# HG changeset patch
# User Yuya Nishihara <yuya@tcha.org>
# Date 2016-01-03 03:39:27
# Node ID 726f8d6cc324ca7f8929c640e140cb6784b8ece1
# Parent  740208f6f6af21329568acd287563bc9d437b253

chg: import frontend sources

These files are copied from
https://bitbucket.org/yuja/chg/ -r f897faa79687

diff --git a/contrib/chg/Makefile b/contrib/chg/Makefile
new file mode 100644
--- /dev/null
+++ b/contrib/chg/Makefile
@@ -0,0 +1,50 @@
+HG = hg
+
+TARGET = chg
+SRCS = chg.c hgclient.c util.c
+OBJS = $(SRCS:.c=.o)
+
+CFLAGS ?= -O2 -Wall -Wextra -pedantic -g
+CPPFLAGS ?= -D_FORTIFY_SOURCE=2
+override CFLAGS += -std=gnu99
+
+DESTDIR =
+PREFIX = /usr/local
+MANDIR = $(PREFIX)/share/man/man1
+
+CHGSOCKDIR = /tmp/chg$(shell id -u)
+CHGSOCKNAME = $(CHGSOCKDIR)/server
+
+.PHONY: all
+all: $(TARGET)
+
+$(TARGET): $(OBJS)
+	$(CC) $(LDFLAGS) -o $@ $(OBJS)
+
+chg.o: hgclient.h util.h
+hgclient.o: hgclient.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: serve
+serve:
+	[ -d $(CHGSOCKDIR) ] || ( umask 077; mkdir $(CHGSOCKDIR) )
+	$(HG) serve --cwd / --cmdserver chgunix \
+		--address $(CHGSOCKNAME) \
+		--config extensions.chgserver= \
+		--config progress.assume-tty=1 \
+		--config cmdserver.log=/dev/stderr
+
+.PHONY: clean
+clean:
+	$(RM) $(OBJS)
+
+.PHONY: distclean
+distclean:
+	$(RM) $(OBJS) $(TARGET)
diff --git a/contrib/chg/README b/contrib/chg/README
new file mode 100644
--- /dev/null
+++ b/contrib/chg/README
@@ -0,0 +1,32 @@
+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
+ $ chg --reload-chg-daemon  # reload configuration files
+
+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 if HGPLAIN or HGPLAINEXCEPT changed, but
+   some behaviors won't change correctly.
+ * 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.
diff --git a/contrib/chg/chg.1 b/contrib/chg/chg.1
new file mode 100644
--- /dev/null
+++ b/contrib/chg/chg.1
@@ -0,0 +1,44 @@
+.\"                                      Hey, EMACS: -*- nroff -*-
+.\" First parameter, NAME, should be all caps
+.\" Second parameter, SECTION, should be 1-8, maybe w/ subsection
+.\" other parameters are allowed: see man(7), man(1)
+.TH CHG 1 "March 3, 2013"
+.\" Please adjust this date whenever revising the manpage.
+.\"
+.\" Some roff macros, for reference:
+.\" .nh        disable hyphenation
+.\" .hy        enable hyphenation
+.\" .ad l      left justify
+.\" .ad b      justify to both left and right margins
+.\" .nf        disable filling
+.\" .fi        enable filling
+.\" .br        insert line break
+.\" .sp <n>    insert n+1 empty lines
+.\" for manpage-specific macros, see man(7)
+.SH NAME
+chg \- a fast client for Mercurial command server
+.SH SYNOPSIS
+.B chg
+.IR command " [" options "] [" arguments "]..."
+.br
+.SH DESCRIPTION
+The
+.B chg
+command is the wrapper for
+.B hg
+command.
+It uses the Mercurial command server to reduce start-up overhead.
+.SH OPTIONS
+This program accepts the same command line syntax as the
+.B hg
+command. Additionally it accepts the following options.
+.TP
+.B \-\-kill\-chg\-daemon
+Terminate the background command servers.
+.TP
+.B \-\-reload\-chg\-daemon
+Reload configuration files.
