Using GNAT.Sockets

Using GNAT.Sockets

[markwork66]

We are just converting to GNAT and I am used to the traditional TCP
send/receive using an address and byte count to send/receive data. I've
used the Receive_Socket command in GNAT.Sockets and I am having trouble
receiving all the bytes. The "Last" parameter is not always equal to
the size of the message I'm sending and I don't see a way to call back
into the procedure to receive the rest of the bytes.

Further, we have many different sized messages and, from my little
playing with GNAT sockets, it seemed the "Item" parameter is the only
way to specify the number of bytes you want to receive. So, does that
mean I would have to declare an array of bytes (the "Item" parameter)
for all of my messages and the then do an unchecked conversion or a
copy_bytes routine to get the data into my Ada message data type?

Any help anybody could provide would be most appreciated.

Re: Using GNAT.Sockets

[Duncan Sands]

Hi markwork66,

On Wed, 2005-04-13 at 08:07 -0700, markwork66@yahoo.com wrote:
> We are just converting to GNAT and I am used to the traditional TCP
> send/receive using an address and byte count to send/receive data. I've
> used the Receive_Socket command in GNAT.Sockets and I am having trouble
> receiving all the bytes. The "Last" parameter is not always equal to
> the size of the message I'm sending and I don't see a way to call back
> into the procedure to receive the rest of the bytes.

there are two things you might be talking about here:

(1) Item'Length is less then the size of your message,
Last is equal to Item'Last.
(2) Last is less than Item'Last, and less than the length of your
message (or rather: Last - Item'First + 1 < your message length).

In case (1), the operating system has transferred as much into your
buffer Item as your buffer can hold.  That's the way it should be.
To get the rest of the data, call Receive_Socket again.

Case (2) happens for Receive_Socket because it happens for the standard
C socket routine recv.  Receive_Socket is quite low level - it is just
a wrapper around recv.  recv can return less than the length of your
message because either (A) the entire message has not yet arrived on
your computer, or your buffer is longer than the socket buffer, (B) the
OS feels like it, or (C) an error occurred.  You've got to expect (A) -
finite speed and finite buffers is a fact of life.  As for (B),
I'm not being facetious - the OS is allowed to return a "short read"
even if it has more data.  This is also the case with files by the way:
even if you read less than the length of a file, the OS is allowed to
nonetheless return less than you asked for.  This is rare.  As for
(C), I guess that's not the problem here.

I'm guessing that you would like a higher-level routine that
automagically takes care of short reads for you.  For that you
can use the stream routines.

> Further, we have many different sized messages and, from my little
> playing with GNAT sockets, it seemed the "Item" parameter is the only
> way to specify the number of bytes you want to receive. So, does that
> mean I would have to declare an array of bytes (the "Item" parameter)
> for all of my messages and the then do an unchecked conversion or a
> copy_bytes routine to get the data into my Ada message data type?

Probably here too you want the stream stuff.

Ciao,

Duncan.

Re: Using GNAT.Sockets

[markp]

Duncan,

Thanks for your reply. In case (1), that is what is occuring. When I
call Receive_Socket again to get the rest of the data, I'm wondering if
the call will place the new data at the beginning of the item buffer.
That would mean I would have to copy it out before I do a subsequent
read. Is this the case?

I do not want a higher level routine. I would like to stay withing the
GNAT.Sockets package.


Thanks again.

Re: Using GNAT.Sockets

[Duncan Sands]

Hi markp,

> Thanks for your reply. In case (1), that is what is occuring. When I
> call Receive_Socket again to get the rest of the data, I'm wondering if
> the call will place the new data at the beginning of the item buffer.
> That would mean I would have to copy it out before I do a subsequent
> read. Is this the case?

Suppose your buffer is My_Buffer, and after the first call you see
Last < My_Buffer'Last (note that if Last < My_Buffer'First then the
connection has gone down).  Then you can do the following:

   procedure Receive_Socket
     (Socket => My_Socket,
      Item   => My_Buffer (Last + 1 .. My_Buffer'Last),
      Last   => Last);

> I do not want a higher level routine. I would like to stay withing the
> GNAT.Sockets package.

GNAT.Sockets provides higher level routines - the stream stuff.

Ciao,

Duncan.

