chg: make is possible to call by default an hg binary located next to chg

When a single version of hg is in use and it's in the PATH, using chg
is just a matter of calling chg.

But when there are multiple installations of hg+chg around, and hg is
referred to with an absolute path, using chg is more annoying because
it requires both changing the invocation to hg to use chg, but also
setting CHGHG.

Currently, we set HGPATH when we build chg to remove the need to set
CHGHG in the previous paragraph. But that means chg now hardcodes its
installation path, which makes the installation not relocatable. Hence
this proposal to make chg find ./hg relative to itself (as opposed to
CHGHG=./hg which find hg relative to cwd).

This only works on linux as written, but since it's opt-in, it sounds
fine.

Tested by hand, as I'm not sure how else to test this.

Differential Revision: https://phab.mercurial-scm.org/D9006

contrib/chg/Makefile

@@ -1,40 +1,43 b''
 TARGET = chg
 SRCS = chg.c hgclient.c procutil.c util.c
 OBJS = $(SRCS:.c=.o)
 
 CFLAGS ?= -O2 -Wall -Wextra -pedantic -g
 CPPFLAGS ?= -D_FORTIFY_SOURCE=2 -D_GNU_SOURCE
 override CFLAGS += -std=gnu99
 ifdef HGPATH
 override CPPFLAGS += -DHGPATH=\"$(HGPATH)\"
 endif
+ifdef HGPATHREL
+override CPPFLAGS += -DHGPATHREL=\"$(HGPATHREL)\"
+endif
 
 DESTDIR =
 PREFIX = /usr/local
 MANDIR = $(PREFIX)/share/man/man1
 
 .PHONY: all
 all: $(TARGET)
 
 $(TARGET): $(OBJS)
 	$(CC) $(LDFLAGS) -o $@ $(OBJS)
 
 chg.o: hgclient.h procutil.h util.h
 hgclient.o: hgclient.h procutil.h util.h
 procutil.o: procutil.h util.h
 util.o: util.h
 
 .PHONY: install
 install: $(TARGET)
 	install -d "$(DESTDIR)$(PREFIX)"/bin
 	install -m 755 "$(TARGET)" "$(DESTDIR)$(PREFIX)"/bin
 	install -d "$(DESTDIR)$(MANDIR)"
 	install -m 644 chg.1 "$(DESTDIR)$(MANDIR)"
 
 .PHONY: clean
 clean:
 	$(RM) $(OBJS)
 
 .PHONY: distclean
 distclean:
 	$(RM) $(OBJS) $(TARGET)

contrib/chg/README

@@ -1,32 +1,40 b''
 cHg
 ===
 
 A fast client for Mercurial command server running on Unix.
 
 Install:
 
  $ make
  $ make install
 
 Usage:
 
  $ chg help                 # show help of Mercurial
  $ alias hg=chg             # replace hg command
  $ chg --kill-chg-daemon    # terminate background server
 
 Environment variables:
 
 Although cHg tries to update environment variables, some of them cannot be
 changed after spawning the server. The following variables are specially
 handled:
 
  * configuration files are reloaded automatically by default.
  * CHGHG or HG specifies the path to the hg executable spawned as the
    background command server.
 
 The following variables are available for testing:
 
  * CHGDEBUG enables debug messages.
  * CHGSOCKNAME specifies the socket path of the background cmdserver.
  * CHGTIMEOUT specifies how many seconds chg will wait before giving up
    connecting to a cmdserver. If it is 0, chg will wait forever. Default: 60
+
+Build environment variables:
+
+ * HGPATH: the path to the hg executable to call when CHGHG and HG are not set,
+   instead of "hg"
+ * HGPATHREL=1: when CHGHG and HG are not set, the hg executable will be ./hg
+   relative to the chg executable. Only works on linux, falls back to "hg"
+   otherwise.

contrib/chg/chg.c

@@ -1,484 +1,517 b''
 /*
  * 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 "procutil.h"
 #include "util.h"
 
 #ifndef PATH_MAX
 #define PATH_MAX 4096
 #endif
 
 struct cmdserveropts {
 	char sockname[PATH_MAX];
 	char initsockname[PATH_MAX];
 	char redirectsockname[PATH_MAX];
 	size_t argsize;
 	const char **args;
 };
 
 static void initcmdserveropts(struct cmdserveropts *opts)
 {
 	memset(opts, 0, sizeof(struct cmdserveropts));
 }
 
 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)
 		abortmsgerrno("cannot create sockdir %s", sockdir);
 
 	struct stat st;
 	r = lstat(sockdir, &st);
 	if (r < 0)
 		abortmsgerrno("cannot stat %s", sockdir);
 	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);
 }
 
