How to write a simple webserver in Erlang?

Question 1

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

Question 2

How is this different fromstackoverflow.com/questions/2084639/… ?

Question 3

@Zed, Zubair is asking for a minimal "hello world" server--it has a single "page" because it is minimal. The question you linked to asks how to make a functional Web app (one-page, but responds to a variety of requests in different ways). I assume the latter will be ajax-y.

Question 4

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])).

Question 5

See{packet, http} forOptions ofgen_tcp:listen for decoding HTTP headers.

Question 6

I was looking at this code, and even though it looks clean, I found an issue. When testing it with Apache Bench, I get aapr_socket_recv: Connection reset by peer (104). it works fine when accessing in a browser, or using curl. Do you have any idea why this is?

Question 7

@MartinKristiansen Remove the linegen_tcp:close(Conn).

Question 8

@FelixLange Thanks for this answer Felix.. Could you please explain the code written. It will be very helpful for erlang enthusiasts like me :-)

Question 9

The lastiolist_to_binary/1 inresponse/1 is unnecessary.

Question 10

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

Question 11

Thats great, so using INets can I write a single module webserver?

Question 12

Another way, similar to thegen_tcp example above but with less code and already offered as a suggestion, is using theinets 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

Question 13

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, tryYAWS. If the former, have a look at theYAWS source code for inspiration

Question 14

I want to make dynamic content, but just wanted to know the bare minimum needed for a web server. I looked at the Yaws source code and my first impression was that alot of code was needed.

Question 15

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.

Question 16

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 exampledo_recv fromgen_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.

Felix Lange 1,60212 silver badges15 bronze badges · Accepted Answer · 2010-02-08 03:42:06Z

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])).

See{packet, http} forOptions ofgen_tcp:listen for decoding HTTP headers.
I was looking at this code, and even though it looks clean, I found an issue. When testing it with Apache Bench, I get aapr_socket_recv: Connection reset by peer (104). it works fine when accessing in a browser, or using curl. Do you have any idea why this is?
@FelixLange Thanks for this answer Felix.. Could you please explain the code written. It will be very helpful for erlang enthusiasts like me :-)

Movatterモバイル変換

Collectives™ on Stack Overflow

How to write a simple webserver in Erlang?

6 Answers6

6 Comments

1 Comment

Comments

1 Comment

Comments

Comments

Your Answer

Sign up orlog in

Post as a guest

Linked

Related

Hot Network Questions

Subscribe to RSS