Re: Using GNAT.Sockets

[markp]

Duncan Sands wrote:
> Hi markp,
>
> > Thanks for your reply. In case (1), that is what is occuring. When
I
> > call Receive_Socket again to get the rest of the data, I'm
wondering if
> > the call will place the new data at the beginning of the item
buffer.
> > That would mean I would have to copy it out before I do a
subsequent
> > read. Is this the case?
>
> Suppose your buffer is My_Buffer, and after the first call you see
> Last < My_Buffer'Last (note that if Last < My_Buffer'First then the
> connection has gone down).  Then you can do the following:
>
>    procedure Receive_Socket
>      (Socket => My_Socket,
>       Item   => My_Buffer (Last + 1 .. My_Buffer'Last),
>       Last   => Last);
>
> > I do not want a higher level routine. I would like to stay withing
the
> > GNAT.Sockets package.
>
> GNAT.Sockets provides higher level routines - the stream stuff.
>
> Ciao,
>
> Duncan.

Duncan,

Thanks for your reply. It does what I want it to do. I have one other
question. My assumption is that I have to read the data into My_buffer,
which is of a type Stream_Elemet_Array. If there a way to read the data
directly into an Ada record type, as opposed to a Stream_Element_Array?
Otherwise, I will have to read the socket and then copy the bytes into
the record type and act on it there. Is there a way to avoid this extra
copy and go directly to my data type?

Thanks once again for your help,

Mark

Re: Using GNAT.Sockets

[Michael Paus]

markp wrote:

> Thanks for your reply. It does what I want it to do. I have one other
> question. My assumption is that I have to read the data into My_buffer,
> which is of a type Stream_Elemet_Array. If there a way to read the data
> directly into an Ada record type, as opposed to a Stream_Element_Array?
> Otherwise, I will have to read the socket and then copy the bytes into
> the record type and act on it there. Is there a way to avoid this extra
> copy and go directly to my data type?

That's where the "stream stuff" comes into play. If you use a
socket stream instead of a plain socket you do not have to care
about buffer sizes and such stuff. Instead you can then use the
stream attributes of your record type. Something like

declare
  Rec : My_Record := My_Record'Input(My_Socket_Stream_Access);
begin
  ...
end;

Michael

Re: Using GNAT.Sockets

[markp]

Micheal,

Thanks for your input. I tried what you said but could not get it to
work. Here is what I did:

type Data_Type is array(1..800) of Byte;
Data               : Data_Type := (others => 0);
.
.
<Created socket using GNAT.Sockets>
.
.
After successful connection I did the following:

My_Stream_Access := GNAT.Sockets.Stream(Socket => Socket);

Then, I tried to read the socket as follows:

Data := Data_Type'Input(My_Stream_Access);

The data I got was incorrect. What di dI do wrong?

Thanks again for your help.

Mark

Re: Using GNAT.Sockets

[Adrien Plisson]

markp wrote:
> type Data_Type is array(1..800) of Byte;
> Data               : Data_Type := (others => 0);
> ..
> ..
> <Created socket using GNAT.Sockets>
> ..
> ..
> After successful connection I did the following:
> 
> My_Stream_Access := GNAT.Sockets.Stream(Socket => Socket);
> 
> Then, I tried to read the socket as follows:
> 
> Data := Data_Type'Input(My_Stream_Access);
> 
> The data I got was incorrect. What di dI do wrong?

who sent the 800 bytes you read on the network ? is it an Ada 
application using streams too (and specifically Data_Type'Output)?

-- 
rien

Re: Using GNAT.Sockets

[markp]

No,

It is an Ada program that does not use streams. It uses simply
address/byte count passed to the TCP. I'm guessing by your answer it
must use streams also. I don't have control over the other side, so,
does this mean I will not be able to use streams on my side?

Mark

Re: Using GNAT.Sockets

[Adrien Plisson]

markp wrote:

> No,
> 
> It is an Ada program that does not use streams. It uses simply
> address/byte count passed to the TCP. I'm guessing by your answer it
> must use streams also. I don't have control over the other side, so,
> does this mean I will not be able to use streams on my side?
> 
> Mark

the 'Input attribute, when used on an array type, first tries to read 
the bounds of the array (ARM95 13.13.2 §26). those bounds are 
definitely NOT part of the data received, since the sender did not use 
streams, and that may explain the corruption you encountered (you are 
lucky: on fr.comp.lang.ada, another poster got a Storage_Error).

the solution is:
- either use 'Read and 'Write instead of 'Input and 'Output
- or rewrite the sender so that it uses 'Input and 'Output.

you should read ARM95 13.13.2 to understand what data are placed on 
the stream when using stream attributes.

