Sockets unit in Lazarus

[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.