fix(server): return -32602 for resource not found (SEP-2164)#2344
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fix(server): return -32602 for resource not found (SEP-2164)#2344
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The SDK previously returned error code 0 for resource-not-found, making it impossible for clients to distinguish this from other errors. Per SEP-2164, servers should return -32602 (Invalid Params) with the uri in the error data field. Adds ResourceNotFoundError subclass of ResourceError so existing code catching ResourceError continues to work. The internal handler converts it to MCPError with INVALID_PARAMS before it reaches the JSON-RPC layer. Spec: modelcontextprotocol/modelcontextprotocol#2164
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Summary
Implements SEP-2164 — standardizes the resource-not-found error code to
-32602(Invalid Params).Problem
The Python SDK currently returns error code
0for resource-not-found, making it impossible for clients to reliably distinguish this from other errors. The spec now requires-32602with the URI in thedatafield.Changes
ResourceNotFoundError(ResourceError)subclass inmcpserver/exceptions.pyMCPServer.read_resource()now raisesResourceNotFoundError(instead of genericResourceError) when the resource doesn't exist_handle_read_resource()catchesResourceNotFoundErrorand converts it toMCPError(code=INVALID_PARAMS, ..., data={"uri": ...})The subclass approach keeps backward compatibility — existing code catching
ResourceErrorcontinues to work unchanged.Wire format (before → after)
{ "jsonrpc": "2.0", "id": 2, "error": { - "code": 0, + "code": -32602, "message": "Unknown resource: file:///nonexistent.txt", - "data": null + "data": {"uri": "file:///nonexistent.txt"} } }Spec: modelcontextprotocol/modelcontextprotocol#2164