rmcp 3.0.0

Rust SDK for Model Context Protocol
Documentation 
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#![cfg(all(
    not(feature = "local"),
    feature = "client",
    feature = "reqwest",
    feature = "transport-streamable-http-server"
))]

use std::borrow::Cow;

use rmcp::{
    ClientLifecycleMode, ClientServiceExt, ServerHandler,
    model::{ClientInfo, DiscoverResult, ErrorCode, ErrorData, ProtocolVersion},
    service::{MaybeSendFuture, RequestContext, RoleServer},
    transport::{
        StreamableHttpClientTransport,
        streamable_http_client::StreamableHttpClientTransportConfig,
        streamable_http_server::{
            StreamableHttpServerConfig, StreamableHttpService, session::local::LocalSessionManager,
        },
    },
};
use tokio_util::sync::CancellationToken;

#[derive(Clone, Default)]
struct DiscoverHttpServer;

impl ServerHandler for DiscoverHttpServer {
    fn supported_protocol_versions(&self) -> Cow<'static, [ProtocolVersion]> {
        Cow::Borrowed(&[ProtocolVersion::V_2026_07_28])
    }
}

#[derive(Clone, Default)]
struct LegacyHttpServer;

impl ServerHandler for LegacyHttpServer {
    fn discover(
        &self,
        _context: RequestContext<RoleServer>,
    ) -> impl Future<Output = Result<DiscoverResult, ErrorData>> + MaybeSendFuture + '_ {
        std::future::ready(Err(ErrorData::new(
            ErrorCode::METHOD_NOT_FOUND,
            "Method not found",
            None,
        )))
    }
}

#[tokio::test]
async fn discover_http_client_bootstraps_headers_without_initialize() {
    let ct = CancellationToken::new();
    let service: StreamableHttpService<DiscoverHttpServer, LocalSessionManager> =
        StreamableHttpService::new(
            || Ok(DiscoverHttpServer),
            Default::default(),
            StreamableHttpServerConfig::default()
                .with_legacy_session_mode(false)
                .with_json_response(true)
                .with_cancellation_token(ct.child_token()),
        );
    let router = axum::Router::new().nest_service("/mcp", service);
    let listener = tokio::net::TcpListener::bind("127.0.0.1:0")
        .await
        .expect("listener should bind");
    let address = listener.local_addr().expect("listener address");
    let server = tokio::spawn({
        let ct = ct.clone();
        async move {
            let _ = axum::serve(listener, router)
                .with_graceful_shutdown(async move { ct.cancelled_owned().await })
                .await;
        }
    });

    let transport = StreamableHttpClientTransport::from_config(
        StreamableHttpClientTransportConfig::with_uri(format!("http://{address}/mcp")),
    );
    let client = ClientInfo::default()
        .serve_with_lifecycle(
            transport,
            ClientLifecycleMode::Discover {
                preferred_versions: vec![ProtocolVersion::V_2026_07_28],
            },
        )
        .await
        .expect("discover HTTP client should start");
    client.list_tools(None).await.expect("list tools");
    client.cancel().await.expect("cancel client");

    ct.cancel();
    server.await.expect("server task");
}

#[tokio::test]
async fn auto_http_client_falls_back_to_stateful_legacy_startup() {
    let ct = CancellationToken::new();
    let service: StreamableHttpService<LegacyHttpServer, LocalSessionManager> =
        StreamableHttpService::new(
            || Ok(LegacyHttpServer),
            Default::default(),
            StreamableHttpServerConfig::default()
                .with_json_response(true)
                .with_cancellation_token(ct.child_token()),
        );
    let router = axum::Router::new().nest_service("/mcp", service);
    let listener = tokio::net::TcpListener::bind("127.0.0.1:0")
        .await
        .expect("listener should bind");
    let address = listener.local_addr().expect("listener address");
    let server = tokio::spawn({
        let ct = ct.clone();
        async move {
            let _ = axum::serve(listener, router)
                .with_graceful_shutdown(async move { ct.cancelled_owned().await })
                .await;
        }
    });

    let transport = StreamableHttpClientTransport::from_config(
        StreamableHttpClientTransportConfig::with_uri(format!("http://{address}/mcp")),
    );
    let client = ClientInfo::default()
        .serve_with_lifecycle(
            transport,
            ClientLifecycleMode::Auto {
                preferred_versions: vec![ProtocolVersion::V_2026_07_28],
                legacy_version: Some(ProtocolVersion::V_2025_11_25),
            },
        )
        .await
        .expect("auto HTTP client should fall back");
    client.list_tools(None).await.expect("list tools");
    client.cancel().await.expect("cancel client");

    ct.cancel();
    server.await.expect("server task");
}