Falcon Introduction

Step 1

The falcon Ruby gem provides a Rack-compatible HTTP/1 & HTTP/2 web server.

Like any other Ruby gem, we can install it with the gem command: gem install falcon

Step 2

Now that we have falcon installed, lets try writing a simple rack server (in ~/config.ru):

Source Code

class App
    def call(env)
        return [200, [], ["Hello World"]]
    end
end

run App.new

Run the server

Once we add the code to config.ru, we can run it: falcon serve --bind http://[::]:80

You can open the application by clicking this link.

Exit the server

To quit falcon, press Ctrl-C when focused on the terminal.

Step 3

Falcon is capable of streaming responses:

Source Code

class App
    # Browsers don't show streaming content until a certain threshold has been met. For most browsers, it's about 1024 bytes. So, we have a comment of about that length which we feed to the client before streaming actual content. For more details see https://stackoverflow.com/questions/16909227
    COMMENT = "<!--#{'-' * 1024}-->"

    def bottles(n)
        n == 1 ? "#{n} bottle" : "#{n} bottles"
    end

    def sing(task, body, count = 99)
        body.write(COMMENT)

        count.downto(1) do |i|
            puts "#{bottles(i)} of beer on the wall..."
            body.write("<p>#{bottles(i)} of beer on the wall, ")
            task.sleep(0.1)
            body.write("#{bottles(i)} of beer, ")
            task.sleep(0.1)
            body.write("take one down and pass it around, ")
            task.sleep(0.1)
            body.write("#{bottles(i-1)} of beer on the wall.</p>")
            task.sleep(0.1)
            body.write("<script>var child; while (child = document.body.firstChild) child.remove();</script>")
        end
    rescue
        puts "Remote end closed connection: #{$!}"
    ensure
        body.close
    end

    def call(env)
        task = Async::Task.current
        body = Async::HTTP::Body::Writable.new

        count = 99

        body.write("<!DOCTYPE html><html><head><title>#{count} Bottles of Beer</title></head><body>")

        task.async do |subtask|
            sing(subtask, body)
        end

        return [200, {'content-type' => 'text/html'}, body]
    end
end

run App.new

Run the server

Once we add the code to config.ru, we can run it: falcon serve --bind http://[::]:80

You can open the application by clicking this link.

cd <directory>	Change directory
ls	List directory
echo 'contents' > <file>	Write contents to a file
cat <file>	Output contents of file

i	In Command Mode	Change into Insert Mode, you can now insert and edit text in the file
esc	In Insert Mode	Change into Command Mode, you can now execute commands
:wq	In Command Mode	Save and Exit

Welcome!

Congratulations!

You've completed the scenario!

Scenario Rating

Steps