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Track Mcp-Session-Id and protocol version in HTTP client

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Per the Streamable HTTP spec, if the server returns an Mcp-Session-Id
header during `initialize`, the client MUST include it on subsequent
requests. Capture the session ID and protocol version from the
`initialize` response and attach them automatically on subsequent
POSTs.

Per the Protocol Version Header section of the spec, the client MUST
also include `MCP-Protocol-Version` on all subsequent requests so the
server can respond based on the negotiated protocol version.

Map 404 responses to a new `SessionExpiredError` (a subclass of
`RequestHandlerError` for backward compatibility) and clear local
session state so callers can start a fresh session with a new
`initialize` request, as required by the spec.

- https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#session-management
- https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#protocol-version-header

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
This commit is contained in:
Ates Goral 2026-04-19 23:29:00 -04:00
commit 07226b7cf1
1 changed files with 275 additions and 10 deletions
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11
docs/building-clients.md
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@ -74,6 +74,17 @@ response = client.call_tool(
)
```
### Sessions
After a successful `initialize` request, the transport captures the `Mcp-Session-Id` header and `protocolVersion` from the response and includes the session ID on subsequent requests. Both are exposed on the transport:
```ruby
http_transport.session_id # => "abc123..."
http_transport.protocol_version # => "2025-11-25"
```
If the server terminates the session, subsequent requests return HTTP 404 and the transport raises `MCP::Client::SessionExpiredError` (a subclass of `RequestHandlerError`). Session state is cleared automatically; callers should start a new session by sending a fresh `initialize` request.
### Authorization
Provide custom headers for authentication: