/*

 * Utilities about process handling - signal and subprocess (ex. pager)

 *

 * Copyright (c) 2011 Yuya Nishihara <yuya@tcha.org>

 *

 * This software may be used and distributed according to the terms of the

 * GNU General Public License version 2 or any later version.

 */

#include <assert.h>

#include <errno.h>

#include <signal.h>

#include <stdio.h>

#include <string.h>

#include <sys/wait.h>

#include <unistd.h>

#include "procutil.h"

#include "util.h"

static pid_t pagerpid = 0;

static pid_t peerpgid = 0;

static pid_t peerpid = 0;

static void forwardsignal(int sig)

{

	assert(peerpid > 0);

	if (kill(peerpid, sig) < 0) {

		abortmsgerrno("cannot kill %d", peerpid);

	}

	debugmsg("forward signal %d", sig);

}

static void forwardsignaltogroup(int sig)

{

	/* prefer kill(-pgid, sig), fallback to pid if pgid is invalid */

	pid_t killpid = peerpgid > 1 ? -peerpgid : peerpid;

	if (kill(killpid, sig) < 0) {

		abortmsgerrno("cannot kill %d", killpid);

	}

	debugmsg("forward signal %d to %d", sig, killpid);

}

static void handlestopsignal(int sig)

{

	sigset_t unblockset, oldset;

	struct sigaction sa, oldsa;

	if (sigemptyset(&unblockset) < 0) {

		goto error;

	}

	if (sigaddset(&unblockset, sig) < 0) {

		goto error;

	}

	memset(&sa, 0, sizeof(sa));

	sa.sa_handler = SIG_DFL;

	sa.sa_flags = SA_RESTART;

	if (sigemptyset(&sa.sa_mask) < 0) {

		goto error;

	}

	forwardsignal(sig);

	if (raise(sig) < 0) { /* resend to self */

		goto error;

	}

	if (sigaction(sig, &sa, &oldsa) < 0) {

		goto error;

	}

	if (sigprocmask(SIG_UNBLOCK, &unblockset, &oldset) < 0) {

		goto error;

	}

	/* resent signal will be handled before sigprocmask() returns */

	if (sigprocmask(SIG_SETMASK, &oldset, NULL) < 0) {

		goto error;

	}

	if (sigaction(sig, &oldsa, NULL) < 0) {

		goto error;

	}

	return;

error:

	abortmsgerrno("failed to handle stop signal");

}

static void handlechildsignal(int sig UNUSED_)

{

	if (peerpid == 0 || pagerpid == 0) {

		return;

	}

	/* if pager exits, notify the server with SIGPIPE immediately.

	 * otherwise the server won't get SIGPIPE if it does not write

	 * anything. (issue5278) */

	if (waitpid(pagerpid, NULL, WNOHANG) == pagerpid) {

		kill(peerpid, SIGPIPE);

	}

}

void setupsignalhandler(pid_t pid, pid_t pgid)

{

	if (pid <= 0) {

		return;

	}

	peerpid = pid;

	peerpgid = (pgid <= 1 ? 0 : pgid);

	struct sigaction sa;

	memset(&sa, 0, sizeof(sa));

	/* deadly signals meant to be sent to a process group:

	 * - SIGHUP: usually generated by the kernel, when termination of a

	 *   process causes that process group to become orphaned

	 * - SIGINT: usually generated by the terminal */

	sa.sa_handler = forwardsignaltogroup;

	sa.sa_flags = SA_RESTART;

	if (sigemptyset(&sa.sa_mask) < 0) {

		goto error;

	}

	if (sigaction(SIGHUP, &sa, NULL) < 0) {

		goto error;

	}

	if (sigaction(SIGINT, &sa, NULL) < 0) {

		goto error;

	}

	/* terminate frontend by double SIGTERM in case of server freeze */

	sa.sa_handler = forwardsignal;

	sa.sa_flags |= SA_RESETHAND;

	if (sigaction(SIGTERM, &sa, NULL) < 0) {

		goto error;

