers
 /// `Content-Type: application/json` for simple request-response tools.
 /// If the handler emits a notification or request before the final response,
 /// the server falls back to `text/event-stream` so no message is lost.
 pub json_response: bool,
 /// Cancellation token for the Streamable HTTP server.
 ///
Expand DownExpand Up@@ -1352,31 +1353,47 @@ where
 let _ = service.waiting().await;
 });
 if self.config.json_response {
 // JSON-direct mode: await the single response and return as
 // application/json, eliminating SSE framing overhead.
 // Allowed by MCP Streamable HTTP spec (2025-06-18).
 // Prefer JSON for a terminal first message. If the handler
 // emits an intermediate notification or request, preserve
 // the complete message sequence by falling back to SSE.
 let cancel = self.config.cancellation_token.child_token();
match tokio::select! {
let Some(message) = (tokio::select! {
 res = receiver.recv() => res,
 _ = cancel.cancelled() => None,
 } {
 Some(message) => {
 tracing::trace!(?message);
 let body = serde_json::to_vec(&message).map_err(|e| {
 internal_error_response("serialize json response")(e)
 })?;
 Ok(Response::builder()
 .status(http::StatusCode::OK)
 .header(http::header::CONTENT_TYPE, JSON_MIME_TYPE)
 .body(Full::new(Bytes::from(body)).boxed())
 .expect("valid response"))
 }
 None => Err(internal_error_response("empty response")(
 }) else {
 return Err(internal_error_response("empty response")(
 std::io::Error::new(
 std::io::ErrorKind::UnexpectedEof,
 "no response message received from handler",
 ),
 )),
 ));
 };
 tracing::trace!(?message);
 if matches!(
 message,
 ServerJsonRpcMessage::Response(_) | ServerJsonRpcMessage::Error(_)
 ) {
 let body = serde_json::to_vec(&message).map_err(|e| {
 internal_error_response("serialize json response")(e)
 })?;
 Ok(Response::builder()
 .status(http::StatusCode::OK)
 .header(http::header::CONTENT_TYPE, JSON_MIME_TYPE)
 .body(Full::new(Bytes::from(body)).boxed())
 .expect("valid response"))
 } else {
 let first = futures::stream::once(async move {
 ServerSseMessage::from_message(message)
 });
 let remaining = ReceiverStream::new(receiver).map(|message| {
 tracing::trace!(?message);
 ServerSseMessage::from_message(message)
 });
 Ok(sse_stream_response(
 first.chain(remaining),
 self.config.sse_keep_alive,
 self.config.cancellation_token.child_token(),
 ))
 }
 } else {
 // SSE mode (default): original behaviour preserved unchanged
Expand Down

120 changes: 118 additions & 2 deletions
crates/rmcp/tests/test_streamable_http_json_response.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -1,13 +1,52 @@
#![cfg(not(feature = "local"))]
use rmcp::transport::streamable_http_server::{
 StreamableHttpServerConfig, StreamableHttpService, session::local::LocalSessionManager,
use rmcp::{
 ErrorData, ServerHandler,
 model::{
 CallToolRequestParams, CallToolResponse, CallToolResult, ContentBlock,
 ProgressNotificationParam, ServerCapabilities, ServerInfo,
 },
 service::RequestContext,
 transport::streamable_http_server::{
 StreamableHttpServerConfig, StreamableHttpService, session::local::LocalSessionManager,
 },
};
use tokio_util::sync::CancellationToken;

mod common;
use common::calculator::Calculator;

const INIT_BODY: &str = r#"{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-03-26","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}"#;
const CALL_WITH_PROGRESS_BODY: &str = r#"{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"progress","arguments":{},"_meta":{"progressToken":"progress-test-1"}}}"#;

#[derive(Clone)]
struct ProgressServer;

impl ServerHandler for ProgressServer {
 fn get_info(&self) -> ServerInfo {
 ServerInfo::new(ServerCapabilities::builder().enable_tools().build())
 }

 async fn call_tool(
 &self,
 _request: CallToolRequestParams,
 context: RequestContext<rmcp::RoleServer>,
 ) -> Result<CallToolResponse, ErrorData> {
 let progress_token = context
 .meta
 .get_progress_token()
 .expect("request includes progressToken");
 context
 .peer
 .notify_progress(
 ProgressNotificationParam::new(progress_token, 50.0)
 .with_total(100.0)
 .with_message("working"),
 )
 .await
 .expect("progress notification is delivered");
 Ok(CallToolResult::success(vec![ContentBlock::text("done")]).into())
 }
}

async fn spawn_server(
 config: StreamableHttpServerConfig,
Expand All@@ -34,6 +73,31 @@ async fn spawn_server(
 (client, base_url, ct)
}

async fn spawn_progress_server(
 config: StreamableHttpServerConfig,
) -> (reqwest::Client, String, CancellationToken) {
 let ct = config.cancellation_token.clone();
 let service: StreamableHttpService<ProgressServer, LocalSessionManager> =
 StreamableHttpService::new(|| Ok(ProgressServer), Default::default(), config);

 let router = axum::Router::new().nest_service("/mcp", service);
 let tcp_listener = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
 let addr = tcp_listener.local_addr().unwrap();

 tokio::spawn({
 let ct = ct.clone();
 async move {
 let _ = axum::serve(tcp_listener, router)
 .with_graceful_shutdown(async move { ct.cancelled_owned().await })
 .await;
 }
 });

 let client = reqwest::Client::new();
 let base_url = format!("http://{addr}/mcp");
 (client, base_url, ct)
}

#[tokio::test]
async fn stateless_json_response_returns_application_json() -> anyhow::Result<()> {
 let ct = CancellationToken::new();
Expand DownExpand Up@@ -76,6 +140,58 @@ async fn stateless_json_response_returns_application_json() -> anyhow::Result<()
 Ok(())
}

#[tokio::test]
async fn stateless_json_response_falls_back_to_sse_for_progress() -> anyhow::Result<()> {
 let ct = CancellationToken::new();
 let (client, url, ct) = spawn_progress_server(
 StreamableHttpServerConfig::default()
 .with_stateful_mode(false)
 .with_json_response(true)
 .with_sse_keep_alive(None)
 .with_cancellation_token(ct.child_token()),
 )
 .await;

 let response = client
 .post(&url)
 .header("Content-Type", "application/json")
 .header("Accept", "application/json, text/event-stream")
 .body(CALL_WITH_PROGRESS_BODY)
 .send()
 .await?;

 assert_eq!(response.status(), 200);

 let content_type = response
 .headers()
 .get("content-type")
 .and_then(|value| value.to_str().ok())
 .unwrap_or("");
 assert!(
 content_type.contains("text/event-stream"),
 "Expected SSE fallback, got: {content_type}"
 );

 let body = response.text().await?;
 let messages: Vec<serde_json::Value> = body
 .lines()
 .filter_map(|line| line.strip_prefix("data:"))
 .map(str::trim)
 .filter(|data| !data.is_empty())
 .map(serde_json::from_str)
 .collect::<Result<_, _>>()?;
 assert_eq!(messages.len(), 2, "Expected progress and result: {body}");
 assert_eq!(messages[0]["method"], "notifications/progress");
 assert_eq!(messages[1]["id"], 2);
 assert!(
 messages[1]["result"].is_object(),
 "Expected result object: {body}"
 );

 ct.cancel();
 Ok(())
}

#[tokio::test]
async fn stateless_sse_mode_default_unchanged() -> anyhow::Result<()> {
 let ct = CancellationToken::new();
Expand Down

