/* SPDX-License-Identifier: GPL-2.0 */

/** \file daemon.c Some helpers for programs that detach from the console. */

#include <pwd.h>
#include <sys/types.h> /* getgrnam() */
#include <grp.h>
#include <signal.h>
#include <sys/resource.h>

#include "para.h"
#include "daemon.h"
#include "string.h"
#include "color.h"

/** The internal state of the daemon. */
struct daemon {
	/** See \ref daemon_flags. */
	unsigned flags;
	/** Set by \ref daemon_set_logfile(). */
	char *logfile_name;
	/** Current loglevel, see \ref daemon_set_loglevel(). */
	int loglevel;
	/** Used by \ref server_uptime() and \ref uptime_str(). */
	time_t startuptime;
	/** The file pointer if the logfile is open. */
	FILE *logfile;
	/** Used for colored log messages. */
	char log_colors[NUM_LOGLEVELS][COLOR_MAXLEN];
	char *old_cwd;
	/*
	 * If these pointers are non-NULL, the functions are called from
	 * daemon_log() before and after writing each log message.
	 */
	void (*pre_log_hook)(void);
	void (*post_log_hook)(void);
};

static struct daemon the_daemon, *me = &the_daemon;

static void daemon_set_default_log_colors(void)
{
	int i;
	static const char *default_log_colors[NUM_LOGLEVELS] = {
		[LL_DEBUG] = "normal",
		[LL_INFO] = "normal",
		[LL_NOTICE] = "normal",
		[LL_WARNING] = "yellow",
		[LL_ERROR] = "red",
		[LL_CRIT] = "magenta bold",
		[LL_EMERG] = "red bold",
	};
	for (i = 0; i < NUM_LOGLEVELS; i++)
		color_parse_or_die(default_log_colors[i], me->log_colors[i]);
}

/**
 * Set the color for log messages of the given severity level.
 *
 * \param arg Must be of the form "severity:[fg [bg]] [attr]".
 */
void daemon_set_log_color_or_die(const char *arg)
{
	unsigned ll;
	const char * const sev[] = {SEVERITIES};
	const char *p = strchr(arg, ':');

	if (!p)
		goto err;
	for (ll = 0; ll < NUM_LOGLEVELS; ll++) {
		const char *name = sev[ll];
		/*
		 * Parse only the first part of the string so that, for
		 * example, the argument "info:something_else" is recognized.
		 * Note that the string comparison is performed
		 * case-insensitively.
		 */
		if (strncasecmp(arg, name, strlen(name)))
			continue;
		return color_parse_or_die(p + 1, me->log_colors[ll]);
	}
err:
	PARA_EMERG_LOG("%s: invalid color argument\n", arg);
	exit(EXIT_FAILURE);
}

/**
 * Initialize color mode if necessary.
 *
 * \param color_arg The argument given to --color.
 * \param color_arg_auto The value for automatic color detection.
 * \param color_arg_no The value to disable colored log messages.
 * \param logfile_given In auto mode colors are disabled if this value is true.
 *
 * If color_arg equals color_arg_no, color mode is disabled. That is, calls to
 * para_log() will not produce colored output. If color_arg equals
 * color_arg_auto, the function detects automatically whether to activate
 * colors. Otherwise color mode is enabled.
 *
 * If color mode is to be enabled, the default colors are set for each
 * loglevel. They can be overwritten by calling daemon_set_log_color_or_die().
 *
 * \return Whether colors have been enabled by the function.
 */
bool daemon_init_colors_or_die(int color_arg, int color_arg_auto,
		int color_arg_no, bool logfile_given)
{
	if (color_arg == color_arg_no)
		return false;
	if (color_arg == color_arg_auto) {
		if (logfile_given)
			return false;
		if (!isatty(STDERR_FILENO))
			return false;
	}
	daemon_set_flag(DF_COLOR_LOG);
	daemon_set_default_log_colors();
	return true;
}