	}

	/* notify the worker about window resize events */

	sa.sa_flags = SA_RESTART;

	if (sigaction(SIGWINCH, &sa, NULL) < 0) {

		goto error;

	}

	/* forward user-defined signals */

	if (sigaction(SIGUSR1, &sa, NULL) < 0) {

		goto error;

	}

	if (sigaction(SIGUSR2, &sa, NULL) < 0) {

		goto error;

	}

	/* propagate job control requests to worker */

	sa.sa_handler = forwardsignal;

	sa.sa_flags = SA_RESTART;

	if (sigaction(SIGCONT, &sa, NULL) < 0) {

		goto error;

	}

	sa.sa_handler = handlestopsignal;

	sa.sa_flags = SA_RESTART;

	if (sigaction(SIGTSTP, &sa, NULL) < 0) {

		goto error;

	}

	/* get notified when pager exits */

	sa.sa_handler = handlechildsignal;

	sa.sa_flags = SA_RESTART;

	if (sigaction(SIGCHLD, &sa, NULL) < 0) {

		goto error;

	}

	return;

error:

	abortmsgerrno("failed to set up signal handlers");

}

void restoresignalhandler(void)

{

	struct sigaction sa;

	memset(&sa, 0, sizeof(sa));

	sa.sa_handler = SIG_DFL;

	sa.sa_flags = SA_RESTART;

	if (sigemptyset(&sa.sa_mask) < 0) {

		goto error;

	}

	if (sigaction(SIGHUP, &sa, NULL) < 0) {

		goto error;

	}

	if (sigaction(SIGTERM, &sa, NULL) < 0) {

		goto error;

	}

	if (sigaction(SIGWINCH, &sa, NULL) < 0) {

		goto error;

	}

	if (sigaction(SIGCONT, &sa, NULL) < 0) {

		goto error;

	}

	if (sigaction(SIGTSTP, &sa, NULL) < 0) {

		goto error;

	}

	if (sigaction(SIGCHLD, &sa, NULL) < 0) {

		goto error;

	}

	/* ignore Ctrl+C while shutting down to make pager exits cleanly */

	sa.sa_handler = SIG_IGN;

	if (sigaction(SIGINT, &sa, NULL) < 0) {

		goto error;

	}

	peerpid = 0;

	return;

error:

	abortmsgerrno("failed to restore signal handlers");

}

/* This implementation is based on hgext/pager.py (post 369741ef7253)

 * Return 0 if pager is not started, or pid of the pager */

pid_t setuppager(const char *pagercmd, const char *envp[])

{

	assert(pagerpid == 0);

	if (!pagercmd) {

		return 0;

	}

	int pipefds[2];

	if (pipe(pipefds) < 0) {

		return 0;

	}

	pid_t pid = fork();

	if (pid < 0) {

		goto error;

	}

	if (pid > 0) {

		close(pipefds[0]);

		if (dup2(pipefds[1], fileno(stdout)) < 0) {

			goto error;

		}

		if (isatty(fileno(stderr))) {

			if (dup2(pipefds[1], fileno(stderr)) < 0) {

				goto error;

			}

		}

		close(pipefds[1]);

		pagerpid = pid;

		return pid;

	} else {

		dup2(pipefds[0], fileno(stdin));

		close(pipefds[0]);

		close(pipefds[1]);

		int r =

		    execle("/bin/sh", "/bin/sh", "-c", pagercmd, NULL, envp);

		if (r < 0) {

			abortmsgerrno("cannot start pager '%s'", pagercmd);

		}

		return 0;

	}

error:

	close(pipefds[0]);

	close(pipefds[1]);

	abortmsgerrno("failed to prepare pager");

	return 0;

}

void waitpager(void)

{

	if (pagerpid == 0) {

		return;

	}

	/* close output streams to notify the pager its input ends */

	fclose(stdout);

	fclose(stderr);

	while (1) {

		pid_t ret = waitpid(pagerpid, NULL, 0);

		if (ret == -1 && errno == EINTR) {

			continue;

		}

		break;

	}

}