4.9 KiB
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 that can be used from either the command line to serve local directories
gmid docs # serve the directory docs over gemini
or as a traditional daemon
gmid -c /etc/gmid.conf
Features
(random order)
- reconfiguration: reload the running configuration without interruption
- sandboxed by default on OpenBSD, Linux and FreeBSD
- IRI support (RFC3987)
- punycode support
- dual stack (IPv4 and IPv6)
- automatic certificate generation for config-less mode
- CGI scripts
- (very) low memory footprint
- event-based asynchronous I/O model
- small codebase, easily hackable
- virtual hosts
- per-location rules
- optional directory listings
- configurable mime types
- chroot support
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. While you should definitely check the manpage because it documents every option in depth, here's an example of what gmid can do.
ipv6 on # enable ipv6
server "example.com" {
cert "/path/to/cert.pem"
key "/path/to/key.pem"
root "/var/gemini/example.com"
lang "it"
cgi "/cgi/*"
location "/files/*" {
auto index on
}
location "/repo/*" {
# change the index file name
index "README.gmi"
}
# redirect /cgi/man/... to man.example.com/...
location "/cgi/man*" {
strip 2
block return 31 "gemini://man.example.com%p"
}
}
server "man.example.com" {
cert "..."
key "..."
root "/var/gemini/man.example.com"
# handle every request with the CGI script `man'
entrypoint "man"
}
Building
gmid depends on a POSIX libc, libevent2, OpenSSL/LibreSSL 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
./configure
make
If the configure scripts fails to pick up something, please open an issue or notify me via email.
To install execute:
make install
Docker
If you have trouble installing LibreSSL or libretls, 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/gmid.conf:...:ro \
-v /path/to/docs:/var/gemini \
gmid -c .../gmid.conf
(ellipses used for brevity)
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"
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 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 restrictions even in the presence of a sandboxed network process.
On OpenBSD, the listener runs with the stdio recvfd rpath inet
pledges, while the executor has stdio sendfd proc exec
; both have
unveiled only the served directories.
On FreeBSD, the executor process is sandboxed with capsicum(4)
.
On Linux, a seccomp(2)
filter is installed in the listener 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/chroot.