feat!: remove SSE transport support (#562)

SSE transport has been removed from the MCP specification in favor of
streamable HTTP. This removes all SSE-specific transport code:

- Remove `transport-sse-client` and `transport-sse-server` features
- Remove `SseClientTransport` and `SseServer` types
- Remove SSE-specific examples (`counter_sse`, `counter_sse_directly`)
- Migrate auth examples from SSE to streamable HTTP
- Update tests to remove SSE transport usage
- Update documentation

BREAKING CHANGE: The following have been removed:
- `transport-sse-client` feature
- `transport-sse-client-reqwest` feature
- `transport-sse-server` feature
- `SseClientTransport` type
- `SseServer` type
- `sse_client` and `sse_server` modules

Users should migrate to streamable HTTP transport which provides
equivalent functionality. See `StreamableHttpClientTransport` and
`StreamableHttpService` for the replacement APIs.

Ref: #561 (comment)

Author: domdomegg

crates/rmcp/Cargo.toml

@@ -33,7 +33,7 @@ schemars = { version = "1.0", optional = true, features = ["chrono04"] }
 # for image encoding
 base64 = { version = "0.22", optional = true }
 
-# for SSE client
+# for HTTP client
 reqwest = { version = "0.12", default-features = false, features = [
   "json",
   "stream",
@@ -99,33 +99,23 @@ server-side-http = [
   "dep:sse-stream",
   "tower",
 ]
-# SSE client
-client-side-sse = ["dep:sse-stream", "dep:http"]
-
-transport-sse-client = ["client-side-sse", "transport-worker"]
-transport-sse-client-reqwest = ["transport-sse-client", "reqwest"]
 
 transport-worker = ["dep:tokio-stream"]
 
+# SSE stream parsing utilities (used by streamable HTTP client for SSE-formatted responses)
+client-side-sse = ["dep:sse-stream", "dep:http"]
 
 # Streamable HTTP client
 transport-streamable-http-client = ["client-side-sse", "transport-worker"]
 transport-streamable-http-client-reqwest = ["transport-streamable-http-client", "reqwest"]
 
-
 transport-async-rw = ["tokio/io-util", "tokio-util/codec"]
 transport-io = ["transport-async-rw", "tokio/io-std"]
 transport-child-process = [
   "transport-async-rw",
   "tokio/process",
   "dep:process-wrap",
 ]
-transport-sse-server = [
-  "transport-async-rw",
-  "transport-worker",
-  "server-side-http",
-  "dep:axum",
-]
 transport-streamable-http-server = [
   "transport-streamable-http-server-session",
   "server-side-http",
@@ -162,8 +152,6 @@ required-features = [
   "reqwest",
   "server",
   "client",
-  "transport-sse-server",
-  "transport-sse-client",
   "transport-child-process",
 ]
 path = "tests/test_with_python.rs"
@@ -173,7 +161,6 @@ name = "test_with_js"
 required-features = [
   "server",
   "client",
-  "transport-sse-server",
   "transport-child-process",
   "transport-streamable-http-server",
   "transport-streamable-http-client",

crates/rmcp/README.md

@@ -203,8 +203,6 @@ RMCP uses feature flags to control which components are included:
   - `transport-async-rw`: Async read/write support
   - `transport-io`: I/O stream support
   - `transport-child-process`: Child process support
-  - `transport-sse-client` / `transport-sse-server`: SSE support (client agnostic)
-    - `transport-sse-client-reqwest`: a default `reqwest` implementation of the SSE client
   - `transport-streamable-http-client` / `transport-streamable-http-server`: HTTP streaming (client agnostic, see [`StreamableHttpClientTransport`] for details)
     - `transport-streamable-http-client-reqwest`: a default `reqwest` implementation of the streamable http client
 - `auth`: OAuth2 authentication support
@@ -214,22 +212,19 @@ RMCP uses feature flags to control which components are included:
 ## Transports
 
 - `transport-io`: Server stdio transport
-- `transport-sse-server`: Server SSE transport
 - `transport-child-process`: Client stdio transport
-- `transport-sse-client`: Client sse transport
 - `transport-streamable-http-server` streamable http server transport
 - `transport-streamable-http-client` streamable http client transport
 
 <details>
 <summary>Transport</summary>
 The transport type must implemented [`Transport`] trait, which allow it send message concurrently and receive message sequentially.
-There are 3 pairs of standard transport types:
+There are 2 pairs of standard transport types:
 
 | transport         | client                                                    | server                                                |
 |:-:                |:-:                                                        |:-:                                                    |
 | std IO            | [`child_process::TokioChildProcess`]                      | [`io::stdio`]                                         |
 | streamable http   | [`streamable_http_client::StreamableHttpClientTransport`] | [`streamable_http_server::session::create_session`]   |
-| sse               | [`sse_client::SseClientTransport`]                        | [`sse_server::SseServer`]                             |
 
