Sockets unit in Lazarus

[NickS]

I was looking at documentation for this unit called "Sockets" in Lazarus. It gave me 2 example units: server and client. Client compiled fine but Server did not. The reason: this line of code:

if not Accept(S, FromName, Sin, Sout) then
PError('Server : Accept : '+fromname) ;

(find the full example here: http://www.freepascal.org/docs-html/.../fpaccept.html its at the bottom)

From what I can understand, the Accept function is deprecated, which makes sense since it won't compile anyways because FromName is a string and it wants something else.

Could someone help me problem solve and replace this line of code with the non-deprecated one: fpAccept. I would be so greatful!

[Murmandamus]

The examples are ancient history, back to a time where they implemented socket-to-file functions, which are now deprecated. Now, they just pass-through to the underlying API socket calls, so those won't compile anymore without recompiling the sockets unit with the legacy symbol defined.

I've had issues with the FP sockets unit being incomplete/wrong in the past. I ended up using my own instead.

If you just want to do it with the sockets unit, no fancy textfile-handling (which is annoying anyway), this should come closer to what you are looking for:

Program Server;

Uses Sockets;

Var
  Buffer           : String[255];
  Count            : LongInt;
  ClientSocket     : Longint;
  ListenSocket     : Longint;
  ServerAddr       : TInetSockAddr;
  ClientAddr       : TInetSockAddr;
  ClientAddrSize   : LongInt;

Procedure PrintError (Const Msg : String);
  Begin
  Writeln (Msg,SocketError);
  Halt(100);
  End;

Begin
  ListenSocket := fpSocket (AF_INET,SOCK_STREAM,0);
  If ListenSocket = SOCKET_ERROR Then
    PrintError ('Server : Socket : ');
  ServerAddr.sin_family := AF_INET;
  { port 50000 in network order }
  ServerAddr.sin_port := htons(50000);
  ServerAddr.sin_addr.s_addr := htonl($7F000001);
  If fpBind(ListenSocket,@ServerAddr,sizeof(ServerAddr)) = SOCKET_ERROR Then
   PrintError ('Server : Bind : ');
  If fpListen (ListenSocket,1) = SOCKET_ERROR Then
   PrintError ('Server : Listen : ');
  Writeln('Waiting for Connect from Client, run now sock_cli in an other tty');
  ClientAddrSize := sizeof(ClientAddr);
  ClientSocket := fpaccept(ListenSocket,@ClientAddr,@ClientAddrSize);
  If ClientSocket = SOCKET_ERROR Then
   PrintError('Server : Accept : ');
  Buffer := 'Message From Server';
  Count := Length(Buffer);
  If (fpsend(ClientSocket,@Buffer[1],Count,0) = Count) Then
    Begin
    Repeat
      Count := fprecv(ClientSocket,@Buffer[1],255,0);
      If (Count <> SOCKET_ERROR) And (Count > 0) Then
        Begin
        SetLength(Buffer,Count);
        Writeln('Server : read : ',Buffer);
        End;
    Until (Count = SOCKET_ERROR) Or (Count = 0);
    End;
  CloseSocket(ClientSocket);
  CloseSocket(ListenSocket);
End.

Program Client;

Uses Sockets;

Procedure PrintError(Const Msg : String);
  Begin
  Writeln(Msg,SocketError);
  Halt(100);
  End;


Var
  ServerAddr       : TInetSockAddr;
  Buffer           : String[255];
  ServerSocket     : Longint;
  Count            : Longint;
  I                : Integer;

Begin
  ServerSocket := fpSocket(AF_INET,SOCK_STREAM,0);
  If ServerSocket = SOCKET_ERROR Then
   PrintError('Client : Socket : ');
  ServerAddr.sin_family := AF_INET;
  { port 50000 in network order }
  ServerAddr.sin_port := htons(50000);
  { localhost : 127.0.0.1 in network order }
  ServerAddr.sin_addr.s_addr :=htonl($7F000001);
  If fpconnect(ServerSocket,@ServerAddr,Sizeof(ServerAddr)) = SOCKET_ERROR Then
   PrintError('Client : Connect : ');
  Buffer := 'This is a textstring sent by the Client.';
  For I := 1 To 10 Do
    Count := fpsend(ServerSocket,@Buffer[1],Length(Buffer),0);
  Count := fprecv(ServerSocket,@Buffer[1],255,0);
  if Count <> SOCKET_ERROR Then
    Begin
    SetLength(Buffer,Count);
    Writeln('Server sent: ',Buffer);
    End;
  CloseSocket(ServerSocket);
End.

[NickS]

This code looks great and compiles! That makes me so happy =) except one problem/my not understanding cause I'm horrible with anything to do with networking. When I run the server it says Server: Socket: 0 then finishes. Is this intended? Again, I'm sorry for knowing so little, I'm trying to learn =P

Once again thank you for your help!

[Murmandamus]

Bleh.. had a copy/paste error in the server. Sorry about that; that code is likely not bug-free, I just syntax-checked it to be sure the compiler wouldn't barf on it. It is one of my personal rules about providing examples. I edited the server code to fix that bug. Try it now and see if it works. There may be an issue with the way I am handling the string buffer, but it should work.

[NickS]

Yeah it doesn't look like its sending the string buffer to the client. When I run the server it says this:

Waiting for Connect from Client, run now sock_cli in an other tty
Server : Accept : 10014

Then it instantly finishes, not sending any buffers or anything. The client runs and simply says:

Client : Connect : 10061

Then finishes. *boggle*

[chronozphere]

Just a general tip for all who want to do network programming: Install wireshark and learn how to use it. It allows you to monitor your network traffic with great detail.

During my computer networks course at university, I had to do some programming assignments and wireshark helped me ALOT there.