fix: propagate error messages in /mcp endpoint responses#2617
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crivetimihai merged 1 commit intoIBM:mainfrom Jan 31, 2026
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Thanks @jonathan-fulton! Important fix - swallowing exceptions and returning empty results was definitely masking real errors from clients. Re-raising to let the MCP SDK convert them to proper JSON-RPC error responses is the right approach. I'll start merging and rebasing. |
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crivetimihai
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Jan 31, 2026
Previously, exceptions in tool invocation were caught and an empty list was returned, hiding error details from clients. Now errors are re-raised to let the MCP SDK properly convert them to JSON-RPC error responses. This ensures clients see actual error messages (e.g., '401 Unauthorized') instead of empty responses. Fixes IBM#2570 Signed-off-by: Jonathan Fulton <jonathan@jonathanfulton.com>
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hughhennelly
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Previously, exceptions in tool invocation were caught and an empty list was returned, hiding error details from clients. Now errors are re-raised to let the MCP SDK properly convert them to JSON-RPC error responses. This ensures clients see actual error messages (e.g., '401 Unauthorized') instead of empty responses. Fixes IBM#2570 Signed-off-by: Jonathan Fulton <jonathan@jonathanfulton.com> Signed-off-by: hughhennnelly <hughhennelly06@gmail.com>
kcostell06
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Feb 24, 2026
Previously, exceptions in tool invocation were caught and an empty list was returned, hiding error details from clients. Now errors are re-raised to let the MCP SDK properly convert them to JSON-RPC error responses. This ensures clients see actual error messages (e.g., '401 Unauthorized') instead of empty responses. Fixes IBM#2570 Signed-off-by: Jonathan Fulton <jonathan@jonathanfulton.com>
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Summary
Fixes error propagation in the
/mcpendpoint tool invocation handler.Problem
When using
server/<server-id>/mcpendpoint for tool invocations, exceptions (e.g., 401 unauthorized errors) resulted in empty responses instead of actual error messages.The previous code caught all exceptions and returned an empty list:
Solution
Re-raise exceptions after logging so the MCP SDK can properly convert them to JSON-RPC error responses:
This ensures clients receive proper error messages instead of empty results.
Testing
Verified that errors are now properly returned in the response body instead of empty results.
Fixes #2570