fix: propagate MCPError from tool handlers as JSON-RPC error#2842
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shiwenbin1617 wants to merge 1 commit into
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fix: propagate MCPError from tool handlers as JSON-RPC error#2842shiwenbin1617 wants to merge 1 commit into
shiwenbin1617 wants to merge 1 commit into
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Previously, only UrlElicitationRequiredError was re-raised; any other MCPError raised inside a tool function was caught by the bare 'except Exception' clause and wrapped into a ToolError, which then surfaced as a CallToolResult(isError=True) instead of a structured JSON-RPC error response. Since UrlElicitationRequiredError is a subclass of MCPError, broadening the guard to 'except MCPError' covers all cases including the original one. Fixes modelcontextprotocol#2770
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Fixes #2770
Root cause
tools/base.pyonly re-raisedUrlElicitationRequiredError; any otherMCPErrorraised inside a tool function fell through to the bareexcept Exceptionclause, got wrapped intoToolError, and surfaced asCallToolResult(isError=True)instead of a structured JSON-RPC error response.Fix
Broaden the guard from
except UrlElicitationRequiredErrortoexcept MCPError. SinceUrlElicitationRequiredErroris a subclass ofMCPError, the existing behaviour for that case is unchanged.Changes
src/mcp/server/mcpserver/tools/base.py: widen re-raise guard (1 line)tests/server/mcpserver/test_url_elicitation_error_throw.py: regression test covering the plainMCPErrorpropagation pathTesting