 #### [IntoTransport](`IntoTransport`) trait
 [`IntoTransport`] is a helper trait that implicitly convert a type into a transport type.

crates/rmcp/src/transport.rs

@@ -2,13 +2,12 @@
 //! The transport type must implemented [`Transport`] trait, which allow it send message concurrently and receive message sequentially.
 //！
 //! ## Standard Transport Types
-//! There are 3 pairs of standard transport types:
+//! There are 2 pairs of standard transport types:
 //!
 //! | transport         | client                                                    | server                                                |
 //! |:-:                |:-:                                                        |:-:                                                    |
 //! | std IO            | [`child_process::TokioChildProcess`]                      | [`io::stdio`]                                         |
 //! | streamable http   | [`streamable_http_client::StreamableHttpClientTransport`] | [`streamable_http_server::StreamableHttpService`]     |
-//! | sse               | [`sse_client::SseClientTransport`]                        | [`sse_server::SseServer`]                             |
 //!
 //！## Helper Transport Types
 //! Thers are several helper transport types that can help you to create transport quickly.
@@ -95,20 +94,6 @@ pub mod io;
 #[cfg_attr(docsrs, doc(cfg(feature = "transport-io")))]
 pub use io::stdio;
 
-#[cfg(feature = "transport-sse-client")]
-#[cfg_attr(docsrs, doc(cfg(feature = "transport-sse-client")))]
-pub mod sse_client;
-#[cfg(feature = "transport-sse-client")]
-#[cfg_attr(docsrs, doc(cfg(feature = "transport-sse-client")))]
-pub use sse_client::SseClientTransport;
-
-#[cfg(feature = "transport-sse-server")]
-#[cfg_attr(docsrs, doc(cfg(feature = "transport-sse-server")))]
-pub mod sse_server;
-#[cfg(feature = "transport-sse-server")]
-#[cfg_attr(docsrs, doc(cfg(feature = "transport-sse-server")))]
-pub use sse_server::SseServer;
-
 #[cfg(feature = "auth")]
 #[cfg_attr(docsrs, doc(cfg(feature = "auth")))]
 pub mod auth;

crates/rmcp/src/transport/auth.rs

@@ -74,7 +74,7 @@ impl CredentialStore for InMemoryCredentialStore {
     }
 }
 
-/// sse client with oauth2 authorization
+/// HTTP client with OAuth 2.0 authorization
 #[derive(Clone)]
 pub struct AuthClient<C> {
     pub http_client: C,
@@ -91,7 +91,7 @@ impl<C: std::fmt::Debug> std::fmt::Debug for AuthClient<C> {
 }
 
 impl<C> AuthClient<C> {
-    /// create new authorized sse client
+    /// Create a new authorized HTTP client
     pub fn new(http_client: C, auth_manager: AuthorizationManager) -> Self {
         Self {
             http_client,

crates/rmcp/src/transport/common.rs

@@ -1,7 +1,4 @@
-#[cfg(any(
-    feature = "transport-streamable-http-server",
-    feature = "transport-sse-server"
-))]
+#[cfg(feature = "transport-streamable-http-server")]
 pub mod server_side_http;
 
 pub mod http_header;
@@ -10,6 +7,9 @@ pub mod http_header;
 #[cfg_attr(docsrs, doc(cfg(feature = "reqwest")))]
 mod reqwest;
 
+// Note: This module provides SSE stream parsing and auto-reconnect utilities.
+// It's used by the streamable HTTP client (which receives SSE-formatted responses),
+// not the removed SSE transport. The name is historical.
 #[cfg(feature = "client-side-sse")]
 #[cfg_attr(docsrs, doc(cfg(feature = "client-side-sse")))]
 pub mod client_side_sse;

crates/rmcp/src/transport/common/auth.rs

@@ -1,7 +1,3 @@
 #[cfg(feature = "transport-streamable-http-client")]
 #[cfg_attr(docsrs, doc(cfg(feature = "transport-streamable-http-client")))]
 mod streamable_http_client;
-
-#[cfg(feature = "transport-sse-client")]
-#[cfg_attr(docsrs, doc(cfg(feature = "transport-sse-client")))]
-mod sse_client;

crates/rmcp/src/transport/common/auth/sse_client.rs

@@ -1,7 +1,3 @@
 #[cfg(feature = "transport-streamable-http-client-reqwest")]
 #[cfg_attr(docsrs, doc(cfg(feature = "transport-streamable-http-client-reqwest")))]
 mod streamable_http_client;
-
-#[cfg(feature = "transport-sse-client-reqwest")]
-#[cfg_attr(docsrs, doc(cfg(feature = "transport-sse-client-reqwest")))]
-mod sse_client;