How to implement a server socket compatible to telnet?

Hello!

For some reasons I had to implement a server socket in C++. Now I want
to do the same in Ada and so I read the GNAT.Sockets-library and
implemented a shorter version of the example given in the g-
socket.ads.

The problem is that I want to implement the server in a kind, that
processes written in other languages like the tool telnet or a Java-
programme are able to communicate with it. But my server isn't able to
print a message sent by the telnet-client, so I think that I've
written something wrong in my code.

Here's the code:

with Ada.Text_IO,
Ada.Exceptions,
GNAT.Sockets;
use Ada.Text_IO,
Ada.Exceptions,
GNAT.Sockets;

procedure Server is
Host : String := "localhost";
Port : Port_Type := 7777;
Address : Sock_Addr_Type;
Server : Socket_Type;
Client : Socket_Type;
Channel : Stream_Access;
begin -- Server
Initialize;
Address.Addr := Addresses (Get_Host_By_Name (Host), 1);
Address.Port := Port;

begin
Create_Socket (Server);
Put_Line ("Server socket created");
exception
when E : Socket_Error =>
Put_Line (Standard_Error, "Create_Socket failed");
end;
-- Create server socket

begin
Set_Socket_Option (Server, Socket_Level, (Reuse_Address,
True));
Put_Line ("Socket address reused");
exception
when E : Socket_Error =>
Put_Line (Standard_Error, "Set_Socket_Option failed");
end;
-- Resuse socket address

begin
Bind_Socket (Server, Address);
Put_Line ("Server socket bound");
exception
when E : Socket_Error =>
Put_Line (Standard_Error, "Bind_Socket failed");
end;
-- Bind server

begin
Listen_Socket (Server);
Put ("Server is listening... ");
exception
when E : Socket_Error =>
Put_Line (Standard_Error, "Listen_Socket failed");
end;
-- Listening...

begin
Accept_Socket (Server, Client, Address);
Put_Line ("Got client connection");
delay 0.2;
Channel := Stream (Client);
Put_Line ("Client streamed");

declare
Message : String := String'input (Channel);
begin
Put_Line (Message);
end;
-- Get client message and print it to the screen

exception
when E : Socket_Error =>
Put_Line (Standard_Error, "Accept_Socket failed");
end;
-- Client handling

begin
Close_Socket (Client);
Put_Line ("Client closed");
Close_Socket (Server);
Put_Line ("Server closed");
exception
when E : Socket_Error =>
Put_Line (Standard_Error, "Close_Socket failed");
end;
-- Close client and server sockets

Finalize;
end Server;


The server's output is:

"Server socket created
Socket address reused
Server socket bound
Server is listening... Got client connection
Client streamed

Client closed
Server closed"


The empty line should be the message sent by telnet, but like you can
see, the message is empty.

So, can anybody explain to me, what I have done wrong?

Thank you,
Matthias

snoopysalive@googlemail.com wrote:
> Hello!
>
> For some reasons I had to implement a server socket in C++. Now I want
> to do the same in Ada and so I read the GNAT.Sockets-library and
> implemented a shorter version of the example given in the g-
> socket.ads.
>
> The problem is that I want to implement the server in a kind, that
> processes written in other languages like the tool telnet or a Java-
> programme are able to communicate with it. But my server isn't able to
> print a message sent by the telnet-client, so I think that I've
> written something wrong in my code.
>


You don't show the client code but if you really really mean it is a
telnet client then your problem is that you are using 'input. Look at
the LRM definitions for these. (looking at ada 95 here for a moment,
ARM95-13-13-2)

S'Input reads and returns one value from Stream, using any bounds or
discriminants written by a corresponding S'Output to determine how much
to read.

So, unless your telnet client is Ada aware and is sending strings
formatted per Ada string semantics with bounds, then this can't work.
The example you started from probably had a client and server who had
agreed upon a protocol that used 'input 'output semantics.

Telnet has not agreed to this protocol.

There are plenty of ways to do what you are trying.

You could probably play around with 'read 'write on characters or with

procedure Receive_Socket
(Socket : Socket_Type;
Item : out Ada.Streams.Stream_Element_Array;
Last : out Ada.Streams.Stream_Element_Offset);

or with a custom overloaded 'read that you implement with something like
Receive_Socket depending upon what you are trying to accomplish.

snoopysalive@googlemail.com wrote:

