How to create a web server using Cowboy without Plug or Phoenix - Part 01

Cowboy is an amazing web server that is used by Plug/Phoenix out of the box, I don’t think Phoenix supports any other web servers at the moment. However, the plug adapter is fairly abstracted, and plug implements this adapter for cowboy through the plug_cowboy hex package. In theory, you should be able to write a new adapter if you just implement the Plug adapter behaviour. The plug cowboy adapter has a lot of interesting code and you’ll learn a lot from reading it. Anyway, this blog post isn’t about Plug or Phoenix. I wanted to show off how you can create a simple Cowboy server without using Plug or Phoenix (I had to learn how to do this while creating my side project webpipe)

We want an application which spins up a cowboy server and renders a hello world message. Here is the required code for that:

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defmodule Hello do
# The handler module which handles all requests, its `init` function is called
# by Cowboy for all matching requests.
defmodule Handler do
def init(req, _opts) do
resp =
:cowboy_req.reply(
_status = 200,
_headers = %{"content-type" => "text/html; charset=utf-8"},
_body = "<!doctype html><h1>Hello, Cowboy!</h1>",
_request = req
)

{:ok, resp, []}
end
end

def start do
# compile the routes
routes =
:cowboy_router.compile([
{:_,
[
# { wildcard, handler module (needs to have an init function), options }
{:_, Handler, []}
]}
])

require Logger
Logger.info("Staring server at http://localhost:4001/")

# start an http server
:cowboy.start_clear(
:hello_http,
[port: 4001],
%{env: %{dispatch: routes}}
)
end
end

Full code on GitHub


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