chg: extract gethgcmd logic to a function

gethgcmd is to get original hg (not chg) binary name. This patch extracts
the logic from execcmdserver to make it available for the following patch.

contrib/chg/chg.c

@@ -1,475 +1,484
 /*
  * A fast client for Mercurial command server
  *
  * Copyright (c) 2011 Yuya Nishihara <[e-mail]>
  *
  * 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 <fcntl.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/file.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <sys/un.h>
 #include <sys/wait.h>
 #include <time.h>
 #include <unistd.h>
 
 #include "hgclient.h"
 #include "util.h"
 
 #ifndef UNIX_PATH_MAX
 #define UNIX_PATH_MAX (sizeof(((struct sockaddr_un *)NULL)->sun_path))
 #endif
 
 struct cmdserveropts {
 	char sockname[UNIX_PATH_MAX];
 	char lockfile[UNIX_PATH_MAX];
 	char pidfile[UNIX_PATH_MAX];
 	size_t argsize;
 	const char **args;
 	int lockfd;
 };
 
 static void initcmdserveropts(struct cmdserveropts *opts) {
 	memset(opts, 0, sizeof(struct cmdserveropts));
 	opts->lockfd = -1;
 }
 
 static void freecmdserveropts(struct cmdserveropts *opts) {
 	free(opts->args);
 	opts->args = NULL;
 	opts->argsize = 0;
 }
 
 /*
  * Test if an argument is a sensitive flag that should be passed to the server.
  * Return 0 if not, otherwise the number of arguments starting from the current
  * one that should be passed to the server.
  */
 static size_t testsensitiveflag(const char *arg)
 {
 	static const struct {
 		const char *name;
 		size_t narg;
 	} flags[] = {
 		{"--config", 1},
 		{"--cwd", 1},
 		{"--repo", 1},
 		{"--repository", 1},
 		{"--traceback", 0},
 		{"-R", 1},
 	};
 	size_t i;
 	for (i = 0; i < sizeof(flags) / sizeof(flags[0]); ++i) {
 		size_t len = strlen(flags[i].name);
 		size_t narg = flags[i].narg;
 		if (memcmp(arg, flags[i].name, len) == 0) {
 			if (arg[len] == '\0') {  /* --flag (value) */
 				return narg + 1;
 			} else if (arg[len] == '=' && narg > 0) {  /* --flag=value */
 				return 1;
 			} else if (flags[i].name[1] != '-') {  /* short flag */
 				return 1;
 			}
 		}
 	}
 	return 0;
 }
 
 /*
  * Parse argv[] and put sensitive flags to opts->args
  */
 static void setcmdserverargs(struct cmdserveropts *opts,
 			     int argc, const char *argv[])
 {
 	size_t i, step;
 	opts->argsize = 0;
 	for (i = 0, step = 1; i < (size_t)argc; i += step, step = 1) {
 		if (!argv[i])
 			continue;  /* pass clang-analyse */
 		if (strcmp(argv[i], "--") == 0)
 			break;
 		size_t n = testsensitiveflag(argv[i]);
 		if (n == 0 || i + n > (size_t)argc)
 			continue;
 		opts->args = reallocx(opts->args,
 				      (n + opts->argsize) * sizeof(char *));
 		memcpy(opts->args + opts->argsize, argv + i,
 		       sizeof(char *) * n);
 		opts->argsize += n;
 		step = n;
 	}
 }
 
 static void preparesockdir(const char *sockdir)
 {
 	int r;
 	r = mkdir(sockdir, 0700);
 	if (r < 0 && errno != EEXIST)
 		abortmsg("cannot create sockdir %s (errno = %d)",
 			 sockdir, errno);
 
 	struct stat st;
 	r = lstat(sockdir, &st);
 	if (r < 0)
 		abortmsg("cannot stat %s (errno = %d)", sockdir, errno);
 	if (!S_ISDIR(st.st_mode))
 		abortmsg("cannot create sockdir %s (file exists)", sockdir);
 	if (st.st_uid != geteuid() || st.st_mode & 0077)
 		abortmsg("insecure sockdir %s", sockdir);
 }
 
 static void setcmdserveropts(struct cmdserveropts *opts)
 {
 	int r;
 	char sockdir[UNIX_PATH_MAX];
 	const char *envsockname = getenv("CHGSOCKNAME");
 	if (!envsockname) {
 		/* by default, put socket file in secure directory
 		 * (permission of socket file may be ignored on some Unices) */
 		const char *tmpdir = getenv("TMPDIR");
 		if (!tmpdir)
 			tmpdir = "/tmp";
 		r = snprintf(sockdir, sizeof(sockdir), "%s/chg%d",
 			     tmpdir, geteuid());
 		if (r < 0 || (size_t)r >= sizeof(sockdir))
 			abortmsg("too long TMPDIR (r = %d)", r);
 		preparesockdir(sockdir);
 	}
 
