[newbie] accept()-ing process under supervision (was:Erlangish way of Iterator pattern)

[Gaspar Chilingarov]

Yeah, i know, you have some tasty things on your pages :)

but i wish to run process which does gen_tcp:accept under supervision -- 
just to be sure that it always listening. processes which serve each 
connections are out of my interest (for now) -- they can crash when they 
want :)


Joe Armstrong (AL/EAB) wrote:
> To solve problems like this I almost always use a module called tcp_server which is
> available at
> 
> 	http://www.sics.se/~joe/tutorials/web_server/tcp_server.erl
> 
> To use it call:
> 
> 	tcp_server:start(Port, Fun, Max)
> 
> This starts a server which listens to Port up to Max simultaneous connections on Port are allowed.
>  
> The *first* time a connection is made to Port Then Fun(Socket) is called. 
> Thereafter messages to the socket result in messages to the handler.
> 
> A typical server is usually written like this:
> 
>     start_server(Port) ->    
>           S = self(),  
>           process_flag(trap_exit, true), 
>           tcp_server:start_raw_server(Port, 
>  				fun(Socket) -> input_handler(Socket, S) end, 
> 				15,
>                              0)
>          loop().
> 
> The loop() process is a central controller that all processes can use to synchronize amongst themselves if necessary It ends up as the variable "Controller" in the input_handler
> 
> A typical server is written like this:
> 
>   input_handler(Socket, Controller) ->
>     receive
> 	{tcp, Socket, Bin} ->
> 	    ...
> 	    gen_tcp:send(Socket, ...)
>  	{tcp_closed, Socket} ->
> 
>  	Any ->
> 	    ... 
>      end.
> 
> tcp_server can be used to build many different things. For example a web server or wiki system.
> 
> If you want to see how to make a web server using tcp_server read my second "spitting in the dust tutorial" on how to
> make a web server.
> 
> This is at
> 
> 	http://www.sics.se/~joe/tutorials/web_server/web_server.html
> 
> This has all the code for a simple web server - the web server itself is split into a http parser (222 lines of code)
> a server (104 lines) and the tcp_server (175) lines. 
> 
> I'll show you the code for the web server - it's like this:
> 
> server(Client, Master) ->
>     receive
> 	{Client, closed} ->
> 	    true;
> 	{Client, Request} ->
> 	    Response = generate_response(Request),
> 	    Client ! {self(), Response},
> 	    server(Client, Master)
>     after 5000 ->
> 	    true
>     end.
> 
> That's all :-)
> 
> The structure used in the web server provides a useful model of how to build these type of things.  It has
> 
> 	- a connection handler (tcp_server) which manages tcp sessions
> 	- a device driver that parses HTTP messages and turns them into Erlang messages
> 	- a pure Erlang server
> 
> The general philosophy is "pretend that all things in the outside world are Erlang processes" - thus to program a web
> server we model the browser as an Erlang process - it sends a {get, File} message to the server. The job of the
> connection handler and device driver is to take the HTTP protocol message and turn them into Erlang terms.
> Having done so, writing the server is a doodle.
> 
>   Cheers
> 
> /Joe
> 
> 
> 
> 
>>-----Original Message-----
>>From: owner-erlang-questions@REDACTED 
>>[mailto:owner-erlang-questions@REDACTED]On Behalf Of Gaspar 
>>Chilingarov
>>Sent: den 25 januari 2005 15:20
>>To: erlang-questions@REDACTED
>>Subject: [newbie] Erlangish way of Iterator pattern
>>
>>
>>Hello!
>>
>>I'm beginning to program in erlang and hit the following problem.
>>in mainstream language i will do the following -- create 
>>Iterator class 
>>to read data from socket or file
>>i.e. class with Open/GetNext functions. Open should just do 
>>all work for 
>>preparing data source and GetNext will return lines of data or 
>>EOF(freeing resources when reaching EOF).
>>
>>
>>what i have in erlang -- i have erlang process, which can accept data 
>>messages and eof messages and do processing. another process hangs 
>>around, waiting for TCP connection and feeding first process 
>>with data 
>>read from TCP. in the same time i have shell script which runs once a 
>>minute and feeds data from some file(or piped command line) 
>>to TCP port.
>>
>>now i want to get rid of shell script, but i wish to have separate 
>>module which will do this -- i.e. 1. running periodically external 
>>command, 2. feeding to another process.
>>
>>are there any idioms in Erlang for this or it should be 
>>implemented in 
>>straight way -- i.e. just another process sitting there and 
>>doing it's 
>>job -- file reading/parsing/feeding to another process ?
>>
>>
>>
>>-- 
>>Gaspar Chilingarov
>>System Administrator
>>
>>t +3749 419763
>>w www.web.am
>>e nm@REDACTED
>>
> 
> 


-- 
Gaspar Chilingarov
System Administrator

t +3749 419763
w www.web.am
e nm@REDACTED