/**
 * Init or change the name of the log file.
 *
 * \param logfile_name The full path of the logfile.
 */
void daemon_set_logfile(const char *logfile_name)
{
	free(me->logfile_name);
	me->logfile_name = NULL;
	if (!logfile_name)
		return;
	if (me->old_cwd && logfile_name[0] != '/')
		me->logfile_name = make_message("%s/%s", me->old_cwd,
			logfile_name);
	else
		me->logfile_name = para_strdup(logfile_name);
}

/**
 * Control the verbosity for logging.
 *
 * This instructs the daemon to not log subsequent messages whose severity is
 * lower than the given value.
 *
 * \param loglevel The new log level.
 */
void daemon_set_loglevel(int loglevel)
{
	assert(loglevel >= 0);
	assert(loglevel < NUM_LOGLEVELS);
	me->loglevel = loglevel;
}

/**
 * Get the current log level of the daemon.
 *
 * \return Greater or equal than zero and less than NUM_LOGLEVELS. This
 * function never fails.
 */
int daemon_get_loglevel(void)
{
	return me->loglevel;
}

/**
 * Register functions to be called before and after a message is logged.
 *
 * \param pre_log_hook Called before the message is logged.
 * \param post_log_hook Called after the message is logged.
 *
 * The purpose of this function is to provide a primitive for multi-threaded
 * applications to serialize the access to the log facility, preventing
 * interleaving log messages. This can be achieved by having the pre-log hook
 * acquire a lock which blocks the other threads on the attempt to log a
 * message at the same time.  The post-log hook is responsible for releasing
 * the lock.
 *
 * If these hooks are unnecessary, for example because the application is
 * single-threaded, this function does not need to be called.
 */
void daemon_set_hooks(void (*pre_log_hook)(void), void (*post_log_hook)(void))
{
	me->pre_log_hook = pre_log_hook;
	me->post_log_hook = post_log_hook;
}

/**
 * Set one of the daemon config flags.
 *
 * \param flag The flag to set.
 *
 * \sa \ref daemon_flags.
 */
void daemon_set_flag(unsigned flag)
{
	me->flags |= flag;
}

static bool daemon_test_flag(unsigned flag)
{
	return me->flags & flag;
}

/**
 * Do the usual stuff to become a daemon.
 *
 * \param parent_waits Whether the parent process should pause before exit.
 *
 * Fork, become session leader, cd to /, and dup fd 0, 1, 2 to /dev/null. If \a
 * parent_waits is false, the parent process terminates immediately.
 * Otherwise, a pipe is created prior to the fork() and the parent tries to
 * read a single byte from the reading end of the pipe. The child is supposed
 * to write to the writing end of the pipe after it completed its setup
 * procedure successfully. This behaviour is useful to let the parent process
 * die with an error if the child process aborts early, since in this case the
 * read() will return non-positive.
 *
 * \return This function either succeeds or calls exit(3). If parent_waits is
 * true, the return value is the file descriptor of the writing end of the
 * pipe. Otherwise the function returns zero.
 *
 * \sa fork(2), setsid(2), dup(2), pause(2).
 */
int daemonize(bool parent_waits)
{
	pid_t pid;
	int null, pipe_fd[2];

