Commit graph go-sdk/mcp/streamable_test.go
Author SHA1 Message Date
Guglielmo Colombo
e01639a318
feat: HTTP Header Standardization for method and name (#907)
## Description

Implements SEP-2243
(https://modelcontextprotocol.io/seps/2243-http-standardization) (HTTP
Header Standardization) for Mcp-Method and Mcp-Name standard headers
(x-mcp-param custom headers will be covvered in separate PR).

Fixes #905
2026-04-29 17:33:39 +02:00
Maciej Kisiel
41e1f941bb
mcp: remove default cross origin protection (#906)
Fixes #902
2026-04-24 11:35:22 +02:00
Kalvin C
35f1b07e48
mcp: accept parameterized Content-Type types (#890)
Use a shared helper for Content-Type parsing in streamable transport
request validation and client response handling.

Follow up to https://github.com/modelcontextprotocol/go-sdk/pull/853,
where we did this for `Accept` headers.

This allows the streamable mcp server to validate the following header
`Content-Type: application/json;charset=utf-8`

Co-authored-by: Maciej Kisiel <mkisiel@google.com>
2026-04-23 08:51:47 -04:00
Benjamin Egelund-Müller
862d78a265
mcp: fix race condition in ServerSession.startKeepalive (#856)
This PR fixes a race condition where `ServerSession.keepaliveCancel` was
accessed in `Close` concurrently with its initialization in
`ServerSession.startKeepalive`. It also removes a now redundant test.

The fix moves keepalive initialization into `ServerSession.Connect`
similar to the implementation in `ClientSession.Connect`. This is safe
because the MCP spec allows keepalive pings before the initialization
messages. From the MCP
[spec](https://modelcontextprotocol.io/specification/2025-11-25/basic/lifecycle)
(emphasis added):
> The client SHOULD NOT send requests **other than pings** before the
server has responded to the initialize request.