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

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fix(streamable-http): preserve progress in JSON mode#990

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alexhancock
merged 1 commit into

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Jul 14, 2026
 Merged


fix(streamable-http): preserve progress in JSON mode
#990
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61 changes: 39 additions & 22 deletions
crates/rmcp/src/transport/streamable_http_server/tower.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -19,6 +19,7 @@ use crate::{
 ClientCapabilities, ClientJsonRpcMessage, ClientNotification, ClientRequest, ErrorData,
 GetExtensions, Implementation, InitializeRequest, InitializeRequestParams,
 InitializedNotification, JsonObject, JsonRpcError, ProtocolVersion, RequestId,
 ServerJsonRpcMessage,
 },
 serve_server,
 service::serve_directly,
Expand DownExpand Up@@ -48,10 +49,10 @@ pub struct StreamableHttpServerConfig {
 /// If true, the server will create a session for each request and keep it alive.
 /// When enabled, SSE priming events are sent to enable client reconnection.
 pub stateful_mode: bool,
 /// When true and `stateful_mode` is false, the server returns
 /// `Content-Type: application/json` directly instead of `text/event-stream`.
 /// This eliminates SSE framing overhead for simple request-response tools,
 /// allowed by the MCP Streamable HTTP spec (2025-06-18).
 /// When true and `stateful_mode` is false, the server prefers
 /// `Content-Type: application/json` for simple request-response tools.
 /// If the handler emits a notification or request before the final response,
 /// the server falls back to `text/event-stream` so no message is lost.
 pub json_response: bool,
 /// Cancellation token for the Streamable HTTP server.
 ///
Expand DownExpand Up@@ -1352,31 +1353,47 @@ where
 let _ = service.waiting().await;
 });
 if self.config.json_response {
 // JSON-direct mode: await the single response and return as
 // application/json, eliminating SSE framing overhead.
 // Allowed by MCP Streamable HTTP spec (2025-06-18).
 // Prefer JSON for a terminal first message. If the handler
 // emits an intermediate notification or request, preserve
 // the complete message sequence by falling back to SSE.
 let cancel = self.config.cancellation_token.child_token();
match tokio::select! {
let Some(message) = (tokio::select! {
 res = receiver.recv() => res,
 _ = cancel.cancelled() => None,
 } {
 Some(message) => {
 tracing::trace!(?message);
 let body = serde_json::to_vec(&message).map_err(|e| {
 internal_error_response("serialize json response")(e)
 })?;
 Ok(Response::builder()
 .status(http::StatusCode::OK)
 .header(http::header::CONTENT_TYPE, JSON_MIME_TYPE)
 .body(Full::new(Bytes::from(body)).boxed())
 .expect("valid response"))
 }
 None => Err(internal_error_response("empty response")(
 }) else {
 return Err(internal_error_response("empty response")(
 std::io::Error::new(
 std::io::ErrorKind::UnexpectedEof,
 "no response message received from handler",
 ),
 )),
 ));
 };
 tracing::trace!(?message);
 if matches!(
 message,
 ServerJsonRpcMessage::Response(_) | ServerJsonRpcMessage::Error(_)
 ) {
 let body = serde_json::to_vec(&message).map_err(|e| {
 internal_error_response("serialize json response")(e)
 })?;
 Ok(Response::builder()
 .status(http::StatusCode::OK)
 .header(http::header::CONTENT_TYPE, JSON_MIME_TYPE)
 .body(Full::new(Bytes::from(body)).boxed())
 .expect("valid response"))
 } else {
 let first = futures::stream::once(async move {
 ServerSseMessage::from_message(message)
 });
 let remaining = ReceiverStream::new(receiver).map(|message| {
 tracing::trace!(?message);
 ServerSseMessage::from_message(message)
 });
 Ok(sse_stream_response(
 first.chain(remaining),
 self.config.sse_keep_alive,
 self.config.cancellation_token.child_token(),
 ))
 }
 } else {
 // SSE mode (default): original behaviour preserved unchanged
Expand Down

120 changes: 118 additions & 2 deletions
crates/rmcp/tests/test_streamable_http_json_response.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -1,13 +1,52 @@
#![cfg(not(feature = "local"))]
use rmcp::transport::streamable_http_server::{
 StreamableHttpServerConfig, StreamableHttpService, session::local::LocalSessionManager,
use rmcp::{
 ErrorData, ServerHandler,
 model::{
 CallToolRequestParams, CallToolResponse, CallToolResult, ContentBlock,
 ProgressNotificationParam, ServerCapabilities, ServerInfo,
 },
 service::RequestContext,
 transport::streamable_http_server::{
 StreamableHttpServerConfig, StreamableHttpService, session::local::LocalSessionManager,
 },
};
use tokio_util::sync::CancellationToken;

mod common;
use common::calculator::Calculator;

const INIT_BODY: &str = r#"{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-03-26","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}"#;
const CALL_WITH_PROGRESS_BODY: &str = r#"{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"progress","arguments":{},"_meta":{"progressToken":"progress-test-1"}}}"#;

#[derive(Clone)]
struct ProgressServer;

impl ServerHandler for ProgressServer {
 fn get_info(&self) -> ServerInfo {
 ServerInfo::new(ServerCapabilities::builder().enable_tools().build())
 }

 async fn call_tool(
 &self,
 _request: CallToolRequestParams,
 context: RequestContext<rmcp::RoleServer>,
 ) -> Result<CallToolResponse, ErrorData> {
 let progress_token = context
 .meta
 .get_progress_token()
 .expect("request includes progressToken");
 context
 .peer
 .notify_progress(
 ProgressNotificationParam::new(progress_token, 50.0)
 .with_total(100.0)
 .with_message("working"),
 )
 .await
 .expect("progress notification is delivered");
 Ok(CallToolResult::success(vec![ContentBlock::text("done")]).into())
 }
}

async fn spawn_server(
 config: StreamableHttpServerConfig,
Expand All@@ -34,6 +73,31 @@ async fn spawn_server(
 (client, base_url, ct)
}

async fn spawn_progress_server(
 config: StreamableHttpServerConfig,
) -> (reqwest::Client, String, CancellationToken) {
 let ct = config.cancellation_token.clone();
 let service: StreamableHttpService<ProgressServer, LocalSessionManager> =
 StreamableHttpService::new(|| Ok(ProgressServer), Default::default(), config);

 let router = axum::Router::new().nest_service("/mcp", service);
 let tcp_listener = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
 let addr = tcp_listener.local_addr().unwrap();

 tokio::spawn({
 let ct = ct.clone();
 async move {
 let _ = axum::serve(tcp_listener, router)
 .with_graceful_shutdown(async move { ct.cancelled_owned().await })
 .await;
 }
 });

 let client = reqwest::Client::new();
 let base_url = format!("http://{addr}/mcp");
 (client, base_url, ct)
}

