Drain connections when more messages are expected#667
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The needs_drain() condition prior to this commit checks the connection state is some kind of idle or otherwise "in sync". However, even when the connection state is Idle, there can be expected messages in the protocol queue. If a client disconnects abruptly at just the right time, needs_drain() would not return true, but the protocol queue is not empty and expected messages from the server are not drained. In this scenario, the connection is checked back in in a tainted state and subsequent usage can produce unexpected results (ProtocolOutOfSync or off-by-1 results mixups). This updates needs_drain() to also account for prepared_statements.has_more_messages() in addition to the "in sync" check, thus triggering a drain when there are more messages expected from the server (and tracked in the protocol queue).
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jbielick
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Dec 10, 2025
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| ProtocolMessage::from(Query::new("SELECT 1")), | ||
| ProtocolMessage::from(Query::new("SELECT 1")), |
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Holding off on this PR because stuffing the ClientRequest like this doesn't seem to be a realistic reproduction. Addressing some of the out-of-sync side effects in #668 instead.
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Purpose
#565
The
needs_drain()condition prior to this commit checks the connection state is some kind of idle or otherwise "in sync". However, even when the connection state is Idle, there can be expected messages in the protocol queue. If a client disconnects abruptly at just the right time, needs_drain() would not return true, but the protocol queue is not empty and expected messages from the server are not drained.In this scenario, the connection is checked back in in a tainted state and subsequent usage can produce unexpected results (ProtocolOutOfSync or off-by-1 results mixups).
Fix
This updates
needs_drain()to also account forprepared_statements.has_more_messages()in addition to the "in sync" check, thus triggering a drain when there are more messages expected from the server (and tracked in the protocol queue).