fix!: answer non-object tools/call params instead of ending the server - #19
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Martin Bens (SpiGAndromeda) merged 1 commit intoSep 12, 2026
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handle_tools_call read `.name` and `.arguments` before checking the type of params. Under `set -o posix` bash inherits errexit into the command substitutions those extractions run in, so jq's failure to index a number, string, array or `true` with those keys ended the whole server with no response, and the request that followed was never answered. In the default mode the server survived and answered `-32602 Invalid tool name: `, but jq wrote its `Cannot index ...` diagnostics straight to the process's stderr, outside `log`.
params is now gated as an object before either field is read, on the same footing as process_request's request-object gate, so the extractions cannot fail in any shell mode and the call answers `-32602 Invalid params: expected an object`. A present `null` or `false` params is normalized to `{}` before dispatch and keeps the `Invalid tool name: ` answer. POSIX mode is not a configuration the SDK claims to support, but it no longer ends the server on this path.
BREAKING CHANGE: the answer for a tools/call whose params is a number, string, array or `true` changes from `-32602 Invalid tool name: ` to `-32602 Invalid params: expected an object`. A consumer matching on that message text updates it; the error code is unchanged.
Fixes #15.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Martin Bens (SpiGAndromeda)
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September 13, 2026 10:50
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Fixes #15.
handle_tools_callread.nameand.argumentsbefore checking the type ofparams. Underset -o posixbash inherits errexit into the command substitutions those extractions run in, so jq's failure to index a number, string, array ortrueended the whole server with no response, and the request that followed was never answered. In the default mode the server survived and answered-32602 Invalid tool name:, but jq wrote itsCannot index ...diagnostics straight to the process's stderr, outsidelog.paramsis now gated as an object at the top ofhandle_tools_call, on the same footing asprocess_request's request-object gate, so the extractions cannot fail in any shell mode and the call answers-32602 Invalid params: expected an object. The gate also fails closed for a direct caller passing invalid JSON. A presentnullorfalseparamsis normalized to{}before dispatch and keeps theInvalid tool name:answer. POSIX mode is not a configuration the SDK claims to support, but it no longer ends the server on this path.Breaking: the answer for a
tools/callwhoseparamsis a number, string, array ortruechanges from-32602 Invalid tool name:to-32602 Invalid params: expected an object. A consumer matching on that message text updates it; the error code is unchanged.New suite
tests/tools_call_params.bats(5 tests): the-32602envelope for number/string/arrayparamsthroughprocess_request, server survival plus a follow-uppinganswered underset -o posixthroughrun_mcp_server, and a clean stderr in the default mode.The sibling defect where a non-object tools or config file document ends the server is #18 and stays separate.