iOS and OS X Network Programming Cookbook

Decoding TCP headers

In the Decoding IP headers recipe of this chapter, we created a decodeIp() function that decoded the IP headers of a packet. In that function, if the protocol type was TCP, we called a decodeTcp() function. We will create the decodeTcp() function in this recipe.

The TCP header is a part of the third layer (Protocol layer) of our header stack.

The TCP header looks like this:

Let's take a look at the fields of the TCP header:

• Source Port: This identifies the port that the packet is being sent from on the sending device.
• Destination Port: This identifies the port that the packet is going to on the receiving device.
• Sequence Number: This ...