-- 
rien

Re: Using GNAT.Sockets

[markp]

I have no control on the other side. I tried using the 'Read, but it
wants 2 parameters. Can you tell me what they are?

Lastly, when the socket connection is lost, by using streams, what kind
of feedback should I expect? An exception? 

Mark

Re: Using GNAT.Sockets

[markp]

I figured out the parameters for the read call.

Data_Type'Read(
   My_Stream_Access,
  Data);

However, when I tried to send a different type of message immediately
after the first one, I get an exception:ADA.IO_EXCEPTIONS.END_ERROR.

What do I need to fix this?

Thanks,

Mark

Re: Using GNAT.Sockets

[Eric Jacoboni]

"markp" <markwork66@yahoo.com> writes:

> I have no control on the other side. I tried using the 'Read, but it
> wants 2 parameters. Can you tell me what they are?

I've had the same problem : writing a simple POP3 client with
Gnat.Sockets and Streams is not so easy. Looks like streams are good
when you write both the server and the clients apps, but not when you
have to talk to a existing server (at least, it's the conclusion where
i am now).

I think i've found a solution to circumvent this problem : using
Gnat.Sockets.Send_Socket and Gnat.Sockets.Receive_Socket procedures.
The problem, now, is to play (well... to fight) with unchecked
conversions between Stream_Element_Array/Stream_Element_Offset and
String/Positive in both direction...

If only AdaSockets wanted to build ok on my plateform!
-- 
�ric Jacoboni, n� il y a 1417300708 secondes

Re: Using GNAT.Sockets

[Pascal Obry]

Eric Jacoboni <jaco@neottia.net> writes:

> I've had the same problem : writing a simple POP3 client with
> Gnat.Sockets and Streams is not so easy. Looks like streams are good

FYI, a POP3 client is provided with AWS. I must say that it is quite trivial
and works on top of AWS.Net's socket layer (based on GNAT.Sockets or AdaSockets
implementations). You can also have a look at the WebMail service which uses
the SMTP and POP3 protocols.

Pascal.

-- 

--|------------------------------------------------------
--| Pascal Obry                           Team-Ada Member
--| 45, rue Gabriel Peri - 78114 Magny Les Hameaux FRANCE
--|------------------------------------------------------
--|              http://www.obry.net
--| "The best way to travel is by means of imagination"
--|
--| gpg --keyserver wwwkeys.pgp.net --recv-key C1082595

Re: Using GNAT.Sockets

[Eric Jacoboni]

Pascal Obry <pascal@obry.net> writes:

> FYI, a POP3 client is provided with AWS.

Yes, i know. But AWS cannot solve my particular problem as:

1) Like AdaSockets, it refuses to build on my system (Mac OS X) and
   i've no so much time/skill to investigate more on that.

2) I was talking about POP3 just for the record. In fact, i'm
   searching some running examples of Ada code to show to my students
   that is a life beside socket(2) while staying on a relative "low"
   level.

-- 
�ric Jacoboni, n� il y a 1417308967 secondes

Re: Using GNAT.Sockets

[Pascal Obry]

Eric Jacoboni <jaco@neottia.net> writes:

> 1) Like AdaSockets, it refuses to build on my system (Mac OS X) and
>    i've no so much time/skill to investigate more on that.

I know some people have been able to build AWS on Mac OSX. But I can't help.

Pascal.