+.SH SEE ALSO
+.BR hg (1),
+.SH AUTHOR
+Written by Yuya Nishihara <yuya@tcha.org>.
diff --git a/contrib/chg/chg.c b/contrib/chg/chg.c
new file mode 100644
--- /dev/null
+++ b/contrib/chg/chg.c
@@ -0,0 +1,331 @@
+/*
+ * A fast client for Mercurial command server
+ *
+ * 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 <fcntl.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.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];
+};
+
+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);
+}
+
+/*
+ * Make lock file that indicates cmdserver process is about to start. Created
+ * lock file will be deleted by server. (0: success, -1: lock exists)
+ */
+static int lockcmdserver(const struct cmdserveropts *opts)
+{
+	int r;
+	char info[32];
+	r = snprintf(info, sizeof(info), "%d", getpid());
+	if (r < 0 || (size_t)r >= sizeof(info))
+		abortmsg("failed to format lock info");
+	r = symlink(info, opts->lockfile);
+	if (r < 0 && errno != EEXIST)
+		abortmsg("failed to make lock %s (errno = %d)",
+			 opts->lockfile, errno);
+	return r;
+}
+
+static void execcmdserver(const struct cmdserveropts *opts)
+{
+	const char *hgcmd = getenv("CHGHG");
+	if (!hgcmd || hgcmd[0] == '\0')
+		hgcmd = getenv("HG");
+	if (!hgcmd || hgcmd[0] == '\0')
+		hgcmd = "hg";
+
+	const char *argv[] = {
+		hgcmd,
+		"serve",
+		"--cwd", "/",
+		"--cmdserver", "chgunix",
+		"--address", opts->sockname,
+		"--daemon-pipefds", opts->lockfile,
+		"--pid-file", opts->pidfile,
+		"--config", "extensions.chgserver=",
+		/* wrap root ui so that it can be disabled/enabled by config */
+		"--config", "progress.assume-tty=1",
+		NULL,
+	};
+	if (execvp(hgcmd, (char **)argv) < 0)
+		abortmsg("failed to exec cmdserver (errno = %d)", errno);
+}
+
+/*
+ * Sleep until lock file is deleted, i.e. cmdserver process starts listening.
+ * If pid is given, it also checks if the child process fails to start.
+ */
+static void waitcmdserver(const 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++) {
+		int r;
+		struct stat lst;
+
+		r = lstat(opts->lockfile, &lst);
+		if (r < 0 && errno == ENOENT)
+			return;  /* lock file deleted by server */
+		if (r < 0)
+			goto cleanup;
+
+		if (pid > 0) {
+			/* collect zombie if child process fails to start */
+			r = waitpid(pid, &pst, WNOHANG);
+			if (r != 0)
+				goto cleanup;
+		}
+
+		nanosleep(&sleepreq, NULL);
+	}
+
+	abortmsg("timed out waiting for cmdserver %s", opts->lockfile);
+	return;
+
+cleanup:
+	if (pid > 0)
+		/* lockfile should be made by this process */
+		unlink(opts->lockfile);
+	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");
+	}
+}
+
+/* Spawn new background cmdserver */
+static void startcmdserver(const struct cmdserveropts *opts)
+{
+	debugmsg("start cmdserver at %s", opts->sockname);
+
+	if (lockcmdserver(opts) < 0) {
+		debugmsg("lock file exists, waiting...");
+		waitcmdserver(opts, 0);
+		return;
+	}
+
+	/* remove dead cmdserver socket if any */
+	unlink(opts->sockname);
+
+	pid_t pid = fork();
+	if (pid < 0)
+		abortmsg("failed to fork cmdserver process");
+	if (pid == 0) {
+		/* bypass uisetup() of pager extension */
+		int nullfd = open("/dev/null", O_WRONLY);