The PR includes a reproducer test case, which fails with the following
error without this fix:
```
> go test -count=10 -race -run ^TestStreamableStatelessKeepaliveRace$ github.com/modelcontextprotocol/go-sdk/mcp                                                                                                                          8s
==================
WARNING: DATA RACE
Write at 0x00c00007fbf0 by goroutine 1095:
  github.com/modelcontextprotocol/go-sdk/mcp.startKeepalive()
      /Users/benjamin/Documents/go-sdk/mcp/shared.go:590 +0x58
  github.com/modelcontextprotocol/go-sdk/mcp.(*ServerSession).startKeepalive()
      /Users/benjamin/Documents/go-sdk/mcp/server.go:1526 +0x130
  github.com/modelcontextprotocol/go-sdk/mcp.(*ServerSession).initialized()
      /Users/benjamin/Documents/go-sdk/mcp/server.go:1059 +0xf8
  github.com/modelcontextprotocol/go-sdk/mcp.init.serverSessionMethod[go.shape.*uint8,go.shape.interface { GetMeta() map[string]interface {}; SetMeta(map[string]interface {}); github.com/modelcontextprotocol/go-sdk/mcp.isResult() }].func27()
      /Users/benjamin/Documents/go-sdk/mcp/shared.go:332 +0x98
  github.com/modelcontextprotocol/go-sdk/mcp.newServerMethodInfo[go.shape.*github.com/modelcontextprotocol/go-sdk/mcp.InitializedParams,go.shape.interface { GetMeta() map[string]interface {}; SetMeta(map[string]interface {}); github.com/modelcontextprotocol/go-sdk/mcp.isResult() },go.shape.struct { github.com/modelcontextprotocol/go-sdk/mcp.Meta "json:\"_meta,omitempty\"" }].func2()
      /Users/benjamin/Documents/go-sdk/mcp/shared.go:272 +0x84
  github.com/modelcontextprotocol/go-sdk/mcp.defaultReceivingMethodHandler[go.shape.*uint8]()
      /Users/benjamin/Documents/go-sdk/mcp/shared.go:152 +0xe8
  github.com/modelcontextprotocol/go-sdk/mcp.defaultReceivingMethodHandler[*github.com/modelcontextprotocol/go-sdk/mcp.ServerSession]()
      /Users/benjamin/Documents/go-sdk/mcp/shared.go:146 +0x60
  github.com/modelcontextprotocol/go-sdk/mcp.handleReceive[go.shape.*uint8]()
      /Users/benjamin/Documents/go-sdk/mcp/shared.go:169 +0x228
  github.com/modelcontextprotocol/go-sdk/mcp.(*ServerSession).handle()
      /Users/benjamin/Documents/go-sdk/mcp/server.go:1445 +0x370
  github.com/modelcontextprotocol/go-sdk/mcp.connect[go.shape.*uint8,go.shape.*uint8].func1.1()
      /Users/benjamin/Documents/go-sdk/mcp/transport.go:170 +0x5c
  github.com/modelcontextprotocol/go-sdk/internal/jsonrpc2.HandlerFunc.Handle()
      /Users/benjamin/Documents/go-sdk/internal/jsonrpc2/jsonrpc2.go:84 +0x48
  github.com/modelcontextprotocol/go-sdk/internal/jsonrpc2.(*Connection).handleAsync.func3()
      /Users/benjamin/Documents/go-sdk/internal/jsonrpc2/conn.go:717 +0xd8

Previous read at 0x00c00007fbf0 by goroutine 1089:
  github.com/modelcontextprotocol/go-sdk/mcp.(*ServerSession).Close()
      /Users/benjamin/Documents/go-sdk/mcp/server.go:1502 +0x34
  github.com/modelcontextprotocol/go-sdk/mcp.(*StreamableHTTPHandler).ServeHTTP.deferwrap1()
      /Users/benjamin/Documents/go-sdk/mcp/streamable.go:519 +0x34
  runtime.deferreturn()
      /opt/homebrew/Cellar/go/1.25.4/libexec/src/runtime/panic.go:589 +0x5c
  github.com/modelcontextprotocol/go-sdk/mcp.TestStreamableStatelessKeepaliveRace.mustNotPanic.func2()
      /Users/benjamin/Documents/go-sdk/mcp/streamable_test.go:2156 +0x94
  net/http.HandlerFunc.ServeHTTP()
      /opt/homebrew/Cellar/go/1.25.4/libexec/src/net/http/server.go:2322 +0x48
  net/http.serverHandler.ServeHTTP()
      /opt/homebrew/Cellar/go/1.25.4/libexec/src/net/http/server.go:3340 +0x270
  net/http.(*conn).serve()
      /opt/homebrew/Cellar/go/1.25.4/libexec/src/net/http/server.go:2109 +0x9b0
  net/http.(*Server).Serve.gowrap3()
      /opt/homebrew/Cellar/go/1.25.4/libexec/src/net/http/server.go:3493 +0x48

Goroutine 1095 (running) created at:
  github.com/modelcontextprotocol/go-sdk/internal/jsonrpc2.(*Connection).handleAsync()
      /Users/benjamin/Documents/go-sdk/internal/jsonrpc2/conn.go:715 +0x334
  github.com/modelcontextprotocol/go-sdk/internal/jsonrpc2.(*Connection).acceptRequest.func2.gowrap1()
      /Users/benjamin/Documents/go-sdk/internal/jsonrpc2/conn.go:676 +0x34

Goroutine 1089 (running) created at:
  net/http.(*Server).Serve()
      /opt/homebrew/Cellar/go/1.25.4/libexec/src/net/http/server.go:3493 +0x5dc
  net/http/httptest.(*Server).goServe.func1()
      /opt/homebrew/Cellar/go/1.25.4/libexec/src/net/http/httptest/server.go:311 +0x98
==================
--- FAIL: TestStreamableStatelessKeepaliveRace (0.14s)
    testing.go:1617: race detected during execution of test
FAIL
FAIL	github.com/modelcontextprotocol/go-sdk/mcp	1.727s
FAIL
```

---------

Co-authored-by: Maciej Kisiel <mkisiel@google.com>
2026-04-03 20:17:49 +02:00
Rafael Dantas Justo
27f29c1cef
mcp: allow Content-Type parameters in streamable transport (#878)
Use `mime.ParseMediaType` to parse the `Content-Type` header instead of
exact string matching. Previously, the server required an exact match on
`application/json`.

This allows the server to accept `application/json` with parameters
(e.g. `charset=utf-8`), even though [they are not
required](https://datatracker.ietf.org/doc/html/rfc4627.html#section-6),
following the robustness principle.

Per [RFC 8259 (section
8.1)](https://datatracker.ietf.org/doc/html/rfc8259.html#section-8.1),
`application/json` is always UTF-8, so such parameters are technically
redundant. However, parsing the media type makes the server more
tolerant of client behaviour, improving compatibility without
compromising security.
2026-04-03 17:42:20 +02:00
Kalvin C
c1a12cfeda
mcp: accept parameterized Accept media types (#853)
Normalize accept tokens before validation so valid headers with media
type parameters still match their base media types.