> Hello!
>
> For some reasons I had to implement a server socket in C++. Now I want
> to do the same in Ada and so I read the GNAT.Sockets-library and
> implemented a shorter version of the example given in the g-
> socket.ads.
>
> The problem is that I want to implement the server in a kind, that
> processes written in other languages like the tool telnet or a Java-
> programme are able to communicate with it. But my server isn't able to
> print a message sent by the telnet-client, so I think that I've
> written something wrong in my code.
>
> Here's the code:
>
> with Ada.Text_IO,
> Ada.Exceptions,
> GNAT.Sockets;
> use Ada.Text_IO,
> Ada.Exceptions,
> GNAT.Sockets;
>
> procedure Server is
> Host : String := "localhost";
> Port : Port_Type := 7777;
> Address : Sock_Addr_Type;
> Server : Socket_Type;
> Client : Socket_Type;
> Channel : Stream_Access;
> begin -- Server
> Initialize;
> Address.Addr := Addresses (Get_Host_By_Name (Host), 1);
> Address.Port := Port;
>
> begin
> Create_Socket (Server);
> Put_Line ("Server socket created");
> exception
> when E : Socket_Error =>
> Put_Line (Standard_Error, "Create_Socket failed");
> end;
> -- Create server socket
>
> begin
> Set_Socket_Option (Server, Socket_Level, (Reuse_Address,
> True));
> Put_Line ("Socket address reused");
> exception
> when E : Socket_Error =>
> Put_Line (Standard_Error, "Set_Socket_Option failed");
> end;
> -- Resuse socket address
>
> begin
> Bind_Socket (Server, Address);
> Put_Line ("Server socket bound");
> exception
> when E : Socket_Error =>
> Put_Line (Standard_Error, "Bind_Socket failed");
> end;
> -- Bind server
>
> begin
> Listen_Socket (Server);
> Put ("Server is listening... ");
> exception
> when E : Socket_Error =>
> Put_Line (Standard_Error, "Listen_Socket failed");
> end;
> -- Listening...
>
> begin
> Accept_Socket (Server, Client, Address);
> Put_Line ("Got client connection");
> delay 0.2;
> Channel := Stream (Client);
> Put_Line ("Client streamed");
>
> declare
> Message : String := String'input (Channel);

My bet is the problem is here above: by using String'Input, you're first trying
to read the bounds of the array. A foreign telnet client won't send
Ada-compliant arrays, but characters one by one.

You can't either use String'Read because you don't know in advance the line
length. So I'd change this to manually read one character at a time until end
of line is detected.

> begin
> Put_Line (Message);
> end;
> -- Get client message and print it to the screen
>
> exception
> when E : Socket_Error =>
> Put_Line (Standard_Error, "Accept_Socket failed");
> end;
> -- Client handling
>
> begin
> Close_Socket (Client);
> Put_Line ("Client closed");
> Close_Socket (Server);
> Put_Line ("Server closed");
> exception
> when E : Socket_Error =>
> Put_Line (Standard_Error, "Close_Socket failed");
> end;
> -- Close client and server sockets
>
> Finalize;
> end Server;
>
>
> The server's output is:
>
> "Server socket created
> Socket address reused
> Server socket bound
> Server is listening... Got client connection
> Client streamed
>
> Client closed
> Server closed"
>
>
> The empty line should be the message sent by telnet, but like you can
> see, the message is empty.
>
> So, can anybody explain to me, what I have done wrong?
>
> Thank you,
> Matthias

If your doing a direct conversion from C to Ada using sockets then you might
need to use the lower-level socket package, "GNAT.Sockets.Thin". This
package has direct library links to the sockets library routines, bypassing the
extra layer of code in "GNAT.Sockets".

Also, in "GNAT.Sockets.Thin", the "Bind" function is called "C_Bind" and is
still a function unlike "sockets where the sockets routines are mostly
procedures and are based on "Ada.Streams", in "GNAT.Sockets".