-- 

--|------------------------------------------------------
--| Pascal Obry                           Team-Ada Member
--| 45, rue Gabriel Peri - 78114 Magny Les Hameaux FRANCE
--|------------------------------------------------------
--|              http://www.obry.net
--| "The best way to travel is by means of imagination"
--|
--| gpg --keyserver wwwkeys.pgp.net --recv-key C1082595

Re: Using GNAT.Sockets

[Björn Lundin]

2005-04-19 kl. 01.00 skrev Eric Jacoboni:

>
> 1) Like AdaSockets, it refuses to build on my system (Mac OS X) and
>    i've no so much time/skill to investigate more on that.

if you can live with linking it static, download adasockets 1.8.4.7

then put

sockets-constants.ads   sockets-naming.ads      sockets-utils.adb
sockets-link.ads        sockets-stream_io.adb   sockets-utils.ads
sockets-multicast.adb   sockets-stream_io.ads   sockets.adb
sockets-multicast.ads   sockets-thin.ads        sockets.ads
sockets-naming.adb      sockets-types.ads       test.adb

into a directory in your SOURCE_PATH of gnat
(socket-thin.ads was called socket-thin.ads.unix,
and sockets-constants.ads was generated by modifying the constants.sh 
script

some constnts failed, but I did not bother, but the failed ones are:

constants.c:150: error: `FIOSSAIOOWN' undeclared (first use in this 
function)
constants.c:150: error: `I_SETSIG' undeclared (first use in this 
function)
constants.c:150: error: `S_RDNORM' undeclared (first use in this 
function)
constants.c:150: error: `S_WRNORM' undeclared (first use in this 
function)


minimac: bnl$ cat sockets-constants.ads
--  This package has been generated automatically on:
--  Darwin minimac.lundin.homelinux.net 7.9.0 Darwin Kernel Version
--  7.9.0: Wed Mar 30 20:11:17 PST 2005; 
root:xnu/xnu-517.12.7.obj~1/RELEASE_P
--  PC Power Macintosh powerpc
--  Generation date: Tue Apr 19 19:09:06 CEST 2005
--  Any change you make here is likely to be lost !
package Sockets.Constants is
    Tcp_Nodelay          : constant := 16#0001#;
    Af_Inet              : constant := 16#0002#;
    Af_Unix              : constant := 16#0001#;
    Sock_Stream          : constant := 16#0001#;
    Sock_Dgram           : constant := 16#0002#;
    Eintr                : constant := 16#0004#;
    Eagain               : constant := 16#0023#;
    Ewouldblock          : constant := 16#0023#;
    Einprogress          : constant := 16#0024#;
    Ealready             : constant := 16#0025#;
    Eisconn              : constant := 16#0038#;
    Econnrefused         : constant := 16#003D#;
    Fndelay              : constant := 16#0004#;
    Fioasync             : constant := -2147195267;
    F_Getfl              : constant := 16#0003#;
    F_Setfl              : constant := 16#0004#;
    Fiossaioown          : constant := 16#0004#;
    So_Rcvbuf            : constant := 16#1002#;
    So_Reuseaddr         : constant := 16#0004#;
    So_Reuseport         : constant := 16#0200#;
    Sol_Socket           : constant := 16#FFFF#;
    Sigterm              : constant := 16#000F#;
    Sigkill              : constant := 16#0009#;
    O_Rdonly             : constant := 16#0000#;
    O_Wronly             : constant := 16#0001#;
    O_Rdwr               : constant := 16#0002#;
    Host_Not_Found       : constant := 16#0001#;
    Try_Again            : constant := 16#0002#;
    No_Recovery          : constant := 16#0003#;
    No_Data              : constant := 16#0004#;
    No_Address           : constant := 16#0004#;
    Pollin               : constant := 16#0001#;
    Pollpri              : constant := 16#0002#;
    Pollout              : constant := 16#0004#;
    Pollerr              : constant := 16#0008#;
    Pollhup              : constant := 16#0010#;
    Pollnval             : constant := 16#0020#;
    I_Setsig             : constant := 16#0020#;
    S_Rdnorm             : constant := 16#0020#;
    S_Wrnorm             : constant := 16#0020#;
    Ipproto_Ip           : constant := 16#0000#;
    Ip_Add_Membership    : constant := 16#000C#;
    Ip_Multicast_Loop    : constant := 16#000B#;
    Ip_Multicast_Ttl     : constant := 16#000A#;
    Ip_Drop_Membership   : constant := 16#000D#;
    O_Nonblock           : constant := 16#0004#;
    Msg_Peek             : constant := 16#0002#;
    Fionbio              : constant := -2147195266;
    Fionread             : constant := 16#4004667F#;
    So_Sndbuf            : constant := 16#1001#;
    Af_Inet6             : constant := 16#001E#;
    Ai_Addrconfig        : constant := 16#0400#;
    Ai_All               : constant := 16#0100#;
    Ai_Canonname         : constant := 16#0002#;
    Ai_Default           : constant := 16#0600#;
    Ai_Mask              : constant := 16#0007#;
    Ai_Numerichost       : constant := 16#0004#;
    Ai_Passive           : constant := 16#0001#;
    Ai_V4mapped          : constant := 16#0800#;
    Ai_V4mapped_Cfg      : constant := 16#0200#;
    Ni_Dgram             : constant := 16#0010#;
    Ni_Maxhost           : constant := 16#0401#;
    Ni_Maxserv           : constant := 16#0020#;
    Ni_Namereqd          : constant := 16#0004#;
    Ni_Nofqdn            : constant := 16#0001#;
    Ni_Numerichost       : constant := 16#0002#;
    Ni_Numericserv       : constant := 16#0008#;
    Ni_Withscopeid       : constant := 16#0020#;
    Ipproto_Ipv6         : constant := 16#0029#;
    Ipv6_Unicast_Hops    : constant := 16#0004#;
    Ipv6_Multicast_If    : constant := 16#0009#;
    Ipv6_Multicast_Hops  : constant := 16#000A#;
    Ipv6_Multicast_Loop  : constant := 16#000B#;
    Ipv6_Join_Group      : constant := 16#000C#;
    Ipv6_Leave_Group     : constant := 16#000D#;
end Sockets.Constants;