This allows the streamable mcp server to validate the following header
`Accept: application/json;charset=utf-8, text/event-stream`

Co-authored-by: Maciej Kisiel <mkisiel@google.com>
2026-03-31 11:17:49 +02:00
Oleksandr Redko
a1f808c86e
all: modernize code (#868)
Use `go fix ./...` to modernize the code.
2026-03-31 10:58:02 +02:00
Oleksandr Redko
b71a8391a6
all: fix typos (#869)
Grammar issues in docs, comments, and error messages.
2026-03-30 18:43:01 +02:00
Maciej Kisiel
755b9ed4df
mcp: re-enable race test after fixing data races (#851)
1. (non-test) Don't queue notifications if there are no connected
sessions.
2. Change `reconnectInitialDelay` to be atomic, as it is modified in
tests.
3. Protect map access with mutex in `TestServerTransportCleanup`.
2026-03-23 08:35:27 +01:00
Maciej Kisiel
a433a831d6
mcp: verify 'Origin' and 'Content-Type' headers (#842)
This PR introduces protection against cross-origin requests by
installing `http.CrossOriginProtection`.
By default, the zero value is used which does not contain any trusted
origins or bypass patterns.
The protection can be customized by providing a custom
`http.CrossOriginProtection` in `mcp.StreamableHTTPOptions`. Currently,
the deny handler set on the protection is ignored.
This default has an MCPGODEBUG option (`disableoriginverification`) to
disable the default protection.
It will be available until `v1.6.0` of the SDK.
We also increase the Go version required by the SDK to 1.25, since this
is the version that introduced `http.CrossOriginProtection`. This is in
line with the SDK's policy of supporting two newest Go versions (1.26
was released in February 2026).

Additionally, we start validating if the `Content-Type` header for
`POST` requests is set to `application/json` to avoid accepting
CORS-safelisted requests.
2026-03-13 11:36:41 +01:00
Robert Findley
4e1c3a34b5
mcp: update latestProtocolVersion to 2025-11-25 (#724)
Update the SDK to use protocol version 2025-11-25 as the latest
supported version. Fix tests and examples that had hardcoded
expectations for the previous version (2025-06-18).

---------

Co-authored-by: Maciej Kisiel <mkisiel@google.com>
2026-03-03 10:30:11 +01:00
Maciej Kisiel
c9317fb5b7
all: client side OAuth support (#785)
This PR introduces client-side OAuth support.

# Overall design philosophy

The main new interface introduced to support client-side OAuth is the
`OAuthHandler`. Contrary to its counter-parts in some other SDKs, it is
intentionally small and generic so that it can support most of the OAuth
authorization flow variants. The main `mcp` package purposefully
delegates almost all auth handling to `OAuthHandler` implementations.
This way, the `mcp` package continues to be largely OAuth agnostic.

The `auth` package comes with a default `OAuthHandler` implementation –
`AuthorizationCodeHandler`, which implements the authorization flow
for the `authorization_code` grant type, as defined in the [MCP
specification](https://modelcontextprotocol.io/specification/2025-11-25/basic/authorization).
It is expected that the `OAuthHandler` implementation granularity will
be roughly per grant type, as this parameter influences the
authorization flow the most.

# Detailed design

## `OAuthHandler` (auth/client.go)

The main interface for the integration consists of two methods:

```go
type OAuthHandler interface {
	// TokenSource returns a token source to be used for outgoing requests.
	// Returned token source might be nil. In that case, the transport will not
	// add any authorization headers to the request.
	TokenSource(context.Context) (oauth2.TokenSource, error)

	// Authorize is called when an HTTP request results in an error that may
	// be addressed by the authorization flow (currently 401 Unauthorized and 403 Forbidden).
	// It is responsible for performing the OAuth flow to obtain an access token.
	// The arguments are the request that failed and the response that was received for it.
	// The headers of the request are available, but the body will have already been consumed
	// when Authorize is called.
	// If the returned error is nil, TokenSource is expected to return a non-nil token source.
	// After a successful call to Authorize, the HTTP request will be retried by the transport.
	// The function is responsible for closing the response body.
	Authorize(context.Context, *http.Request, *http.Response) error
}
```

`StreamableClientTransport` accepts this interface as a field and uses
the `TokenSource` method to add an `Authorization: Bearer` header to
outgoing requests to the MCP server. If the request fails with `401:
Unauthorized` or `403: Forbidden`, the transport calls `Authorize` to
perform the authorization flow. If `Authorize` returns a non-nil error,
the request is retried once. `Authorize` errors do not result in
termination of the client session (unless they happen during
connection initialization), as some OAuth flows are multi-legged and it should be
acceptable to retry for example when the authorization grant was
received.

*Note:* There was already an `OAuthHandler` type defined as part of a
previous iteration of OAuth support. It was renamed to
`OAuthHandlerLegacy`. This is the only backwards incompatible API change
in the experimental client `auth` part (protected by the
`mcp_go_client_oauth` Go build tag). The cost of replacing previous
usages is deemed worthwhile to maintain clear naming, under the
assumption that the experimental client `auth` part was not widely used.