+		if (nullfd >= 0) {
+			dup2(nullfd, fileno(stdout));
+			close(nullfd);
+		}
+		execcmdserver(opts);
+	} else {
+		waitcmdserver(opts, pid);
+	}
+}
+
+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 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;
+
+	sigaction(SIGHUP, &sa, NULL);
+	sigaction(SIGINT, &sa, NULL);
+
+	/* terminate frontend by double SIGTERM in case of server freeze */
+	sa.sa_flags |= SA_RESETHAND;
+	sigaction(SIGTERM, &sa, NULL);
+}
+
+/* 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;
+	setcmdserveropts(&opts);
+
+	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 = hgc_open(opts.sockname);
+	if (!hgc) {
+		startcmdserver(&opts);
+		hgc = hgc_open(opts.sockname);
+	}
+	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);
+	return exitcode;
+}
diff --git a/contrib/chg/hgclient.c b/contrib/chg/hgclient.c
new file mode 100644
--- /dev/null
+++ b/contrib/chg/hgclient.c
@@ -0,0 +1,527 @@
+/*
+ * A command server client that uses Unix domain socket
+ *
+ * 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 <arpa/inet.h>  /* for ntohl(), htonl() */
+#include <assert.h>
+#include <ctype.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/un.h>
+#include <unistd.h>
+
+#include "hgclient.h"
+#include "util.h"
+
+enum {
+	CAP_GETENCODING = 0x0001,
+	CAP_RUNCOMMAND = 0x0002,
+	/* cHg extension: */
+	CAP_ATTACHIO = 0x0100,
+	CAP_CHDIR = 0x0200,
+	CAP_GETPAGER = 0x0400,
+	CAP_SETENV = 0x0800,
+};
+
+typedef struct {
+	const char *name;
+	unsigned int flag;
+} cappair_t;
+
+static const cappair_t captable[] = {
+	{"getencoding", CAP_GETENCODING},
+	{"runcommand", CAP_RUNCOMMAND},
+	{"attachio", CAP_ATTACHIO},
+	{"chdir", CAP_CHDIR},
+	{"getpager", CAP_GETPAGER},
+	{"setenv", CAP_SETENV},
+	{NULL, 0},  /* terminator */
+};
+
+typedef struct {
+	char ch;
+	char *data;
+	size_t maxdatasize;
+	size_t datasize;
+} context_t;
+
+struct hgclient_tag_ {
+	int sockfd;
+	pid_t pid;
+	context_t ctx;
+	unsigned int capflags;
+};
+
+static const size_t defaultdatasize = 4096;
+
+static void initcontext(context_t *ctx)
+{
+	ctx->ch = '\0';
+	ctx->data = malloc(defaultdatasize);
+	ctx->maxdatasize = (ctx->data) ? defaultdatasize : 0;
+	ctx->datasize = 0;
+	debugmsg("initialize context buffer with size %zu", ctx->maxdatasize);
+}
+
+static void enlargecontext(context_t *ctx, size_t newsize)
+{
+	if (newsize <= ctx->maxdatasize)
+		return;
+
+	newsize = defaultdatasize
+		* ((newsize + defaultdatasize - 1) / defaultdatasize);
+	char *p = realloc(ctx->data, newsize);
+	if (!p)
+		abortmsg("failed to allocate buffer");
+	ctx->data = p;
+	ctx->maxdatasize = newsize;
+	debugmsg("enlarge context buffer to %zu", ctx->maxdatasize);
+}
+
+static void freecontext(context_t *ctx)
+{
+	debugmsg("free context buffer");
+	free(ctx->data);
+	ctx->data = NULL;
+	ctx->maxdatasize = 0;
+	ctx->datasize = 0;
+}
+
+/* Read channeled response from cmdserver */
+static void readchannel(hgclient_t *hgc)
+{
+	assert(hgc);
+
+	ssize_t rsize = recv(hgc->sockfd, &hgc->ctx.ch, sizeof(hgc->ctx.ch), 0);
+	if (rsize != sizeof(hgc->ctx.ch))
+		abortmsg("failed to read channel");
