c# socket receive byte array length

Question

i'm trying to learn to use sockets in c# and i've a doubt, i'm using a code something like this:

byte[] data = new byte[64]; 
int length = 0;
length = sock.Receive(data);
//more code...

So, the byte[] data is filled with the recived data and the left space in the array is filled with 0s, Is the byte[] allocated into memory completely (all 64bytes)? If it's so, is there a way to make the byte[] the same size as the actual sent data?

Answer 1

You can check sock.Available to see what has already come in. (so far)

byte[] data = new byte[sock.Available]; 
int length = sock.Receive(data);
//more code...

Note: Since you may or may not know what is coming in next on the network it usually makes more sense to read only a header (with size info) first or to allocate more space than necessary, and call .Recieve() multiple times until the end of a record is reached.

Note: This code assumes you already know there is some data to receive and you've waited long enough for some useful amount of data to be ready.

If you do choose to use length headers, .Available can help you avoid reading a partial header and having to re-assemble it which is nice. (Only large messages may need manual reassembly in that case)

Answer 2

You simply need to use the return value from Receive to understand how much data has arrived. You can shorten the buffer using Array.Resize if you want but that normally would be a sign that something is wrong.

Also note, that TCP is a stream of bytes and does not preserve message boundaries.