fix: prevent infinite retry loop in StreamableHTTP client reconnection#2398
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chernistry wants to merge 2 commits intomodelcontextprotocol:mainfrom
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fix: prevent infinite retry loop in StreamableHTTP client reconnection#2398chernistry wants to merge 2 commits intomodelcontextprotocol:mainfrom
chernistry wants to merge 2 commits intomodelcontextprotocol:mainfrom
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The `_handle_reconnection` method reset its attempt counter to 0 when a stream ended normally (without exception), causing an infinite retry loop when the server repeatedly dropped connections after partially delivering events. This is because the recursive call on the "stream ended without response" path passed `attempt=0` instead of incrementing. Change the normal-close reconnection path to pass `attempt + 1`, matching the exception path, so total reconnection attempts are tracked across the entire chain regardless of how each individual stream ended. Fixes modelcontextprotocol#2393 Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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The previous fix (attempt + 1 unconditionally) broke legitimate multi-reconnection scenarios where the server checkpoints progress between disconnections. Now we check whether new SSE events were delivered (last_event_id changed) — if so, reset the counter; if not, increment it toward MAX_RECONNECTION_ATTEMPTS. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
Fix
_handle_reconnection()infinite retry loop when a server repeatedly drops connections after partially delivering SSE events (#2393).Approach: Track whether each reconnection made forward progress (received new SSE events with a different
last_event_id). If progress was made, reset the attempt counter — the server is legitimately checkpointing work across disconnections. If no progress was made (same or no new event IDs), increment the counter towardMAX_RECONNECTION_ATTEMPTSto prevent infinite loops.This preserves the existing multi-reconnection behavior tested by
test_streamable_http_multiple_reconnectionswhile preventing the infinite loop in #2393.Fixes #2393
Details
The bug is on this line: when the SSE stream ends normally (iterator exhausted, no exception),
_handle_reconnectioncalls itself recursively withattempt=0. This means every connection that drops before delivering a response/error resets the counter, andMAX_RECONNECTION_ATTEMPTSis never reached.The fix compares
reconnect_last_event_idagainst the incominglast_event_id:Test plan
test_handle_reconnection_does_not_retry_infinitelyuses a static event ID (no progress) and verifies termination withinMAX_RECONNECTION_ATTEMPTStest_streamable_http_multiple_reconnectionscontinues to pass — it delivers new event IDs on each reconnection (progress), so the counter resets as expected🤖 Generated with Claude Code