+
+	uint32_t datasize_n;
+	rsize = recv(hgc->sockfd, &datasize_n, sizeof(datasize_n), 0);
+	if (rsize != sizeof(datasize_n))
+		abortmsg("failed to read data size");
+
+	/* datasize denotes the maximum size to write if input request */
+	hgc->ctx.datasize = ntohl(datasize_n);
+	enlargecontext(&hgc->ctx, hgc->ctx.datasize);
+
+	if (isupper(hgc->ctx.ch) && hgc->ctx.ch != 'S')
+		return;  /* assumes input request */
+
+	size_t cursize = 0;
+	while (cursize < hgc->ctx.datasize) {
+		rsize = recv(hgc->sockfd, hgc->ctx.data + cursize,
+			     hgc->ctx.datasize - cursize, 0);
+		if (rsize < 0)
+			abortmsg("failed to read data block");
+		cursize += rsize;
+	}
+}
+
+static void sendall(int sockfd, const void *data, size_t datasize)
+{
+	const char *p = data;
+	const char *const endp = p + datasize;
+	while (p < endp) {
+		ssize_t r = send(sockfd, p, endp - p, 0);
+		if (r < 0)
+			abortmsg("cannot communicate (errno = %d)", errno);
+		p += r;
+	}
+}
+
+/* Write lengh-data block to cmdserver */
+static void writeblock(const hgclient_t *hgc)
+{
+	assert(hgc);
+
+	const uint32_t datasize_n = htonl(hgc->ctx.datasize);
+	sendall(hgc->sockfd, &datasize_n, sizeof(datasize_n));
+
+	sendall(hgc->sockfd, hgc->ctx.data, hgc->ctx.datasize);
+}
+
+static void writeblockrequest(const hgclient_t *hgc, const char *chcmd)
+{
+	debugmsg("request %s, block size %zu", chcmd, hgc->ctx.datasize);
+
+	char buf[strlen(chcmd) + 1];
+	memcpy(buf, chcmd, sizeof(buf) - 1);
+	buf[sizeof(buf) - 1] = '\n';
+	sendall(hgc->sockfd, buf, sizeof(buf));
+
+	writeblock(hgc);
+}
+
+/* Build '\0'-separated list of args. argsize < 0 denotes that args are
+ * terminated by NULL. */
+static void packcmdargs(context_t *ctx, const char *const args[],
+			ssize_t argsize)
+{
+	ctx->datasize = 0;
+	const char *const *const end = (argsize >= 0) ? args + argsize : NULL;
+	for (const char *const *it = args; it != end && *it; ++it) {
+		const size_t n = strlen(*it) + 1;  /* include '\0' */
+		enlargecontext(ctx, ctx->datasize + n);
+		memcpy(ctx->data + ctx->datasize, *it, n);
+		ctx->datasize += n;
+	}
+
+	if (ctx->datasize > 0)
+		--ctx->datasize;  /* strip last '\0' */
+}
+
+/* Extract '\0'-separated list of args to new buffer, terminated by NULL */
+static const char **unpackcmdargsnul(const context_t *ctx)
+{
+	const char **args = NULL;
+	size_t nargs = 0, maxnargs = 0;
+	const char *s = ctx->data;
+	const char *e = ctx->data + ctx->datasize;
+	for (;;) {
+		if (nargs + 1 >= maxnargs) {  /* including last NULL */
+			maxnargs += 256;
+			args = realloc(args, maxnargs * sizeof(args[0]));
+			if (!args)
+				abortmsg("failed to allocate args buffer");
+		}
+		args[nargs] = s;
+		nargs++;
+		s = memchr(s, '\0', e - s);
+		if (!s)
+			break;
+		s++;
+	}
+	args[nargs] = NULL;
+	return args;
+}
+
+static void handlereadrequest(hgclient_t *hgc)
+{
+	context_t *ctx = &hgc->ctx;
+	size_t r = fread(ctx->data, sizeof(ctx->data[0]), ctx->datasize, stdin);
+	ctx->datasize = r;
+	writeblock(hgc);
+}
+
+/* Read single-line */
+static void handlereadlinerequest(hgclient_t *hgc)
+{
+	context_t *ctx = &hgc->ctx;
+	if (!fgets(ctx->data, ctx->datasize, stdin))
