text: /****************************************************************************
   * bfs                                                                      *
   * Copyright (C) 2019 Tavian Barnes <tavianator@tavianator.com>             *
   *                                                                          *
   * Permission to use, copy, modify, and/or distribute this software for any *
   * purpose with or without fee is hereby granted.                           *
   *                                                                          *
   * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES *
   * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF         *
   * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR  *
   * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES   *
   * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN    *
   * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF  *
   * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.           *
   ****************************************************************************/
  
  /**
   * There's no standard Unix utility that creates a socket file, so this small
   * program does the job.
   */
  
  #include <errno.h>
  #include <libgen.h>
  #include <stdio.h>
  #include <string.h>
  #include <stdlib.h>
  #include <sys/socket.h>
  #include <sys/un.h>
  #include <unistd.h>
  
  /**
   * Print an error message.
   */
  static void errmsg(const char *cmd, const char *path) {
  	fprintf(stderr, "%s: '%s': %s.\n", cmd, path, strerror(errno));
  }
  
  /**
   * struct sockaddr_un::sun_path is very short, so we chdir() into the target
   * directory before creating sockets in case the full path is too long but the
   * file name is not.
   */
  static int chdir_parent(const char *path) {
  	char *copy = strdup(path);
  	if (!copy) {
  		return -1;
  	}
  	const char *dir = dirname(copy);
  
  	int ret = chdir(dir);
  
  	int error = errno;
  	free(copy);
  	errno = error;
  
  	return ret;
  }
  
  /**
   * Initialize a struct sockaddr_un with the right filename.
   */
  static int init_sun(struct sockaddr_un *sock, const char *path) {
  	size_t len = strlen(path);
  	if (len == 0 || path[len - 1] == '/') {
  		errno = ENOENT;
  		return -1;
  	}
  
  	char *copy = strdup(path);
  	if (!copy) {
  		return -1;
  	}
  	const char *base = basename(copy);
  
  	len = strlen(base);
  	if (len >= sizeof(sock->sun_path)) {
  		free(copy);
  		errno = ENAMETOOLONG;
  		return -1;
  	}
  
  	sock->sun_family = AF_UNIX;
  	memcpy(sock->sun_path, base, len + 1);
  	free(copy);
  	return 0;
  }
  
  int main(int argc, char *argv[]) {
  	const char *cmd = argc > 0 ? argv[0] : "mksock";
  
  	if (argc != 2) {
  		fprintf(stderr, "Usage: %s NAME\n", cmd);
  		return EXIT_FAILURE;
  	}
  
  	const char *path = argv[1];
  
  	if (chdir_parent(path) != 0) {
  		errmsg(cmd, path);
  		return EXIT_FAILURE;
  	}
  
  	struct sockaddr_un sock;
  	if (init_sun(&sock, path) != 0) {
  		errmsg(cmd, path);
  		return EXIT_FAILURE;
  	}
  
  	int fd = socket(AF_UNIX, SOCK_STREAM, 0);
  	if (fd < 0) {
  		errmsg(cmd, path);
  		return EXIT_FAILURE;
  	}
  
  	int ret = EXIT_SUCCESS;
  
  	if (bind(fd, (struct sockaddr *)&sock, sizeof(sock)) != 0) {
  		errmsg(cmd, path);
  		ret = EXIT_FAILURE;
  	}
  
  	if (close(fd) != 0) {
  		errmsg(cmd, path);
  		ret = EXIT_FAILURE;
  	}
  
  	return ret;
  }
  