mcp_memory/
http.rs

1//! MCP **Streamable HTTP** transport (the 2025-03-26 transport that
2//! superseded the older HTTP+SSE pair).
3//!
4//! * `POST /mcp` — the client sends one JSON-RPC message (or a batch array).
5//!   The reply is delivered as `application/json` by default, or as a one-shot
6//!   `text/event-stream` (SSE) event when the client `Accept`s it. A body of
7//!   only notifications gets `202 Accepted` with no content.
8//! * `GET /mcp` — opens a standalone server→client SSE stream. This server has
9//!   no server-initiated messages, so the stream simply stays open with
10//!   keep-alives; it exists for spec compliance.
11//!
12//! `/` is also wired to the same handlers for convenience. The JSON-RPC
13//! semantics are identical to the stdio and TCP transports — only framing
14//! differs (see [`crate::server::dispatch_http_body`]).
15
16use std::convert::Infallible;
17use std::sync::{Arc, Mutex};
18
19use axum::extract::{DefaultBodyLimit, State};
20use axum::http::{header, HeaderMap, StatusCode};
21use axum::response::sse::{Event, KeepAlive, Sse};
22use axum::response::{IntoResponse, Response};
23use axum::routing::post;
24use axum::{Json, Router};
25use futures::Stream;
26use serde_json::json;
27use tokio::net::TcpListener;
28use tracing::{error, info};
29
30use crate::errors::{MCSError, Result};
31use crate::kg::KnowledgeGraph;
32use crate::server;
33
34type AppState = Arc<Mutex<KnowledgeGraph>>;
35
36/// Build the axum router for the HTTP transport. Exposed so tests can drive it
37/// with `tower::ServiceExt::oneshot` without binding a socket.
38pub fn router(kg: AppState) -> Router {
39    Router::new()
40        .route("/mcp", post(post_handler).get(get_handler))
41        .route("/", post(post_handler).get(get_handler))
42        .layer(DefaultBodyLimit::max(server::MAX_REQUEST_BYTES))
43        .with_state(kg)
44}
45
46/// Bind `addr` and serve the HTTP transport until the process is killed.
47pub async fn run(addr: &str, kg: AppState) -> Result<()> {
48    let listener = TcpListener::bind(addr).await.map_err(MCSError::IoError)?;
49    info!("Listening for HTTP (Streamable) MCP on http://{addr}/mcp");
50    axum::serve(listener, router(kg)).await.map_err(MCSError::IoError)?;
51    Ok(())
52}
53
54fn wants_sse(headers: &HeaderMap) -> bool {
55    headers
56        .get(header::ACCEPT)
57        .and_then(|v| v.to_str().ok())
58        .is_some_and(|a| a.contains("text/event-stream"))
59}
60
61async fn post_handler(State(kg): State<AppState>, headers: HeaderMap, body: String) -> Response {
62    // The dispatch path locks the graph and may perform a blocking fsync, so
63    // run it off the async worker pool (keeps the HTTP reactor responsive).
64    let result = tokio::task::spawn_blocking(move || server::dispatch_http_body(&body, &kg)).await;
65
66    let outcome = match result {
67        Ok(inner) => inner,
68        Err(join_err) => {
69            error!("dispatch task panicked: {join_err}");
70            return (StatusCode::INTERNAL_SERVER_ERROR, "internal error").into_response();
71        }
72    };
73
74    match outcome {
75        // Body held only notifications → nothing to return.
76        Ok(None) => StatusCode::ACCEPTED.into_response(),
77        Ok(Some(value)) => {
78            if wants_sse(&headers) {
79                // One JSON-RPC reply delivered as a single SSE event, then close.
80                let json = serde_json::to_string(&value).unwrap();
81                let stream = futures::stream::once(async move {
82                    Ok::<Event, Infallible>(Event::default().data(json))
83                });
84                Sse::new(stream).into_response()
85            } else {
86                Json(value).into_response()
87            }
88        }
89        Err(e) => {
90            // Malformed JSON body → JSON-RPC parse error.
91            let resp = json!({
92                "jsonrpc": "2.0",
93                "error": { "code": -32700, "message": format!("Parse error: {e}") },
94                "id": null
95            });
96            (StatusCode::BAD_REQUEST, Json(resp)).into_response()
97        }
98    }
99}
100
101async fn get_handler() -> Sse<impl Stream<Item = std::result::Result<Event, Infallible>>> {
102    // No server-initiated messages: an open, keep-alive'd stream for compliance.
103    let stream = futures::stream::pending::<std::result::Result<Event, Infallible>>();
104    Sse::new(stream).keep_alive(KeepAlive::default())
105}
mcp_memory/http.rs

mcp_memory/
http.rs
