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

   1 /*
   2  * tl-append: time-logger appending shell
   3  * Copyright (C) 2023  Scott Worley <scottworley@scottworley.com>
   4  *
   5  * This program is free software: you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation, version 3.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  16  */
  17
  18 #define _POSIX_C_SOURCE 199309L
  19
  20 #include <errno.h>
  21 #include <fcntl.h>
  22 #include <stdio.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <sys/file.h>
  26 #include <time.h>
  27 #include <unistd.h>
  28
  29 #include "common.h"
  30
  31 const int BUF_SIZE = 1024;
  32
  33 const char PROMPT[] = "\33[H" /* Move cursor 'home' */
  34                       "\33[J" /* Clear screen */
  35                       "> ";
  36 const char ACKNOWLEDGE[] = "[OK]";
  37 const char WAITING[] = "[Waiting on lock...]\n";
  38 const struct timespec ACKNOWLEDGE_DELAY = {0, 300000000};
  39
  40 typedef struct {
  41   int interactive;
  42   int fcntl_lock;
  43   int flock_lock;
  44 } conf_t;
  45
  46 void usage() {
  47   die("usage: tl-append [-i] [-C dir] [--no-fnctl-lock] [--no-flock-lock]");
  48 }
  49
  50 conf_t parse_command_line(int argc, char *argv[]) {
  51   conf_t conf;
  52   conf.interactive = 0;
  53   conf.fcntl_lock = 1;
  54   conf.flock_lock = 1;
  55
  56   for (int i = 1; i < argc; i++) {
  57     if (strcmp(argv[i], "-i") == 0 && isatty(2))
  58       conf.interactive = 1;
  59     else if (strcmp(argv[i], "--no-fnctl-lock") == 0)
  60       conf.fcntl_lock = 0;
  61     else if (strcmp(argv[i], "--no-flock-lock") == 0)
  62       conf.flock_lock = 0;
  63     else if (strcmp(argv[i], "-C") == 0) {
  64       if (i + 1 >= argc)
  65         die("-C requires a directory");
  66       if (chdir(argv[i + 1]) == -1)
  67         die_err("Couldn't change directory");
  68       i++;
  69     } else
  70       usage();
  71   }
  72
  73   return conf;
  74 }
  75
  76 static void read_line(conf_t *conf, char *buf) {
  77   if (conf->interactive)
  78     if (fputs(PROMPT, stderr) == EOF)
  79       die("I/O error writing prompt");
  80   if (fgets(buf, BUF_SIZE, stdin) == NULL) {
  81     if (ferror(stdin))
  82       die("I/O error reading line");
  83     if (feof(stdin)) {
  84       buf[0] = '\0'; /* Unclear if fgets does this already */
  85       return;
  86     }
  87     die("Unexpected error reading line");
  88   }
  89 }
  90
  91 static void write_line(const char *now, FILE *f, const char *line) {
  92   if (f == NULL)
  93     die_err("Error opening output file");
  94   if (fputs(now, f) == EOF)
  95     die("Error writing to output file");
  96   if (fputc(' ', f) == EOF)
  97     die("Error writing to output file");
  98   if (fputs(line, f) == EOF)
  99     die("Error writing to output file");
 100 }
 101
 102 static void take_fcntl_lock(conf_t *conf, FILE *f) {
 103   if (!conf->fcntl_lock)
 104     return;
 105   struct flock lock;
 106   lock.l_type = F_WRLCK;
 107   lock.l_whence = SEEK_SET;
 108   lock.l_start = 0;
 109   lock.l_len = 0;
 110   int fd = fileno(f);
 111   if (fd == -1)
 112     die_err("Couldn't get file descriptor for locking");
 113   if (fcntl(fd, F_SETLK, &lock) == 0)
 114     return;
 115   if (errno != EACCES && errno != EAGAIN)
 116     die_err("Couldn't take fcntl lock");
 117   if (fputs(WAITING, stderr) == EOF)
 118     die("Error writing waiting message");
 119   if (fcntl(fd, F_SETLKW, &lock) == 0)
 120     return;
 121   die_err("Couldn't take fcntl lock");
 122 }
 123
 124 static void take_flock_lock(conf_t *conf, FILE *f) {
 125   if (!conf->flock_lock)
 126     return;
 127   int fd = fileno(f);
 128   if (fd == -1)
 129     die_err("Couldn't get file descriptor for locking");
 130   if (flock(fd, LOCK_EX | LOCK_NB) == 0)
 131     return;
 132   if (errno != EWOULDBLOCK)
 133     die_err("Couldn't take flock lock");
 134   if (fputs(WAITING, stderr) == EOF)
 135     die("Error writing waiting message");
 136   if (flock(fd, LOCK_EX) == 0)
 137     return;
 138   die_err("Couldn't take flock lock");
 139 }
 140
 141 static void take_lock(conf_t *conf, FILE *f) {
 142   take_fcntl_lock(conf, f);
 143   take_flock_lock(conf, f);
 144 }
 145
 146 static void write_acknowledgment(conf_t *conf) {
 147   if (conf->interactive) {
 148     if (fputs(ACKNOWLEDGE, stderr) == EOF)
 149       die("Error writing acknowledgment");
 150     if (nanosleep(&ACKNOWLEDGE_DELAY, NULL) == -1 && errno != EINTR)
 151       die_err("Error sleeping");
 152   }
 153 }
 154
 155 static void lock_and_write_line(conf_t *conf, const char *line) {
 156   char *now = encode_time(time(NULL));
 157   FILE *f = fopen(FILENAME, "a");
 158
 159   take_lock(conf, f);
 160   write_line(now, f, line);
 161
 162   if (fclose(f) != 0)
 163     die_err("Error closing output file");
 164
 165   free(now);
 166   write_acknowledgment(conf);
 167 }
 168
 169 int main(int argc, char *argv[]) {
 170   conf_t conf = parse_command_line(argc, argv);
 171   char buf[BUF_SIZE];
 172   for (read_line(&conf, buf); buf[0]; read_line(&conf, buf)) {
 173     lock_and_write_line(&conf, buf);
 174   }
 175   return 0;
 176 }