Base64_encode all response body in module

[Constantine Yarovoy]

Hi, at the moment I am developing module to `base64_encode` all the
response body.
For this purpose I wrote my "body filter" in module.

As I understood, there's a chain, with each element of a chain holding
buffer and having pointer to the next chain element.
How can I iterate all buffers in a chain and base64_encode them?
Thanks in advance.