Fix: Replace Mono.zip with Mono.when in StdioServerTransportProvider#sendMessage - #846
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Mono.zip cancels the slower Mono<Void> source when the faster one completes empty, so sendMessage could proceed before both inbound and outbound readiness signals fired. Mono.when waits for both. Fixes modelcontextprotocol#303.
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Summary
Replaces
Mono.zip()withMono.when()inStdioMcpSessionTransport#sendMessageto correctly wait for both inbound and outbound ready signals before sending messages.Problem
Mono.zip()onMono<Void>sources cancels the slower publisher when the faster one completes empty. As explained by @chemicL, this means the slower of the two ready signals (inboundReadyoroutboundReady) gets cancelled instead of being awaited.Fix
Changed
Mono.zip(inboundReady.asMono(), outboundReady.asMono())toMono.when(inboundReady.asMono(), outboundReady.asMono())which properly waits for all sources to complete before proceeding.Testing
All 9 existing
StdioServerTransportProviderTestspass.Fixes #303