EC
ESHUTDOWN
Linux / POSIXERRORCommonNetworkHIGH confidence

Cannot Send After Transport Endpoint Shutdown

Production Risk

Programming error; track socket shutdown state.

What this means

ESHUTDOWN (errno 108) is returned when a send operation is attempted on a socket that has been shut down for writing.

Why it happens
  1. 1Calling send() after shutdown(SHUT_WR) or shutdown(SHUT_RDWR)
  2. 2Writing to a socket after signaling end-of-stream
How to reproduce

send() after shutdown(SHUT_WR).

trigger — this will error
trigger — this will error
shutdown(sockfd, SHUT_WR);  // signal end of writes
// Attempt to send more data
send(sockfd, buf, len, 0);
// Returns -1, errno = ESHUTDOWN

expected output

send: Cannot send after transport endpoint shutdown (ESHUTDOWN)

Fix

Do not send after shutdown

WHEN Managing half-close protocol patterns

Do not send after shutdown
// Track shutdown state
bool write_shut = false;
shutdown(sockfd, SHUT_WR);
write_shut = true;
// Guard all sends:
if (!write_shut) send(sockfd, buf, len, 0);

Why this works

Once shutdown(SHUT_WR) is called, no further sends are possible on that socket.

Sources
Official documentation ↗

Linux Programmer Manual shutdown(2)

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