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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Sockets Example Sought
Date: Fri, 23 Nov 2012 23:08:01 +0000
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Date: 2012-11-23T23:08:01+00:00
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Robert Love <rblove@airmail.net> writes:

> On 2012-11-23 18:32:52 +0000, Simon Wright said:
>
>> Robert Love <rblove@airmail.net> writes:
>>
>>> Does anyone have an example of a multi-client server in Ada they
>>> care to share?  It should use the Gnat.Sockets package.  I've seen
>>> samples but they don't seem complete, or at least my understanding
>>> isn't complete<grin>.
>>>
>>> Thanks in advance.
>>
>> task body Server in http://goo.gl/bXVw7 ? (lines 59 .. 143)
>
> What happens at line 120, the else clause on if Server =
> Socket_Server? Is that where data is read in on the socket?
>
> I assume the client opens the socket and the server detects it, then
> at various times the client makes data requests by sending string
> data.

Yes, pretty much. I've added some comments, see the end (these won't
show up via the URL I gave, which is to a specific revision; ).

> The Respond function called just seems to call HTTP.Respond, which is
> not in this file.

Yes. It's in ews-http.ad[sb]; HTTP.Initialize reads the HTTP request,
HTTP.Find works out what sort of response is required, and HTTP.Respond
generates it.

-snippet-

      loop
         declare
            Read_Sockets : GNAT.Sockets.Socket_Set_Type;
            Status : GNAT.Sockets.Selector_Status;
            use type GNAT.Sockets.Selector_Status;
         begin
            --  Initialize Read_Sockets with the sockets in use
            --  (Write_Sockets remains empty, we don't care if a
            --  socket becomes writable; we'll just block in that
            --  case).
            GNAT.Sockets.Copy (Sockets, Read_Sockets);
            --  Wait until something happens on one of the sockets.
            GNAT.Sockets.Check_Selector
              (Selector, Read_Sockets, Write_Sockets, Status);
            if Status = GNAT.Sockets.Completed then
               --  This was a successful completion. Find out which
               --  socket woke us up and deal with it. If there was
               --  more than one, we'll find out next time round the
               --  loop.
               declare
                  Socket : GNAT.Sockets.Socket_Type;
                  use type GNAT.Sockets.Socket_Type;
               begin
                  --  Which socket?
                  GNAT.Sockets.Get (Read_Sockets, Socket);
                  if Socket = Server_Socket then
                     --  It was the server; a new client has called
                     --  connect(). Accept the connection ...
                     GNAT.Sockets.Accept_Socket
                       (Server_Socket, Socket, Address);
                     Trace (Logging_Via, "connection", Socket, Tracing);
                     --  ... and add the new connected socket to the
                     --  set of sockets in use.
                     GNAT.Sockets.Set (Sockets, Socket);
                  elsif Socket = GNAT.Sockets.No_Socket then
                     --  None of our sockets has data/connection
                     --  available; don't care why.
                     Logging_Via ("server got No_Socket", Error);
                  else
                     --  There's an HTTP request to be read on one of
                     --  our connected clients' sockets; deal with it.
                     Trace (Logging_Via, "request", Socket, Tracing);
                     Respond (Socket, Sockets, Logging_Via, Tracing);
                  end if;
               end;
            else
               --  Unexpected, non-fatal error.
               Logging_Via ("server: Check_Selector returned " & Status'Img,
                            Error);
            end if;
            --  Clean up.
            GNAT.Sockets.Empty (Read_Sockets);
         exception
            when E : others =>
               Log (Logging_Via,
                    "server failed in inner loop",
                    With_Exception => E);
         end;
      end loop;