 	const char *basename = (envsockname) ? envsockname : sockdir;
 	const char *sockfmt = (envsockname) ? "%s" : "%s/server";
 	const char *lockfmt = (envsockname) ? "%s.lock" : "%s/lock";
 	const char *pidfmt = (envsockname) ? "%s.pid" : "%s/pid";
 	r = snprintf(opts->sockname, sizeof(opts->sockname), sockfmt, basename);
 	if (r < 0 || (size_t)r >= sizeof(opts->sockname))
 		abortmsg("too long TMPDIR or CHGSOCKNAME (r = %d)", r);
 	r = snprintf(opts->lockfile, sizeof(opts->lockfile), lockfmt, basename);
 	if (r < 0 || (size_t)r >= sizeof(opts->lockfile))
 		abortmsg("too long TMPDIR or CHGSOCKNAME (r = %d)", r);
 	r = snprintf(opts->pidfile, sizeof(opts->pidfile), pidfmt, basename);
 	if (r < 0 || (size_t)r >= sizeof(opts->pidfile))
 		abortmsg("too long TMPDIR or CHGSOCKNAME (r = %d)", r);
 }
 
 /*
  * Acquire a file lock that indicates a client is trying to start and connect
  * to a server, before executing a command. The lock is released upon exit or
  * explicit unlock. Will block if the lock is held by another process.
  */
 static void lockcmdserver(struct cmdserveropts *opts)
 {
 	if (opts->lockfd == -1) {
 		opts->lockfd = open(opts->lockfile, O_RDWR | O_CREAT | O_NOFOLLOW, 0600);
 		if (opts->lockfd == -1)
 			abortmsg("cannot create lock file %s", opts->lockfile);
 	}
 	int r = flock(opts->lockfd, LOCK_EX);
 	if (r == -1)
 		abortmsg("cannot acquire lock");
 }
 
 /*
  * Release the file lock held by calling lockcmdserver. Will do nothing if
  * lockcmdserver is not called.
  */
 static void unlockcmdserver(struct cmdserveropts *opts)
 {
 	if (opts->lockfd == -1)
 		return;
 	flock(opts->lockfd, LOCK_UN);
 	close(opts->lockfd);
 	opts->lockfd = -1;
 }
 
-static void execcmdserver(const struct cmdserveropts *opts)
+static const char *gethgcmd(void)
 {
-	const char *hgcmd = getenv("CHGHG");
+	static const char *hgcmd = NULL;
+	if (!hgcmd) {
+		hgcmd = getenv("CHGHG");
 	if (!hgcmd || hgcmd[0] == '\0')
 		hgcmd = getenv("HG");
 	if (!hgcmd || hgcmd[0] == '\0')
 		hgcmd = "hg";
+	}
+	return hgcmd;
+}
+
+static void execcmdserver(const struct cmdserveropts *opts)
+{
+	const char *hgcmd = gethgcmd();
 
 	const char *baseargv[] = {
 		hgcmd,
 		"serve",
 		"--cwd", "/",
 		"--cmdserver", "chgunix",
 		"--address", opts->sockname,
 		"--daemon-postexec", "none",
 		"--pid-file", opts->pidfile,
 		"--config", "extensions.chgserver=",
 		/* wrap root ui so that it can be disabled/enabled by config */
 		"--config", "progress.assume-tty=1",
 	};
 	size_t baseargvsize = sizeof(baseargv) / sizeof(baseargv[0]);
 	size_t argsize = baseargvsize + opts->argsize + 1;
 
 	const char **argv = mallocx(sizeof(char *) * argsize);
 	memcpy(argv, baseargv, sizeof(baseargv));
 	memcpy(argv + baseargvsize, opts->args, sizeof(char *) * opts->argsize);
 	argv[argsize - 1] = NULL;
 
 	if (execvp(hgcmd, (char **)argv) < 0)
 		abortmsg("failed to exec cmdserver (errno = %d)", errno);
 	free(argv);
 }
 
 /* Retry until we can connect to the server. Give up after some time. */
 static hgclient_t *retryconnectcmdserver(struct cmdserveropts *opts, pid_t pid)
 {
 	static const struct timespec sleepreq = {0, 10 * 1000000};
 	int pst = 0;
 
 	for (unsigned int i = 0; i < 10 * 100; i++) {
 		hgclient_t *hgc = hgc_open(opts->sockname);
 		if (hgc)
 			return hgc;
 
 		if (pid > 0) {
 			/* collect zombie if child process fails to start */
 			int r = waitpid(pid, &pst, WNOHANG);
 			if (r != 0)
 				goto cleanup;
 		}
 
 		nanosleep(&sleepreq, NULL);
 	}
 
 	abortmsg("timed out waiting for cmdserver %s", opts->sockname);
 	return NULL;
 
 cleanup:
 	if (WIFEXITED(pst)) {
 		abortmsg("cmdserver exited with status %d", WEXITSTATUS(pst));
 	} else if (WIFSIGNALED(pst)) {
 		abortmsg("cmdserver killed by signal %d", WTERMSIG(pst));
 	} else {
 		abortmsg("error white waiting cmdserver");
 	}
 	return NULL;
 }
 
