Fix off-by-one error in reconnection attempts#1356
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stephentoub merged 4 commits intomainfrom Feb 23, 2026
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…n loop When ReceiveUnsolicitedMessagesAsync calls SendGetSseRequestWithRetriesAsync, the first attempt is an initial GET SSE connection (not a reconnection). Previously, this initial attempt was counted against MaxReconnectionAttempts, meaning with the default value of 2, only 1 actual reconnection was made. Fix: initialize attempt = -1 when LastEventId is null (initial connection), so the initial attempt doesn't consume a reconnection slot. When LastEventId is set (pure reconnection from POST SSE resume), attempt starts at 0 as before. Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>
…axReconnectionAttempts Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>
stephentoub
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@copilot there are build failures |
…ic TaskCompletionSource Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>
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stephentoub
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Feb 22, 2026
jeffhandley
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Pull request overview
This pull request fixes an off-by-one error in the SSE (Server-Sent Events) reconnection retry logic for the Streamable HTTP client transport. The bug caused the initial GET SSE connection to be incorrectly counted as a reconnection attempt, effectively reducing the configured MaxReconnectionAttempts by one.
Changes:
- Fixed the retry counter initialization to distinguish initial connections from reconnections
- Added comprehensive test coverage to verify the fix
- Ensured .NET Framework compatibility using generic
TaskCompletionSource<bool>
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
src/ModelContextProtocol.Core/Client/StreamableHttpClientSessionTransport.cs |
Fixed off-by-one error by initializing attempt = -1 for initial connections (when LastEventId is null) and attempt = 0 for reconnections (when LastEventId is set), with clear inline comments explaining the logic |
tests/ModelContextProtocol.Tests/Transport/HttpClientTransportTests.cs |
Added test StreamableHttp_InitialGetSseConnection_DoesNotCountAgainstMaxReconnectionAttempts that verifies the initial connection plus configured reconnection attempts equals the total number of GET requests, and added System.Text import for test setup |
MackinnonBuck
approved these changes
Feb 23, 2026
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SendGetSseRequestWithRetriesAsyncretry loopattempt = -1whenstate.LastEventIdis null (initial connection case inReceiveUnsolicitedMessagesAsync)TaskCompletionSource<bool>instead of non-genericTaskCompletionSource💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.