GmCapsule: Extensible Gemini/Titan Server

GmCapsule is a Gemini server written in Python.

Extensibility is achieved with Python modules that get loaded at launch from the configured directories. A set of built-in extension modules is provided for common functionality like CGI and for serving static files.

The supported protocols are Gemini and Titan. Both are accepted via the same TCP port.

GmCapsule can be used in a few different ways:

`gmcapsuled` is a simple command line utility for loading a configuration file and running the server. Use the `--help` option to see usage instructions.


Alternatively, you can clone the Git repository and run the server without installing the Python module.

See also

CGI examples: Titan

These examples assume `gmcapsuled` running on localhost.

Here is a simple CGI Python script that we'll use:

import os
import sys

titan_data =

print("20 text/gemini\r")
print("Client cert hashes:", os.getenv('REMOTE_IDENT'))
print("Titan token:", os.getenv('TITAN_TOKEN'))
print("You uploaded %d bytes." % len(titan_data))

Method 1: CGI entry point in server config

Place the above script file anywhere you'd like, say "scripts/", and add this to the server config:

protocol = titan
path = /hello-world
command = /usr/bin/python3 scripts/

(file paths are relative to where you start `gmcapsuled`)

Then open "titan://localhost/hello-world" in the client to start an upload.

Method 2: CGI bin_root

The advantage of setting the `bin_root` is that you can add and remove scripts in your CGI directory without restarting the server.

Normally executables inside the bin_root are assumed to be Gemini CGI scripts. To make them use Titan, append ",titan" to the executable name. So, let's create a bin_root directory called "./cgi-bin", and your script should be named:


Don't forget to set the file as executable.

The bin_root is configured in the server config:

bin_root = ./cgi-bin

You can then open "titan://localhost/hello-world" in the client to start an upload.

Methods 1 and 2 are mutually exclusive, you can choose which one works best for you.

Method 3: Extension module

It's actually quite simple to create a simple Titan upload handler via a Python extension module. Add a custom modules directory in the server config:

modules = ./mymod

Create this Python source file as "./mymod/":

def titan_upload_handler(req):
    response = 'Client cert hash: ' + req.identity.fp_cert
    response += '\nYou uploaded %d bytes.\n' % len(req.content)
    return response

def init(capsule):
    """Extension module initialization."""    

Open "titan://localhost/titan-hello" to start the upload.

The original Gemtext version of this page can be accessed with a Gemini client: gemini://