2.7 KiB
gmid
dead simple, zero configuration Gemini server
gmid is a simple and minimal Gemini server. It can run without configuration, so it's well suited for local development, but at the same time has a configuration file flexible enough to meet the requirements of most capsules.
gmid was initially written to serve static files, but can also
optionally execute CGI scripts. It was also written with security in
mind: on Linux, FreeBSD and OpenBSD is sandboxed via seccomp(2)
,
capsicum(4)
and pledge(2)
+unveil(2)
respectively.
Features
- IRI support (RFC3987)
- dual stack: can serve over both IPv4 and IPv6
- CGI scripts
- (very) low memory footprint
- small codebase, easily hackable
- virtual hosts
- sandboxed by default on OpenBSD, Linux and FreeBSD
Drawbacks
- not suited for very busy hosts. If you receive an high number of connection per-second you'd probably want to run multiple gmid instances behind relayd/haproxy or a different server.
Building
gmid depends on a POSIX libc and libtls (provided either by LibreSSL or libretls). At build time, flex and yacc (or GNU bison) are also needed.
The build is as simple as
make
or
make static
to enjoy your ~2.3M statically-linked gmid.
To install execute:
make install
If you have trouble installing LibreSSL or libretls, as they aren't
available as package on various Linux distribution, you can use Docker
to build a gmid
image with:
docker build -t gmid .
and then run it with something along the lines of
docker run --rm -it -p 1965:1965 \
-v /path/to/cert.pem:...:ro \
-v /path/to/key.pem:...:ro \
-v /path/to/docs:/var/gemini \
gmid -f -d /var/gemini -K ... -C ...
ellipses used for brevity.
Architecture/Security considerations
gmid is composed by two processes: a listener and an executor. The listener process is the only one that needs internet access and is sandboxed. When a CGI script needs to be executed, the executor (outside of the sandbox) sets up a pipe and gives one end to the listener, while the other is bound to the CGI script standard output. This way, is still possible to execute CGI scripts without restriction even in the presence of a sandbox.
On OpenBSD, the listener process runs with the stdio recvfd rpath inet
pledges and has unveil(2)
ed only the directories that it
serves; the executor has stdio sendfd proc exec
as pledges.
On FreeBSD, the executor process is sandboxed with capsicum(4)
.
On Linux, a seccomp(2)
filter is installed to allow only certain
syscalls, see sandbox.c for more information on the BPF
program.
In any case, you are invited to run gmid inside some sort of container/jail.