Re: Finding the end of a stream from a socket

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 2017-10-21 04:05, Andrew Shvets wrote:

> I've been recently trying to make a small TCP server (a toy.) I have
> a channel that reads Characters and was trying to find the end of
> the stream. Reading the documentation, I came across the following
> in  g-socket.ads:
> 
> type Stream_Access is access all Ada.Streams.Root_Stream_Type'Class;
> --  Same interface as Ada.Streams.Stream_IO
> 
> I was trying to have a way to find out when the last Character was 
> read from the stream. I could catch the Ada.IO_Exceptions.End_Error 
> exception, but I'm wondering if there is a better way.

End_Error is the best possible way, when applied. GNAT socket streams do 
not raise End_Error, AFAIK.

> while not Ada.Streams.Stream_IO.End_Of_File(Channel) loop
>    Character'Read(Channel, Received_Char);
>    Ada.Text_IO.Put(Received_Char);
> end loop;

This is a bad idea even when if it can work. In the case of sockets 
there is no file end. When the connection is closed by the peer the 
stream will stop both returning data and blocking. I suppose that will 
cause Constraint_Error in Character'Read.

In practice there is a higher level protocol on top of the socket 
stream, so that it is always known how many octets to read next.

Regarding your case, try this:

    Buffer : Stream_Element_Array (1..Buffer_Size);
    Last   : Stream_Element_Offset;
begin
    loop
       Receive_Socket (Socket, Buffer, Last);
       exit when Last < Buffer'First; -- Connection is closed by the peer
       for Octet in Buffer'First..Last loop -- Dump octets as-is
          Put (Character'Val (Buffer (Octet)));
       end loop;
    end loop;

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de