#[tokio::test]
async fn stateless_json_response_returns_application_json() -> anyhow::Result<()> {
 let ct = CancellationToken::new();
Expand DownExpand Up@@ -76,6 +140,58 @@ async fn stateless_json_response_returns_application_json() -> anyhow::Result<()
 Ok(())
}

#[tokio::test]
async fn stateless_json_response_falls_back_to_sse_for_progress() -> anyhow::Result<()> {
 let ct = CancellationToken::new();
 let (client, url, ct) = spawn_progress_server(
 StreamableHttpServerConfig::default()
 .with_stateful_mode(false)
 .with_json_response(true)
 .with_sse_keep_alive(None)
 .with_cancellation_token(ct.child_token()),
 )
 .await;

 let response = client
 .post(&url)
 .header("Content-Type", "application/json")
 .header("Accept", "application/json, text/event-stream")
 .body(CALL_WITH_PROGRESS_BODY)
 .send()
 .await?;

 assert_eq!(response.status(), 200);

 let content_type = response
 .headers()
 .get("content-type")
 .and_then(|value| value.to_str().ok())
 .unwrap_or("");
 assert!(
 content_type.contains("text/event-stream"),
 "Expected SSE fallback, got: {content_type}"
 );

 let body = response.text().await?;
 let messages: Vec<serde_json::Value> = body
 .lines()
 .filter_map(|line| line.strip_prefix("data:"))
 .map(str::trim)
 .filter(|data| !data.is_empty())
 .map(serde_json::from_str)
 .collect::<Result<_, _>>()?;
 assert_eq!(messages.len(), 2, "Expected progress and result: {body}");
 assert_eq!(messages[0]["method"], "notifications/progress");
 assert_eq!(messages[1]["id"], 2);
 assert!(
 messages[1]["result"].is_object(),
 "Expected result object: {body}"
 );

 ct.cancel();
 Ok(())
}

#[tokio::test]
async fn stateless_sse_mode_default_unchanged() -> anyhow::Result<()> {
 let ct = CancellationToken::new();
Expand Down

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Strip utm_, fbclid, gclid, etc. from all links on page\n(function() {\n var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',\n 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',\n 'ref', 'ref_src', 'source', 'medium', 'campaign'];\n \n function cleanUrl(url) {\n try {\n var u = new URL(url, window.location.origin);\n var changed = false;\n trackingParams.forEach(function(p) {\n if (u.searchParams.has(p)) {\n u.searchParams.delete(p);\n changed = true;\n }\n });\n return changed ? u.toString() : url;\n } catch (e) {\n return url;\n }\n }\n \n function cleanLinks() {\n document.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n \n cleanLinks();\n \n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1) {\n if (node.tagName === 'A') cleanLinks();\n node.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Remove Tracking Parameters from Links");
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

Skip to content
fix(streamable-http): preserve progress in JSON mode#990

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privacy statement. We’ll occasionally send you account related emails.

Already on GitHub?
Sign in
to your account

 Merged

alexhancock
merged 1 commit into

from

Jul 14, 2026
 Merged


fix(streamable-http): preserve progress in JSON mode
#990
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61 changes: 39 additions & 22 deletions
crates/rmcp/src/transport/streamable_http_server/tower.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -19,6 +19,7 @@ use crate::{
 ClientCapabilities, ClientJsonRpcMessage, ClientNotification, ClientRequest, ErrorData,
 GetExtensions, Implementation, InitializeRequest, InitializeRequestParams,
 InitializedNotification, JsonObject, JsonRpcError, ProtocolVersion, RequestId,
 ServerJsonRpcMessage,
 },
 serve_server,
 service::serve_directly,
Expand DownExpand Up@@ -48,10 +49,10 @@ pub struct StreamableHttpServerConfig {
 /// If true, the server will create a session for each request and keep it alive.
 /// When enabled, SSE priming events are sent to enable client reconnection.
 pub stateful_mode: bool,
 /// When true and `stateful_mode` is false, the server returns
 /// `Content-Type: application/json` directly instead of `text/event-stream`.
 /// This eliminates SSE framing overhead for simple request-response tools,
 /// allowed by the MCP Streamable HTTP spec (2025-06-18).
 /// When true and `stateful_mode` is false, the server prefers
 /// `Content-Type: application/json` for simple request-response tools.
 /// If the handler emits a notification or request before the final response,
 /// the server falls back to `text/event-stream` so no message is lost.
 pub json_response: bool,
 /// Cancellation token for the Streamable HTTP server.
 ///
Expand DownExpand Up@@ -1352,31 +1353,47 @@ where
 let _ = service.waiting().await;
 });
 if self.config.json_response {
 // JSON-direct mode: await the single response and return as
 // application/json, eliminating SSE framing overhead.
 // Allowed by MCP Streamable HTTP spec (2025-06-18).
 // Prefer JSON for a terminal first message. If the handler
 // emits an intermediate notification or request, preserve
 // the complete message sequence by falling back to SSE.
 let cancel = self.config.cancellation_token.child_token();
match tokio::select! {
let Some(message) = (tokio::select! {
 res = receiver.recv() => res,
 _ = cancel.cancelled() => None,
 } {
 Some(message) => {
 tracing::trace!(?message);
 let body = serde_json::to_vec(&message).map_err(|e| {
 internal_error_response("serialize json response")(e)
 })?;
 Ok(Response::builder()
 .status(http::StatusCode::OK)
 .header(http::header::CONTENT_TYPE, JSON_MIME_TYPE)
 .body(Full::new(Bytes::from(body)).boxed())
 .expect("valid response"))
 }
 None => Err(internal_error_response("empty response")(
 }) else {
 return Err(internal_error_response("empty response")(
 std::io::Error::new(
 std::io::ErrorKind::UnexpectedEof,
 "no response message received from handler",
 ),
 )),
 ));
 };
 tracing::trace!(?message);
 if matches!(
 message,
 ServerJsonRpcMessage::Response(_) | ServerJsonRpcMessage::Error(_)
 ) {
 let body = serde_json::to_vec(&message).map_err(|e| {
 internal_error_response("serialize json response")(e)
 })?;
 Ok(Response::builder()
 .status(http::StatusCode::OK)
 .header(http::header::CONTENT_TYPE, JSON_MIME_TYPE)
 .body(Full::new(Bytes::from(body)).boxed())
 .expect("valid response"))
 } else {
 let first = futures::stream::once(async move {
 ServerSseMessage::from_message(message)
 });
 let remaining = ReceiverStream::new(receiver).map(|message| {
 tracing::trace!(?message);
 ServerSseMessage::from_message(message)
 });
 Ok(sse_stream_response(
 first.chain(remaining),
 self.config.sse_keep_alive,
 self.config.cancellation_token.child_token(),
 ))
 }
 } else {
 // SSE mode (default): original behaviour preserved unchanged
Expand Down