By doing this, I get to use 'socket' 'connect' put_line' and 'get'
properly by testing with my webserver

minimac: bnl$ cat test.adb
with sockets; use sockets;
with Text_io;
procedure test is
   My_sock : socket_fd;
begin
   Socket(My_sock);
   Connect(My_Sock,"della",80);
   Put_Line(My_Sock, "GET /");
   Text_Io.Put_Line(Get(My_Sock));
end test;



>
Björn Lundin
bnl at spray dot se

Re: Using GNAT.Sockets

[Eric Jacoboni]

Bj�rn Lundin <bnl@spray.se> writes:

> if you can live with linking it static
[snip]

Thanks a lot, it works!

-- 
�ric Jacoboni, n� il y a 1417381620 secondes

Re: Using GNAT.Sockets

[Marc A. Criley]

markp wrote:

> Thanks for your reply. It does what I want it to do. I have one other
> question. My assumption is that I have to read the data into My_buffer,
> which is of a type Stream_Elemet_Array. If there a way to read the data
> directly into an Ada record type, as opposed to a Stream_Element_Array?
> Otherwise, I will have to read the socket and then copy the bytes into
> the record type and act on it there. Is there a way to avoid this extra
> copy and go directly to my data type?

Take a look at "A Socket-Based Manifestion of Streams" at 
http://www.sigada.org/ada_letters/june2001/socket_streams.pdf

Marc A. Criley

Re: Using GNAT.Sockets

[Bob Spooner]

Hi Markwork66,

<markwork66@yahoo.com> wrote in message
news:1113404846.310840.322920@z14g2000cwz.googlegroups.com...
> We are just converting to GNAT and I am used to the traditional TCP
> send/receive using an address and byte count to send/receive data. I've
> used the Receive_Socket command in GNAT.Sockets and I am having trouble
> receiving all the bytes. The "Last" parameter is not always equal to
> the size of the message I'm sending and I don't see a way to call back
> into the procedure to receive the rest of the bytes.
>
> Further, we have many different sized messages and, from my little
> playing with GNAT sockets, it seemed the "Item" parameter is the only
> way to specify the number of bytes you want to receive. So, does that
> mean I would have to declare an array of bytes (the "Item" parameter)
> for all of my messages and the then do an unchecked conversion or a
> copy_bytes routine to get the data into my Ada message data type?
>
> Any help anybody could provide would be most appreciated.
>
I'm assuming that you are using TCP/IP, which is a stream-oriented protocol.
The messages you are sending may be broken up into shorter lengths depending
on the characteristics of the underlying mechanism used for moving the
information. There are several solutions to your problem, among them:

1) If you are using the same compiler and type of computer, operating
system, etc. at both ends of the circuit, you can use the default streams
mechanism to send the messages by using the Input and Output attributes.
Unlike C++, the default representation format for the streams facility for
Ada is binary rather than ASCII.