 /*
  * Check if a socket directory exists and is only owned by the current user.
  * Return 1 if so, 0 if not. This is used to check if XDG_RUNTIME_DIR can be
  * used or not. According to the specification [1], XDG_RUNTIME_DIR should be
  * ignored if the directory is not owned by the user with mode 0700.
  * [1]: https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
  */
 static int checkruntimedir(const char *sockdir)
 {
 	struct stat st;
 	int r = lstat(sockdir, &st);
 	if (r < 0) /* ex. does not exist */
 		return 0;
 	if (!S_ISDIR(st.st_mode)) /* ex. is a file, not a directory */
 		return 0;
 	return st.st_uid == geteuid() && (st.st_mode & 0777) == 0700;
 }
 
 static void getdefaultsockdir(char sockdir[], size_t size)
 {
 	/* by default, put socket file in secure directory
 	 * (${XDG_RUNTIME_DIR}/chg, or /${TMPDIR:-tmp}/chg$UID)
 	 * (permission of socket file may be ignored on some Unices) */
 	const char *runtimedir = getenv("XDG_RUNTIME_DIR");
 	int r;
 	if (runtimedir && checkruntimedir(runtimedir)) {
 		r = snprintf(sockdir, size, "%s/chg", runtimedir);
 	} else {
 		const char *tmpdir = getenv("TMPDIR");
 		if (!tmpdir)
 			tmpdir = "/tmp";
 		r = snprintf(sockdir, size, "%s/chg%d", tmpdir, geteuid());
 	}
 	if (r < 0 || (size_t)r >= size)
 		abortmsg("too long TMPDIR (r = %d)", r);
 }
 
 static void setcmdserveropts(struct cmdserveropts *opts)
 {
 	int r;
 	char sockdir[PATH_MAX];
 	const char *envsockname = getenv("CHGSOCKNAME");
 	if (!envsockname) {
 		getdefaultsockdir(sockdir, sizeof(sockdir));
 		preparesockdir(sockdir);
 	}
 
 	const char *basename = (envsockname) ? envsockname : sockdir;
 	const char *sockfmt = (envsockname) ? "%s" : "%s/server";
 	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->initsockname, sizeof(opts->initsockname), "%s.%u",
 	             opts->sockname, (unsigned)getpid());
 	if (r < 0 || (size_t)r >= sizeof(opts->initsockname))
 		abortmsg("too long TMPDIR or CHGSOCKNAME (r = %d)", r);
 }
 
+/* If the current program is, say, /a/b/c/chg, returns /a/b/c/hg. */
+static char *getrelhgcmd(void)
+{
+	ssize_t n;
+	char *res, *slash;
+	int maxsize = 4096;
+	res = malloc(maxsize);
+	if (res == NULL)
+		goto cleanup;
+	n = readlink("/proc/self/exe", res, maxsize);
+	if (n < 0 || n >= maxsize)
+		goto cleanup;
+	res[n] = '\0';
+	slash = strrchr(res, '/');
+	if (slash == NULL)
+		goto cleanup;
+	/* 4 is strlen("/hg") + nul byte */
+	if (slash + 4 >= res + maxsize)
+		goto cleanup;
+	memcpy(slash, "/hg", 4);
+	return res;
+ cleanup:
+	free(res);
+	return NULL;
+}
+
 static const char *gethgcmd(void)
 {
 	static const char *hgcmd = NULL;
+#ifdef HGPATHREL
+	int tryrelhgcmd = 1;
+#else
+	int tryrelhgcmd = 0;
+#endif
 	if (!hgcmd) {
 		hgcmd = getenv("CHGHG");
 		if (!hgcmd || hgcmd[0] == '\0')
 			hgcmd = getenv("HG");
+		if (tryrelhgcmd && (!hgcmd || hgcmd[0] == '\0'))
+			hgcmd = getrelhgcmd();
 		if (!hgcmd || hgcmd[0] == '\0')
 #ifdef HGPATH
 			hgcmd = (HGPATH);
 #else
 			hgcmd = "hg";
 #endif
 	}
 	return hgcmd;
 }
 
 static void execcmdserver(const struct cmdserveropts *opts)
 {
 	const char *hgcmd = gethgcmd();
 
 	const char *baseargv[] = {
 	    hgcmd,
 	    "serve",
 	    "--cmdserver",
 	    "chgunix",
 	    "--address",
 	    opts->initsockname,
 	    "--daemon-postexec",
 	    "chdir:/",
 	};
 	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));
 	if (opts->args) {
 		size_t size = sizeof(char *) * opts->argsize;
 		memcpy(argv + baseargvsize, opts->args, size);
 	}
 	argv[argsize - 1] = NULL;
 