120 changes: 118 additions & 2 deletions
crates/rmcp/tests/test_streamable_http_json_response.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -1,13 +1,52 @@
#![cfg(not(feature = "local"))]
use rmcp::transport::streamable_http_server::{
 StreamableHttpServerConfig, StreamableHttpService, session::local::LocalSessionManager,
use rmcp::{
 ErrorData, ServerHandler,
 model::{
 CallToolRequestParams, CallToolResponse, CallToolResult, ContentBlock,
 ProgressNotificationParam, ServerCapabilities, ServerInfo,
 },
 service::RequestContext,
 transport::streamable_http_server::{
 StreamableHttpServerConfig, StreamableHttpService, session::local::LocalSessionManager,
 },
};
use tokio_util::sync::CancellationToken;

mod common;
use common::calculator::Calculator;

const INIT_BODY: &str = r#"{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-03-26","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}"#;
const CALL_WITH_PROGRESS_BODY: &str = r#"{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"progress","arguments":{},"_meta":{"progressToken":"progress-test-1"}}}"#;

#[derive(Clone)]
struct ProgressServer;

impl ServerHandler for ProgressServer {
 fn get_info(&self) -> ServerInfo {
 ServerInfo::new(ServerCapabilities::builder().enable_tools().build())
 }

 async fn call_tool(
 &self,
 _request: CallToolRequestParams,
 context: RequestContext<rmcp::RoleServer>,
 ) -> Result<CallToolResponse, ErrorData> {
 let progress_token = context
 .meta
 .get_progress_token()
 .expect("request includes progressToken");
 context
 .peer
 .notify_progress(
 ProgressNotificationParam::new(progress_token, 50.0)
 .with_total(100.0)
 .with_message("working"),
 )
 .await
 .expect("progress notification is delivered");
 Ok(CallToolResult::success(vec![ContentBlock::text("done")]).into())
 }
}

async fn spawn_server(
 config: StreamableHttpServerConfig,
Expand All@@ -34,6 +73,31 @@ async fn spawn_server(
 (client, base_url, ct)
}

async fn spawn_progress_server(
 config: StreamableHttpServerConfig,
) -> (reqwest::Client, String, CancellationToken) {
 let ct = config.cancellation_token.clone();
 let service: StreamableHttpService<ProgressServer, LocalSessionManager> =
 StreamableHttpService::new(|| Ok(ProgressServer), Default::default(), config);

 let router = axum::Router::new().nest_service("/mcp", service);
 let tcp_listener = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
 let addr = tcp_listener.local_addr().unwrap();

 tokio::spawn({
 let ct = ct.clone();
 async move {
 let _ = axum::serve(tcp_listener, router)
 .with_graceful_shutdown(async move { ct.cancelled_owned().await })
 .await;
 }
 });

 let client = reqwest::Client::new();
 let base_url = format!("http://{addr}/mcp");
 (client, base_url, ct)
}

#[tokio::test]
async fn stateless_json_response_returns_application_json() -> anyhow::Result<()> {
 let ct = CancellationToken::new();
Expand DownExpand Up@@ -76,6 +140,58 @@ async fn stateless_json_response_returns_application_json() -> anyhow::Result<()
 Ok(())
}

#[tokio::test]
async fn stateless_json_response_falls_back_to_sse_for_progress() -> anyhow::Result<()> {
 let ct = CancellationToken::new();
 let (client, url, ct) = spawn_progress_server(
 StreamableHttpServerConfig::default()
 .with_stateful_mode(false)
 .with_json_response(true)
 .with_sse_keep_alive(None)
 .with_cancellation_token(ct.child_token()),
 )
 .await;

 let response = client
 .post(&url)
 .header("Content-Type", "application/json")
 .header("Accept", "application/json, text/event-stream")
 .body(CALL_WITH_PROGRESS_BODY)
 .send()
 .await?;

 assert_eq!(response.status(), 200);

 let content_type = response
 .headers()
 .get("content-type")
 .and_then(|value| value.to_str().ok())
 .unwrap_or("");
 assert!(
 content_type.contains("text/event-stream"),
 "Expected SSE fallback, got: {content_type}"
 );

 let body = response.text().await?;
 let messages: Vec<serde_json::Value> = body
 .lines()
 .filter_map(|line| line.strip_prefix("data:"))
 .map(str::trim)
 .filter(|data| !data.is_empty())
 .map(serde_json::from_str)
 .collect::<Result<_, _>>()?;
 assert_eq!(messages.len(), 2, "Expected progress and result: {body}");
 assert_eq!(messages[0]["method"], "notifications/progress");
 assert_eq!(messages[1]["id"], 2);
 assert!(
 messages[1]["result"].is_object(),
 "Expected result object: {body}"
 );

 ct.cancel();
 Ok(())
}

#[tokio::test]
async fn stateless_sse_mode_default_unchanged() -> anyhow::Result<()> {
 let ct = CancellationToken::new();
Expand Down

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Auto-enable theater mode on YouTube\n(function() {\n function tryTheater() {\n var btn = document.querySelector('button[aria-label=\"Theater mode\"], ytd-player #player button[title=\"Theater mode\"]');\n if (btn && !btn.classList.contains('activated')) {\n btn.click();\n }\n }\n \n // Try immediately\n tryTheater();\n \n // Try after navigation (SPA)\n var lastUrl = location.href;\n setInterval(function() {\n if (location.href !== lastUrl) {\n lastUrl = location.href;\n setTimeout(tryTheater, 500);\n }\n }, 1000);\n \n // Also try on player load\n var observer = new MutationObserver(tryTheater);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "YouTube Theater Mode Default");
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

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fix(streamable-http): preserve progress in JSON mode#990

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alexhancock
merged 1 commit into