	if (parent_waits && pipe(pipe_fd) < 0)
		goto err;
	PARA_INFO_LOG("subsequent log messages go to %s\n", me->logfile_name?
		 me->logfile_name : "/dev/null");
	pid = fork();
	if (pid < 0)
		goto err;
	if (pid) { /* parent exits */
		if (parent_waits) {
			char c;
			close(pipe_fd[1]);
			exit(read(pipe_fd[0], &c, 1) <= 0?
				EXIT_FAILURE : EXIT_SUCCESS);
		}
		exit(EXIT_SUCCESS);
	}
	if (parent_waits)
		close(pipe_fd[0]);
	/* become session leader */
	if (setsid() < 0)
		goto err;
	me->old_cwd = getcwd(NULL, 0);
	if (chdir("/") < 0)
		goto err;
	null = open("/dev/null", O_RDWR);
	if (null < 0)
		goto err;
	if (dup2(null, STDIN_FILENO) < 0)
		goto err;
	if (dup2(null, STDOUT_FILENO) < 0)
		goto err;
	if (dup2(null, STDERR_FILENO) < 0)
		goto err;
	close(null);
	return parent_waits? pipe_fd[1] : 0;
err:
	PARA_EMERG_LOG("fatal: %s\n", strerror(errno));
	exit(EXIT_FAILURE);
}

/**
 * Close the log file of the daemon.
 */
void daemon_close_log(void)
{
	if (!me->logfile)
		return;
	PARA_INFO_LOG("closing logfile\n");
	fclose(me->logfile);
	me->logfile = NULL;
}

/**
 * Open the logfile in append mode.
 *
 * This function either succeeds or exits.
 */
void daemon_open_log_or_die(void)
{
	FILE *new_log;

	if (!me->logfile_name)
		return;
	new_log = fopen(me->logfile_name, "a");
	if (!new_log) {
		PARA_EMERG_LOG("can not open %s: %s\n", me->logfile_name,
			strerror(errno));
		exit(EXIT_FAILURE);
	}
	daemon_close_log();
	me->logfile = new_log;
	/* equivalent to setlinebuf(), but portable */
	setvbuf(me->logfile, NULL, _IOLBF, 0);
}

/**
 * Log the startup message containing the paraslash version.
 *
 * \param name The name of the executable.
 *
 * First the given \a name is prefixed with the string "para_". Next the git
 * version is appended. The resulting string is logged with priority "INFO".
 */
void daemon_log_welcome(const char *name)
{
	PARA_INFO_LOG("welcome to para_%s-%s\n", name, paraslash_version());
}

/**
 * Renice the calling process.
 *
 * \param prio The priority value to set.
 *
 * Errors are not considered fatal, but a warning message is logged if the
 * underlying call to setpriority(2) fails.
 */
void daemon_set_priority(int prio)
{
	if (setpriority(PRIO_PROCESS, 0, prio) < 0)
		PARA_WARNING_LOG("could not set priority to %d: %s\n", prio,
			strerror(errno));
}

/**
 * Give up superuser privileges.
 *
 * \param username The user to switch to.
 * \param groupname The group to switch to.
 *
 * This function returns immediately if not invoked with EUID zero. Otherwise,
 * it tries to obtain the GID of \a groupname and the UID of \a username.  On
 * success, effective and real GID/UID and the saved set-group-ID/set-user-ID
 * are all set accordingly. On errors, an appropriate message is logged and
 * exit() is called to terminate the process.
 *
 * \sa getpwnam(3), getuid(2), setuid(2), getgrnam(2), setgid(2)
 */
void daemon_drop_privileges_or_die(const char *username, const char *groupname)
{
	struct passwd *p;
	char *tmp;

	if (geteuid())
		return;
	if (groupname) {
		struct group *g = getgrnam(groupname);
		if (!g) {
			PARA_EMERG_LOG("failed to get group %s: %s\n",
				groupname, strerror(errno));
			exit(EXIT_FAILURE);
		}
		if (setgid(g->gr_gid) < 0) {
			PARA_EMERG_LOG("failed to set group id %d: %s\n",
				(int)g->gr_gid, strerror(errno));
			exit(EXIT_FAILURE);
		}
	}
	if (!username) {
		PARA_EMERG_LOG("root privileges, but no user option given\n");
		exit(EXIT_FAILURE);
	}
	tmp = para_strdup(username);
	p = getpwnam(tmp);
	free(tmp);
	if (!p) {
		PARA_EMERG_LOG("%s: no such user\n", username);
		exit(EXIT_FAILURE);
	}
	PARA_INFO_LOG("dropping root privileges\n");
	if (setuid(p->pw_uid) < 0) {
		PARA_EMERG_LOG("failed to set effective user ID (%s)",
			strerror(errno));
		exit(EXIT_FAILURE);
	}
	PARA_DEBUG_LOG("uid: %d, euid: %d\n", (int)getuid(), (int)geteuid());
}

