Redirecting Buffers

The following example appeared in Receiving Data in TCP Mode:

Tibbo BASIC

							sub on_sock_data_arrival
								sock.setdata(sock.getdata(sock.txfree))
								sock.send
							end sub
						

This example shows how to send all data incoming to the RX buffer out from the TX buffer, in just two lines of code. However fast, this technique still passes all data through your Tibbo BASIC/C code, even though you are not processing (altering, sampling) it in any way.

A much more efficient and advanced way to do this would be using a technique called buffer redirection (buffer shorting). With buffer shorting, instead of receiving the data into the RX buffer of your socket, you are receiving it directly into the TX buffer of another object that is supposed to send out this data. This can be a socket (the same or a different one), the ser. object, etc.

To use buffer shorting, you invoke the sock.redir method and specify the buffer to which the data is to be redirected. Once this is done, the on_sock_data_arrival event won't be generated at all, because the data will be going directly to the TX buffer that you have specified. As soon as the data enters this buffer, it will automatically be committed for sending. Here is an example:

Tibbo BASIC

							sub on_sys_init
								sock.num=0
								sock.redir(PL_REDIR_SOCK0) ' This is a loopback for socket 0.
							end sub
						

The performance advantage here is enormous, due to two factors: first, you are not handling the data programmatically, so the VM isn't involved at all. And, second, the data being received is received directly into the TX buffer from which it is transmitted, so there is less copying in memory.

Of course, you cannot do anything at all with this data — you are just pumping it through. However, very often this is precisely what is needed! Additionally, you can still process inband commands/replies (messages).

To stop redirection, you can use sock.redir(0), which means "receive data into the RX buffer of the socket in a normal fashion."

Redirection and UDP

Using Buffers in UDP Mode explained that the sock. object preserves buffer boundaries when storing UDP datagrams in the RX and TX buffers. To achieve this, the sock. object uses special datagram headers that are also stored in these buffers. This means that the buffers contain not only data, but also an additional "service" information.

When an RX buffer of a "UDP socket" (i.e., a socket running in the UDP mode) is redirected to a TX buffer of another UDP socket, datagram boundaries are preserved. The receiving socket will still send out the data subdivided into the original datagrams.

When an RX buffer of a UDP socket is redirected to a TX buffer of a TCP socket or serial port, the service information is removed and datagram boundaries are dissolved. To the receiving TCP socket or serial port, the data appears to be a stream.

A warning note icon. Please note that buffer redirection should not be used on a socket that is running in the TLS mode. This is because the TX and RX buffers of a socket running in the TLS mode only contain the encrypted data.