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Jul 14, 2026
 Merged


fix(streamable-http): preserve progress in JSON mode
#990
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61 changes: 39 additions & 22 deletions
crates/rmcp/src/transport/streamable_http_server/tower.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -19,6 +19,7 @@ use crate::{
 ClientCapabilities, ClientJsonRpcMessage, ClientNotification, ClientRequest, ErrorData,
 GetExtensions, Implementation, InitializeRequest, InitializeRequestParams,
 InitializedNotification, JsonObject, JsonRpcError, ProtocolVersion, RequestId,
 ServerJsonRpcMessage,
 },
 serve_server,
 service::serve_directly,
Expand DownExpand Up@@ -48,10 +49,10 @@ pub struct StreamableHttpServerConfig {
 /// If true, the server will create a session for each request and keep it alive.
 /// When enabled, SSE priming events are sent to enable client reconnection.
 pub stateful_mode: bool,
 /// When true and `stateful_mode` is false, the server returns
 /// `Content-Type: application/json` directly instead of `text/event-stream`.
 /// This eliminates SSE framing overhead for simple request-response tools,
 /// allowed by the MCP Streamable HTTP spec (2025-06-18).
 /// When true and `stateful_mode` is false, the server prefers
 /// `Content-Type: application/json` for simple request-response tools.
 /// If the handler emits a notification or request before the final response,
 /// the server falls back to `text/event-stream` so no message is lost.
 pub json_response: bool,
 /// Cancellation token for the Streamable HTTP server.
 ///
Expand DownExpand Up@@ -1352,31 +1353,47 @@ where
 let _ = service.waiting().await;
 });
 if self.config.json_response {
 // JSON-direct mode: await the single response and return as
 // application/json, eliminating SSE framing overhead.
 // Allowed by MCP Streamable HTTP spec (2025-06-18).
 // Prefer JSON for a terminal first message. If the handler
 // emits an intermediate notification or request, preserve
 // the complete message sequence by falling back to SSE.
 let cancel = self.config.cancellation_token.child_token();
match tokio::select! {
let Some(message) = (tokio::select! {
 res = receiver.recv() => res,
 _ = cancel.cancelled() => None,
 } {
 Some(message) => {
 tracing::trace!(?message);
 let body = serde_json::to_vec(&message).map_err(|e| {
 internal_error_response("serialize json response")(e)
 })?;
 Ok(Response::builder()
 .status(http::StatusCode::OK)
 .header(http::header::CONTENT_TYPE, JSON_MIME_TYPE)
 .body(Full::new(Bytes::from(body)).boxed())
 .expect("valid response"))
 }
 None => Err(internal_error_response("empty response")(
 }) else {
 return Err(internal_error_response("empty response")(
 std::io::Error::new(
 std::io::ErrorKind::UnexpectedEof,
 "no response message received from handler",
 ),
 )),
 ));
 };
 tracing::trace!(?message);
 if matches!(
 message,
 ServerJsonRpcMessage::Response(_) | ServerJsonRpcMessage::Error(_)
 ) {
 let body = serde_json::to_vec(&message).map_err(|e| {
 internal_error_response("serialize json response")(e)
 })?;
 Ok(Response::builder()
 .status(http::StatusCode::OK)
 .header(http::header::CONTENT_TYPE, JSON_MIME_TYPE)
 .body(Full::new(Bytes::from(body)).boxed())
 .expect("valid response"))
 } else {
 let first = futures::stream::once(async move {
 ServerSseMessage::from_message(message)
 });
 let remaining = ReceiverStream::new(receiver).map(|message| {
 tracing::trace!(?message);
 ServerSseMessage::from_message(message)
 });
 Ok(sse_stream_response(
 first.chain(remaining),
 self.config.sse_keep_alive,
 self.config.cancellation_token.child_token(),
 ))
 }
 } else {
 // SSE mode (default): original behaviour preserved unchanged
Expand Down

120 changes: 118 additions & 2 deletions
crates/rmcp/tests/test_streamable_http_json_response.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -1,13 +1,52 @@
#![cfg(not(feature = "local"))]
use rmcp::transport::streamable_http_server::{
 StreamableHttpServerConfig, StreamableHttpService, session::local::LocalSessionManager,
use rmcp::{
 ErrorData, ServerHandler,
 model::{
 CallToolRequestParams, CallToolResponse, CallToolResult, ContentBlock,
 ProgressNotificationParam, ServerCapabilities, ServerInfo,
 },
 service::RequestContext,
 transport::streamable_http_server::{
 StreamableHttpServerConfig, StreamableHttpService, session::local::LocalSessionManager,
 },
};
use tokio_util::sync::CancellationToken;

mod common;
use common::calculator::Calculator;

const INIT_BODY: &str = r#"{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-03-26","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}"#;
const CALL_WITH_PROGRESS_BODY: &str = r#"{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"progress","arguments":{},"_meta":{"progressToken":"progress-test-1"}}}"#;

#[derive(Clone)]
struct ProgressServer;

impl ServerHandler for ProgressServer {
 fn get_info(&self) -> ServerInfo {
 ServerInfo::new(ServerCapabilities::builder().enable_tools().build())
 }

 async fn call_tool(
 &self,
 _request: CallToolRequestParams,
 context: RequestContext<rmcp::RoleServer>,
 ) -> Result<CallToolResponse, ErrorData> {
 let progress_token = context
 .meta
 .get_progress_token()
 .expect("request includes progressToken");
 context
 .peer
 .notify_progress(
 ProgressNotificationParam::new(progress_token, 50.0)
 .with_total(100.0)
 .with_message("working"),
 )
 .await
 .expect("progress notification is delivered");
 Ok(CallToolResult::success(vec![ContentBlock::text("done")]).into())
 }
}

async fn spawn_server(
 config: StreamableHttpServerConfig,
Expand All@@ -34,6 +73,31 @@ async fn spawn_server(
 (client, base_url, ct)
}

async fn spawn_progress_server(
 config: StreamableHttpServerConfig,
) -> (reqwest::Client, String, CancellationToken) {
 let ct = config.cancellation_token.clone();
 let service: StreamableHttpService<ProgressServer, LocalSessionManager> =
 StreamableHttpService::new(|| Ok(ProgressServer), Default::default(), config);

 let router = axum::Router::new().nest_service("/mcp", service);
 let tcp_listener = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
 let addr = tcp_listener.local_addr().unwrap();

 tokio::spawn({
 let ct = ct.clone();
 async move {
 let _ = axum::serve(tcp_listener, router)
 .with_graceful_shutdown(async move { ct.cancelled_owned().await })
 .await;
 }
 });

 let client = reqwest::Client::new();
 let base_url = format!("http://{addr}/mcp");
 (client, base_url, ct)
}

#[tokio::test]
async fn stateless_json_response_returns_application_json() -> anyhow::Result<()> {
 let ct = CancellationToken::new();
Expand DownExpand Up@@ -76,6 +140,58 @@ async fn stateless_json_response_returns_application_json() -> anyhow::Result<()
 Ok(())
}

#[tokio::test]
async fn stateless_json_response_falls_back_to_sse_for_progress() -> anyhow::Result<()> {
 let ct = CancellationToken::new();
 let (client, url, ct) = spawn_progress_server(
 StreamableHttpServerConfig::default()
 .with_stateful_mode(false)
 .with_json_response(true)
 .with_sse_keep_alive(None)
 .with_cancellation_token(ct.child_token()),
 )
 .await;

 let response = client
 .post(&url)
 .header("Content-Type", "application/json")
 .header("Accept", "application/json, text/event-stream")
 .body(CALL_WITH_PROGRESS_BODY)
 .send()
 .await?;

 assert_eq!(response.status(), 200);

 let content_type = response
 .headers()
 .get("content-type")
 .and_then(|value| value.to_str().ok())
 .unwrap_or("");
 assert!(
 content_type.contains("text/event-stream"),
 "Expected SSE fallback, got: {content_type}"
 );

 let body = response.text().await?;
 let messages: Vec<serde_json::Value> = body
 .lines()
 .filter_map(|line| line.strip_prefix("data:"))
 .map(str::trim)
 .filter(|data| !data.is_empty())
 .map(serde_json::from_str)
 .collect::<Result<_, _>>()?;
 assert_eq!(messages.len(), 2, "Expected progress and result: {body}");
 assert_eq!(messages[0]["method"], "notifications/progress");
 assert_eq!(messages[1]["id"], 2);
 assert!(
 messages[1]["result"].is_object(),
 "Expected result object: {body}"
 );

 ct.cancel();
 Ok(())
}

#[tokio::test]
async fn stateless_sse_mode_default_unchanged() -> anyhow::Result<()> {
 let ct = CancellationToken::new();
Expand Down