## `AuthorizationCodeHandler` (auth/authorization_code.go)

This is the `OAuthHandler` implementation that fulfills the [MCP
specification](https://modelcontextprotocol.io/specification/2025-11-25/basic/authorization).
In particular, in supports:

- Protected Resource Metadata discovery and fetching
- Authorization Server Metadata discovery and fetching
- Client registration
  - OpenID Connect metadata document
  - Pre-registration
  - Dynamic Client Registration
- PKCE
- `client_secret_post`, `client_secret_basic` token endpoint
auth methods
- Automatic refresh of tokens

### Authorization Server redirect

As part of the flow for the `authorization_code` grant type, the client
needs to point the user to the authorization URL, so that they confirm
the access request. This design proposes that it will be supported via a
pluggable dependency that will initiate this process in an
application-specific way:

```go
type AuthorizationCodeHandler struct {
	...

	// AuthorizationCodeFetcher is a required function called to initiate the authorization flow.
	// It is responsible for opening the URL in a browser for the user to start the authorization process.
	// It should return the authorization code and state once the Authorization Server
	// redirects back to the RedirectURL.
	AuthorizationCodeFetcher func(ctx context.Context, args *AuthorizationArgs) (*AuthorizationResult, error)

	...
}
```

The function is supposed perform any application specific logic to handle the redirect
from the Authorization Server and return the resulting code and state.

## `oauthex` changes

Some additional/adjusted building blocks that may be useful when
creating `OAuthHandler` implementations are present in the `oauthex`
package:

- `auth_meta.go`: Authorization Server Metadata utilities:
  - `GetAuthServerMeta`: get Authorization Server Metadata from a URL
- `dcr.go`: Dynamic Client Registration utilities (unchanged)
- `resource_meta.go`: Protected Resource Metadata utilities:
- `GetProtectedResourceMetadata`: get Protected Resource Metadata from a
URL
  - `ParseWWWAuthenticate` – as per name (unchanged)
- [deprecated] `GetProtectedResourceMetadataFromID` and
`GetProtectedResourceMetadataFromHeader` in favor of more generic
`GetProtectedResourceMetadata`. They will be kept under the Go build tag
and removed one version of the SDK in the future.
2026-02-27 15:30:13 +01:00
Paul Carleton
67bd3f2e2b
mcp: add automatic DNS rebinding protection for localhost servers (#760)
## Summary

Add DNS rebinding protection that is automatically enabled when requests
arrive via localhost (127.0.0.1, [::1]). This protects against malicious
websites using DNS rebinding to interact with local MCP servers.

(note: this was a claude assisted PR, mostly wanted to see how difficult
passing this test would be for this SDK)

## Design Goal: Secure by Default

The primary goal is to make it difficult to run a localhost server
without these protections by mistake. There are other approaches that
could provide secure defaults (e.g., a helper for `ListenAndServe` that
does the localhost check), but using `http.LocalAddrContextKey` for
runtime detection seemed like the most backwards compatible approach and
least likely to be disabled by accident.

With this implementation:
- **No code changes required** - existing servers get protection
automatically
- **No opt-in needed** - protection activates based on the connection's
local address
- **Explicit opt-out** - users must deliberately set
`DisableLocalhostProtection: true`

## Changes

- Add `DisableLocalhostProtection` option to `StreamableHTTPOptions`
- Add `isLocalhostAddr` and `isLocalhostHost` helper functions  
- Validate Host header at start of `ServeHTTP`, rejecting non-localhost
Host headers with 403 Forbidden

## How it works

The protection uses `http.LocalAddrContextKey` to detect the
connection's local address at runtime. When a request arrives via
localhost (127.0.0.1 or [::1]), the handler validates that the Host
header also matches a localhost value. If not, the request is rejected
with 403 Forbidden.

This approach means:
- Protection is enabled for requests arriving via localhost, regardless
of whether the server listens on `127.0.0.1` or `0.0.0.0`
- Requests arriving via non-localhost IPs (e.g., external network
requests) are **not** affected

### Edge case: Reverse proxies

If a reverse proxy (e.g., Envoy, nginx) runs on the same host and
forwards requests to the MCP server via localhost while preserving the
original Host header, those requests would be rejected. In this case,
users should either:
1. Set `DisableLocalhostProtection: true`
2. Configure the proxy to rewrite the Host header to localhost

## Testing

- Added unit tests for `isLocalhostAddr` and `isLocalhostHost` helper
functions
- Added integration tests for the full protection flow
- Verified against the MCP conformance test suite:
  - `localhost-host-rebinding-rejected`: PASS
  - `localhost-host-valid-accepted`: PASS