/**
 * Set the startup time.
 *
 * This should be called once on startup. It sets the start time to the
 * current time. The stored time is used for retrieving the server uptime.
 *
 * \sa time(2), \ref daemon_get_uptime(), \ref daemon_get_uptime_str().
 */
void daemon_set_start_time(void)
{
	time(&me->startuptime);
}

/**
 * Get the uptime.
 *
 * \param current_time The current time.
 *
 * The \a current_time pointer may be \p NULL. In this case the function
 * obtains the current time from the system.
 *
 * \return This returns the server uptime in seconds, i.e. the difference
 * between the current time and the value stored previously via \ref
 * daemon_set_start_time().
 */
time_t daemon_get_uptime(const struct timeval *current_time)
{
	time_t t;

	if (current_time)
		return current_time->tv_sec - me->startuptime;
	time(&t);
	return difftime(t, me->startuptime);
}

/**
 * Construct a string containing the current uptime.
 *
 * \param current_time See a \ref daemon_get_uptime().
 *
 * \return A dynamically allocated string of the form "days:hours:minutes".
 */
__malloc char *daemon_get_uptime_str(const struct timeval *current_time)
{
	long t = daemon_get_uptime(current_time);
	return make_message("%li:%02li:%02li", t / 86400,
		(t / 3600) % 24, (t / 60) % 60);
}

/**
 * The log function for para_server and para_audiod.
 *
 * \param ll The log level.
 * \param fmt The format string describing the log message.
 */
__printf_2_3 void daemon_log(int ll, const char* fmt,...)
{
	va_list argp;
	FILE *fp;
	struct tm *tm;
	char *color;
	bool log_time = daemon_test_flag(DF_LOG_TIME), log_timing =
		daemon_test_flag(DF_LOG_TIMING);

	ll = PARA_MIN(ll, NUM_LOGLEVELS - 1);
	ll = PARA_MAX(ll, LL_DEBUG);
	if (ll < me->loglevel)
		return;

	fp = me->logfile? me->logfile : stderr;
	if (me->pre_log_hook)
		me->pre_log_hook();
	color = daemon_test_flag(DF_COLOR_LOG)? me->log_colors[ll] : NULL;
	if (color)
		fprintf(fp, "%s", color);
	if (log_time || log_timing) {
		struct timeval tv;
		clock_get_realtime(&tv);
		if (daemon_test_flag(DF_LOG_TIME)) { /* print date and time */
			time_t t1 = tv.tv_sec;
			char str[100];
			tm = localtime(&t1);
			strftime(str, sizeof(str), "%b %d %H:%M:%S", tm);
			fprintf(fp, "%s%s", str, log_timing? ":" : " ");
		}
		if (log_timing) /* print milliseconds */
			fprintf(fp, "%04lu ", (long unsigned)tv.tv_usec / 1000);
	}
	if (daemon_test_flag(DF_LOG_HOSTNAME))
		fprintf(fp, "%s ", para_hostname());
	if (daemon_test_flag(DF_LOG_LL)) /* log loglevel */
		fprintf(fp, "(%d) ", ll);
	if (daemon_test_flag(DF_LOG_PID)) { /* log pid */
		pid_t mypid = getpid();
		fprintf(fp, "(%d) ", (int)mypid);
	}
	va_start(argp, fmt);
	vfprintf(fp, fmt, argp);
	va_end(argp);
	if (color)
		fprintf(fp, "%s", COLOR_RESET);
	if (me->post_log_hook)
		me->post_log_hook();
}