This kind of function is highly dependent on the proxy used,
therefore parsing was added for x-forwarded-for instead and we
just let users write the function that works for them. The code
can be easily extracted if anyone was using the function.
This allows us to change the max chunk length on a per chunk basis
instead of for the whole stream. It's also much easier to use this
way even if we don't want to change the chunk size.
Defaults to a maximum of 1000000 bytes.
Also standardize the te_identity and te_chunked decoding functions.
Now they both try to read as much as possible (up to the limit),
making body reading much faster when not using chunked encoding.