## Related

- Spec:
https://modelcontextprotocol.io/specification/2025-11-25/basic/security_best_practices#local-mcp-server-compromise
- TypeScript SDK implementation: `localhostHostValidation()` middleware
- Conformance test: `dns-rebinding-protection` scenario

---------

Co-authored-by: Maciek Kisiel <mkisiel@google.com>
2026-02-13 16:23:32 +01:00
Maciek Kisiel
d0922abcd3 mcp: allow SSE messages with empty data (SEP-1699) 2026-02-05 15:36:53 +01:00
FanOne
7ecd8049c6
mcp: export session missing error (#771)
Fix: #715

- export session missing error
- modify `errSessionMissing` to `ErrSessionMissing`
- add unit test about session missing error
2026-02-03 15:46:49 +01:00
Sam Morrow
52e03de6c8
mcp: add Allow header to 405 responses per RFC 9110 §15.5.6 (#757)
405 Method Not Allowed responses MUST include an Allow header listing
supported methods, per RFC 9110 Section 15.5.6. This fixes issues with
strict HTTP gateways (like Apigee) that treat 405 responses without an
Allow header as malformed, returning 502 Bad Gateway errors.

## Changes

- **SSEHandler**: Add `Allow: GET, POST` header for unsupported methods
- **StreamableHTTPHandler**: Add Allow header for GET-without-session case:
  - Stateless mode: `Allow: POST, DELETE` (GET is never valid)
  - Stateful mode: `Allow: GET, POST, DELETE` (GET is valid once you have
a session)
- Add tests to verify Allow header presence in all 405 responses

## RFC 9110 Reference

[Section 15.5.6 (405 Method Not
Allowed)](https://httpwg.org/specs/rfc9110.html#status.405):

> The origin server MUST generate an Allow header field in a 405
response containing a list of the target resource's currently supported
methods.

## Testing

All existing tests pass, plus new tests added:
- `TestSSE405AllowHeader` - verifies SSE handler compliance
- `TestStreamable405AllowHeader` - verifies Streamable handler
compliance in both stateful and stateless modes

---------

Co-authored-by: omgitsads <4619+omgitsads@users.noreply.github.com>
2026-01-22 09:43:45 +01:00
Robert Findley
b3399e6730
mcp: use args struct for CloseSSEStream (#718)
Change CloseSSEStream from func(time.Duration) to
func(CloseSSEStreamArgs) for forward compatibility, allowing new fields
to be added without breaking existing callers.
2025-12-11 15:13:38 -05:00
Robert Findley
87c81260e2
mcp: gate prime and close events on protocol version 2025-11-25 (#696)
The prime and close SSE events (SEP-1699) were added in protocol version
2025-11-25. Only send these events when the client negotiates that
version or later.

- In servePOST, extract protocol version from InitializeParams for
initialize requests, otherwise use the Mcp-Protocol-Version header
- In serveGET/acquireStream, read protocol version from header
- Only set closeLocked callback when prime/close is supported
- Add unexported protocolVersion field to ClientSessionOptions for
testing

Fixes #686
2025-12-08 15:24:41 -05:00
Robert Findley
18cd63599d
auth, mcp: add UserID to TokenInfo for session hijacking prevention (#695)
Add a UserID field to auth.TokenInfo that TokenVerifiers can populate
from JWT "sub" claims or token introspection. The streamable HTTP
transport uses this to bind sessions to users, rejecting requests where
the user ID doesn't match the session's original user.

Fixes #589
2025-12-08 14:32:33 -05:00
Robert Findley
272e0cd4f5
mcp: better handling for streamable context cancellation (#677)
After walking through our handling of streamable client context
cancellation (due to encountering a shutdown deadlock), I think I've
settled on a more coherent strategy for handling call cancellation:

- In our call handler, retire the request if the call exits due to
cancellation: the caller will never see the actual result anyway.
- In connectSSE, use the actual request context (the same context used
in Write) for the client request, so that it terminates when the context
is cancelled. Thread through the initialization context for the
standalone SSE request.

Also, a couple minor improvements:
- Use a detached context for the background context of the client
connection. We want to preserve context values (see #513), but it is not
right to cancel the connection after Connect has already returned, if
the context times out.
- Don't use Last-Event-ID != "" as the signal for whether the connectSSE
call is initial: if the standalone SSE stream disconnects without an
event ID, we'll still reconnect it, and don't want to do so without a
delay.

+ tests, updating the streamable client connection test harness to
accomodate the new aspects being exercised.

Fixes #662
2025-12-03 12:26:50 -05:00
Robert Findley
623780125c
mcp: support SSE polling and server disconnects (SEP-1699) (#663)
This CL implements support for SEP-1699, adding the following new API:

- Event.Retry corresponds to the 'retry' field of a server sent event.
This is used to signal client retry behavior.
- RequestExtra.CloseStream is set by the streamable transport to allow
closing a stream.

