btc_wire_proto is a library that serialises and deserialises messages in the Bitcoin wire format. Getting the data from (and sending it to) the network, finding peers, validating blocks, building a block chain, etc. are all out of scope.
Specification of the protocol is here: en.bitcoin.it/wiki/Protocol_specification
This library differs from the others in that it leverages bindata to do the heavy lifting. Results in less, easier-to-read, more robust code.