 	const char *lc_ctype_env = getenv("LC_CTYPE");
 	if (lc_ctype_env == NULL) {
 		if (putenv("CHG_CLEAR_LC_CTYPE=") != 0)
 			abortmsgerrno("failed to putenv CHG_CLEAR_LC_CTYPE");
 	} else {
 		if (setenv("CHGORIG_LC_CTYPE", lc_ctype_env, 1) != 0) {
 			abortmsgerrno("failed to setenv CHGORIG_LC_CTYPE");
 		}
 	}
 
 	if (putenv("CHGINTERNALMARK=") != 0)
 		abortmsgerrno("failed to putenv");
 	if (execvp(hgcmd, (char **)argv) < 0)
 		abortmsgerrno("failed to exec cmdserver");
 	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;
 
 	debugmsg("try connect to %s repeatedly", opts->initsockname);
 
 	unsigned int timeoutsec = 60; /* default: 60 seconds */
 	const char *timeoutenv = getenv("CHGTIMEOUT");
 	if (timeoutenv)
 		sscanf(timeoutenv, "%u", &timeoutsec);
 
 	for (unsigned int i = 0; !timeoutsec || i < timeoutsec * 100; i++) {
 		hgclient_t *hgc = hgc_open(opts->initsockname);
 		if (hgc) {
 			debugmsg("rename %s to %s", opts->initsockname,
 			         opts->sockname);
 			int r = rename(opts->initsockname, opts->sockname);
 			if (r != 0)
 				abortmsgerrno("cannot rename");
 			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->initsockname);
 	return NULL;
 
 cleanup:
 	if (WIFEXITED(pst)) {
 		if (WEXITSTATUS(pst) == 0)
 			abortmsg("could not connect to cmdserver "
 			         "(exited with status 0)");
 		debugmsg("cmdserver exited with status %d", WEXITSTATUS(pst));
 		exit(WEXITSTATUS(pst));
 	} else if (WIFSIGNALED(pst)) {
 		abortmsg("cmdserver killed by signal %d", WTERMSIG(pst));
 	} else {
 		abortmsg("error while waiting for cmdserver");
 	}
 	return NULL;
 }
 
 /* Connect to a cmdserver. Will start a new server on demand. */
 static hgclient_t *connectcmdserver(struct cmdserveropts *opts)
 {
 	const char *sockname =
 	    opts->redirectsockname[0] ? opts->redirectsockname : opts->sockname;
 	debugmsg("try connect to %s", sockname);
 	hgclient_t *hgc = hgc_open(sockname);
 	if (hgc)
 		return hgc;
 
 	/* prevent us from being connected to an outdated server: we were
 	 * told by a server to redirect to opts->redirectsockname and that
 	 * address does not work. we do not want to connect to the server
 	 * again because it will probably tell us the same thing. */
 	if (sockname == opts->redirectsockname)
 		unlink(opts->sockname);
 
 	debugmsg("start cmdserver at %s", opts->initsockname);
 
 	pid_t pid = fork();
 	if (pid < 0)
 		abortmsg("failed to fork cmdserver process");
 	if (pid == 0) {
 		execcmdserver(opts);
 	} else {
 		hgc = retryconnectcmdserver(opts, pid);
 	}
 
 	return hgc;
 }
 
 static void killcmdserver(const struct cmdserveropts *opts)
 {
 	/* resolve config hash */
 	char *resolvedpath = realpath(opts->sockname, NULL);
 	if (resolvedpath) {
 		unlink(resolvedpath);
 		free(resolvedpath);
 	}
 }
 
 /* Run instructions sent from the server like unlink and set redirect path
  * Return 1 if reconnect is needed, otherwise 0 */
 static int runinstructions(struct cmdserveropts *opts, const char **insts)
 {
 	int needreconnect = 0;
 	if (!insts)
 		return needreconnect;
 
 	assert(insts);
 	opts->redirectsockname[0] = '\0';
 	const char **pinst;
 	for (pinst = insts; *pinst; pinst++) {
 		debugmsg("instruction: %s", *pinst);
 		if (strncmp(*pinst, "unlink ", 7) == 0) {
 			unlink(*pinst + 7);
 		} else if (strncmp(*pinst, "redirect ", 9) == 0) {
 			int r = snprintf(opts->redirectsockname,
 			                 sizeof(opts->redirectsockname), "%s",
 			                 *pinst + 9);
 			if (r < 0 || r >= (int)sizeof(opts->redirectsockname))
 				abortmsg("redirect path is too long (%d)", r);
 			needreconnect = 1;
 		} else if (strncmp(*pinst, "exit ", 5) == 0) {
 			int n = 0;
 			if (sscanf(*pinst + 5, "%d", &n) != 1)
 				abortmsg("cannot read the exit code");
 			exit(n);
 		} else if (strcmp(*pinst, "reconnect") == 0) {
 			needreconnect = 1;
 		} else {
 			abortmsg("unknown instruction: %s", *pinst);
 		}
 	}
 	return needreconnect;
 }
 