The streamable server transport is updated to set CloseStream for calls,
allowing server operations or middleware to close the underlying stream.
If the configured 'reconnectAfter' delay is set, a 'retry' message is
sent prior to terminating the stream.

The streamable client transport is updated to read the configured delay.

Fixes #630
2025-12-01 16:21:37 -05:00
Robert Findley
2ce44d45e9
all: expose JSON-RPC error codes, and support URLElicitationRequired errors (#655)
Expose the jsonrpc.Error type to allow access to underlying JSON-RPC
error codes. Also, expose common JSON-RPC error codes in the jsonrpc
package, and MCP error codes in the mcp package.

Also, implement support for the MCP URL elicitation required error
(-32042), enabling servers to request out-of-band user authorization and
clients to automatically handle these requests with retry logic.

Server-side:
- Add CodeURLElicitationRequired constant
- Add URLElicitationRequiredError() constructor.

Client-side:
- Add urlElicitationMiddleware to intercept URLElicitationRequired
  errors and retry calls.
- Update callElicitationCompleteHandler to signal waiting operations.
- Fix capability advertisement to support both form and URL modes.

Fixes #452
Fixes #623
2025-12-01 11:29:17 -05:00
Raphael MANSUY
9ef2b2742e
Fix: Skip non-message SSE events in processStream (#637)
Fixes #636

## Problem
The StreamableClientTransport tries to JSON-decode ALL SSE events,
including ping events sent by servers for keep-alive purposes. This
causes errors like 'invalid character 'p' looking for beginning of
value' when encountering non-JSON event data.

## Solution
Modified processStream to check evt.Name and skip events that are not
'message' events (or unnamed events, which default to 'message' per SSE
spec).

## Changes
- Added event name check in processStream before attempting JSON decode
- Added test case for ping event filtering
- Added test for scanning multiple events including ping events

## Testing
- All existing tests pass
- New tests verify ping events are properly filtered
- Tested with DeepWiki MCP server which sends ping events
2025-11-13 20:48:23 -05:00
Robert Findley
d256a9c109
mcp: don't persist failed streamable sessions (#605)
If a stateful streamable session fails to initialize, it is unusable.
Avoid allocating resources by closing the session immediately.

Also:
- Fix a bug where InitializeParams is not guarded with its mutex.
- Fix a resource leak where sessions are persisted with session id "",
even though they are unaddressable.
- Add a relevant benchmark, and update tests.

Fixes #578
2025-10-27 16:29:16 -04:00
Robert Findley
ae6bda692b
mcp: establish the streamable client standalone SSE stream in Connect (#604)
When Connect returns, client should be guaranteed that the streamable
SSE stream is connected.

Fixes #583
2025-10-27 14:03:22 -04:00
Robert Findley
f01e7faaf5
mcp: add StreamableHTTPOptions.SessionTimeout (#594)
Add a timeout option for the streamable HTTP handler that automatically
cleans up idle sessions.

Also, fix a bug in the streamable client, where we hang on a request
even though the client can never get a response (because the HTTP
request terminated without a response or Last-Event-Id).

Fixes #499
2025-10-23 09:17:20 -04:00
Robert Findley
cfa7a515a9
mcp: add StreamableHTTPOptions.EventStore (#593)
Allow users to enable streamable replay by setting a non-nil event
store.

Updates #587
2025-10-20 14:58:24 -04:00
Robert Findley
8aee8d39bd
mcp: clean up stream metadata after completion (#592)
Address longstanding TODOs to clean up stream metadata after streams are
complete:

- Interpret a missing stream as a complete stream.
- Remove the request->stream mapping when the request completes. Any
writes after that point will fail as there can be no recipient.

Tested using examples/client/loadtest, and updating
TestStreamableTransports to check in-band and out-of-band behavior.
2025-10-20 14:57:56 -04:00
Robert Findley
104d39c609
mcp: allow disabling stream replay; disable by default (#585)
This CL implements two changes that must be logically connected.

The first is to provide a mechanism for disabling stream replay.
Previously, our documentation stated that if
StreamableServerTransport.EventStore was nil, a default in-memory event
store would be used. In that case, there would be no way to completely
disable stream replay, and as described in #576, there are many cases
where replay is undesirable.

But of course changing the behavior of the transport zero value
implicitly affects its default behavior, and so this CL also implements
the proposal #580: stream replay is disabled by default.

Implementing this change required a significant refactoring, as
previously we were relying on the event store for serialized message
delivery from the JSON-RPC layer to the MCP layer: the connection would
write to the event store, and independently the stream (be it an
incoming POST or replay GET) would iterate and serve messages in the
stream.

