README


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cgit - CGI for Git
==================

This is an attempt to create a fast web interface for the Git SCM, using a
built-in cache to decrease server I/O pressure.

Installation
------------

Building cgit involves building a proper version of Git. How to do this
depends on how you obtained the cgit sources:

a) If you're working in a cloned cgit repository, you first need to
initialize and update the Git submodule:

    $ git submodule init     # register the Git submodule in .git/config
    $ $EDITOR .git/config    # if you want to specify a different url for git
    $ git submodule update   # clone/fetch and checkout correct git version

b) If you're building from a cgit tarball, you can download a proper git
version like this:

    $ make get-git

When either a) or b) has been performed, you can build and install cgit like
this:

    $ make
    $ sudo make install

This will install `cgit.cgi` and `cgit.css` into `/var/www/htdocs/cgit`. You
can configure this location (and a few other things) by providing a `cgit.conf`
file (see the Makefile for details).

If you'd like to compile without Lua support, you may use:

    $ make NO_LUA=1

And if you'd like to specify a Lua implementation, you may use:

    $ make LUA_PKGCONFIG=lua5.1

If this is not specified, the Lua implementation will be auto-detected,
preferring LuaJIT if many are present. Acceptable values are generally "lua",
"luajit", "lua5.1", and "lua5.2".


Dependencies
------------

* libzip
* libcrypto (OpenSSL)
* libssl (OpenSSL)
* optional: luajit or lua, most reliably used when pkg-config is available

Apache configuration
--------------------

A new `Directory` section must probably be added for cgit, possibly something
like this:

    <Directory "/var/www/htdocs/cgit/">
        AllowOverride None
        Options +ExecCGI
        Order allow,deny
        Allow from all
    </Directory>


Runtime configuration
---------------------

The file `/etc/cgitrc` is read by cgit before handling a request. In addition
to runtime parameters, this file may also contain a list of repositories
displayed by cgit (see `cgitrc.5.txt` for further details).

The cache
---------

When cgit is invoked it looks for a cache file matching the request and
returns it to the client. If no such cache file exists (or if it has expired),
the content for the request is written into the proper cache file before the
file is returned.

If the cache file has expired but cgit is unable to obtain a lock for it, the
stale cache file is returned to the client. This is done to favour page
throughput over page freshness.

The generated content contains the complete response to the client, including
the HTTP headers `Modified` and `Expires`.

Online presence
---------------

* The cgit homepage is hosted by cgit at <http://git.zx2c4.com/cgit/about/>

* Patches, bug reports, discussions and support should go to the cgit
  mailing list: <cgit@lists.zx2c4.com>. To sign up, visit
  <http://lists.zx2c4.com/mailman/listinfo/cgit>
/* Copyright (C) 2018  Curtis McEnroe <june@causal.agency>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <err.h>
#include <poll.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <sysexits.h>
#include <unistd.h>
#include <errno.h>

#include "chat.h"

static struct {
	bool wait;
	bool pipe;
	int fd;
} spawn;

void eventWait(const char *argv[static 2]) {
	uiHide();
	pid_t pid = fork();
	if (pid < 0) err(EX_OSERR, "fork");
	if (!pid) {
		execvp(argv[0], (char *const *)argv);
		err(EX_CONFIG, "%s", argv[0]);
	}
	spawn.wait = true;
}

void eventPipe(const char *argv[static 2]) {
	if (spawn.pipe) {
		uiLog(TagStatus, UIHot, L"event: existing pipe");
		return;
	}

	int rw[2];
	int error = pipe(rw);
	if (error) err(EX_OSERR, "pipe");

	pid_t pid = fork();
	if (pid < 0) err(EX_OSERR, "fork");
	if (!pid) {
		close(rw[0]);
		close(STDIN_FILENO);
		dup2(rw[1], STDOUT_FILENO);
		dup2(rw[1], STDERR_FILENO);
		close(rw[1]);
		execvp(argv[0], (char *const *)argv);
		perror(argv[0]);
		exit(EX_CONFIG);
	}

	close(rw[1]);
	spawn.fd = rw[0];
	spawn.pipe = true;
}

static void pipeRead(void) {
	char buf[256];
	ssize_t len = read(spawn.fd, buf, sizeof(buf) - 1);
	if (len < 0) err(EX_IOERR, "read");
	if (len) {
		buf[len] = '\0';
		len = strcspn(buf, "\n");
		uiFmt(TagStatus, UIHot, "event: %.*s", (int)len, buf);
	} else {
		close(spawn.fd);
		spawn.pipe = false;
	}
}

static void sigchld(int sig) {
	(void)sig;
	int status;
	pid_t pid = wait(&status);
	if (pid < 0) err(EX_OSERR, "wait");
	if (WIFEXITED(status) && WEXITSTATUS(status)) {
		uiFmt(TagStatus, UIHot, "event: exit %d", WEXITSTATUS(status));
	} else if (WIFSIGNALED(status)) {
		uiFmt(TagStatus, UIHot, "event: signal %d", WTERMSIG(status));
	}
	spawn.wait = false;
}

static void sigint(int sig) {
	(void)sig;
	input(TagStatus, "/quit");
	uiExit();
	exit(EX_OK);
}

void eventLoop(int ui, int irc) {
	signal(SIGINT, sigint);
	signal(SIGCHLD, sigchld);

	struct pollfd fds[3] = {
		{ irc, POLLIN, 0 },
		{ ui, POLLIN, 0 },
		{ -1, POLLIN, 0 },
	};
	for (;;) {
		nfds_t nfds = 2;
		if (spawn.wait) nfds = 1;
		if (spawn.pipe) {
			fds[2].fd = spawn.fd;
			nfds = 3;
		}

		int ready = poll(fds, nfds, -1);
		if (ready < 0) {
			if (errno != EINTR) err(EX_IOERR, "poll");
			uiRead();
			uiDraw();
			continue;
		}

		if (fds[0].revents) ircRead();
		if (nfds > 1 && fds[1].revents) uiRead();
		if (nfds > 2 && fds[2].revents) pipeRead();

		if (nfds > 1) uiDraw();
	}
}