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An Experimental Gemini Server

Project description


An experimental TCP server for the new, under development Gemini Protocol. Learn more about Gemini here.

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pypi version build

Table of Contents


  • A built-in static file server with support for gemini directories and CGI scripts.
  • A complete framework for writing robust gemini applications like astrobotany.
  • A lean, modern codebase with type hints and black formatting.
  • A solid foundation built on top of the twisted asynchronous networking engine.


Requires Python 3.7 or newer.

The latest stable release can be installed from PyPI:

$ pip install jetforce

Or, install from source:

$ git clone
$ cd jetforce
$ pip install .

Or, install into a python virtual environment:

# Create a project directory somewhere
$ mkdir /opt/jetforce

# Activate a virtual environment and install jetforce
$ python3 -m virtualenv /opt/jetforce/venv
$ source /opt/jetforce/venv/bin/activate
$ pip install jetforce

# The launch script will be installed here
$ /opt/jetforce/venv/bin/jetforce


Use the --help flag to view command-line options:

usage: jetforce [-h] [-V] [--host HOST] [--port PORT] [--hostname HOSTNAME]
                [--tls-certfile FILE] [--tls-keyfile FILE] [--tls-cafile FILE]
                [--tls-capath DIR] [--dir DIR] [--cgi-dir DIR] [--index-file FILE]
                [--default-lang DEFAULT_LANG] [--rate-limit RATE_LIMIT]

An Experimental Gemini Protocol Server

optional arguments:
  -h, --help            show this help message and exit
  -V, --version         show program's version number and exit

server configuration:
  --host HOST           Server address to bind to (default:
  --port PORT           Server port to bind to (default: 1965)
  --hostname HOSTNAME   Server hostname (default: localhost)
  --tls-certfile FILE   Server TLS certificate file (default: None)
  --tls-keyfile FILE    Server TLS private key file (default: None)
  --tls-cafile FILE     A CA file to use for validating clients (default: None)
  --tls-capath DIR      A directory containing CA files for validating clients (default:

fileserver configuration:
  --dir DIR             Root directory on the filesystem to serve (default: /var/gemini)
  --cgi-dir DIR         CGI script directory, relative to the server's root directory
                        (default: cgi-bin)
  --index-file FILE     If a directory contains a file with this name, that file will be
                        served instead of auto-generating an index page (default: index.gmi)
  --default-lang DEFAULT_LANG
                        A lang parameter that will be used for all text/gemini responses
                        (default: None)
  --rate-limit RATE_LIMIT
                        Enable IP rate limiting, e.g. '60/5m' (60 requests per 5 minutes)
                        (default: None)

Setting the hostname

The server's hostname should be set to the DNS name that you expect to receive traffic from. For example, if your jetforce server is running on "gemini://", you should set the hostname to "". Any URLs that do not match this hostname will be refused by the server, including URLs that use a direct IP address such as "gemini://".

IDNs (domain names that contain unicode characters) should be defined using their ASCII punycode representation. For example, the domain name café should be represented as --hostname

Setting the host

The server's host should be set to the local socket that you want to bind to:

  • --host "" - Accept local connections only
  • --host "" - Accept remote connections over IPv4
  • --host "::" - Accept remote connections over IPv6
  • --host "" - Accept remote connections over any interface (IPv4 + IPv6)

TLS Certificates

The gemini specification requires that all connections be sent over TLS.

If you do not provide a TLS certificate file using the --tls-certfile flag, jetforce will automatically generate a temporary cert for you to use. This is great for making development easier, but before you expose your server to the public internet you should setup something more permanent. You can generate your own self-signed server certificate, or obtain one from a Certificate Authority like Let's Encrypt.

Here's an example openssl command that you can use to generate a self-signed certificate:

$ openssl req -newkey rsa:2048 -nodes -keyout {hostname}.key \
    -nodes -x509 -out {hostname}.crt -subj "/CN={hostname}"

Jetforce also supports TLS client certificates (both self-signed and CA authorised). Requests that are made with client certificates will include additional CGI/environment variables with information about the TLS connection.

You can specify a CA for client validation with the --tls-cafile or --tls-capath flags. Connections validated by the CA will have the TLS_CLIENT_AUTHORISED environment variable set to True. Instructions on how to generate CA's are outside of the scope of this readme, but you can find many helpful tutorials online.

