gmid/README.md

# gmid

gmid is a fast Gemini server written with security in mind.  I
initially wrote it to serve static files, but it has grown into a
featureful server.


## Features

(random order)

 - sandboxed by default on OpenBSD, Linux and FreeBSD
 - reconfiguration: reload the running configuration without
   interruption
 - automatic redirect/error pages (see `block return`)
 - IRI support (RFC3987)
 - automatic certificate generation for config-less mode
 - reverse proxying
 - CGI and FastCGI support
 - virtual hosts
 - location rules
 - event-based asynchronous I/O model
 - low memory footprint
 - small codebase, easily hackable


## Internationalisation (IRIs, UNICODE, punycode, all that stuff)

Even thought the current Gemini specification doesn't mention anything
in this regard, I do think these are important things and so I tried
to implement them in the most user-friendly way I could think of.

For starters, gmid has full support for IRI (RFC3987 —
Internationalized Resource Identifiers).  IRIs are a superset of URIs,
so there aren't incompatibilities with URI-only clients.

There is full support also for punycode.  In theory, the user doesn't
even need to know that punycode is a thing.  The hostname in the
configuration file can (and must be) in the decoded form (e.g. `naïve`
and not `xn--nave-6pa`), gmid will do the rest.

The only missing piece is UNICODE normalisation of the IRI path: gmid
doesn't do that (yet).


## Configuration

gmid has a rich configuration file, heavily inspired by OpenBSD'
httpd, with every detail carefully documented in the manpage.  Here's
a minimal example of a config file:

```conf
server "example.com" {
	cert "/path/to/cert.pem"
	key  "/path/to/key.pem"
	root "/var/gemini/example.com"
}
```

and a slightly more complex one

```conf
ipv6 on     # enable ipv6

# define a macro
cert_root = "/path/to/keys"

server "example.com" {
	alias "foobar.com"

	cert $cert_root "/example.com.crt"
	key  $cert_root "/example.com.pem"
	root "/var/gemini/example.com"

	# lang for text/gemini files
	lang "en"

	# execute CGI scripts in /cgi/
	cgi "/cgi/*"

	# only for locations that matches /files/*
	location "/files/*" {
		# generate directory listings
		auto index on
	}

	location "/repo/*" {
		# change the index file name
		index "README.gmi"
		lang "it"
	}
}
```


## Building

gmid depends on a POSIX libc, libevent2, OpenSSL/LibreSSL and libtls
(provided either by LibreSSL or libretls).  At build time, yacc (or
GNU bison) is also needed.

The build is as simple as

    ./configure
    make

or `make static` to build a statically-linked executable.

If the configure scripts fails to pick up something, please open an
issue or notify me via email.

To install execute:

    make install

Please keep in mind that the master branch, from time to time, may be
accidentally broken on some platforms.  gmid is developed primarily on
OpenBSD/amd64 and commits on the master branch don't get always tested
in other OSes.  Before tagging a release however, a comprehensive
testing on various platform is done to ensure that everything is
working as intended.


### Docker

If you have trouble installing LibreSSL or libretls, in `contrib`
there's a sample Dockerfile.  See [the contrib page][contrib-page] for
more information.

[contrib-page]: https://gmid.omarpolo.com/contrib.html#dockerfile

### Local libretls

This is **NOT** recommended, please try to port LibreSSL/LibreTLS to
your distribution of choice or use docker instead.

However, it's possible to statically-link `gmid` to locally-installed
libretls quite easily.  (It's how I test gmid on Fedora, for instance)

Let's say you have compiled and installed libretls in `$LIBRETLS`,
then you can build `gmid` with

    ./configure CFLAGS="-I$LIBRETLS/include" \
                LDFLAGS="$LIBRETLS/lib/libtls.a -lssl -lcrypto -lpthread -levent"
    make

### Testing

Execute

    make regress

to start the suite.  Keep in mind that the regression tests will
create files inside the `regress` directory and bind the 10965 port.


## Architecture/Security considerations

gmid is composed by four processes: the parent process, the logger,
the listener and the executor.  The parent process is the only one
that doesn't drop privileges, but all it does is to wait for a SIGHUP
to reload the configuration and spawn a new generation of children
process.  The logger process gathers the logs and prints 'em to
stderr or syslog (for the time being.)  The listener process is the
only one that needs internet access and is sandboxed by default.  The
executor process exists only to fork and execute CGI scripts, and
optionally to connect to FastCGI applications.

On OpenBSD the processes are all `pledge(2)`d and `unveil(2)`ed.

On FreeBSD, the listener and logger process are sandboxed with `capsicum(4)`.

On Linux, a `seccomp(2)` filter is installed in the listener to allow
only certain syscalls, see [sandbox.c](sandbox.c) for more information
about the BPF program.  If available, landlock is used to limit the
portion of the file system gmid can access (requires linux 5.13+.)

In any case, it's advisable to run gmid inside some sort of
container/jail/chroot.