git.scottworley.com Git - tl-append/blob - tl-append.c

   1 #define _POSIX_C_SOURCE 199309L
   2
   3 #include <errno.h>
   4 #include <fcntl.h>
   5 #include <stdio.h>
   6 #include <stdlib.h>
   7 #include <string.h>
   8 #include <time.h>
   9 #include <unistd.h>
  10
  11 #include "common.h"
  12
  13 const int BUF_SIZE = 1024;
  14
  15 const char PROMPT[] = "\33[H" /* Move cursor 'home' */
  16                       "\33[J" /* Clear screen */
  17                       "> ";
  18 const char ACKNOWLEDGE[] = "[OK]";
  19 const char WAITING[] = "[Waiting on lock...]\n";
  20 const struct timespec ACKNOWLEDGE_DELAY = {0, 300000000};
  21
  22 typedef struct {
  23   int interactive;
  24 } conf_t;
  25
  26 conf_t parse_command_line(int argc, char *argv[]) {
  27   conf_t conf;
  28   conf.interactive = 0;
  29
  30   for (int i = 1; i < argc; i++) {
  31     if (strcmp(argv[i], "-i") == 0 && isatty(2))
  32       conf.interactive = 1;
  33   }
  34
  35   return conf;
  36 }
  37
  38 static void read_line(conf_t *conf, char *buf) {
  39   if (conf->interactive)
  40     if (fputs(PROMPT, stderr) == EOF)
  41       die("I/O error writing prompt");
  42   if (fgets(buf, BUF_SIZE, stdin) == NULL) {
  43     if (ferror(stdin))
  44       die("I/O error reading line");
  45     if (feof(stdin)) {
  46       buf[0] = '\0'; /* Unclear if fgets does this already */
  47       return;
  48     }
  49     die("Unexpected error reading line");
  50   }
  51 }
  52
  53 static void write_line(const char *now, FILE *f, const char *line) {
  54   if (f == NULL)
  55     die_err("Error opening output file");
  56   if (fputs(now, f) == EOF)
  57     die("Error writing to output file");
  58   if (fputc(' ', f) == EOF)
  59     die("Error writing to output file");
  60   if (fputs(line, f) == EOF)
  61     die("Error writing to output file");
  62 }
  63
  64 static void take_lock(FILE *f) {
  65   struct flock lock;
  66   lock.l_type = F_WRLCK;
  67   lock.l_whence = SEEK_SET;
  68   lock.l_start = 0;
  69   lock.l_len = 0;
  70   int fd = fileno(f);
  71   if (fd == -1)
  72     die_err("Couldn't get file descriptor for locking");
  73   if (fcntl(fd, F_SETLK, &lock) == 0)
  74     return;
  75   if (errno != EACCES && errno != EAGAIN)
  76     die_err("Couldn't take lock");
  77   if (fputs(WAITING, stderr) == EOF)
  78     die("Error writing waiting message");
  79   if (fcntl(fd, F_SETLKW, &lock) == 0)
  80     return;
  81   die_err("Couldn't take lock");
  82 }
  83
  84 static void write_acknowledgment(conf_t *conf) {
  85   if (conf->interactive) {
  86     if (fputs(ACKNOWLEDGE, stderr) == EOF)
  87       die("Error writing acknowledgment");
  88     if (nanosleep(&ACKNOWLEDGE_DELAY, NULL) == -1 && errno != EINTR)
  89       die_err("Error sleeping");
  90   }
  91 }
  92
  93 static void lock_and_write_line(conf_t *conf, const char *line) {
  94   const char *now = encode_time(time(NULL));
  95   FILE *f = fopen(FILENAME, "a");
  96
  97   take_lock(f);
  98   write_line(now, f, line);
  99
 100   if (fclose(f) != 0)
 101     die_err("Error closing output file");
 102
 103   write_acknowledgment(conf);
 104 }
 105
 106 int main(int argc, char *argv[]) {
 107   conf_t conf = parse_command_line(argc, argv);
 108   char buf[BUF_SIZE];
 109   for (read_line(&conf, buf); buf[0]; read_line(&conf, buf)) {
 110     lock_and_write_line(&conf, buf);
 111   }
 112   return 0;
 113 }