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Subject: Re: unix socket hang when connect
To: cygwin AT cygwin DOT com
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Date: Mon, 7 Apr 2025 12:00:51 +0200
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From: Christian Franke via Cygwin <cygwin AT cygwin DOT com>
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Cc: Christian Franke <Christian DOT Franke AT t-online DOT de>
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Yuyi Wang via Cygwin wrote:
> Below is a simple unix socket testing code. It creates a unix socket server and
> a client to connect to it immediately. It works on Linux and macOS, but hangs on
> cygwin. bind + listen work well, but seems that the connect method never returns.
>
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> #include <unistd.h>
> #include <sys/socket.h>
> #include <sys/un.h>
> #include <errno.h>
>
> #define SOCKET_PATH "/tmp/example_socket"
>
> int main() {
>      int server_fd, client_fd;
>      struct sockaddr_un server_addr;
>      socklen_t client_len;
>
>      server_fd = socket(AF_UNIX, SOCK_STREAM, 0);
>      if (server_fd == -1) {
>          perror("server socket");
>          exit(EXIT_FAILURE);
>      }
>
>      memset(&server_addr, 0, sizeof(server_addr));
>      server_addr.sun_family = AF_UNIX;
>      strncpy(server_addr.sun_path, SOCKET_PATH, sizeof(server_addr.sun_path) - 1);
>
>      if (bind(server_fd, (struct sockaddr*)&server_addr, sizeof(server_addr)) == -1) {
>          perror("bind");
>          exit(EXIT_FAILURE);
>      }
>
>      if (listen(server_fd, 1) == -1) {
>          perror("listen");
>          exit(EXIT_FAILURE);
>      }
>
>      printf("Server is listening on %s\n", SOCKET_PATH);
>
>      client_fd = socket(AF_UNIX, SOCK_STREAM, 0);
>      if (client_fd == -1) {
>          perror("client socket");
>          exit(EXIT_FAILURE);
>      }
>
>      if (connect(client_fd, (struct sockaddr*)&server_addr, sizeof(server_addr)) == -1) {
>          perror("connect");
>          exit(EXIT_FAILURE);
>      }
>
>      printf("Client connected to server\n");
>
>      close(client_fd);
>      close(server_fd);
>      unlink(SOCKET_PATH);
>
>      return 0;
> }

May be this issue which also affected postfix:
https://sourceware.org/legacy-ml/cygwin/2014-08/msg00420.html

Try:
setsockopt(sd, SOL_SOCKET, SO_PEERCRED, NULL, 0);

available since:
https://cygwin.com/git/?p=newlib-cygwin.git;a=commit;h=697b9afe0
and may still work (I don't know).

-- 
Regards,
Christian


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