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ENOTCONN
ENOTCONN means a connection-oriented operation was issued without a current peer association. It can occur because connection establishment never completed, a prior failure cleared the state, the application raced a close against I/O, or a pooled socket was returned before its lifecycle was fully reset.
Native Winsock code uses WSAENOTCONN through WSAGetLastError(). A wrapper may expose this portable macro, but the root cause is found in the socket state machine: each send or receive needs to be associated with a connection attempt and a terminal outcome.
Check the lifecycle boundary
- Record when the socket was created, bound, connected, accepted, shut down, and closed, with a monotonic sequence number.
- Verify that completion of a nonblocking connect was checked before scheduling data I/O.
- Prevent a close callback from racing with a queued send or receive; ownership must decide which operation wins.
- For datagram code, distinguish a connected datagram socket from an unconnected one that requires a destination on each send.
References
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