+		ctx->data[0] = '\0';
+	ctx->datasize = strlen(ctx->data);
+	writeblock(hgc);
+}
+
+/* Execute the requested command and write exit code */
+static void handlesystemrequest(hgclient_t *hgc)
+{
+	context_t *ctx = &hgc->ctx;
+	enlargecontext(ctx, ctx->datasize + 1);
+	ctx->data[ctx->datasize] = '\0';  /* terminate last string */
+
+	const char **args = unpackcmdargsnul(ctx);
+	if (!args[0] || !args[1])
+		abortmsg("missing command or cwd in system request");
+	debugmsg("run '%s' at '%s'", args[0], args[1]);
+	int32_t r = runshellcmd(args[0], args + 2, args[1]);
+	free(args);
+
+	uint32_t r_n = htonl(r);
+	memcpy(ctx->data, &r_n, sizeof(r_n));
+	ctx->datasize = sizeof(r_n);
+	writeblock(hgc);
+}
+
+/* Read response of command execution until receiving 'r'-esult */
+static void handleresponse(hgclient_t *hgc)
+{
+	for (;;) {
+		readchannel(hgc);
+		context_t *ctx = &hgc->ctx;
+		debugmsg("response read from channel %c, size %zu",
+			 ctx->ch, ctx->datasize);
+		switch (ctx->ch) {
+		case 'o':
+			fwrite(ctx->data, sizeof(ctx->data[0]), ctx->datasize,
+			       stdout);
+			break;
+		case 'e':
+			fwrite(ctx->data, sizeof(ctx->data[0]), ctx->datasize,
+			       stderr);
+			break;
+		case 'd':
+			/* assumes last char is '\n' */
+			ctx->data[ctx->datasize - 1] = '\0';
+			debugmsg("server: %s", ctx->data);
+			break;
+		case 'r':
+			return;
+		case 'I':
+			handlereadrequest(hgc);
+			break;
+		case 'L':
+			handlereadlinerequest(hgc);
+			break;
+		case 'S':
+			handlesystemrequest(hgc);
+			break;
+		default:
+			if (isupper(ctx->ch))
+				abortmsg("cannot handle response (ch = %c)",
+					 ctx->ch);
+		}
+	}
+}
+
+static unsigned int parsecapabilities(const char *s, const char *e)
+{
+	unsigned int flags = 0;
+	while (s < e) {
+		const char *t = strchr(s, ' ');
+		if (!t || t > e)
+			t = e;
+		const cappair_t *cap;
+		for (cap = captable; cap->flag; ++cap) {
+			size_t n = t - s;
+			if (strncmp(s, cap->name, n) == 0 &&
+			    strlen(cap->name) == n) {
+				flags |= cap->flag;
+				break;
+			}
+		}
+		s = t + 1;
+	}
+	return flags;
+}
+
+static void readhello(hgclient_t *hgc)
+{
+	readchannel(hgc);
+	context_t *ctx = &hgc->ctx;
+	if (ctx->ch != 'o')
+		abortmsg("unexpected channel of hello message (ch = %c)",
+			 ctx->ch);
+	enlargecontext(ctx, ctx->datasize + 1);
+	ctx->data[ctx->datasize] = '\0';
+	debugmsg("hello received: %s (size = %zu)", ctx->data, ctx->datasize);
+
+	const char *s = ctx->data;
+	const char *const dataend = ctx->data + ctx->datasize;
+	while (s < dataend) {
+		const char *t = strchr(s, ':');
+		if (!t || t[1] != ' ')
+			break;
+		const char *u = strchr(t + 2, '\n');
+		if (!u)
+			u = dataend;
+		if (strncmp(s, "capabilities:", t - s + 1) == 0) {
+			hgc->capflags = parsecapabilities(t + 2, u);
+		} else if (strncmp(s, "pid:", t - s + 1) == 0) {
+			hgc->pid = strtol(t + 2, NULL, 10);
+		}
+		s = u + 1;
+	}
+	debugmsg("capflags=0x%04x, pid=%d", hgc->capflags, hgc->pid);
+}
+
+static void attachio(hgclient_t *hgc)
+{
+	debugmsg("request attachio");
+	static const char chcmd[] = "attachio\n";
+	sendall(hgc->sockfd, chcmd, sizeof(chcmd) - 1);
