Re: Sockets (reading)

On Aug 26, 2009, at 11:56 AM, Bob McConnell wrote:

From: Philip Thompson

During a socket read, why would all the requested number of bytes not get sent? For example, I request 1000 bytes: <?php $data = @socket_read ($socket, 2048, PHP_BINARY_READ); ?> This is actually in a loop, so I can get all the data if split up. So, for example, here's how the data split up in 3 iterations (for 1000 bytes): 650 bytes 200 bytes 150 bytes But if I can accept up to 2048 bytes per socket read, why would it not pull all 1000 bytes initially in 1 step? Any thoughts on this would be greatly appreciated!

Because that's the way TCP/IP works, by design. TCP is a stream protocol. It guarantees all of the bytes written to one end of the pipe will come out the other end in the same order, but not necessarily in the same groupings. There are a number of buffers along the way that might split them up, as well as limits on packet sizes in the various networks it passed through. So you get what is available in the last buffer when a timer expires, no more, and no less. If you have serialized data that needs to be grouped in specific blocks, your application will need to keep track of those blocks, reassembling or splitting the streamed data as necessary. You could use UDP which does guarantee that packets will be kept together, but that protocol doesn't guarantee delivery. Bob McConnell

Thank you for your input. Is it guaranteed that at least 1 byte will be sent each time? For example, if I know the data length... <?php $input = ''; for ($i=0; $i<$dataLength; $i++) {

    // Read 1 byte at a time
    if (($data = @socket_read ($socket, 1, PHP_BINARY_READ)) !== false) {
        $input .= $data;
    }

} return $input; ?> Or is this a completely unreasonable and unnecessary way to get the data? Thanks, ~Philip