Getting Started

Installation

Add the gem to your project:

$ bundle add falcon

Or, if you prefer, install it globally:

$ gem install falcon

Core Concepts

Falcon is a high-performance web server for Ruby. It is designed to be fast, lightweight, and easy to use.

• Asynchronous: Falcon is built on top of the fiber scheduler and the async gem which allow it to handle thousands of connections concurrently.
• Rack Compatible: Falcon is a Rack server. It can run any Rack application, including Rails, Sinatra, and Roda with no modifications.
• Secure: Falcon supports TLS out of the box. It can generate self-signed certificates for localhost.
• HTTP/2: Falcon is build on top of the async-http gem which supports HTTP/2. It can serve multiple requests over a single connection.
• WebSockets: Falcon supports WebSockets using the async-websocket gem which takes advantage of Rack 3 streaming responses. You can build complex real-time applications with ease.

Rack

Falcon is a Rack server. This means it can run any Rack application, including Rails, Sinatra, and Roda. It is compatible with the Rack 2 and Rack 3 specifications. Typically these applications have a config.ru file that defines the application. Falcon can run these applications directly:

# config.ru

run do |env|
	[200, {'Content-Type' => 'text/plain'}, ['Hello, World!']]
end

Then run the application with:

$ falcon serve

Running a Local Server

For local application development, you can use the falcon serve command. This will start a local server on https://localhost:9292. Falcon generates self-signed certificates for localhost. This allows you to test your application with HTTPS locally.

To run on a different port:

$ falcon serve --port 3000

Using with Rackup

You can invoke Falcon via rackup:

$ rackup --server falcon

This will run a single-threaded instance of Falcon using http/1. While it works fine, it's not recommended to use rackup with falcon, because performance will be limited.

Self-Signed TLS with Curl

In order to use curl with self-signed localhost certificates, you need to specify --insecure or the path of the certificate to validate the request:

> curl -v https://localhost:9292 --cacert ~/.localhost/localhost.crt
*   Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 9292 (#0)
* ALPN, offering http/1.1
* Cipher selection: ALL:!EXPORT:!EXPORT40:!EXPORT56:!aNULL:!LOW:!RC4:@STRENGTH
* successfully set certificate verify locations:
*   CAfile: /Users/samuel/.localhost/localhost.crt
  CApath: none
* TLSv1.2 (OUT), TLS header, Certificate Status (22):
* TLSv1.2 (OUT), TLS handshake, Client hello (1):
* TLSv1.2 (IN), TLS handshake, Server hello (2):
* TLSv1.2 (IN), TLS handshake, Certificate (11):
* TLSv1.2 (IN), TLS handshake, Server key exchange (12):
* TLSv1.2 (IN), TLS handshake, Request CERT (13):
* TLSv1.2 (IN), TLS handshake, Server finished (14):
* TLSv1.2 (OUT), TLS handshake, Certificate (11):
* TLSv1.2 (OUT), TLS handshake, Client key exchange (16):
* TLSv1.2 (OUT), TLS change cipher, Change cipher spec (1):
* TLSv1.2 (OUT), TLS handshake, Finished (20):
* TLSv1.2 (IN), TLS change cipher, Change cipher spec (1):
* TLSv1.2 (IN), TLS handshake, Finished (20):
* SSL connection using TLSv1.2 / ECDHE-RSA-AES256-GCM-SHA384
* ALPN, server accepted to use http/1.1
* Server certificate:
*  subject: O=Development/CN=localhost
*  start date: Aug 10 00:31:43 2018 GMT
*  expire date: Aug  7 00:31:43 2028 GMT
*  subjectAltName: host "localhost" matched cert's "localhost"
*  issuer: O=Development/CN=localhost
*  SSL certificate verify ok.
> GET / HTTP/1.1
> Host: localhost:9292
> User-Agent: curl/7.63.0
> Accept: */*
> 
< HTTP/1.1 301
< location: /index
< cache-control: max-age=86400
< content-length: 0
< 
* Connection #0 to host localhost left intact