+	readchannel(hgc);
+	context_t *ctx = &hgc->ctx;
+	if (ctx->ch != 'I')
+		abortmsg("unexpected response for attachio (ch = %c)", ctx->ch);
+
+	static const int fds[3] = {STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO};
+	struct msghdr msgh;
+	memset(&msgh, 0, sizeof(msgh));
+	struct iovec iov = {ctx->data, ctx->datasize};  /* dummy payload */
+	msgh.msg_iov = &iov;
+	msgh.msg_iovlen = 1;
+	char fdbuf[CMSG_SPACE(sizeof(fds))];
+	msgh.msg_control = fdbuf;
+	msgh.msg_controllen = sizeof(fdbuf);
+	struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msgh);
+	cmsg->cmsg_level = SOL_SOCKET;
+	cmsg->cmsg_type = SCM_RIGHTS;
+	cmsg->cmsg_len = CMSG_LEN(sizeof(fds));
+	memcpy(CMSG_DATA(cmsg), fds, sizeof(fds));
+	msgh.msg_controllen = cmsg->cmsg_len;
+	ssize_t r = sendmsg(hgc->sockfd, &msgh, 0);
+	if (r < 0)
+		abortmsg("sendmsg failed (errno = %d)", errno);
+
+	handleresponse(hgc);
+	int32_t n;
+	if (ctx->datasize != sizeof(n))
+		abortmsg("unexpected size of attachio result");
+	memcpy(&n, ctx->data, sizeof(n));
+	n = ntohl(n);
+	if (n != sizeof(fds) / sizeof(fds[0]))
+		abortmsg("failed to send fds (n = %d)", n);
+}
+
+static void chdirtocwd(hgclient_t *hgc)
+{
+	if (!getcwd(hgc->ctx.data, hgc->ctx.maxdatasize))
+		abortmsg("failed to getcwd (errno = %d)", errno);
+	hgc->ctx.datasize = strlen(hgc->ctx.data);
+	writeblockrequest(hgc, "chdir");
+}
+
+/*!
+ * Open connection to per-user cmdserver
+ *
+ * If no background server running, returns NULL.
+ */
+hgclient_t *hgc_open(const char *sockname)
+{
+	int fd = socket(AF_UNIX, SOCK_STREAM, 0);
+	if (fd < 0)
+		abortmsg("cannot create socket (errno = %d)", errno);
+
+	/* don't keep fd on fork(), so that it can be closed when the parent
+	 * process get terminated. */
+	int flags = fcntl(fd, F_GETFD);
+	if (flags < 0)
+		abortmsg("cannot get flags of socket (errno = %d)", errno);
+	if (fcntl(fd, F_SETFD, flags | FD_CLOEXEC) < 0)
+		abortmsg("cannot set flags of socket (errno = %d)", errno);
+
+	struct sockaddr_un addr;
+	addr.sun_family = AF_UNIX;
+	strncpy(addr.sun_path, sockname, sizeof(addr.sun_path));
+	addr.sun_path[sizeof(addr.sun_path) - 1] = '\0';
+
+	debugmsg("connect to %s", addr.sun_path);
+	int r = connect(fd, (struct sockaddr *)&addr, sizeof(addr));
+	if (r < 0) {
+		close(fd);
+		if (errno == ENOENT || errno == ECONNREFUSED)
+			return NULL;
+		abortmsg("cannot connect to %s (errno = %d)",
+			 addr.sun_path, errno);
+	}
+
+	hgclient_t *hgc = malloc(sizeof(hgclient_t));
+	if (!hgc)
+		abortmsg("failed to allocate hgclient object");
+	memset(hgc, 0, sizeof(*hgc));
+	hgc->sockfd = fd;
+	initcontext(&hgc->ctx);
+
+	readhello(hgc);
+	if (!(hgc->capflags & CAP_RUNCOMMAND))
+		abortmsg("insufficient capability: runcommand");
+	if (hgc->capflags & CAP_ATTACHIO)
+		attachio(hgc);
+	if (hgc->capflags & CAP_CHDIR)
+		chdirtocwd(hgc);
+
+	return hgc;
+}
+
+/*!
+ * Close connection and free allocated memory
+ */
+void hgc_close(hgclient_t *hgc)
+{
+	assert(hgc);
+	freecontext(&hgc->ctx);
+	close(hgc->sockfd);
+	free(hgc);
+}
+
+pid_t hgc_peerpid(const hgclient_t *hgc)
+{
+	assert(hgc);
+	return hgc->pid;
+}
+
+/*!
