fix(mcp-bridge): retain partial stdout and stderr across read timeouts - #13988
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When reading lines from the spawned MCP process via proc:stdout_read_line() and proc:stderr_read_line(), a read timeout sets the 3rd return value (partial data). On subsequent reads, the multiple assignment was overwriting the partial buffer with nil upon reading the remaining line, discarding the buffered data and sending truncated/corrupted payloads. Retain and accumulate partial stdout/stderr buffers across read timeouts, clearing them only after successfully joining with the completed line. Fixes apache#13987 Signed-off-by: bhuvan-somisetty <somisettybhuvan5@gmail.com>
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Description
In
apisix/plugins/mcp-bridge.lua, the event loop reads lines from the spawned process pipe viaproc:stdout_read_line()andproc:stderr_read_line(). When a read timeout occurs mid-line,ngx.pipereturnsnil, "timeout", partial_data.Previously,
line, _, stdout_partial = proc:stdout_read_line()assigned the 3rd return value tostdout_partialon every read. When the remaining portion of the line arrived in a subsequent iteration,proc:stdout_read_line()returnedline, nil, nil, which immediately overwrittenstdout_partialwithnilbefore the concatenation could happen. As a result, the buffered partial chunk was discarded and only the trailing fragment was dispatched to the MCP client.This change fixes partial chunk handling in
mcp-bridge:stdout_partial = (stdout_partial or "") .. partial).stdout_partial/stderr_partialonly after successfully constructing the complete message.Which issue(s) this PR fixes:
Fixes #13987
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