recv function not receive all bytes - sockets

Question

I'm using delphi (RAD Studio 10) to make a little app client and server. The server only send text.
The next functions returns correctly the number of bytes sent. For example I send 'hello' (client side):
procedure TTCPConnection.Write(S: String);
var buff : string;
begin
buff = S+EOL;
WriteBuffer(buff, Length(buff));
end;
Where: S = 'hello' and EOL = #13#10, so buff = 'hello'+EOL.
procedure TTCPConnection.WriteBuffer(var Buffer; const Len: Cardinal);
var
a : Int16;
begin
a := send(FSocket, Buffer, Len, 0);
if (a = SOCKET_ERROR) and FConnected then
begin
HandleError;
Disconnect;
end;
end;
in the previous function: send(FSocket, Buffer, Len, 0) return 7, number of bytes sent ('hello+EOL').
Server side:
function TTCPConnection.ReadLn(Delim: String = EOL): String;
const BUFFER_SIZE = 255;
var
Buff, Buf: string;
I, L: Cardinal;
begin
Result := '';
I := 1;
L := 1;
SetLength(Buff, BUFFER_SIZE);
Buf := AnsiString(Buff);
while Connected and (L <= Cardinal(Length(Delim))) do
begin
if recv(FSocket, Buffer, Len, 0) < 1 then exit;
Buf := Buff[I];
if Buff[I] = Delim[L] then
...
...
end;
(In the previous code I include Buf var for debugger purposes only). When I debug obtain this result:
Buff = {'h', #0, 'e', #0, 'l', #0, 'l'} (7 bytes) and the next time this line is executed recv(FSocket, Buffer, Len, 0) the program does nothing, I guess this is because recv function has nothing to receive (7 bytes were sent).
I need help to make all bytes are received correctly. I do not know why they are in that order (h-#0-e-#0-l-#0-l).

Answer 1

Starting with RAD Studio 2009, string consists of WideChar characters. Char is an alias for WideChar and is 16 bit. The Length() function returns number of characters, not bytes.
You may want to consider using TEncoding to convert your string to a TBytes (array of byte) for sending and vice versa for receiving. I don't know your TTCPConnection class, so it may be you need to tweek the code, but here for the sending part using TEncoding.UTF8:
procedure TTCPConnection.Write(S: String);
var buff : TBytes;
begin
buff := TEncoding.UTF8.GetBytes(S+EOL); // Convert to bytes using UTF8 encoding
WriteBuffer(buff, Length(buff));
end;
And here is my receiver code from a testproject in XE5 where I used the TTcpServer component
procedure TForm3.TcpServer1Accept(Sender: TObject;
ClientSocket: TCustomIpClient);
var
a: array[0..255] of byte;
b: TBytes;
i, n: integer;
s: string;
begin
n := ClientSocket.ReceiveBuf(a,255,0);
SetLength(b, n);
for i := Low(b) to High(b) do b[i] := a[i]; // copy from the receive buffer
s := TEncoding.UTF8.GetString(b); // convert UTF8 bytes to string
Memo1.Lines.Add(format('%4d %s',[n,s]));
end;
Finally a few useful links to the documentation:
TEncoding
UTF-8 Conversion Routines