In <ca7b2304-6726-479b-89a0-67486c3dc06f@f63g2000hsf.googlegroups.com>, "snoopysalive@googlemail.com" <snoopysalive@googlemail.com> writes:
>Hello!
>
>For some reasons I had to implement a server socket in C++. Now I want
>to do the same in Ada and so I read the GNAT.Sockets-library and
>implemented a shorter version of the example given in the g-
>socket.ads.
>
>The problem is that I want to implement the server in a kind, that
>processes written in other languages like the tool telnet or a Java-
>programme are able to communicate with it. But my server isn't able to
>print a message sent by the telnet-client, so I think that I've
>written something wrong in my code.
>
>Here's the code:
>
>with Ada.Text_IO,
> Ada.Exceptions,
> GNAT.Sockets;
>use Ada.Text_IO,
> Ada.Exceptions,
> GNAT.Sockets;
>
>procedure Server is
> Host : String := "localhost";
> Port : Port_Type := 7777;
> Address : Sock_Addr_Type;
> Server : Socket_Type;
> Client : Socket_Type;
> Channel : Stream_Access;
>begin -- Server
> Initialize;
> Address.Addr := Addresses (Get_Host_By_Name (Host), 1);
> Address.Port := Port;
>
> begin
> Create_Socket (Server);
> Put_Line ("Server socket created");
> exception
> when E : Socket_Error =>
> Put_Line (Standard_Error, "Create_Socket failed");
> end;
> -- Create server socket
>
> begin
> Set_Socket_Option (Server, Socket_Level, (Reuse_Address,
>True));
> Put_Line ("Socket address reused");
> exception
> when E : Socket_Error =>
> Put_Line (Standard_Error, "Set_Socket_Option failed");
> end;
> -- Resuse socket address
>
> begin
> Bind_Socket (Server, Address);
> Put_Line ("Server socket bound");
> exception
> when E : Socket_Error =>
> Put_Line (Standard_Error, "Bind_Socket failed");
> end;
> -- Bind server
>
> begin
> Listen_Socket (Server);
> Put ("Server is listening... ");
> exception
> when E : Socket_Error =>
> Put_Line (Standard_Error, "Listen_Socket failed");
> end;
> -- Listening...
>
> begin
> Accept_Socket (Server, Client, Address);
> Put_Line ("Got client connection");
> delay 0.2;
> Channel := Stream (Client);
> Put_Line ("Client streamed");
>
> declare
> Message : String := String'input (Channel);
> begin
> Put_Line (Message);
> end;
> -- Get client message and print it to the screen
>
> exception
> when E : Socket_Error =>
> Put_Line (Standard_Error, "Accept_Socket failed");
> end;
> -- Client handling
>
> begin
> Close_Socket (Client);
> Put_Line ("Client closed");
> Close_Socket (Server);
> Put_Line ("Server closed");
> exception
> when E : Socket_Error =>
> Put_Line (Standard_Error, "Close_Socket failed");
> end;
> -- Close client and server sockets
>
> Finalize;
>end Server;
>
>
>The server's output is:
>
>"Server socket created
>Socket address reused
>Server socket bound
>Server is listening... Got client connection
>Client streamed
>
>Client closed
>Server closed"
>
>
>The empty line should be the message sent by telnet, but like you can
>see, the message is empty.
>
>So, can anybody explain to me, what I have done wrong?
>
>Thank you,
>Matthias

Thanks to all the answers of you three. Actually, I also suspected
that the problem could have something to do sort of incompatibility of
programmes written in C and those written in Ada. So, I'll try out
your solution hints. Thank you!

anon@anon.org (anon) writes:

> If your doing a direct conversion from C to Ada using sockets then you
> might need to use the lower-level socket package, "GNAT.Sockets.Thin".
> This package has direct library links to the sockets library routines,
> bypassing the extra layer of code in "GNAT.Sockets".

GNAT.Sockets.Thin says:

-- This package provides a target dependent thin interface to the sockets
-- layer for use by the GNAT.Sockets package (g-socket.ads). This package
-- should not be directly with'ed by an applications program.

which means that AdaCore feels free to change the interface in
incompatible ways at any time.

- Bob

What's your point? "GNAT.Sockets.Thin" is a universal interface to the
system socket library just like "Interface.C" is for interfacing C code. Plus,
most socket routines are standardized, in todays OS. Only the single
"GNAT.Sockets.Constants" file is altered, due to system control flags, but
most of the constants that are used for normal socket functions are
standardized as well.

And since Adacore (GNAT) is the only game around for Ada-2005 specs
there is no reason to get upset with portability because what vendor would
you port your code to!


In <wccsktcecuk.fsf@shell01.TheWorld.com>, Robert A Duff <bobduff@shell01.TheWorld.com> writes:
>anon@anon.org (anon) writes:
>
>> If your doing a direct conversion from C to Ada using sockets then you
>> might need to use the lower-level socket package, "GNAT.Sockets.Thin".
>> This package has direct library links to the sockets library routines,
>> bypassing the extra layer of code in "GNAT.Sockets".
>
>GNAT.Sockets.Thin says:
>
>-- This package provides a target dependent thin interface to the sockets
>-- layer for use by the GNAT.Sockets package (g-socket.ads). This package
>-- should not be directly with'ed by an applications program.
>
>which means that AdaCore feels free to change the interface in
>incompatible ways at any time.
>
>- Bob

anon@anon.org (anon) writes:

> What's your point?

My point is that AdaCore might change the interface GNAT.Sockets.Thin
on whim, whereas it won't change the interface GNAT.Sockets so easily,
since the latter is a documented interface. That's all -- if you're
happy with such, use GNAT.Sockets.Thin as you like.

