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Fix FIN_WAIT_2 accumulation by draining sockets before close #600

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renaudallard wants to merge 2 commits into from
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Fix FIN_WAIT_2 accumulation by draining sockets before close #600

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004da4b
Fix FIN_WAIT_2 accumulation by draining sockets before close
renaudallard Mar 19, 2026
1be64ef
Address review: move close_socket to sock.c, bump drain timeout to 10s
renaudallard Mar 29, 2026
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9 changes: 3 additions & 6 deletions src/conns.c
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,7 @@
#include "conns.h"
#include "heap.h"
#include "log.h"
#include "sock.h"
#include "stats.h"

void conn_struct_init(struct conn_s *connptr) {
Expand Down Expand Up @@ -82,14 +83,10 @@ void conn_destroy_contents (struct conn_s *connptr)
assert (connptr != NULL);

if (connptr->client_fd != -1)
if (close (connptr->client_fd) < 0)
log_message (LOG_INFO, "Client (%d) close message: %s",
connptr->client_fd, strerror (errno));
close_socket (connptr->client_fd);
connptr->client_fd = -1;
if (connptr->server_fd != -1)
if (close (connptr->server_fd) < 0)
log_message (LOG_INFO, "Server (%d) close message: %s",
connptr->server_fd, strerror (errno));
close_socket (connptr->server_fd);
connptr->server_fd = -1;

if (connptr->cbuffer)
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1 change: 1 addition & 0 deletions src/reqs.c
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Expand Up @@ -1281,6 +1281,7 @@ static void relay_connection (struct conn_s *connptr)
if (write_buffer (connptr->server_fd, connptr->cbuffer) < 0)
break;
}
shutdown (connptr->server_fd, SHUT_WR);
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@rofl0r rofl0r Mar 29, 2026

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why another shutdown() here ?

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@renaudallard renaudallard Mar 29, 2026

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It mirrors the pre-existing shutdown(client_fd, SHUT_WR) above. Both initiate the close handshake early so that by the time close_socket() runs in conn_destroy_contents, the remote FIN may already have arrived and the drain loop returns immediately.


return;
}
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37 changes: 37 additions & 0 deletions src/sock.c
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Expand Up @@ -212,6 +212,43 @@ int opensock (const char *host, int port, const char *bind_to)
return sockfd;
}

/*
* Gracefully close a socket by completing the TCP close handshake.
* Send FIN via shutdown(SHUT_WR), then drain remaining data until
* the remote FIN arrives (read returns 0). This keeps the fd open
* until both sides have exchanged FINs, preventing the socket from
* being orphaned in FIN_WAIT_2.
*
* Without this, close() orphans the socket while still in FIN_WAIT_2.
* Linux reaps orphaned FIN_WAIT_2 via net.ipv4.tcp_fin_timeout, but
* OpenBSD has no equivalent, so they persist indefinitely.
*/
void close_socket (int fd)
{
char drain[4096];
ssize_t n;
struct timeval tv;

shutdown (fd, SHUT_WR);

tv.tv_sec = 10;
tv.tv_usec = 0;
setsockopt (fd, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof (tv));

for (;;) {
n = read (fd, drain, sizeof (drain));
if (n > 0)
continue;
if (n == 0)
break;
if (errno == EINTR)
continue;
break;
}

close (fd);
}

/*
* Set the socket to non blocking -rjkaes
*/
Expand Down
1 change: 1 addition & 0 deletions src/sock.h
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Expand Up @@ -53,6 +53,7 @@ union sockaddr_union {
extern int opensock (const char *host, int port, const char *bind_to);
extern int listen_sock (const char *addr, uint16_t port, sblist* listen_fds);

extern void close_socket (int fd);
extern int socket_nonblocking (int sock);
extern int socket_blocking (int sock);

Expand Down