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Remove or un-stick sticky/fixed headers that block content\n(function() {\n function unstick() {\n document.querySelectorAll('header, nav, [role=\"banner\"], .header, .navbar, .sticky, .fixed-top, [style*=\"position: fixed\"], [style*=\"position:sticky\"]').forEach(function(el) {\n if (el.style.position === 'fixed' || el.style.position === 'sticky' || \n getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {\n el.style.position = 'static';\n el.style.top = 'auto';\n el.style.zIndex = 'auto';\n }\n });\n }\n \n unstick();\n \n var observer = new MutationObserver(unstick);\n observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });\n})();", "Kill Sticky Headers");
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
fix(streamable-http): preserve progress in JSON mode#990

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 Merged

alexhancock
merged 1 commit into

from

Jul 14, 2026
 Merged


fix(streamable-http): preserve progress in JSON mode
#990
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61 changes: 39 additions & 22 deletions
crates/rmcp/src/transport/streamable_http_server/tower.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -19,6 +19,7 @@ use crate::{
 ClientCapabilities, ClientJsonRpcMessage, ClientNotification, ClientRequest, ErrorData,
 GetExtensions, Implementation, InitializeRequest, InitializeRequestParams,
 InitializedNotification, JsonObject, JsonRpcError, ProtocolVersion, RequestId,
 ServerJsonRpcMessage,
 },
 serve_server,
 service::serve_directly,
Expand DownExpand Up@@ -48,10 +49,10 @@ pub struct StreamableHttpServerConfig {
 /// If true, the server will create a session for each request and keep it alive.
 /// When enabled, SSE priming events are sent to enable client reconnection.
 pub stateful_mode: bool,
 /// When true and `stateful_mode` is false, the server returns
 /// `Content-Type: application/json` directly instead of `text/event-stream`.
 /// This eliminates SSE framing overhead for simple request-response tools,
 /// allowed by the MCP Streamable HTTP spec (2025-06-18).
 /// When true and `stateful_mode` is false, the server prefers
 /// `Content-Type: application/json` for simple request-response tools.
 /// If the handler emits a notification or request before the final response,
 /// the server falls back to `text/event-stream` so no message is lost.
 pub json_response: bool,
 /// Cancellation token for the Streamable HTTP server.
 ///
Expand DownExpand Up@@ -1352,31 +1353,47 @@ where
 let _ = service.waiting().await;
 });
 if self.config.json_response {
 // JSON-direct mode: await the single response and return as
 // application/json, eliminating SSE framing overhead.
 // Allowed by MCP Streamable HTTP spec (2025-06-18).
 // Prefer JSON for a terminal first message. If the handler
 // emits an intermediate notification or request, preserve
 // the complete message sequence by falling back to SSE.
 let cancel = self.config.cancellation_token.child_token();
match tokio::select! {
let Some(message) = (tokio::select! {
 res = receiver.recv() => res,
 _ = cancel.cancelled() => None,
 } {
 Some(message) => {
 tracing::trace!(?message);
 let body = serde_json::to_vec(&message).map_err(|e| {
 internal_error_response("serialize json response")(e)
 })?;
 Ok(Response::builder()
 .status(http::StatusCode::OK)
 .header(http::header::CONTENT_TYPE, JSON_MIME_TYPE)
 .body(Full::new(Bytes::from(body)).boxed())
 .expect("valid response"))
 }
 None => Err(internal_error_response("empty response")(
 }) else {
 return Err(internal_error_response("empty response")(
 std::io::Error::new(
 std::io::ErrorKind::UnexpectedEof,
 "no response message received from handler",
 ),
 )),
 ));
 };
 tracing::trace!(?message);
 if matches!(
 message,
 ServerJsonRpcMessage::Response(_) | ServerJsonRpcMessage::Error(_)
 ) {
 let body = serde_json::to_vec(&message).map_err(|e| {
 internal_error_response("serialize json response")(e)
 })?;
 Ok(Response::builder()
 .status(http::StatusCode::OK)
 .header(http::header::CONTENT_TYPE, JSON_MIME_TYPE)
 .body(Full::new(Bytes::from(body)).boxed())
 .expect("valid response"))
 } else {
 let first = futures::stream::once(async move {
 ServerSseMessage::from_message(message)
 });
 let remaining = ReceiverStream::new(receiver).map(|message| {
 tracing::trace!(?message);
 ServerSseMessage::from_message(message)
 });
 Ok(sse_stream_response(
 first.chain(remaining),
 self.config.sse_keep_alive,
 self.config.cancellation_token.child_token(),
 ))
 }
 } else {
 // SSE mode (default): original behaviour preserved unchanged
Expand Down

120 changes: 118 additions & 2 deletions
crates/rmcp/tests/test_streamable_http_json_response.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -1,13 +1,52 @@
#![cfg(not(feature = "local"))]
use rmcp::transport::streamable_http_server::{
 StreamableHttpServerConfig, StreamableHttpService, session::local::LocalSessionManager,
use rmcp::{
 ErrorData, ServerHandler,
 model::{
 CallToolRequestParams, CallToolResponse, CallToolResult, ContentBlock,
 ProgressNotificationParam, ServerCapabilities, ServerInfo,
 },
 service::RequestContext,
 transport::streamable_http_server::{
 StreamableHttpServerConfig, StreamableHttpService, session::local::LocalSessionManager,
 },
};
use tokio_util::sync::CancellationToken;

mod common;
use common::calculator::Calculator;

const INIT_BODY: &str = r#"{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-03-26","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}"#;
const CALL_WITH_PROGRESS_BODY: &str = r#"{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"progress","arguments":{},"_meta":{"progressToken":"progress-test-1"}}}"#;

#[derive(Clone)]
struct ProgressServer;

impl ServerHandler for ProgressServer {
 fn get_info(&self) -> ServerInfo {
 ServerInfo::new(ServerCapabilities::builder().enable_tools().build())
 }

 async fn call_tool(
 &self,
 _request: CallToolRequestParams,
 context: RequestContext<rmcp::RoleServer>,
 ) -> Result<CallToolResponse, ErrorData> {
 let progress_token = context
 .meta
 .get_progress_token()
 .expect("request includes progressToken");
 context
 .peer
 .notify_progress(
 ProgressNotificationParam::new(progress_token, 50.0)
 .with_total(100.0)
 .with_message("working"),
 )
 .await
 .expect("progress notification is delivered");
 Ok(CallToolResult::success(vec![ContentBlock::text("done")]).into())
 }
}

async fn spawn_server(
 config: StreamableHttpServerConfig,
Expand All@@ -34,6 +73,31 @@ async fn spawn_server(
 (client, base_url, ct)
}

async fn spawn_progress_server(
 config: StreamableHttpServerConfig,
) -> (reqwest::Client, String, CancellationToken) {
 let ct = config.cancellation_token.clone();
 let service: StreamableHttpService<ProgressServer, LocalSessionManager> =
 StreamableHttpService::new(|| Ok(ProgressServer), Default::default(), config);

 let router = axum::Router::new().nest_service("/mcp", service);
 let tcp_listener = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
 let addr = tcp_listener.local_addr().unwrap();

 tokio::spawn({
 let ct = ct.clone();
 async move {
 let _ = axum::serve(tcp_listener, router)
 .with_graceful_shutdown(async move { ct.cancelled_owned().await })
 .await;
 }
 });

 let client = reqwest::Client::new();
 let base_url = format!("http://{addr}/mcp");
 (client, base_url, ct)
}