>... "GNAT.Sockets.Thin" is a universal interface to the
> system socket library just like "Interface.C" is for interfacing C code. Plus,
> most socket routines are standardized, in todays OS. Only the single
> "GNAT.Sockets.Constants" file is altered, due to system control flags, but
> most of the constants that are used for normal socket functions are
> standardized as well.
>
> And since Adacore (GNAT) is the only game around for Ada-2005 specs
> there is no reason to get upset with portability because what vendor would
> you port your code to!
>
>
> In <wccsktcecuk.fsf@shell01.TheWorld.com>, Robert A Duff <bobduff@shell01.TheWorld.com> writes:
>>anon@anon.org (anon) writes:
>>
>>> If your doing a direct conversion from C to Ada using sockets then you
>>> might need to use the lower-level socket package, "GNAT.Sockets.Thin".
>>> This package has direct library links to the sockets library routines,
>>> bypassing the extra layer of code in "GNAT.Sockets".
>>
>>GNAT.Sockets.Thin says:
>>
>>-- This package provides a target dependent thin interface to the sockets
>>-- layer for use by the GNAT.Sockets package (g-socket.ads). This package
>>-- should not be directly with'ed by an applications program.
>>
>>which means that AdaCore feels free to change the interface in
>>incompatible ways at any time.
>>
>>- Bob

Your just trying to make Trouble and Destroy Ada! Because in that concept
you should NEVER use "GNAT.Sockets" either. That means that Ada will be
cripple because it will NEVER be able to use the Internet or Com ports, or
USB because those I/O packages are not define in the RM. Because these
extra hardware packages are not apart of the RM they must be defined
somewhere, and Adacore has choosen to places these hardware packages in
its GNAT subpackages. And in most cases they use "STADARDIZE" calls
into the OS or hardware. But in you concept the only hardware I/O package
for GNAT Ada are disk, keyboard, or simple video aka basically OS and BIOS
I/O calls. But a language must have I/O and the ability to expand beyond its
RM or it DIES! But may be that's what you want!

This "STADARDIZE" calls concepts explains one reason why the UART
package has taken so long to become apart of the GNAT system, there is
no true standards on calls for the UART even though the ports and functions
have been well defined for years.

And there is only vendor that does not maintains a level of Standardizing
behavior, and that is Sun with Java. In evey new version of Java there are
some routines that have been "DEPRECATED", but most people do not say
"DO NOT USE" that routine or package because SUN may change it. That's
because those progammers and uses want JAVA to be succeed.

So, if you want GNAT Ada to succeed as well, do not cut any package down.
You should show the person who ask the question how it should be done. And
in this case, either by writing code, given a package. Or posting a link to a
telnet program written in Ada that they can download and check out for
themselves.



In <wcctzds5oc4.fsf@shell01.TheWorld.com>, Robert A Duff <bobduff@shell01.TheWorld.com> writes:
>anon@anon.org (anon) writes:
>
>> What's your point?
>
>My point is that AdaCore might change the interface GNAT.Sockets.Thin
>on whim, whereas it won't change the interface GNAT.Sockets so easily,
>since the latter is a documented interface. That's all -- if you're
>happy with such, use GNAT.Sockets.Thin as you like.
>
>>... "GNAT.Sockets.Thin" is a universal interface to the
>> system socket library just like "Interface.C" is for interfacing C code. Plus,
>> most socket routines are standardized, in todays OS. Only the single
>> "GNAT.Sockets.Constants" file is altered, due to system control flags, but
>> most of the constants that are used for normal socket functions are
>> standardized as well.
>>
>> And since Adacore (GNAT) is the only game around for Ada-2005 specs
>> there is no reason to get upset with portability because what vendor would
>> you port your code to!
>>
>>
>> In <wccsktcecuk.fsf@shell01.TheWorld.com>, Robert A Duff <bobduff@shell01.TheWorld.com> writes:
>>>anon@anon.org (anon) writes:
>>>
>>>> If your doing a direct conversion from C to Ada using sockets then you
>>>> might need to use the lower-level socket package, "GNAT.Sockets.Thin".
>>>> This package has direct library links to the sockets library routines,
>>>> bypassing the extra layer of code in "GNAT.Sockets".
>>>
>>>GNAT.Sockets.Thin says:
>>>
>>>-- This package provides a target dependent thin interface to the sockets
>>>-- layer for use by the GNAT.Sockets package (g-socket.ads). This package
>>>-- should not be directly with'ed by an applications program.
>>>
>>>which means that AdaCore feels free to change the interface in
>>>incompatible ways at any time.
>>>
>>>- Bob

>>>>> "anon" == anon <anon@anon.org> writes:

anon> You should show the person who ask the question how it should be
anon> done. And in this case, either by writing code, given a
anon> package. Or posting a link to a telnet program written in Ada
anon> that they can download and check out for themselves.

Wow, good advice! Why didn't you follow it yourself? Where is your
code or your link?

You're a troll.

Sam
--
Samuel Tardieu -- sam@rfc1149.net -- http://www.rfc1149.net/