+ * Execute the specified Mercurial command
+ *
+ * @return result code
+ */
+int hgc_runcommand(hgclient_t *hgc, const char *const args[], size_t argsize)
+{
+	assert(hgc);
+
+	packcmdargs(&hgc->ctx, args, argsize);
+	writeblockrequest(hgc, "runcommand");
+	handleresponse(hgc);
+
+	int32_t exitcode_n;
+	if (hgc->ctx.datasize != sizeof(exitcode_n)) {
+		abortmsg("unexpected size of exitcode");
+	}
+	memcpy(&exitcode_n, hgc->ctx.data, sizeof(exitcode_n));
+	return ntohl(exitcode_n);
+}
+
+/*!
+ * (Re-)send client's stdio channels so that the server can access to tty
+ */
+void hgc_attachio(hgclient_t *hgc)
+{
+	assert(hgc);
+	if (!(hgc->capflags & CAP_ATTACHIO))
+		return;
+	attachio(hgc);
+}
+
+/*!
+ * Get pager command for the given Mercurial command args
+ *
+ * If no pager enabled, returns NULL. The return value becomes invalid
+ * once you run another request to hgc.
+ */
+const char *hgc_getpager(hgclient_t *hgc, const char *const args[],
+			 size_t argsize)
+{
+	assert(hgc);
+
+	if (!(hgc->capflags & CAP_GETPAGER))
+		return NULL;
+
+	packcmdargs(&hgc->ctx, args, argsize);
+	writeblockrequest(hgc, "getpager");
+	handleresponse(hgc);
+
+	if (hgc->ctx.datasize < 1 || hgc->ctx.data[0] == '\0')
+		return NULL;
+	enlargecontext(&hgc->ctx, hgc->ctx.datasize + 1);
+	hgc->ctx.data[hgc->ctx.datasize] = '\0';
+	return hgc->ctx.data;
+}
+
+/*!
+ * Update server's environment variables
+ *
+ * @param envp  list of environment variables in "NAME=VALUE" format,
+ *              terminated by NULL.
+ */
+void hgc_setenv(hgclient_t *hgc, const char *const envp[])
+{
+	assert(hgc && envp);
+	if (!(hgc->capflags & CAP_SETENV))
+		return;
+	packcmdargs(&hgc->ctx, envp, /*argsize*/ -1);
+	writeblockrequest(hgc, "setenv");
+}
diff --git a/contrib/chg/hgclient.h b/contrib/chg/hgclient.h
new file mode 100644
--- /dev/null
+++ b/contrib/chg/hgclient.h
@@ -0,0 +1,29 @@
+/*
+ * A command server client that uses Unix domain socket
+ *
+ * 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.
+ */
+
+#ifndef HGCLIENT_H_
+#define HGCLIENT_H_
+
+#include <sys/types.h>
+
+struct hgclient_tag_;
+typedef struct hgclient_tag_ hgclient_t;
+
+hgclient_t *hgc_open(const char *sockname);
+void hgc_close(hgclient_t *hgc);
+
+pid_t hgc_peerpid(const hgclient_t *hgc);
+
+int hgc_runcommand(hgclient_t *hgc, const char *const args[], size_t argsize);
+void hgc_attachio(hgclient_t *hgc);
+const char *hgc_getpager(hgclient_t *hgc, const char *const args[],
+			 size_t argsize);
+void hgc_setenv(hgclient_t *hgc, const char *const envp[]);
+
+#endif  /* HGCLIENT_H_ */
diff --git a/contrib/chg/util.c b/contrib/chg/util.c
new file mode 100644
--- /dev/null
+++ b/contrib/chg/util.c
@@ -0,0 +1,121 @@
+/*
+ * Utility functions
+ *
+ * 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 <signal.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "util.h"
+
+void abortmsg(const char *fmt, ...)
+{
+	va_list args;
+	va_start(args, fmt);
+	fputs("\033[1;31mchg: abort: ", stderr);
+	vfprintf(stderr, fmt, args);
+	fputs("\033[m\n", stderr);
+	va_end(args);
+
+	exit(255);
+}
+
+static int debugmsgenabled = 0;
+
+void enabledebugmsg(void)
+{
+	debugmsgenabled = 1;
+}
+
+void debugmsg(const char *fmt, ...)
