Read all available bytes from TCP Socket (unknown byte count) - sockets

Question

I am having Problems useing the Indy TIdTCPClient.
I want to call a function, everytime if there is Data available on the socket. For this I have a Thread calling IdTCPClient->Socket->Readable(100).
The function itself looks like this:
TMemoryStream *mStream = new TMemoryStream;
int len = 0;
try
{
if(!Form1->IdTCPClient2->Connected())
Form1->IdTCPClient2->Connect();
mStream->Position = 0;
do
{
Form1->IdTCPClient2->Socket->ReadStream(mStream, 1);
}
while(Form1->IdTCPClient2->Socket->Readable(100));
len = mStream->Position;
mStream->Position = 0;
mStream->Read(Buffer, len);
}catch(Exception &Ex) {
Form1->DisplaySSH->Lines->Add(Ex.Message);
Form1->DisplaySSH->GoToTextEnd();
}
delete mStream;
It will not be called directly within the thread, but the thread triggers an event, which is calling this function. Which means I am using Readable(100) twice, without reading data in betwee.
So since I dont know how many bytes I have to read I thought I can read one byte, check if there is more available and then read another byte.
The Problem here is that the do while loop doesnt loop, it just runs once.
I am guessing that Readable does not quite wokt the way I need it to.
Is there any other way to receive all the bytes available in the Socket?

Answer 1

You should not be using Readable() directly in this situation. That call reports whether the underlying socket has pending unread data in its internal kernel buffer. That does not take into account that the TIdIOHandler may already have unread data in its InputBuffer that is left over from a previous read operation.
Use the TIdIOHandler::CheckForDataOnSource() method instead of TIdIOHandler::Readable():
TMemoryStream *mStream = new TMemoryStream;
try
{
if (!Form1->IdTCPClient2->Connected())
Form1->IdTCPClient2->Connect();
mStream->Position = 0;
do
{
if (Form1->IdTCPClient2->IOHander->InputBufferIsEmpty())
{
if (!Form1->IdTCPClient2->IOHander->CheckForDataOnSource(100))
break;
}
Form1->IdTCPClient2->IOHandler->ReadStream(mStream, Form1->IdTCPClient2->IOHandler->InputBuffer->Size, false);
/* alternatively:
Form1->IdTCPClient2->IOHandler->InputBuffer->ExtractToStream(mStream);
*/
}
while (true);
// use mStream as needed...
}
catch (const Exception &Ex) {
Form1->DisplaySSH->Lines->Add(Ex.Message);
Form1->DisplaySSH->GoToTextEnd();
}
delete mStream;
Or, you can alternatively use TIdIOHandler::ReadBytes() instead of TIdIOHandler::ReadStream(). If you set its AByteCount parameter to -1, it will return only the bytes that are currently available (if the InputBuffer is empty, ReadBytes() will wait up to the ReadTimeout interval for the socket to receive any new bytes) 1:
try
{
if (!Form1->IdTCPClient2->Connected())
Form1->IdTCPClient2->Connect();
TIdBytes data;
do
{
if (Form1->IdTCPClient2->IOHander->InputBufferIsEmpty())
{
if (!Form1->IdTCPClient2->IOHander->CheckForDataOnSource(100))
break;
}
Form1->IdTCPClient2->IOHandler->ReadBytes(data, -1, true);
/* alternatively:
Form1->IdTCPClient2->IOHandler->InputBuffer->ExtractToBytes(data, -1, true);
*/
}
while (true);
// use data as needed...
}
catch (const Exception &Ex) {
Form1->DisplaySSH->Lines->Add(Ex.Message);
Form1->DisplaySSH->GoToTextEnd();
}
1: make sure you are using an up-to-date snapshot of Indy 10. Prior to Oct 6 2016, there was a logic bug in ReadBytes() when AByteCount=-1 that didn't take the InputBuffer into account before checking the socket for new bytes.