fix(streamable): emit event: message in SSE proxy responses#5674
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syf2211 wants to merge 2 commits into
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fix(streamable): emit event: message in SSE proxy responses#5674syf2211 wants to merge 2 commits into
syf2211 wants to merge 2 commits into
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The streamable-http proxy wrote JSON-RPC responses as data-only SSE frames. Clients such as @ai-sdk/mcp require an explicit event: message line and silently drop event-less frames, causing initialize to hang. Add event: message to both success and error SSE write paths and a regression test that verifies the frame format. Fixes stacklok#5655 Signed-off-by: syf2211 <syf2211@users.noreply.github.com>
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Codecov Report❌ Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## main #5674 +/- ##
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- Coverage 70.43% 70.36% -0.07%
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Files 651 651
Lines 66305 66305
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- Hits 46700 46654 -46
- Misses 16231 16290 +59
+ Partials 3374 3361 -13 ☔ View full report in Codecov by Harness. 🚀 New features to boost your workflow:
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Move nolint comment to its own line so the Fprintf stays within the 130-character limit enforced by golangci-lint. Signed-off-by: syf2211 <syf2211@users.noreply.github.com>
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Summary
Add an explicit
event: messageline to JSON-RPC SSE frames emitted by the streamable-http proxy, matching reference MCP server transports and fixing clients that require named events.Motivation
The streamable proxy wrote
data:-only SSE frames. While valid per the WHATWG SSE spec, this diverges from MCP reference transports and breaks spec-lenient clients such as@ai-sdk/mcp, which only dispatch frames whereevent === "message". Those clients hang oninitializeagainst stdio servers fronted by this proxy.Fixes #5655
Changes
handleSingleRequestSSEto emitevent: message\ndata: ...\n\nTestSSEResponseIncludesEventMessageregression test instreamable_proxy_spec_test.goTests
go test ./pkg/transport/proxy/streamable/... -count=1— all passedNotes
data:frames continue to work