+{
+	if (!debugmsgenabled)
+		return;
+
+	va_list args;
+	va_start(args, fmt);
+	fputs("\033[1;30mchg: debug: ", stderr);
+	vfprintf(stderr, fmt, args);
+	fputs("\033[m\n", stderr);
+	va_end(args);
+}
+
+/*
+ * Execute a shell command in mostly the same manner as system(), with the
+ * give environment variables, after chdir to the given cwd. Returns a status
+ * code compatible with the Python subprocess module.
+ */
+int runshellcmd(const char *cmd, const char *envp[], const char *cwd)
+{
+	enum { F_SIGINT = 1, F_SIGQUIT = 2, F_SIGMASK = 4, F_WAITPID = 8 };
+	unsigned int doneflags = 0;
+	int status = 0;
+	struct sigaction newsa, oldsaint, oldsaquit;
+	sigset_t oldmask;
+
+	/* block or mask signals just as system() does */
+	newsa.sa_handler = SIG_IGN;
+	newsa.sa_flags = 0;
+	if (sigemptyset(&newsa.sa_mask) < 0)
+		goto done;
+	if (sigaction(SIGINT, &newsa, &oldsaint) < 0)
+		goto done;
+	doneflags |= F_SIGINT;
+	if (sigaction(SIGQUIT, &newsa, &oldsaquit) < 0)
+		goto done;
+	doneflags |= F_SIGQUIT;
+
+	if (sigaddset(&newsa.sa_mask, SIGCHLD) < 0)
+		goto done;
+	if (sigprocmask(SIG_BLOCK, &newsa.sa_mask, &oldmask) < 0)
+		goto done;
+	doneflags |= F_SIGMASK;
+
+	pid_t pid = fork();
+	if (pid < 0)
+		goto done;
+	if (pid == 0) {
+		sigaction(SIGINT, &oldsaint, NULL);
+		sigaction(SIGQUIT, &oldsaquit, NULL);
+		sigprocmask(SIG_SETMASK, &oldmask, NULL);
+		if (cwd && chdir(cwd) < 0)
+			_exit(127);
+		const char *argv[] = {"sh", "-c", cmd, NULL};
+		if (envp) {
+			execve("/bin/sh", (char **)argv, (char **)envp);
+		} else {
+			execv("/bin/sh", (char **)argv);
+		}
+		_exit(127);
+	} else {
+		if (waitpid(pid, &status, 0) < 0)
+			goto done;
+		doneflags |= F_WAITPID;
+	}
+
+done:
+	if (doneflags & F_SIGINT)
+		sigaction(SIGINT, &oldsaint, NULL);
+	if (doneflags & F_SIGQUIT)
+		sigaction(SIGQUIT, &oldsaquit, NULL);
+	if (doneflags & F_SIGMASK)
+		sigprocmask(SIG_SETMASK, &oldmask, NULL);
+
+	/* no way to report other errors, use 127 (= shell termination) */
+	if (!(doneflags & F_WAITPID))
+		return 127;
+	if (WIFEXITED(status))
+		return WEXITSTATUS(status);
+	if (WIFSIGNALED(status))
+		return -WTERMSIG(status);
+	return 127;
+}
diff --git a/contrib/chg/util.h b/contrib/chg/util.h
new file mode 100644
--- /dev/null
+++ b/contrib/chg/util.h
@@ -0,0 +1,24 @@
+/*
+ * Utility functions
+ *
+ * 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.
+ */
+
+#ifndef UTIL_H_
+#define UTIL_H_
+
+#ifdef __GNUC__
+#define PRINTF_FORMAT_ __attribute__((format(printf, 1, 2)))
+#endif
+
+void abortmsg(const char *fmt, ...) PRINTF_FORMAT_;
+
+void enabledebugmsg(void);
+void debugmsg(const char *fmt, ...) PRINTF_FORMAT_;
+
+int runshellcmd(const char *cmd, const char *envp[], const char *cwd);
+
+#endif  /* UTIL_H_ */