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Date: Thu, 7 Mar 2013 22:48:00 +0900
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Subject: Re: Unix domain accept() and getperrname() doesn't return the client address.
From: Tanaka Akira <akr AT fsij DOT org>
To: cygwin AT cygwin DOT com
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2013/3/4 Corinna Vinschen:

> It's not exactly intentional, but known.  The socket's peername is not
> transmitted during the local socket credential exchange.  So far the
> server assumes an unbound socket on the client side because, well, I
> guess the reason is "nobody asked for it yet".  This could probably
> be implemented with not too much effort, if necessary.

I see.  Thank you.

Is it also known that recvfrom() on Unix domain datagram socket
returns an AF_INET address?

% uname -srvm
CYGWIN_NT-5.1 1.7.18s(0.263/5/3) 20130301 15:56:19 i686
% cat tst-server.c
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <netinet/in.h>
#include <arpa/inet.h>

int main(int argc, char *argv[])
{
  int s;
  int ret;
  struct sockaddr_un saddr, raddr;
  socklen_t len;
  ssize_t ssize;
  char buf[4096];

  unlink("socket-server");

  memset(&saddr, '\0', sizeof(saddr));
  saddr.sun_family = AF_UNIX;
  strcpy(saddr.sun_path, "socket-server");

  s = socket(AF_UNIX, SOCK_DGRAM, 0);
  if (s == -1) { perror("socket"); exit(EXIT_FAILURE); }

  ret = bind(s, (struct sockaddr *)&saddr, sizeof(saddr));
  if (ret == -1) { perror("bind"); exit(EXIT_FAILURE); }

  len = sizeof(raddr);
  ssize = recvfrom(s, buf, sizeof(buf), 0, (struct sockaddr *)&raddr, &len);
  if (ssize == -1) { perror("recvfrom"); exit(EXIT_FAILURE); }

  printf("socklen: %d\n", (int)len);
  printf("sun_family: %d\n", (int)raddr.sun_family);

  if (raddr.sun_family == AF_INET) {
    struct sockaddr_in *addr_in = (struct sockaddr_in *)&raddr;
    uint16_t port = ntohs(addr_in->sin_port);
    printf("AF_INET address: %s:%d\n", inet_ntoa(addr_in->sin_addr), port);
  }

  return EXIT_SUCCESS;
}
% cat tst-client.c
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/un.h>

int main(int argc, char *argv[])
{
  int c;
  int ret;
  struct sockaddr_un saddr, caddr;
  ssize_t ssize;

  unlink("socket-client");

  memset(&saddr, '\0', sizeof(saddr));
  saddr.sun_family = AF_UNIX;
  strcpy(saddr.sun_path, "socket-server");

  memset(&caddr, '\0', sizeof(caddr));
  caddr.sun_family = AF_UNIX;
  strcpy(caddr.sun_path, "socket-client");

  c = socket(AF_UNIX, SOCK_DGRAM, 0);
  if (c == -1) { perror("socket"); exit(EXIT_FAILURE); }

  ret = bind(c, (struct sockaddr *)&caddr, sizeof(caddr));
  if (ret == -1) { perror("bind"); exit(EXIT_FAILURE); }

  ssize = sendto(c, "msg", 3, 0, (struct sockaddr *)&saddr, sizeof(saddr));
  if (ssize == -1) { perror("sendto"); exit(EXIT_FAILURE); }

  exit(EXIT_SUCCESS);
}
% gcc -Wall tst-server.c -o tst-server
% gcc -Wall tst-client.c -o tst-client
% ( ./tst-server & sleep 1; ./tst-client; wait )
socklen: 16
sun_family: 2
AF_INET address: 127.0.0.1:1590
-- 
Tanaka Akira

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