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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 FreeBSD and OpenBSD is sandboxed via 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 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 a POSIX libc and libtls. It can probably be linked against libretls, but I've never tried.

See INSTALL.gmi for more info, but the build is as simple as

make

The Makefile isn't able to produce a statically linked executable (yet), so for that you have to execute by hand

make
cc -static *.o /usr/lib/lib{crypto,tls,ssl}.a -o gmid
strip gmid

to enjoy your ~2.3M statically-linked gmid.

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 if 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. Furthermore, the executor process has stdio sendfd proc exec as pledges.

On FreeBSD, the listener process is sandboxed with capsicum(4).

On linux, a seccomp filter is installed for the listener process.