fag.c

   1 /* forkaftergrep (C) 2017 Tobias Girstmair, GPLv3 */
   2 //TODO: supply user arguments to grep
   3 //demo: ./fag -e -V "MPD server running at" mopidy
   4
   5 #define _XOPEN_SOURCE 500
   6 #define _DEFAULT_SOURCE
   7 #include <errno.h>
   8 #include <fcntl.h>
   9 #include <stdio.h>
  10 #include <stdlib.h>
  11 #include <string.h>
  12 #include <sysexits.h>
  13 #include <sys/time.h>
  14 #include <sys/wait.h>
  15 #include <unistd.h>
  16 #include "fag.h"
  17
  18 struct opt opts = {0, 0, 0, NULL, NULL, STDOUT_FILENO};
  19
  20 int main (int argc, char** argv) {
  21         int opt;
  22         opterr = 0;
  23
  24         /* the `+' forces getopt to stop at the first non-option */
  25         while ((opt = getopt (argc, argv, "+t:k::eVhv")) != -1) {
  26                 switch (opt) {
  27                 case 't':
  28                         opts.timeout = atoi (optarg);
  29                         break;
  30                 case 'k':
  31                         opts.kill_sig = optarg ? atoi (optarg) : SIGTERM;
  32                         break;
  33                 case 'e':
  34                         opts.stream = STDERR_FILENO;
  35                         break;
  36                 case 'V':
  37                         opts.verbose = 1;
  38                         break;
  39                 case 'h':
  40                         fprintf (stderr, VERTEXT USAGE
  41                                 "Options:\n"
  42                                 "\t-t N\ttimeout after N seconds\n"
  43                                 "\t-k [M]\tsend signal M to child after timeout (default: 15/SIGTERM)\n"
  44                                 "\t-e\tgrep on stderr instead of stdout\n", argv[0]);
  45                         return EX_OK;
  46                 case 'v':
  47                         fprintf (stderr, VERTEXT);
  48                         return EX_OK;
  49                 default:
  50                         fprintf (stderr, "Unrecognized option: %c\n" USAGE, optopt, argv[0]);
  51                         return EX_USAGE;
  52                 }
  53         }
  54
  55         /* the first non-option argument is the search string */
  56         if (optind < argc) {
  57                 opts.pattern = argv[optind++];
  58         } else {
  59                 fprintf (stderr, USAGE "(Missing PATTERN)\n", argv[0]);
  60                 return EX_USAGE;
  61         }
  62
  63         /* the remaining are the program to be run */
  64         if (optind < argc) {
  65                 opts.argv = &(argv[optind]);
  66         } else {
  67                 fprintf (stderr, USAGE "(Missing PROGRAM)\n", argv[0]);
  68                 return EX_USAGE;
  69         }
  70
  71         int retval = fork_after_grep (opts);
  72
  73         return retval;
  74 }
  75
  76 int fork_after_grep (struct opt opts) {
  77         int pipefd[2];
  78         pid_t cpid;
  79         int status;
  80
  81         char buf[BUF_SIZE];
  82         int nbytes;
  83
  84         struct timeval begin, now, diff;
  85
  86         if (pipe(pipefd) == -1) {
  87                 fprintf (stderr, "pipe error (userprog)\n");
  88                 return EX_OSERR;
  89         }
  90
  91         if ((cpid = fork()) == -1) {
  92                 fprintf (stderr, "fork error (userprog): %s", strerror (errno));
  93                 close (pipefd[0]);
  94                 close (pipefd[1]);
  95                 return EX_OSERR;
  96         }
  97
  98         if (cpid == 0) {
  99                 close (pipefd[0]);
 100                 dup2 (pipefd[1], opts.stream);
 101                 close (pipefd[1]);
 102                 close (opts.stream==STDOUT_FILENO?STDERR_FILENO:STDOUT_FILENO);
 103
 104                 if (setsid () == -1) {
 105                         fprintf (stderr, "setsid error (userprog): %s", strerror (errno));
 106                         _exit (EX_OSERR);
 107                 }
 108
 109                 execvp (opts.argv[0], opts.argv);
 110                 fprintf (stderr, "exec error (userprog): %s", strerror (errno));
 111                 _exit (EX_UNAVAILABLE);
 112         } else {
 113                 pid_t grep_cpid;
 114                 int pipefd_togrep[2];
 115                 int grep_status;
 116                 /* `-q': don't print anything; exit with 0 on match; with 1 on error */
 117                 char* grepargv[] = {"grep", "-q", opts.pattern, NULL};
 118
 119                 close (pipefd[1]);
 120                 fcntl (pipefd[0], F_SETFL, fcntl (pipefd[0], F_GETFL, 0) | O_NONBLOCK);
 121
 122                 gettimeofday (&begin, NULL); /* for timeout */
 123
 124                 if (pipe(pipefd_togrep) == -1) {
 125                         fprintf (stderr, "pipe error (grep)\n");
 126                         close (pipefd[0]);
 127                         close (pipefd[1]);
 128                         return EX_OSERR;
 129                 }
 130
 131                 if ((grep_cpid = fork()) == -1) {
 132                         fprintf (stderr, "fork error (grep): %s", strerror (errno));
 133                         close (pipefd[0]);
 134                         close (pipefd[1]);
 135                         close (pipefd_togrep[0]);
 136                         close (pipefd_togrep[1]);
 137                         return EX_OSERR;
 138                 }
 139
 140                 if (grep_cpid == 0) {
 141                         close (pipefd_togrep[1]);
 142                         dup2 (pipefd_togrep[0], STDIN_FILENO);
 143                         close (pipefd_togrep[0]);