Static Files

Jetforce will serve static files in the /var/gemini/ directory by default. Files ending with *.gmi will be interpreted as the text/gemini type. If a directory is requested, jetforce will look for a file named index.gmi in that directory to return. Otherwise, a directory file listing will be automatically generated.

Virtual Hosting

For the sake of keeping the command line arguments straightforward and easy to understand, configuring virtual hosting is not supported via the command line. However, it is readily available using only a few lines of python and a custom launch script. Check out examples/ for more information.

Jetforce does not (yet) support virtual hosting at the TLS-layer using SNI. This means that you cannot return different server TLS certificates for different domains. The suggested workaround is to use a single certificate with multiple subjectAltName attributes. There is also an sni_callback() hook in the server codebase that can be subclassed to implement custom TLS behavior.


Jetforce supports a simplified version of CGI scripting. It doesn't exactly follow the RFC 3875 specification for CGI, but it gets the job done for the purposes of Gemini.

Any executable file placed in the server's cgi-bin/ directory will be considered a CGI script. When a CGI script is requested by a gemini client, the jetforce server will execute the script and pass along information about the request using environment variables.

The CGI script must then write the gemini response to the stdout stream. This includes the status code and meta string on the first line, and the optional response body on subsequent lines. The bytes generated by the CGI script will be forwarded verbatim to the gemini client, without any additional modification by the server.

CGI Environment Variables

Name Example Value
GATEWAY_INTERFACE CGI/1.1 (for compatibility with RFC 3875)
SERVER_SOFTWARE jetforce/0.0.7
GEMINI_URL gemini://
SCRIPT_NAME /cgi-bin/example.cgi
PATH_INFO /extra
QUERY_STRING hello%20world

CGI Environment Variables - Authenticated

Additional CGI variables will be included only when the client connection uses a TLS client certificate:

Name Example Value
REMOTE_USER mozz123 (the certificate subject CN attribute)
TLS_CLIENT_HASH SHA256:86341FB480BFE333C343530D75ABF99D1437F69338F36C684C8831B63C993A96
TLS_CLIENT_NOT_BEFORE 2020-04-05T04:18:22Z
TLS_CLIENT_NOT_AFTER 2021-04-05T04:18:22Z
TLS_CLIENT_AUTHORISED 0 (not authorised) / 1 (authorised) †

† Requires the server to be configured with a CA for validating client certificates.


Jetforce is intended to be run behind a process manager that handles daemonizing the script, redirecting output to system logs, etc. I prefer to use systemd for this because it's installed on my operating system and easy to set up.

Here's how I configure my server over at gemini://

# /etc/systemd/system/jetforce.service
Description=Jetforce Server

ExecStart=/usr/local/bin/jetforce \
    --host \
    --port 1965 \
    --hostname \
    --dir /var/gemini \
    --tls-certfile /etc/letsencrypt/live/ \
    --tls-keyfile /etc/letsencrypt/live/ \
    --tls-cafile /etc/pki/tls/jetforce_client/ca.cer

  • --host allows the server to accept external connections from any IP address over IPv4.
  • PYTHONUNBUFFERED=1 disables buffering stderr and is sometimes necessary for logging to work.
  • --tls-certfile and --tls-keyfile point to my WWW server's Let's Encrypt certificate chain.
  • --tls-cafile points to a self-signed CA that I created in order to test accepting client TLS connections.

With this service installed, I can start and stop the server using

systemctl start jetforce
systemctl stop jetforce

And I can view the server logs using

journalctl -u jetforce -f


You are exposing a server to the internet. You (yes you!) are responsible for securing your server and setting up appropriate access permissions. This likely means not running jetforce as the root user. Security best practices are outside of the scope of this document and largely depend on your individual threat model.


To view the project's release history, see the CHANGELOG file.


This project is licensed under the Floodgap Free Software License.

The Floodgap Free Software License (FFSL) has one overriding mandate: that software using it, or derivative works based on software that uses it, must be free. By free we mean simply "free as in beer" -- you may put your work into open or closed source packages as you see fit, whether or not you choose to release your changes or updates publicly, but you must not ask any fee for it.

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