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Gemini Server

This is a server framework in Node.js for the Gemini Protocol based on Express.

Typescript type definitions are included.

TLS is a required part of the Gemini protocol. You can generate keys/certificates using openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem -days 365 -nodes -subj '/CN=localhost'


npm install --save gemini-server


Create a gemini server

const gemini = require("gemini-server").default;

const app = gemini(options);

where options is an object with the following properties:

cert: certificate file key: key file

Handle a request to a route

This uses the express conventions, with the modification that the only method is on.

app.on(path, handler);


app.on(path, ...middleware, handler);

Where handler is a function which takes in a Request and a Response, and returns nothing. And middleware is 0 or more functions which take (req, res, next) and return nothing. A middleware function should call next() to continue onto the next function for handling. It should not call next and should instead set the res object if it should return. NOTE: middleware looks similar to express middleware, but isn't compatible.

Examples of path: / for the root of the site /foo /foo/bar /user/:name *

Examples of handler: function(req, res){ // do stuff } general form gemini.static(dir) serve a directory gemini.redirect(url) redirect to a url

Examples of middleware: gemini.requireInput(prompt="Input requested") Proceed to handler only if user input is given, otherwise request input.

gemini.requireCert Proceed to handler only if user certificate is provided, otherwise request a certificate.

Listen for connections







gemini.serveStatic(path, ?options) serves the files in a directory

Options Description default
index Serves files named index with extensions specified in indexExtensions when accessing a directory without specifying any file true
indexExtensions Defines the extensions to be served by the option index ['.gemini', '.gmi']
redirectOnDirectory Redirects an user to URL with / appended if the supplied path is the name of a directory true

If another handler/middleware is chained behind the static middleware it will get called in case of a file/directory being unaccessable, making it possible to supply a custom "Not Found"-pages.

app.on("/someFiles", gemini.serveStatic("src/files"));


gemini.redirect(url) will redirect to the specified url

app.on("/redirectMe", gemini.redirect("/goingHereInstead"));

app.on("/redirectOther", gemini.redirect(""));

Request object

The request object is passed to request handlers. req.url The URL object of the request req.path The path component of the url req.query The query component of the url (used for handling input) req.params The params of a matched route req.cert The certificate object, if the client sent one req.fingerprint The fingerprint of the certificate object, if the client sent one

Response object

The response object is passed to request handlers. Methods on it can be chained, as each both returns and modifies the request object. res.status(s) Set the status of the response (see the gemini docs). s is an int res.getStatus() return the current status associated with the response

res.file(filename) serve the specified file

res.error(status, message) or res.error(message) Alert the client of an error in processing or, mimeType='text/plain') Serve raw data as text, or as whatever format you want if you specify the mime type.

res.input(prompt, sensitive=false) Prompt the client for input. Prompt should be a string. sensitive defaults to false, and should be true if the input is sensitive.

res.certify(info="Please include a certificate.") Request a certificate from the client. Useful for sessions or login. Optional info message.

res.redirect(url) Redirect the client to the specified url.


A middleware registered through app.use will be executed before every route handler. If a path is given as the first argument, only that path will be affected.

app.use((req, res, next) => {
  console.log(`Route ${req.path} was called`);
app.use("/foo", (req, res, next) => {
  console.log(`Foo route was called`);


We include support for the titan protocol, a sister protocol to gemini. This can be enabled by creating the gemini server with

const options = {
  cert: readFileSync("cert.pem"),
  key: readFileSync("key.pem"),
  titanEnabled: true

const app = gemini(options);

or simply by defining a titan route.

app.titan can be used similarly to app.on, to include handlers for titan routes. In such a handler, the request object will also have the following properties: data: Buffer | null uploadSize: number token: string | null mimeType: string | null

app.use will also work for titan routes.

Example Server (Typescript)

import { readFileSync } from "fs";
import gemini, { Request, Response, TitanRequest, NextFunction } from "../lib/index";

const options = {
  cert: readFileSync("cert.pem"),
  key: readFileSync("key.pem"),
  titanEnabled: true

const app = gemini(options);

app.use((req: Request, _res: Response, next: NextFunction) => {
  console.log("Handling path", req.path);

app.on("/", (_req: Request, res: Response) => {

app.on("/input", (req: Request, res: Response) => {
  if (req.query) {"you typed " + req.query);
  } else {
    res.input("type something");

app.on("/paramTest/:foo", (req: Request, res: Response) => {"you went to " +;

app.on("/async", async (req: Request, res: Response) => {
  if (req.query) {
      return new Promise(r => {
        setTimeout(r, 500);
      }).then(() => {"you typed " + req.query);
  } else {
    res.input("type something");

  gemini.requireInput("enter something"),
  (req: Request, res: Response) => {"thanks. you typed " + req.query);

app.on("/other", (_req: Request, res: Response) => {"welcome to the other page");

app.use("/static", gemini.serveStatic("./examplePages"));

app.on("/redirectMe", gemini.redirect("/other"));

app.on("/cert", (req: Request, res: Response) => {
  if (!req.fingerprint) {
  } else {"thanks for the cert");

app.on("/protected", gemini.requireCert, (_req: Request, res: Response) => {"only clients with certificates can get here");

app.titan("/titan", (req: TitanRequest, res: Response) => {
  console.log(req);"Titan Data: \n" +"utf-8"));

app.titan("/titanCert", gemini.requireCert, (req: TitanRequest, res: Response) => {"You can use gemini middleware in a titan request");

app.on("/titan", (_req: Request, res: Response) => {"not a titan request!");

app.use("/titan", (req: Request | TitanRequest, _res: Response, next: () => void) => {
  console.log(`Is TitanRequest? ${req instanceof TitanRequest}`)

app.listen(() => {


  • Documentation
  • Utility functions
    • Static directory serving
      • automatic index file
  • Certificates
  • Middleware support
  • Session helper functions
  • Router
  • View engines


Node server for the gemini protocol, based on express







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