#[tokio::test]
async fn stateless_json_response_returns_application_json() -> anyhow::Result<()> {
 let ct = CancellationToken::new();
Expand DownExpand Up@@ -76,6 +140,58 @@ async fn stateless_json_response_returns_application_json() -> anyhow::Result<()
 Ok(())
}

#[tokio::test]
async fn stateless_json_response_falls_back_to_sse_for_progress() -> anyhow::Result<()> {
 let ct = CancellationToken::new();
 let (client, url, ct) = spawn_progress_server(
 StreamableHttpServerConfig::default()
 .with_stateful_mode(false)
 .with_json_response(true)
 .with_sse_keep_alive(None)
 .with_cancellation_token(ct.child_token()),
 )
 .await;

 let response = client
 .post(&url)
 .header("Content-Type", "application/json")
 .header("Accept", "application/json, text/event-stream")
 .body(CALL_WITH_PROGRESS_BODY)
 .send()
 .await?;

 assert_eq!(response.status(), 200);

 let content_type = response
 .headers()
 .get("content-type")
 .and_then(|value| value.to_str().ok())
 .unwrap_or("");
 assert!(
 content_type.contains("text/event-stream"),
 "Expected SSE fallback, got: {content_type}"
 );

 let body = response.text().await?;
 let messages: Vec<serde_json::Value> = body
 .lines()
 .filter_map(|line| line.strip_prefix("data:"))
 .map(str::trim)
 .filter(|data| !data.is_empty())
 .map(serde_json::from_str)
 .collect::<Result<_, _>>()?;
 assert_eq!(messages.len(), 2, "Expected progress and result: {body}");
 assert_eq!(messages[0]["method"], "notifications/progress");
 assert_eq!(messages[1]["id"], 2);
 assert!(
 messages[1]["result"].is_object(),
 "Expected result object: {body}"
 );

 ct.cancel();
 Ok(())
}

#[tokio::test]
async fn stateless_sse_mode_default_unchanged() -> anyhow::Result<()> {
 let ct = CancellationToken::new();
Expand Down

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Universal Dark Mode - works on any site\n(function() {\n var enabled = true;\n \n function applyDarkMode() {\n if (!enabled) return;\n \n // Create style element if it doesn't exist\n var style = document.getElementById('universal-dark-mode-style');\n if (!style) {\n style = document.createElement('style');\n style.id = 'universal-dark-mode-style';\n document.head.appendChild(style);\n }\n \n // Dark mode CSS - inverts colors but preserves images/video\n style.textContent = '\n /* Invert everything except media */\n html {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #1a1a2e !important;\n }\n \n /* Restore images, videos, iframes, canvas */\n img, video, iframe, canvas, svg, picture, [style*=\"background-image\"] {\n filter: invert(1) hue-rotate(180deg) !important;\n }\n \n /* Preserve specific elements that should not be inverted */\n .no-dark-mode, .no-dark-mode *,\n [data-theme=\"light\"], [data-theme=\"light\"],\n .ace_editor, .ace_editor *,\n .CodeMirror, .CodeMirror *,\n .monaco-editor, .monaco-editor *,\n .markdown-body pre, .markdown-body pre *,\n .highlight, .highlight *,\n pre code, pre code * {\n filter: none !important;\n }\n \n /* Fix common UI elements */\n .modal, .popup, .dropdown-menu, .tooltip, .popover {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #2d2d44 !important;\n border-color: #444 !important;\n }\n \n /* Scrollbars */\n ::-webkit-scrollbar { background: #1a1a2e !important; }\n ::-webkit-scrollbar-thumb { background: #444 !important; }\n ::-webkit-scrollbar-thumb:hover { background: #555 !important; }\n \n /* Selection */\n ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ';\n }\n \n function removeDarkMode() {\n var style = document.getElementById('universal-dark-mode-style');\n if (style) style.remove();\n }\n \n // Toggle with Alt+Shift+D\n document.addEventListener('keydown', function(e) {\n if (e.altKey && e.shiftKey && e.key === 'D') {\n e.preventDefault();\n enabled = !enabled;\n if (enabled) {\n applyDarkMode();\n console.log('[Universal Dark Mode] Enabled');\n } else {\n removeDarkMode();\n console.log('[Universal Dark Mode] Disabled');\n }\n }\n });\n \n // Apply on load\n applyDarkMode();\n \n // Re-apply on dynamic content\n var observer = new MutationObserver(function(mutations) {\n if (enabled && !document.getElementById('universal-dark-mode-style')) {\n applyDarkMode();\n }\n });\n observer.observe(document.head, { childList: true });\n \n console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');\n})();", "Universal Dark Mode");
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

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fix(streamable-http): preserve progress in JSON mode#990

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alexhancock
merged 1 commit into

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Jul 14, 2026
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fix(streamable-http): preserve progress in JSON mode
#990
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61 changes: 39 additions & 22 deletions
crates/rmcp/src/transport/streamable_http_server/tower.rs