 /* Connect to a cmdserver. Will start a new server on demand. */
 static hgclient_t *connectcmdserver(struct cmdserveropts *opts)
 {
 	hgclient_t *hgc = hgc_open(opts->sockname);
 	if (hgc)
 		return hgc;
 
 	lockcmdserver(opts);
 	hgc = hgc_open(opts->sockname);
 	if (hgc) {
 		unlockcmdserver(opts);
 		debugmsg("cmdserver is started by another process");
 		return hgc;
 	}
 
 	debugmsg("start cmdserver at %s", opts->sockname);
 
 	pid_t pid = fork();
 	if (pid < 0)
 		abortmsg("failed to fork cmdserver process");
 	if (pid == 0) {
 		/* do not leak lockfd to hg */
 		close(opts->lockfd);
 		/* bypass uisetup() of pager extension */
 		int nullfd = open("/dev/null", O_WRONLY);
 		if (nullfd >= 0) {
 			dup2(nullfd, fileno(stdout));
 			close(nullfd);
 		}
 		execcmdserver(opts);
 	} else {
 		hgc = retryconnectcmdserver(opts, pid);
 	}
 
 	unlockcmdserver(opts);
 	return hgc;
 }
 
 static void killcmdserver(const struct cmdserveropts *opts, int sig)
 {
 	FILE *fp = fopen(opts->pidfile, "r");
 	if (!fp)
 		abortmsg("cannot open %s (errno = %d)", opts->pidfile, errno);
 	int pid = 0;
 	int n = fscanf(fp, "%d", &pid);
 	fclose(fp);
 	if (n != 1 || pid <= 0)
 		abortmsg("cannot read pid from %s", opts->pidfile);
 
 	if (kill((pid_t)pid, sig) < 0) {
 		if (errno == ESRCH)
 			return;
 		abortmsg("cannot kill %d (errno = %d)", pid, errno);
 	}
 }
 
 static pid_t peerpid = 0;
 
 static void forwardsignal(int sig)
 {
 	assert(peerpid > 0);
 	if (kill(peerpid, sig) < 0)
 		abortmsg("cannot kill %d (errno = %d)", peerpid, errno);
 	debugmsg("forward signal %d", sig);
 }
 
 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:
 	abortmsg("failed to handle stop signal (errno = %d)", errno);
 }
 
 static void setupsignalhandler(pid_t pid)
 {
 	if (pid <= 0)
 		return;
 	peerpid = pid;
 
 	struct sigaction sa;
 	memset(&sa, 0, sizeof(sa));
 	sa.sa_handler = forwardsignal;
 	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_flags |= SA_RESETHAND;
 	if (sigaction(SIGTERM, &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;
 
 	return;
 
 error:
 	abortmsg("failed to set up signal handlers (errno = %d)", errno);
 }
 
 /* This implementation is based on hgext/pager.py (pre 369741ef7253) */
 static void setuppager(hgclient_t *hgc, const char *const args[],
 		       size_t argsize)
 {
 	const char *pagercmd = hgc_getpager(hgc, args, argsize);
 	if (!pagercmd)
 		return;
 
 	int pipefds[2];
 	if (pipe(pipefds) < 0)
 		return;
 	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]);
 		hgc_attachio(hgc);  /* reattach to pager */
 		return;
 	} else {
 		dup2(pipefds[0], fileno(stdin));
 		close(pipefds[0]);
 		close(pipefds[1]);
 
 		int r = execlp("/bin/sh", "/bin/sh", "-c", pagercmd, NULL);
 		if (r < 0) {
 			abortmsg("cannot start pager '%s' (errno = %d)",
 				 pagercmd, errno);
 		}
 		return;
 	}
 
 error:
 	close(pipefds[0]);
 	close(pipefds[1]);
 	abortmsg("failed to prepare pager (errno = %d)", errno);
 }
 
 int main(int argc, const char *argv[], const char *envp[])
 {
 	if (getenv("CHGDEBUG"))
 		enabledebugmsg();
 
 	struct cmdserveropts opts;
 	initcmdserveropts(&opts);
 	setcmdserveropts(&opts);
 	setcmdserverargs(&opts, argc, argv);
 
 	if (argc == 2) {
 		int sig = 0;
 		if (strcmp(argv[1], "--kill-chg-daemon") == 0)
 			sig = SIGTERM;
 		if (strcmp(argv[1], "--reload-chg-daemon") == 0)
 			sig = SIGHUP;
 		if (sig > 0) {
 			killcmdserver(&opts, sig);
 			return 0;
 		}
 	}
 
 	hgclient_t *hgc = connectcmdserver(&opts);
 	if (!hgc)
 		abortmsg("cannot open hg client");
 
 	setupsignalhandler(hgc_peerpid(hgc));
 	hgc_setenv(hgc, envp);
 	setuppager(hgc, argv + 1, argc - 1);
 	int exitcode = hgc_runcommand(hgc, argv + 1, argc - 1);
 	hgc_close(hgc);
 	freecmdserveropts(&opts);
 	return exitcode;
 }