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.


Repository layout
-----------------

    source/      the C sources, the build fragment and the version script
    libraries/   the bundled Git tree, tracked as a submodule
    assets/      cgit.css, cgit.js and the images cgit serves
    extensions/  optional runtime filter scripts
    examples/    a commented cgitrc, git hooks and web server configs
    tools/       developer tooling (preview server and release build)
    tests/       the test suite
    build/       everything the build generates, and not tracked in git


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).

Lua is optional and only powers the lua: filter extensions (authentication,
email and commit-message filters in extensions/). A plain build auto-detects a
Lua through pkg-config, preferring LuaJIT, and falls back to a Lua-less binary
when none is found. Acceptable values are generally "luajit", "lua", "lua5.4",
"lua5.3", "lua5.2" and "lua5.1".

To pin an implementation:

    $ make LUA_PKGCONFIG=lua5.4

To build without Lua, so the binary needs no Lua at runtime:

    $ make NO_LUA=1


Previewing locally
------------------

cgit is a CGI program, so trying it out normally means configuring a web server.
For development there is a small dependency-free preview server at
`tools/serve.py` that runs the built binary and serves the static assets. It
needs only Python 3.

    $ python3 tools/serve.py --config /path/to/cgitrc --port 8080

It is a development aid and is not meant to face the internet.


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

* zlib
* optional: luajit or lua, most reliably used when pkg-config is available

cgit builds without OpenSSL or libcurl, so no development packages for those are
needed.


Web server configuration
------------------------

cgit is a CGI program. Complete, commented configurations for nginx, Apache and
lighttpd live in `examples/servers/`, each explaining how that server routes
requests to the binary and serves the static assets off disk.


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). A fully commented starting
point with every option at its default is in `examples/cgitrc`.


Securing an instance
--------------------

A public instance needs a few deliberate choices, all set in cgitrc and
documented in `cgitrc.5.txt`.

* Keep private repositories out of `scan-path`, or set `strict-export` to a
  marker filename so only repositories that contain it are published.

* Gate the whole instance behind a login with `auth-filter`. Two example filters
  ship in `extensions/`, `auth-inline.lua` and `auth-file.lua`.

* Terminate TLS at the web server in front of cgit.

* The example configs in `examples/servers/` set a Content-Security-Policy and
  related headers at the web server, where they also cover the static assets.

* `max-blob-size` bounds how much a single request reads into memory, and
  defaults to 10 MB.

* Leave `enable-cache-list` off, since it exposes the cache path and the URLs
  other visitors requested.

* Build the deployed binary with the hardening flags via
  `tools/release-build.sh`.


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`.