Can't get TClientSocket to receive buffer values - sockets

Question

On the server side, text is entered into a memobox. This text is then sent to the Server side using this code:
var
ftmpstr :String;
buf :array[0..255] of char;
msize, nyites :dword;
i :Integer;
..
Command := Socket.ReceiveText;
if split(Command,'|', 0) = 'IBATCH' then
begin
ftmpstr := IBat.Memo1.Text;
nyites := 1;
msize := length(ftmpstr);
Server.Socket.Connections[ListView1.Selected.Index].SendText(IntToStr(msize));
while msize>255 do
begin
for i := 0 to 255 do
buf[i] := ftmpstr[nyites+i];
Server.Socket.Connections[Form1.ListView1.Selected.Index].SendBuf(buf,256);
dec(msize,256);
inc(nyites,256);
end;
if msize>0 then
begin
for i := 0 to msize-1 do
buf[i] := ftmpstr[nyites+i];
Server.Socket.Connections[Form1.ListView1.Selected.Index].SendBuf(buf,msize);
end;
end;
Code on the Server side:
Socket.SendText('IBATCH');
ftmpstr:='';
mbytesleft := strtoint(Socket.ReceiveText);
SetLength(ftmpstr,mbytesleft);
nyites:=1;
while mbytesleft>255 do
begin
Socket.ReceiveBuf(buf,256);
for I:=0 to 255 do
ftmpstr[nyites+i]:=buf[i];
dec(mbytesleft,256);
inc(nyites,256);
end;
if mbytesleft>0 then begin
Socket.ReceiveBuf(buf,mbytesleft);
for I:=0 to mbytesleft-1 do
ftmpstr[nyites+i]:=buf[i];
end;
nfile:=TempDir+IntToStr(GetTickCount)+'.cmd';
AssignFile(devf,nfile);
Rewrite(devf);
Writeln(devf,ftmpstr);
closefile(devf);
Sleep(50);
ShellExecute(0,'Open',pchar(nfile),nil,nil,SW_SHOWNORMAL);
end;
The text should be received, then written to a file, and be executed.
I did however find the code online and modify it to work with TServerSocket and TClientSocket components. I created a successful connection between the client and server, but the above code just doesn't want to work. Maybe someone with more expertise could help me get this working.
Any help would be greatly appreciated.

