HSCountingInputStream is a simple example of an NSInputStream subclass
that works around the bugs you'll run into if you try to pass such a subclass
to NSURLRequest or CFHTTPMessageRef. See my blog
for more information on the gory details of how it works.
Note:
This sample uses a few language features only available if you're using Xcode 4 and the LLVM Compiler 2.0, such as instance variables defined in the @implementation block. It also relies on the modern runtime to synthesize the instance variables. I used these features because they're cool and I wanted people to be aware of them.
So if it won't compile for you, that's probably why. It shouldn't be hard to make the necessary changes to make it work for x86 or GCC 4.2, if that's what you need to do.