[v1.x] Buffer per-request StreamableHTTP streams; store priming event before dispatch#2948
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[v1.x] Buffer per-request StreamableHTTP streams; store priming event before dispatch#2948maxisbey wants to merge 1 commit into
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… before dispatch Backport of #2934. Gives the per-request _request_streams[EventMessage] sites a small bounded buffer (REQUEST_STREAM_BUFFER_SIZE = 16) so the serial message_router can deposit a response and move on instead of head-of-line blocking the session on a lazily-started sse_writer. Replaces _maybe_send_priming_event with _mint_priming_event (stores + returns the wire dict) and extracts the inline sse_writer closure to _run_sse_writer. The POST handler now mints priming before any per-request state is registered and before the request is dispatched, so the priming row precedes anything message_router can store for that stream by data dependency. Adds a finally to replay_sender; uses a generic 500 body in the outer except. Fixes #1764.
felixweinberger
approved these changes
Jun 22, 2026
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Backport of #2934.
Buffers the per-request
_request_streams[EventMessage]channels (REQUEST_STREAM_BUFFER_SIZE = 16) so the serialmessage_routercan deposit a response and move on instead of head-of-line blocking the session on a lazily-startedsse_writer; and stores the priming event before the request is dispatched so its event-store position precedes anythingmessage_routercan store for that stream by data dependency.v1.x adaptations vs main
_run_sse_writerchecksevent_message.message.root(v1.x'sJSONRPCMessageis aRootModel)._mint_priming_eventkeeps v1.x'sprotocol_version < "2025-11-25"string compare (nois_version_at_leaston this branch).tests/interaction/transports/which doesn't exist on v1.x; instead, the three_maybe_send_priming_eventunit tests are rewritten against_mint_priming_eventto keep the no-store / old-pv / retry-field branches covered._run_sse_writercarries a# pragma: no covermatching the closure it replaces (v1.x's coverage of that path is subprocess-only and the branch has nostrict-no-cover).Motivation and Context
Fixes #1764.
How Has This Been Tested?
tests/server/test_streamable_http_router.py(HOL test + priming-failure test, withJSONRPCMessage(...)wrapping for the RootModel).tests/shared/test_streamable_http.pypriming unit tests rewritten for_mint_priming_event.Breaking Changes
None.
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