In order to achieve the goals of this CL, it was necessary to decouple
storage from delivery. The 'stream' abstraction now tracks a delivery
callback that writes straight to the HTTP response. It would have been
convenient to store the ongoing http.ResponseWriter directly in the
stream (this is how typescript does it), but due to the design of our
EventStore API, only the HTTP handler knows the next event index, so a
'deliver' abstraction was an unfortunate requirement (suggestions for
how to further simplify this are welcome).

More simplification is possible: in particular, as a result of this
refactoring it should be entirely possible to clean up streams once
we've received all responses. Any replay would only need access to the
EventStore, if at all. This is left to a follow-up CL, to limit this
already significant change.

Furthermore, a nice consequence of this refactoring is that, when not
using event storage, servers can get synchronous feedback that message
delivery failed, which should avoid unnecessary work. We can
additionally cancel ongoing requests on early client termination, but
that is also left to a follow-up CL.

Throughout, the terminology 'standalone SSE stream' replaced 'hanging
GET' when referring to the non-replay GET request issued by the client.
This is consistent with other SDKs.

Fixes #576
Updates #580
2025-10-16 12:11:49 -04:00
Friedrich Große
010bdbc64d
mcp: fix goroutine leaks in unit tests (#496)
This PR fixes goroutine leaks in all unit tests.

To find the leaks I integrated https://github.com/uber-go/goleak and I
suggest to keep using it to catch any future regressions.

I used the folowing script to more easily find individual tests which
were leaking goroutines:

```
for t in $(go test -run=Nothing -list=. ./mcp | grep -v ok); do go test ./mcp -run="$t" > /dev/null && echo -n . || echo -e "\nDetected leak: $t"; done
```
2025-10-16 11:13:30 -04:00
Robert Findley
9d6e3074f9
mcp: add a explicit test for concurrent streamable sessions (#584)
We seem not to have a test that explicitly exercises concurrent
streamable sessions. Add one.
2025-10-15 14:43:45 -04:00
Robert Findley
547b5c1426
mcp: fix panics with nil logger; ensure test handlers do not panic (#557)
PR 501 added logging to the streamable server, but didn't pass a non-nil
logger to the streamable transport (an oversight). However, tests still
passed due to net/http's panic recovery.

Update test servers to enforce that handlers do not panic, and fix the
panic by:
1. Passing along the configured logger to the session transport.
2. Using ensureLogger in Connect, since we technically allow
StreamableServerTransports to be constructed by the user.

Fixes #556
2025-10-06 13:34:20 -04:00
Robert Findley
6dbf6c6450
all: minor cleanup (#545)
Also fix a flaky test case in TestStreamableServerTransport.
2025-09-30 15:53:00 -04:00
Manuel Ibar
5d64d61974
mcp: fix context propagation in StreamableClientTransport (#514)
## Problem
Context propagation was broken in `StreamableClientTransport` because:
1. `Connect()` used `context.Background()` instead of the parent context
2. `Close()` created a race condition where DELETE requests were
cancelled before completion

## Solution  
- Use parent context when creating the connection context in `Connect()`
- Reorder `Close()` operations to perform cleanup DELETE before
cancelling context

## Impact
- Request-scoped values (auth tokens, trace IDs) now propagate correctly
to background HTTP operations
- Eliminates race condition in cleanup operations  
- Maintains proper Go context semantics

Fixes #513
2025-09-23 12:27:39 -04:00
Friedrich Große
02f0b25286
Move GetSessionID closure into ServerOptions (#488)
Fixes: #478.
2025-09-18 12:21:02 -04:00
Robert Findley
353d46ff86
mcp: remove the StreamID type (#490)
The streamID type did not carry its weight. Remove it.

Fixes #484.
2025-09-18 12:01:07 -04:00
Jonathan Amsterdam
140b93980c
mcp: add CallToolResult.getError (#481)
Provide a way for middleware to get the error from a tool call,
demonstrating that we can add this functionality without making a
breaking change.

Leave getError unexported for now; we can export it (and setError) at
any time.

For #64.
2025-09-18 08:08:23 -04:00
Rob Findley
9f1b8646bd mcp: propertly validate against JSON, independent of Go values
Our validation logic was avoiding double-unmarshalling as much as
possible, by parsing before validation and validating the Go type.

This only works if the Go type has the same structure as its JSON
representation, which may not be the case in the presence of types with
custom MarshalJSON or UnmarshalJSON methods (such as time.Time).

But even if the Go type doesn't use any custom marshalling, validation
is broken, because we can't differentiate zero values from missing
values.