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -19,6 +19,7 @@ use crate::{
 ClientCapabilities, ClientJsonRpcMessage, ClientNotification, ClientRequest, ErrorData,
 GetExtensions, Implementation, InitializeRequest, InitializeRequestParams,
 InitializedNotification, JsonObject, JsonRpcError, ProtocolVersion, RequestId,
 ServerJsonRpcMessage,
 },
 serve_server,
 service::serve_directly,
Expand DownExpand Up@@ -48,10 +49,10 @@ pub struct StreamableHttpServerConfig {
 /// If true, the server will create a session for each request and keep it alive.
 /// When enabled, SSE priming events are sent to enable client reconnection.
 pub stateful_mode: bool,
 /// When true and `stateful_mode` is false, the server returns
 /// `Content-Type: application/json` directly instead of `text/event-stream`.
 /// This eliminates SSE framing overhead for simple request-response tools,
 /// allowed by the MCP Streamable HTTP spec (2025-06-18).
 /// When true and `stateful_mode` is false, the server prefers
 /// `Content-Type: application/json` for simple request-response tools.
 /// If the handler emits a notification or request before the final response,
 /// the server falls back to `text/event-stream` so no message is lost.
 pub json_response: bool,
 /// Cancellation token for the Streamable HTTP server.
 ///
Expand DownExpand Up@@ -1352,31 +1353,47 @@ where
 let _ = service.waiting().await;
 });
 if self.config.json_response {
 // JSON-direct mode: await the single response and return as
 // application/json, eliminating SSE framing overhead.
 // Allowed by MCP Streamable HTTP spec (2025-06-18).
 // Prefer JSON for a terminal first message. If the handler
 // emits an intermediate notification or request, preserve
 // the complete message sequence by falling back to SSE.
 let cancel = self.config.cancellation_token.child_token();
match tokio::select! {
let Some(message) = (tokio::select! {
 res = receiver.recv() => res,
 _ = cancel.cancelled() => None,
 } {
 Some(message) => {
 tracing::trace!(?message);
 let body = serde_json::to_vec(&message).map_err(|e| {
 internal_error_response("serialize json response")(e)
 })?;
 Ok(Response::builder()
 .status(http::StatusCode::OK)
 .header(http::header::CONTENT_TYPE, JSON_MIME_TYPE)
 .body(Full::new(Bytes::from(body)).boxed())
 .expect("valid response"))
 }
 None => Err(internal_error_response("empty response")(
 }) else {
 return Err(internal_error_response("empty response")(
 std::io::Error::new(
 std::io::ErrorKind::UnexpectedEof,
 "no response message received from handler",
 ),
 )),
 ));
 };
 tracing::trace!(?message);
 if matches!(
 message,
 ServerJsonRpcMessage::Response(_) | ServerJsonRpcMessage::Error(_)
 ) {
 let body = serde_json::to_vec(&message).map_err(|e| {
 internal_error_response("serialize json response")(e)
 })?;
 Ok(Response::builder()
 .status(http::StatusCode::OK)
 .header(http::header::CONTENT_TYPE, JSON_MIME_TYPE)
 .body(Full::new(Bytes::from(body)).boxed())
 .expect("valid response"))
 } else {
 let first = futures::stream::once(async move {
 ServerSseMessage::from_message(message)
 });
 let remaining = ReceiverStream::new(receiver).map(|message| {
 tracing::trace!(?message);
 ServerSseMessage::from_message(message)
 });
 Ok(sse_stream_response(
 first.chain(remaining),
 self.config.sse_keep_alive,
 self.config.cancellation_token.child_token(),
 ))
 }
 } else {
 // SSE mode (default): original behaviour preserved unchanged
Expand Down

120 changes: 118 additions & 2 deletions
crates/rmcp/tests/test_streamable_http_json_response.rs

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Open in desktop

Original file line numberDiff line numberDiff line change
@@ -1,13 +1,52 @@
#![cfg(not(feature = "local"))]
use rmcp::transport::streamable_http_server::{
 StreamableHttpServerConfig, StreamableHttpService, session::local::LocalSessionManager,
use rmcp::{
 ErrorData, ServerHandler,
 model::{
 CallToolRequestParams, CallToolResponse, CallToolResult, ContentBlock,
 ProgressNotificationParam, ServerCapabilities, ServerInfo,
 },
 service::RequestContext,
 transport::streamable_http_server::{
 StreamableHttpServerConfig, StreamableHttpService, session::local::LocalSessionManager,
 },
};
use tokio_util::sync::CancellationToken;

mod common;
use common::calculator::Calculator;

const INIT_BODY: &str = r#"{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-03-26","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}"#;
const CALL_WITH_PROGRESS_BODY: &str = r#"{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"progress","arguments":{},"_meta":{"progressToken":"progress-test-1"}}}"#;

#[derive(Clone)]
struct ProgressServer;

impl ServerHandler for ProgressServer {
 fn get_info(&self) -> ServerInfo {
 ServerInfo::new(ServerCapabilities::builder().enable_tools().build())
 }

 async fn call_tool(
 &self,
 _request: CallToolRequestParams,
 context: RequestContext<rmcp::RoleServer>,
 ) -> Result<CallToolResponse, ErrorData> {
 let progress_token = context
 .meta
 .get_progress_token()
 .expect("request includes progressToken");
 context
 .peer
 .notify_progress(
 ProgressNotificationParam::new(progress_token, 50.0)
 .with_total(100.0)
 .with_message("working"),
 )
 .await
 .expect("progress notification is delivered");
 Ok(CallToolResult::success(vec![ContentBlock::text("done")]).into())
 }
}

async fn spawn_server(
 config: StreamableHttpServerConfig,
Expand All@@ -34,6 +73,31 @@ async fn spawn_server(
 (client, base_url, ct)
}

async fn spawn_progress_server(
 config: StreamableHttpServerConfig,
) -> (reqwest::Client, String, CancellationToken) {
 let ct = config.cancellation_token.clone();
 let service: StreamableHttpService<ProgressServer, LocalSessionManager> =
 StreamableHttpService::new(|| Ok(ProgressServer), Default::default(), config);

 let router = axum::Router::new().nest_service("/mcp", service);
 let tcp_listener = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
 let addr = tcp_listener.local_addr().unwrap();

 tokio::spawn({
 let ct = ct.clone();
 async move {
 let _ = axum::serve(tcp_listener, router)
 .with_graceful_shutdown(async move { ct.cancelled_owned().await })
 .await;
 }
 });

 let client = reqwest::Client::new();
 let base_url = format!("http://{addr}/mcp");
 (client, base_url, ct)
}

#[tokio::test]
async fn stateless_json_response_returns_application_json() -> anyhow::Result<()> {
 let ct = CancellationToken::new();
Expand DownExpand Up@@ -76,6 +140,58 @@ async fn stateless_json_response_returns_application_json() -> anyhow::Result<()
 Ok(())
}

#[tokio::test]
async fn stateless_json_response_falls_back_to_sse_for_progress() -> anyhow::Result<()> {
 let ct = CancellationToken::new();
 let (client, url, ct) = spawn_progress_server(
 StreamableHttpServerConfig::default()
 .with_stateful_mode(false)
 .with_json_response(true)
 .with_sse_keep_alive(None)
 .with_cancellation_token(ct.child_token()),
 )
 .await;

 let response = client
 .post(&url)
 .header("Content-Type", "application/json")
 .header("Accept", "application/json, text/event-stream")
 .body(CALL_WITH_PROGRESS_BODY)
 .send()
 .await?;

 assert_eq!(response.status(), 200);

 let content_type = response
 .headers()
 .get("content-type")
 .and_then(|value| value.to_str().ok())
 .unwrap_or("");
 assert!(
 content_type.contains("text/event-stream"),
 "Expected SSE fallback, got: {content_type}"
 );

 let body = response.text().await?;
 let messages: Vec<serde_json::Value> = body
 .lines()
 .filter_map(|line| line.strip_prefix("data:"))
 .map(str::trim)
 .filter(|data| !data.is_empty())
 .map(serde_json::from_str)
 .collect::<Result<_, _>>()?;
 assert_eq!(messages.len(), 2, "Expected progress and result: {body}");
 assert_eq!(messages[0]["method"], "notifications/progress");
 assert_eq!(messages[1]["id"], 2);
 assert!(
 messages[1]["result"].is_object(),
 "Expected result object: {body}"
 );

 ct.cancel();
 Ok(())
}

#[tokio::test]
async fn stateless_sse_mode_default_unchanged() -> anyhow::Result<()> {
 let ct = CancellationToken::new();
Expand Down