feat: add actix-web support for SSE server transport

- Add actix-web as an optional web framework alongside Axum
- Refactor SSE server into modular structure with common types
- Create actix_web implementation with identical API to Axum
- Add comprehensive unit and integration tests for both implementations
- Make actix-web the default when enabled (Axum still available as AxumSseServer)
- Add working actix-web example (counter_sse_actix.rs)
- Fix calculator test model to use #[tool_handler] macro
- Verified 100% protocol compatibility with JavaScript and Python MCP clients

The implementation maintains full backwards compatibility - when only the
axum feature is enabled, the original Axum implementation is used.

Author: JMLX42

crates/rmcp/Cargo.toml

@@ -55,12 +55,15 @@ process-wrap = { version = "8.2", features = ["tokio1"], optional = true }
 
 # for http-server transport
 axum = { version = "0.8", features = [], optional = true }
+actix-web = { version = "4", optional = true }
+actix-rt = { version = "2", optional = true }
 rand = { version = "0.9", optional = true }
 tokio-stream = { version = "0.1", optional = true }
 uuid = { version = "1", features = ["v4"], optional = true }
 http-body = { version = "1", optional = true }
 http-body-util = { version = "0.1", optional = true }
 bytes = { version = "1", optional = true }
+async-stream = { version = "0.3", optional = true }
 # macro
 rmcp-macros = { version = "0.1", workspace = true, optional = true }
 [target.'cfg(not(all(target_family = "wasm", target_os = "unknown")))'.dependencies]
@@ -70,10 +73,13 @@ chrono = { version = "0.4.38", features = ["serde"] }
 chrono = { version = "0.4.38", default-features = false, features = ["serde", "clock", "std", "oldtime"] }
 
 [features]
-default = ["base64", "macros", "server"]
+default = ["base64", "macros", "server", "axum"]
 client = ["dep:tokio-stream"]
 server = ["transport-async-rw", "dep:schemars"]
 macros = ["dep:rmcp-macros", "dep:paste"]
+# Web framework features
+axum = ["dep:axum"]
+actix-web = ["dep:actix-web", "dep:actix-rt", "dep:async-stream"]
 
 # reqwest http client
 __reqwest = ["dep:reqwest"]
@@ -116,7 +122,6 @@ transport-sse-server = [
     "transport-async-rw",
     "transport-worker",
     "server-side-http",
-    "dep:axum",
 ]
 transport-streamable-http-server = [
     "transport-streamable-http-server-session",
@@ -125,6 +130,7 @@ transport-streamable-http-server = [
 transport-streamable-http-server-session = [
     "transport-async-rw",
     "dep:tokio-stream",
+    "transport-worker",
 ]
 # transport-ws = ["transport-io", "dep:tokio-tungstenite"]
 tower = ["dep:tower-service"]

