CODEWITHSUNDEEP
erlang
yazz.com
yazz.com

Reputation: 58786

How to write a simple webserver in Erlang?

Using the default Erlang installation what is the minimum code needed to produce a "Hello world" producing web server?

Upvotes: 36

Views: 25023

Answers (6)

Jon Gretar
Jon Gretar

Reputation: 5412

For a web server using only the built in libraries check out inets http_server. When in need of some more power but still with simplicity you should check out the mochiweb library. You can google for loads of example code.

Upvotes: 11

spacez320
spacez320

Reputation: 163

Another way, similar to the gen_tcp example above but with less code and already offered as a suggestion, is using the inets library.

%%%
%%% A simple "Hello, world" server in the Erlang.
%%%

-module(hello_erlang).
-export([
  main/1,
  run_server/0,
  start/0
]).

main(_) ->
  start(),
  receive
    stop -> ok
  end.

run_server() ->
  ok = inets:start(),
  {ok, _} = inets:start(httpd, [
    {port, 0},
    {server_name, "hello_erlang"},
    {server_root, "/tmp"},
    {document_root, "/tmp"},
    {bind_address, "localhost"}
  ]).

start() -> run_server().

Keep in mind, this exposes your /tmp directory.

To run, simply:

$ escript ./hello_erlang.erl

Upvotes: 8

typingduck
typingduck

Reputation: 835

Just one fix for Felix's answer and it addresses the issues Martin is seeing. Before closing a socket, all data being sent from the client should be received (using for example do_recv from gen_tcp description).

Otherwise there's a race condition for the browser/proxy sending the HTTP request being quick enough to send the http request before the socket is closed.

Upvotes: 1

Tristan Sloughter
Tristan Sloughter

Reputation: 326

For a very easy to use webserver for building restful apps or such check out the gen_webserver behaviour: http://github.com/martinjlogan/gen_web_server.

Upvotes: 4

Felix Lange
Felix Lange

Reputation: 1582

Taking "produce" literally, here is a pretty small one. It doesn't even read the request (but does fork on every request, so it's not as minimal possible).

-module(hello).
-export([start/1]).

start(Port) ->
    spawn(fun () -> {ok, Sock} = gen_tcp:listen(Port, [{active, false}]), 
                    loop(Sock) end).

loop(Sock) ->
    {ok, Conn} = gen_tcp:accept(Sock),
    Handler = spawn(fun () -> handle(Conn) end),
    gen_tcp:controlling_process(Conn, Handler),
    loop(Sock).

handle(Conn) ->
    gen_tcp:send(Conn, response("Hello World")),
    gen_tcp:close(Conn).

response(Str) ->
    B = iolist_to_binary(Str),
    iolist_to_binary(
      io_lib:fwrite(
         "HTTP/1.0 200 OK\nContent-Type: text/html\nContent-Length: ~p\n\n~s",
         [size(B), B])).

Upvotes: 56

Paul Butcher
Paul Butcher

Reputation: 6956

Do you actually want to write a web server in Erlang, or do you want an Erlang web server so that you can create dynamic web content using Erlang?

If the latter, try YAWS. If the former, have a look at the YAWS source code for inspiration

Upvotes: 7

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