dvtm-editor.c

   1 /* edit-stream.c --- invoke $EDITOR as filter */
   2 /* Copyright (C) 2016 Dmitry Bogatov <KAction@gnu.org> ISC licensed */
   3
   4 #define _POSIX_C_SOURCE 200809L
   5 #include <stdlib.h>
   6 #include <sys/types.h>
   7 #include <sys/stat.h>
   8 #include <fcntl.h>
   9 #include <unistd.h>
  10 #include <sys/wait.h>
  11
  12 /* stdio.h would be overkill */
  13 #define write2(str) write(2, str, sizeof(str))
  14
  15 int
  16 main(int argc, char **argv)
  17 {
  18         int return_value = 1;
  19         const char *tty = ttyname(2); /* POSIX.1-2001, did you knew? */
  20         if (!tty) {
  21                 write2("stderr is not tty");
  22                 return 1;
  23         }
  24         int in = open(tty, O_RDONLY);
  25         if (in == -1) {
  26                 write2("failed to open tty for reading");
  27                 return 1;
  28         }
  29         char tempname[] = "/tmp/edit-stream.XXXXXX";
  30         int tempfd = mkstemp(tempname);
  31         if (tempfd == -1) {
  32                 write2("failed to open temporary file");
  33                 goto err_close_tty;
  34         }
  35         /* POSIX does not mandates modes of temporary file. */
  36         if (fchmod(tempfd, 0600) == -1) {
  37                 write2("failed to change mode of temporary file");
  38                 goto err_remove_tempfile;
  39         }
  40         char buffer[2048];
  41         ssize_t bytes;
  42         while ((bytes = read(0, buffer, sizeof(buffer))) > 0) {
  43                 /* Here actually must be loop, since write(2) does not guarates
  44                  * that it will be able to write everything. But I am reckless.
  45                  */
  46                 if (write(tempfd, buffer, bytes) != bytes) {
  47                         write2("failed to write data to temporary file");
  48                         goto err_remove_tempfile;
  49                 }
  50         }
  51         if (fsync(tempfd) == -1) {
  52                 write2("failed to fsync temporary file");
  53                 goto err_remove_tempfile;
  54         }
  55         if (close(tempfd) == -1) {
  56                 write2("failed to close temporary file");
  57                 goto err_remove_tempfile;
  58         }
  59         if (dup2(in, 0) == -1) {
  60                 write2("failed to set tty as stdin");
  61                 goto err_remove_tempfile;
  62         }
  63         int stdout = dup(1);
  64         if (stdout == -1) {
  65                 write2("failed to create copy of stdout");
  66                 goto err_remove_tempfile;
  67         }
  68         /* Descriptor 2 (stderr) still points to tty */
  69         if (dup2(2, 1) == -1) {
  70                 write2("failed to set tty as stdout");
  71                 goto err_close_stdout;
  72         }
  73         const char *editor = getenv("EDITOR");
  74         if (!editor) {
  75                 write2("EDITOR is not set");
  76                 goto err_close_stdout;
  77         }
  78         pid_t pid = fork();
  79         if (pid == 0) {
  80                 close(stdout);
  81                 close(tempfd);
  82                 close(in);
  83                 execlp(editor, editor, tempname, NULL);
  84                 _exit(129);
  85         }
  86         int status;
  87         if (wait(&status) == -1) {
  88                 write2("wait failed");
  89                 goto err_close_stdout;
  90         }
  91         if (!(WIFEXITED(status) && WEXITSTATUS(status) == 0)) {
  92                 write2("editor invocation failed");
  93                 goto err_close_stdout;
  94         }
  95         int tempfd_r = open(tempname, O_RDONLY);
  96         if (tempfd_r == -1) {
  97                 write2("failed to open for reading edited temporary file");
  98                 goto err_close_stdout;
  99         }
 100         while ((bytes = read(tempfd_r, buffer, sizeof(buffer))) > 0) {
 101                 if (write(stdout, buffer, bytes) != bytes) {
 102                         write2("failed to write data to stdout");
 103                         goto err_close_tempfile_read;
 104                 }
 105         }
 106
 107         return_value = 0;
 108
 109 /* Clean up on error is best efford. Descriptors are closed, files
 110    are unlinked, but nothing is checked. */
 111 err_close_tempfile_read:
 112         close(tempfd_r);
 113 err_close_stdout:
 114         close(stdout);
 115 err_remove_tempfile:
 116         close(tempfd);
 117         unlink(tempname);
 118 err_close_tty:
 119         close(in);
 120
 121         close(0);
 122         close(1);
 123         close(2);
 124
 125         return return_value;
 126 }