Bite the bullet and use double-unmarshalling for both input and output
schemas. Coincidentally, this fixes three bugs:
- We were accepting case-insensitive JSON keys, since we parsed first,
  even though they should have been rejected. A number of tests were
  wrong.
- Defaults were overriding present-yet-zero values, as noted in an
  incorrect test case.
- When "arguments" was missing, validation wasn't performed, no defaults
  were applied, and unmarshalling failed even if all properties were
  optional.

First unmarshalling to map[string]any allows us to fix all these bugs.
Unfortunately, it means a 3x increase in the number of reflection
operations (we need to unmarshal, apply defaults and validate,
re-marshal with the defaults, and then unmarshal into the Go type).
However, this is not likely to be a significant overhead, and we can
always optimize in the future.

Update github.com/google/jsonschema-go to pick up necessary improvements
supporting this change.

Additionally, fix the error codes for invalid tool parameters, to be
consistent with other SDKs (Invalid Params: -32602).

Fixes #447
Fixes #449
Updates #450
2025-09-12 10:50:19 -04:00
ankitm123
bf3ff50a16 mcp: remove json-rpc batching for more recent protocol versions
JSON-RPC batching support is removed for protocol versions greater than or
equal to protocolVersion20250618

Fixes #21
2025-09-11 10:50:56 -04:00
Rob Findley
728e0e3ac9 mcp: improve error messages from Wait for streamable clients
Previously, the error message received from ClientSession.Wait would
only report the closeErr, which would often be nil even if the client
transport was broken. Wait should return the reason the session
terminated, if abnormal.

I'm not sure of the exact semantics of this, but surely returning nil is
less useful than returning a meaningful non-nil error. We can refine our
handling of errors once we have more feedback.

Also add a test for client termination on HTTP server shutdown,
described in #265. This should work as long as (1) the session is
stateful (with a hanging GET), or (2) the session is stateless but the
client has a keepalive ping.

Also: don't send DELETE if the session was terminated with 404; +test.

Fixes #265
2025-09-10 11:24:26 -04:00
Rob Findley
b1c75f04d8 mcp: remove deprecated transport constructors
In #272, we made transports open structs and deprecated their
constructors. However, we left the constructors in place to allow go:fix
directives to facilitate migration.

Now let's remove the constructors before cutting the release.

Fixes #305
2025-09-10 11:21:46 -04:00
Rob Findley
4656930de8 mcp: avoid "null" when tools fail to return content
For some reason, this was a regression from v0.3.1, for some of our
examples. Fix it and address the existing TODO.
2025-09-05 16:57:02 -04:00
Rob Findley
9d34aff732 mcp: avoid "null" in structuredContent
Avoid a typed nil in structuredContent (yet another typed nil), leading
to "null" on the wire.

Fixes #417
2025-09-04 19:48:51 -04:00
Rob Findley
ee5141621c mcp: be strict about returning the Mcp-Session-Id header
Rather than returning the Mcp-Session-Id header for all responses, only
return it from initialize, per the spec.

Fixes #412
2025-09-04 15:34:05 -04:00
Rob Findley
a4313f92bf mcp: refactor the streamable client test to be more flexible
Use a fake streamable server to facilitate testing client behavior.
For this commit, just update the existing test (moved to a new file for
isolation). Subsequent CLs will add more tests.

Improve one client error message that occurred while debuging tests.

For #393
2025-09-04 14:09:37 -04:00
Rob Findley
07b9cee8cc mcp: flush headers immediately for the hanging GET
Flush headers immediately for the persistent hanging GET of the
streamable transport; otherwise, clients may time out.

Fixes #410
2025-09-04 12:40:07 -04:00
Rob Findley
a1eb4849b7 mcp: correctly disallow GET requests on stateless servers
The condition sessionID == "" was not quite right for disallowing GET
requests. Since we decided to differentiate "stateless" vs "sessionless"
servers, we need to disallow GET requests for both.

For #393
2025-09-03 19:25:25 -04:00
Jonathan Amsterdam
d0c5943f25
add HTTP Request to TokenVerifier (#404)
The request might be needed to verify the token.

Fixes #403.
2025-09-03 16:23:42 -04:00
ccpro
1c20560beb
mcp: export jsonResponse field
Exporting StreamableHTTPOptions.JSONResponse is helpful for some users behind proxies that don't work well with text/event-stream.

For #211

Co-authored-by: ccpro10 <co1797249167@gmail.com>
2025-09-03 11:35:19 -04:00
Jonathan Amsterdam
7769b2a959
mcp: set content to marshaled output (#398)
The ToolHandler constructed by ToolFor sets the result's Content to the
marshaled output, following the spec's suggestion.

See
https://modelcontextprotocol.io/specification/2025-06-18/server/tools#structured-content.

Also, set StructuredContent to the marshaled RawMessage to avoid a
double marshal.

Fixes #391.
2025-09-03 10:37:27 -04:00