feat: support mcp 2.x alongside mcp 1.x - #342
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mcp 2.x redesigned the lowlevel Server API: the list_tools/call_tool decorators are gone (handlers are now registered as constructor callbacks), handler signatures gained an explicit request-context and params argument, and handlers must return typed ListToolsResult / CallToolResult instead of a bare content list. It also dropped the in-memory test helper and renamed several fields (isError -> is_error, inputSchema -> input_schema, and JSONRPCMessage became a raw Union type). Change the server to version-branch on whether the decorator API exists: - mcp 1.x: unchanged decorator path. - mcp 2.x: constructor-callback handlers with jsonschema argument validation and filtered exception results, mirroring the 1.x call_tool contract; HTTP request info is still extracted from the per-request context (now passed explicitly). - Relax the dependency cap to mcp>=1.12,<3 and add a tests/_mcp_compat shim so the full suite runs under both major versions. The SSE transport now parses version-agnostically via a TypeAdapter. The full unit suite passes under both mcp 1.12.1 and mcp 2.1.1.
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feat: support mcp 2.x alongside mcp 1.x
Why this matters
mcp 2.x is now out, and this package could not even import against it. Every fresh
pip install fastapi-mcptoday resolves to mcp 2.x and breaks at setup_server() — the lowlevelServerAPI was redesigned and almost everything the library used is gone. (PR #331 was the stopgap, capping<2; this PR is the real fix.)The changes needed to run on 2.x:
setup_server()now version-branches on whether the decorator API exists:on_list_tools/on_call_tool), each receiving an explicit request context + typed params, returning typedListToolsResult/CallToolResult.request_ctxContextVar, 2.x passes the context into the handler. Shared_extract_http_request_infohelper.call_toolcontract: arguments are validated against the tool's JSON schema and handler exceptions become error results (is_error=True) instead of protocol errors.mcp>=1.12.0,<3.0.0.jsonschemadeclared explicitly (now a direct import).tests/_mcp_compatshim so the test suite runs unchanged under both majors, and made the SSE transport parse JSON-RPC version-agnostically via aTypeAdapter.Verification
isError->is_error,inputSchema->input_schema, and the removed in-memory test helper are all handled compatibly.Note
I could not regenerate
uv.locklocally (nouvon this machine); it should be refreshed withuv lockbefore merging. I also authored this against my fork (K4bain), mirroring the existing adoption PRs (#331-341) from the maintained community fork.