pager.c

/*
 * Copyright (c) 2018 Rob Clark <[email protected]>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include <errno.h>
#include <signal.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>

#include "pager.h"

static pid_t pager_pid;

static void
pager_death(int n)
{
   exit(0);
}

void
pager_open(void)
{
   int fd[2];

   if (pipe(fd) < 0) {
      fprintf(stderr, "Failed to create pager pipe: %m\n");
      exit(-1);
   }

   pager_pid = fork();
   if (pager_pid < 0) {
      fprintf(stderr, "Failed to fork pager: %m\n");
      exit(-1);
   }

   if (pager_pid == 0) {
      const char *less_opts;

      dup2(fd[0], STDIN_FILENO);
      close(fd[0]);
      close(fd[1]);

      less_opts = "FRSMKX";
      setenv("LESS", less_opts, 1);

      execlp("less", "less", NULL);

   } else {
      /* we want to kill the parent process when pager exits: */
      signal(SIGCHLD, pager_death);
      dup2(fd[1], STDOUT_FILENO);
      close(fd[0]);
      close(fd[1]);
   }
}

int
pager_close(void)
{
   siginfo_t status;

   close(STDOUT_FILENO);

   while (true) {
      memset(&status, 0, sizeof(status));
      if (waitid(P_PID, pager_pid, &status, WEXITED) < 0) {
         if (errno == EINTR)
            continue;
         return -errno;
      }

      return 0;
   }
}