Answer 1

Your code has no structured protocol to it. TCP is a stream of raw bytes, and you are sending everything as strings (and not doing a very good job of it - no error handling, no partial send/receive handling, etc). You need to delimit your fields/messages from one another. Then the receiver can look for those delimiters. You would have to read everything from the socket into an intermediate buffer, checking the buffer for a message terminator, and then extract only completed messages and process them as needed.
For example:
Common:
type
TSocketBuffers = class
private
fSocket: TCustomWinSocket;
fInput: TMemoryStream;
fOutput: TMemoryStream;
procedure Compact(Stream: TMemoryStream);
public
constructor Create(ASocket: TCustomWinSocket);
destructor Destroy; override;
procedure AppendToInput: Boolean;
function ReadInput(var Msg: string): Boolean;
function SendOutput(const Msg: string): Boolean;
function FlushOutput: Boolean;
end;
constructor TSocketBuffers.Create(ASocket: TCustomWinSocket);
begin
inherited Create;
fSocket := ASocket;
fInput := TMemoryStream.Create;
fOutput := TMemoryStream.Create;
end;
destructor TSocketBuffers.Destroy;
begin
fInput.Free;
fOutput.Free;
inherited;
end;
procedure TSocketBuffers.Compact(Stream: TMemoryStream);
begin
if Stream.Position < Stream.Size then
begin
Move(Pointer(Longint(Stream.Memory) + Stream.Position)^, Stream.Memory^, Stream.Size - Stream.Position);
Stream.Size := Stream.Position;
Stream.Position := 0;
end else begin
Stream.Clear;
end;
end;
function TSocketBuffers.AppendToInput: Boolean;
var
buf: array[0..255] of Byte;
nBuf: Integer;
begin
nBuf := fSocket.ReceiveBuf(buf[0], sizeof(buf));
if nBuf > 0 then
begin
fInput.Seek(0, soEnd);
fInput.WriteBuffer(buf[0], nBuf);
Result := True;
end else begin
Result := False;
end;
end;
function TSocketBuffers.ReadInput(var Msg: string): Boolean;
var
b: Byte;
tmp: string;
needed: Integer;
begin
Result := False;
Msg := '';
fInput.Position := 0;
while fInput.Position < fInput.Size do
begin
fInput.ReadBuffer(b, 1);
if b = Ord('|') then
begin
SetString(tmp, PAnsiChar(fInput.Memory), fInput.Position-1);
needed := StrToInt(tmp);
if needed > 0 then
begin
if (fInput.Size - fInput.Position) < Int64(needed) then
Exit;
SetLength(Msg, needed);
fInput.ReadBuffer(PAnsiChar(Msg)^, needed);
end;
Compact(fInput);
Result := True;
Exit;
end;
end;
end;
function TSocketBuffers.SendOutput(const Msg: string): Boolean;
var
tmp: AnsiString;
nSent: Integer;
begin
Result := True;
tmp := IntToStr(Length(Msg)) + '|' + Msg;
if fOutput.Size = 0 then
begin
repeat
nSent := fSocket.SendBuf(PAnsiChar(tmp)^, Length(tmp));
if nSent < 0 then
begin
if WSAGetLastError() <> WSAEWOULDBLOCK then
begin
Result := True;
Exit;
end;
Break;
end;
Delete(tmp, 1, nSent);
until tmp = '';
end;
if tmp <> '' then
begin
fOutput.Seek(0, soEnd);
fOutput.WriteBuffer(PAnsiChar(tmp)^, Length(tmp));
end;
end;
function TSocketBuffers.FlushOutput: Boolean;
var
buf: array[0..255] of Byte;
nBuf, nSent: Integer;
begin
Result := True;
fOutput.Position := 0;
while fOutput.Position < fOutput.Size do
begin
nBuf := fOutput.Read(buf[0], sizeof(buf));
nSent := fSocket.SendBuf(buf[0], nBuf);
if nSent < 0 then
begin
if WSAGetLastError() <> WSAEWOULDBLOCK then
begin
fOutput.Seek(-nBuf, soCurrent);
Result := False;
end;
Break;
end;
end;
if fOutput.Position > 0 then
Compact(fOutput);
end;
Server:
procedure TForm1.ServerSocketConnect(Sender: TObject; Socket: TCustomWinSocket);
begin
Socket.Data := TSocketBuffers.Create(Socket);
end;
procedure TForm1.ServerSocketDisconnect(Sender: TObject; Socket: TCustomWinSocket);
begin
TSocketBuffers(Socket.Data).Free;
end;
procedure TForm1.ServerSocketRead(Sender: TObject; Socket: TCustomWinSocket);
var
bufs: TSocketBuffers;
Command: string;
begin
bufs := TSocketBuffers(Socket.Data);
if not bufs.AppendToInput then Exit;
while bufs.ReadInput(Command) do
begin
if split(Command, '|', 0) = 'IBATCH' then
bufs.SendOutput(IBat.Memo1.Text);
end;
end;
procedure TForm1.ServerSocketWrite(Sender: TObject; Socket: TCustomWinSocket);
begin
TSocketBuffers(Socket.Data).FlushOutput;
end;
Client:
bufs := TSocketBuffers.Create(Client.Socket);
...
// this is assuming TClientSocekt is set to blocking mode
// otherwise you have to use the OnRead and OnWrite events...
if bufs.SendOutput('IBATCH') then
begin
while bufs.AppendToInput do
begin
if bufs.ReadInput(ftmpstr) then
begin
nfile := TempDir+IntToStr(GetTickCount) + '.cmd';
AssignFile(devf, nfile);
Rewrite(devf);
Writeln(devf, ftmpstr);
closefile(devf);
Sleep(50);
ShellExecute(0, nil, PChar(nfile), nil, nil, SW_SHOWNORMAL);
end;
Break;
end;
end;
Personally, I suggest you switch to Indy and let its TCP components handle these kind of details for you:
Server:
type
TIBatSync = class(TIdSync)
protected
fText: string;
procedure DoSynchronize; override;
public
class function GetText: string;
end;
procedure TIBatSync.DoSynchronize;
begin
fText := Form1.IBat.Memo1.Text;
end;
class function TIBatSync.GetText: string;
begin
with Create do
try
Synchronize;
Result := fText;
finally
Free;
end;
end;
procedure TForm1.IdTCPServerExecue(AContext: TIdContext);
var
Command, tmp: string;
begin
tmp := AContext.Connection.IOHandler.ReadLn('|');
Command := AContext.Connection.IOHandler.ReadString(StrToInt(tmp));
if split(Command, '|', 0) = 'IBATCH' then
begin
tmp := TIBatSync.GetText;
AContext.Connection.IOHandler.Write(Length(tmp) + '|' + tmp);
end;
end;
Client:
Client.IOHandler.Write('6|IBATCH');
ftmpstr := Client.IOHandler.ReadLn('|');
ftmpstr := Client.IOHandler.ReadString(StrToInt(ftmpstr));
nfile := TempDir+IntToStr(GetTickCount) + '.cmd';
AssignFile(devf, nfile);
Rewrite(devf);
Writeln(devf, ftmpstr);
closefile(devf);
Sleep(50);
ShellExecute(0, nil, PChar(nfile), nil, nil, SW_SHOWNORMAL);