2) You can layer a record protocol on top of TCP/IP where you prepend your
message with a fixed-length integer field representing the number of bytes
in the message. Then when you receive the message, you first read the number
of bytes, and then issue additional reads until you have received the entire
message.

I hope this helps.

Bob

Re: Using GNAT.Sockets

[markp]

Bob,

Thanks for your reply. My basic quesion is I realize that a socket read
will not necessarily return all the data requested. The Receive_Socket
item input parameter takes and array. Will a subsequent read place data
at the beginning of the array, meaning I have to copy data out before I
read again?

Thanks again.

Re: Using GNAT.Sockets

[Michael Paus]

markp wrote:

> Bob,
> 
> Thanks for your reply. My basic quesion is I realize that a socket read
> will not necessarily return all the data requested. The Receive_Socket
> item input parameter takes and array. Will a subsequent read place data
> at the beginning of the array, meaning I have to copy data out before I
> read again?

Yes it does but you do not have to copy your data. Just have a look at
Duncans example. He told you already how to do it. You just have to call
this in a loop until Last = My_Buffer'Last.

   procedure Receive_Socket
     (Socket => My_Socket,
      Item   => My_Buffer (Last + 1 .. My_Buffer'Last),
      Last   => Last);

The first byte will be stored at the first position of the buffer array
you provide, but in the above example we specify a sub-range of the
whole buffer and so the first element of this is at the index Last + 1
of the whole buffer and this is exactly what you need.

Michael

Re: Using GNAT.Sockets

[Bob Spooner]

Well, it's not _quite_ that simple...
"Michael Paus" <pausnospam@nospamib-paus.com> wrote in message
news:d3o9le$cgm$1@online.de...
> markp wrote:
>
> > Bob,
> >
> > Thanks for your reply. My basic quesion is I realize that a socket read
> > will not necessarily return all the data requested. The Receive_Socket
> > item input parameter takes and array. Will a subsequent read place data
> > at the beginning of the array, meaning I have to copy data out before I
> > read again?
>
> Yes it does but you do not have to copy your data. Just have a look at
> Duncans example. He told you already how to do it. You just have to call
> this in a loop until Last = My_Buffer'Last.
>
>    procedure Receive_Socket
>      (Socket => My_Socket,
>       Item   => My_Buffer (Last + 1 .. My_Buffer'Last),
>       Last   => Last);
>
> The first byte will be stored at the first position of the buffer array
> you provide, but in the above example we specify a sub-range of the
> whole buffer and so the first element of this is at the index Last + 1
> of the whole buffer and this is exactly what you need.
>
> Michael

Your buffer needs to be big enough to read the largest message you expect,
and for the shorter messages, you need to use a slice of the buffer equal to
the size of the message being read so that you don't read in some of the
following message along with the current message.

Bob

Re: Using GNAT.Sockets

[Michael Paus]

Bob Spooner wrote:

> Well, it's not _quite_ that simple...
> "Michael Paus" <pausnospam@nospamib-paus.com> wrote in message
> news:d3o9le$cgm$1@online.de...
> 
>>markp wrote:
>>
>>
>>>Bob,
>>>
>>>Thanks for your reply. My basic quesion is I realize that a socket read
>>>will not necessarily return all the data requested. The Receive_Socket
>>>item input parameter takes and array. Will a subsequent read place data
>>>at the beginning of the array, meaning I have to copy data out before I
>>>read again?
>>
>>Yes it does but you do not have to copy your data. Just have a look at
>>Duncans example. He told you already how to do it. You just have to call
>>this in a loop until Last = My_Buffer'Last.
>>
>>   procedure Receive_Socket
>>     (Socket => My_Socket,
>>      Item   => My_Buffer (Last + 1 .. My_Buffer'Last),
>>      Last   => Last);
>>
>>The first byte will be stored at the first position of the buffer array
>>you provide, but in the above example we specify a sub-range of the
>>whole buffer and so the first element of this is at the index Last + 1
>>of the whole buffer and this is exactly what you need.
>>
>>Michael
> 
> 
> Your buffer needs to be big enough to read the largest message you expect,
> and for the shorter messages, you need to use a slice of the buffer equal to
> the size of the message being read so that you don't read in some of the
> following message along with the current message.

Yes, of course the assumption in the above example is that your intention
is to finally read exactly My_Buffer'Length bytes.

Michael