 /*
  * Test whether the command and the environment is unsupported or not.
  *
  * If any of the stdio file descriptors are not present (rare, but some tools
  * might spawn new processes without stdio instead of redirecting them to the
  * null device), then mark it as not supported because attachio won't work
  * correctly.
  *
  * The command list is not designed to cover all cases. But it's fast, and does
  * not depend on the server.
  */
 static int isunsupported(int argc, const char *argv[])
 {
 	enum { SERVE = 1,
 	       DAEMON = 2,
 	       SERVEDAEMON = SERVE | DAEMON,
 	};
 	unsigned int state = 0;
 	int i;
 	/* use fcntl to test missing stdio fds */
 	if (fcntl(STDIN_FILENO, F_GETFD) == -1 ||
 	    fcntl(STDOUT_FILENO, F_GETFD) == -1 ||
 	    fcntl(STDERR_FILENO, F_GETFD) == -1) {
 		debugmsg("stdio fds are missing");
 		return 1;
 	}
 	for (i = 0; i < argc; ++i) {
 		if (strcmp(argv[i], "--") == 0)
 			break;
 		/*
 		 * there can be false positives but no false negative
 		 * we cannot assume `serve` will always be first argument
 		 * because global options can be passed before the command name
 		 */
 		if (strcmp("serve", argv[i]) == 0)
 			state |= SERVE;
 		else if (strcmp("-d", argv[i]) == 0 ||
 		         strcmp("--daemon", argv[i]) == 0)
 			state |= DAEMON;
 	}
 	return (state & SERVEDAEMON) == SERVEDAEMON;
 }
 
 static void execoriginalhg(const char *argv[])
 {
 	debugmsg("execute original hg");
 	if (execvp(gethgcmd(), (char **)argv) < 0)
 		abortmsgerrno("failed to exec original hg");
 }
 
 int main(int argc, const char *argv[], const char *envp[])
 {
 	if (getenv("CHGDEBUG"))
 		enabledebugmsg();
 
 	if (!getenv("HGPLAIN") && isatty(fileno(stderr)))
 		enablecolor();
 
 	if (getenv("CHGINTERNALMARK"))
 		abortmsg("chg started by chg detected.\n"
 		         "Please make sure ${HG:-hg} is not a symlink or "
 		         "wrapper to chg. Alternatively, set $CHGHG to the "
 		         "path of real hg.");
 
 	if (isunsupported(argc - 1, argv + 1))
 		execoriginalhg(argv);
 
 	struct cmdserveropts opts;
 	initcmdserveropts(&opts);
 	setcmdserveropts(&opts);
 	setcmdserverargs(&opts, argc, argv);
 
 	if (argc == 2) {
 		if (strcmp(argv[1], "--kill-chg-daemon") == 0) {
 			killcmdserver(&opts);
 			return 0;
 		}
 	}
 
 	hgclient_t *hgc;
 	size_t retry = 0;
 	while (1) {
 		hgc = connectcmdserver(&opts);
 		if (!hgc)
 			abortmsg("cannot open hg client");
 		hgc_setenv(hgc, envp);
 		const char **insts = hgc_validate(hgc, argv + 1, argc - 1);
 		int needreconnect = runinstructions(&opts, insts);
 		free(insts);
 		if (!needreconnect)
 			break;
 		hgc_close(hgc);
 		if (++retry > 10)
 			abortmsg("too many redirections.\n"
 			         "Please make sure %s is not a wrapper which "
 			         "changes sensitive environment variables "
 			         "before executing hg. If you have to use a "
 			         "wrapper, wrap chg instead of hg.",
 			         gethgcmd());
 	}
 
 	setupsignalhandler(hgc_peerpid(hgc), hgc_peerpgid(hgc));
 	atexit(waitpager);
 	int exitcode = hgc_runcommand(hgc, argv + 1, argc - 1);
 	restoresignalhandler();
 	hgc_close(hgc);
 	freecmdserveropts(&opts);
 
 	return exitcode;
 }