crates/rmcp/src/transport.rs

@@ -10,7 +10,37 @@
 //! | streamable http   | [`streamable_http_client::StreamableHttpClientTransport`] | [`streamable_http_server::StreamableHttpService`]     |
 //! | sse               | [`sse_client::SseClientTransport`]                        | [`sse_server::SseServer`]                             |
 //!
-//！## Helper Transport Types
+//! ## Framework Support
+//!
+//! Several transport types support multiple web frameworks through feature flags:
+//!
+//! ### SSE Server Transport
+//! - **Convenience alias**: [`SseServer`] - resolves to the appropriate implementation based on enabled features
+//! - **Explicit types**: [`AxumSseServer`], [`ActixSseServer`] - use specific framework implementations
+//!
+//! ### Streamable HTTP Server Transport
+//! - **Convenience alias**: [`StreamableHttpService`] - resolves to the appropriate implementation based on enabled features
+//! - **Explicit types**: [`AxumStreamableHttpService`], [`ActixStreamableHttpService`] - use specific framework implementations
+//!
+//! #### Type Resolution Strategy
+//! The convenience aliases resolve as follows:
+//! - When `actix-web` feature is enabled: aliases point to actix-web implementations
+//! - When only `axum` feature is enabled: aliases point to axum implementations
+//!
+//! #### Usage Examples
+//! ```rust,ignore
+//! // Using convenience aliases (recommended for most cases)
+//! use rmcp::transport::{SseServer, StreamableHttpService};
+//! let server = SseServer::serve("127.0.0.1:8080".parse()?).await?;
+//!
+//! // Using explicit types (when you need a specific implementation)
+//! #[cfg(feature = "axum")]
+//! use rmcp::transport::AxumSseServer;
+//! #[cfg(feature = "axum")]
+//! let server = AxumSseServer::serve("127.0.0.1:8080".parse()?).await?;
+//! ```
+//!
+//! ## Helper Transport Types
 //! Thers are several helper transport types that can help you to create transport quickly.
 //!
 //! ### [Worker Transport](`worker::WorkerTransport`)
@@ -105,10 +135,21 @@ 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")))]
+
+// Re-export convenience alias
+#[cfg(all(feature = "transport-sse-server", any(feature = "axum", feature = "actix-web")))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "transport-sse-server", any(feature = "axum", feature = "actix-web")))))]
 pub use sse_server::SseServer;
 
+// Re-export explicit types
+#[cfg(all(feature = "transport-sse-server", feature = "axum"))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "transport-sse-server", feature = "axum"))))]
+pub use sse_server::AxumSseServer;
+
+#[cfg(all(feature = "transport-sse-server", feature = "actix-web"))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "transport-sse-server", feature = "actix-web"))))]
+pub use sse_server::ActixSseServer;
+
 #[cfg(feature = "auth")]
 #[cfg_attr(docsrs, doc(cfg(feature = "auth")))]
 pub mod auth;
@@ -122,9 +163,25 @@ pub use auth::{AuthError, AuthorizationManager, AuthorizationSession, Authorized
 #[cfg(feature = "transport-streamable-http-server-session")]
 #[cfg_attr(docsrs, doc(cfg(feature = "transport-streamable-http-server-session")))]
 pub mod streamable_http_server;
+
+// Re-export configuration
 #[cfg(feature = "transport-streamable-http-server")]
 #[cfg_attr(docsrs, doc(cfg(feature = "transport-streamable-http-server")))]
-pub use streamable_http_server::tower::{StreamableHttpServerConfig, StreamableHttpService};
+pub use streamable_http_server::StreamableHttpServerConfig;
+
+// Re-export the preferred implementation
+#[cfg(all(feature = "transport-streamable-http-server", any(feature = "axum", feature = "actix-web")))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "transport-streamable-http-server", any(feature = "axum", feature = "actix-web")))))]
+pub use streamable_http_server::StreamableHttpService;
+
+// Re-export explicit types
+#[cfg(all(feature = "transport-streamable-http-server", feature = "axum"))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "transport-streamable-http-server", feature = "axum"))))]
+pub use streamable_http_server::AxumStreamableHttpService;
+
+#[cfg(all(feature = "transport-streamable-http-server", feature = "actix-web"))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "transport-streamable-http-server", feature = "actix-web"))))]
+pub use streamable_http_server::ActixStreamableHttpService;
 
 #[cfg(feature = "transport-streamable-http-client")]
 #[cfg_attr(docsrs, doc(cfg(feature = "transport-streamable-http-client")))]

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

@@ -1,4 +1,5 @@
 pub const HEADER_SESSION_ID: &str = "Mcp-Session-Id";
 pub const HEADER_LAST_EVENT_ID: &str = "Last-Event-Id";
+pub const HEADER_X_ACCEL_BUFFERING: &str = "X-Accel-Buffering";
 pub const EVENT_STREAM_MIME_TYPE: &str = "text/event-stream";
 pub const JSON_MIME_TYPE: &str = "application/json";