Comments and more improvement.

more logic to not do extra processing. A lot more comments to explain whats happening.
I agree.

There is only one way to put and retrieve data (using CURLINFO_PRIVATE). But I am using that to get the actual data out (that too indirectly through casting). I was not able to figure out a way to put metadata with a curl easy handle (easy handle represents a worker for a single url). And hence to have something out implemented this id extractor... which is also pathetic module.. can do a much better job using std::regex and stuff.