 144
 145                         close (STDERR_FILENO);
 146                         close (STDOUT_FILENO);
 147
 148                         execvp (grepargv[0], grepargv);
 149                         fprintf (stderr, "exec error (grep): %s", strerror (errno));
 150                         _exit (EX_UNAVAILABLE);
 151                 } else {
 152                         close (pipefd_togrep[0]);
 153                         for (;;) {
 154                                 usleep (20000);
 155                                 memset (buf, 0, BUF_SIZE); /* necessary for opts.verbose */
 156                                 nbytes = read (pipefd[0], buf, BUF_SIZE);
 157                                 if (nbytes == -1) {
 158                                         switch (errno) {
 159                                         case EAGAIN:
 160                                                 break;
 161                                         default:
 162                                                 fprintf (stderr, "read error (userprog): %s", strerror (errno));
 163                                                 close (pipefd[0]);
 164                                                 close (pipefd[1]);
 165                                                 close (pipefd_togrep[1]);
 166                                                 //TODO: kill grep?
 167                                                 return EX_IOERR;
 168                                         }
 169                                 } else if (nbytes == 0) {
 170                                         fprintf (stderr, "Child program exited prematurely (userprog).\n");
 171                                         close (pipefd[0]);
 172                                         close (pipefd[1]);
 173                                         close (pipefd_togrep[1]);
 174                                         //TODO: kill grep?
 175                                         if (waitpid (cpid, &status, WNOHANG) > 0 && WIFEXITED (status)) {
 176                                                 return WEXITSTATUS (status);
 177                                         }
 178                                         return EX_UNAVAILABLE;
 179                                 } else {
 180                                         /* have new userprog-data, send it to grep */
 181                                         if (opts.verbose) {
 182                                                 fputs (buf, stderr);
 183                                         }
 184
 185                                         write(pipefd_togrep[1], buf, strlen(buf));
 186                                 }
 187
 188                                 if (waitpid (grep_cpid, &grep_status, WNOHANG) > 0 && WIFEXITED (grep_status)) {
 189                                         close (pipefd_togrep[1]);
 190
 191                                         if (WEXITSTATUS(grep_status) == 0) {
 192                                                 /* grep exited with match found */
 193                                                 printf ("%d\n", cpid);
 194
 195                                                 /* create a new child to keep pipe alive (will exit with exec'd program) */
 196                                                 if (!fork ()) {
 197                                                         while (kill(cpid, 0) != -1 && errno != ESRCH ) sleep (1);
 198                                                         close (pipefd[0]);
 199                                                         close (pipefd[1]);
 200                                                         _exit(0);
 201                                                 }
 202                                                 close (pipefd[0]);
 203                                                 close (pipefd[1]);
 204                                                 return EX_OK;
 205                                         } else {
 206                                                 /* grep exited due to an error */
 207                                                 fprintf (stderr, "grep exited due to an error.");
 208                                                 close (pipefd[0]);
 209                                                 close (pipefd[1]);
 210                                                 close (pipefd_togrep[1]);
 211                                                 return EX_IOERR;
 212                                         }
 213                                 }
 214
 215                                 if (opts.timeout > 0) {
 216                                         gettimeofday (&now, NULL);
 217                                         timersub (&now, &begin, &diff);
 218                                         if (diff.tv_sec >= opts.timeout) {
 219                                                 fprintf (stderr, "Timeout reached. \n");
 220                                                 if (opts.kill_sig > 0) kill (cpid, opts.kill_sig);
 221                                                 close (pipefd[0]);
 222                                                 close (pipefd[1]);
 223                                                 close (pipefd_togrep[1]);
 224                                                 //TODO: kill grep?
 225                                                 return EX_UNAVAILABLE;
 226                                         }
 227                                 }
 228                         }
 229                 }
 230         }
 231 }