| Filename | Latest commit message | Latest commit date |
|---|---|---|
22be2cc5ad`ClientLifecycleMode::Auto` only fell back from `server/discover` on `-32601`, so legacy servers that reject the probe with other codes (`-32600`, `-32602`, implementation-defined errors) failed to connect even though `initialize` would have succeeded. The previous attempt (indicates_legacy_server) classified the failure after the fact by reverse-engineering the error type. This rewrite moves the classification into `discover_startup` itself, where the full context (request id, response correlation, transport state) is still available. `discover_startup` now returns `DiscoverOutcome`: `Modern` on success, `Legacy(error)` when the probe received a complete, correlated JSON-RPC error whose code is not a modern-era rejection. Every other failure becomes `Err`, so `Auto` simply matches the outcome — no methods on `ClientInitializeError`, no downcast, no transport-specific types leaking into the generic lifecycle layer. Additional fixes that fall out naturally: - Response correlation is now checked in `expect_response` for both success and error branches. Previously error responses skipped id correlation entirely. A new `UncorrelatedErrorResponse` variant surfaces responses that cannot be tied to the request. - When both discover and the legacy fallback fail, a `LegacyFallbackFailed` compound error preserves both phases instead of discarding the discover error. Fixes #1040. |
||
| .. | ||
| src | ||
| tests | ||
| build.rs | ||
| Cargo.toml | ||
| CHANGELOG.md | ||
| README.md | ||
rmcp
The official Rust SDK for the Model Context Protocol. Build MCP servers that expose tools, resources, and prompts to AI assistants — or build clients that connect to them.
For getting started, usage guides, and full MCP feature documentation (resources, prompts, sampling, roots, logging, completions, subscriptions, etc.), see the main README.
Feature Flags
| Feature | Description | Default |
|---|---|---|
server |
Server functionality and the tool system | ✅ |
client |
Client functionality | |
macros |
#[tool] / #[prompt] macros (re-exports rmcp-macros) |
✅ |
schemars |
JSON Schema generation for tool definitions | |
auth |
OAuth 2.0 authentication support | |
elicitation |
Elicitation support |
Transport features
| Feature | Description |
|---|---|
transport-io |
Server-side stdio transport |
transport-child-process |
Client-side stdio transport (spawns a child process) |
transport-async-rw |
Generic async read/write transport |
transport-streamable-http-client |
Streamable HTTP client (transport-agnostic) |
transport-streamable-http-client-reqwest |
Streamable HTTP client with default reqwest backend |
transport-streamable-http-server |
Streamable HTTP server transport |
TLS backend options (for HTTP transports)
| Feature | Description |
|---|---|
reqwest |
Uses rustls — pure Rust TLS (recommended default) |
reqwest-native-tls |
Uses platform-native TLS (OpenSSL / Secure Transport / SChannel) |
reqwest-tls-no-provider |
Uses rustls without a default crypto provider (bring your own) |
Transports
The transport layer is pluggable. Two built-in pairs cover the most common cases:
| Client | Server | |
|---|---|---|
| stdio | TokioChildProcess |
stdio |
| Streamable HTTP | StreamableHttpClientTransport |
StreamableHttpService |
Any type that implements the Transport trait can be used. The IntoTransport helper trait provides automatic conversions from:
(Sink, Stream)or a combinedSink + Stream(AsyncRead, AsyncWrite)or a combinedAsyncRead + AsyncWrite- A
Workerimplementation - A
Transportimplementation directly
License
This project is licensed under the terms specified in the repository's LICENSE file.