i2ptunnel: Prep for keepalive

First part of keepalive changes.

• Add utilities to find end-of-message
• Move GunzipOutputStream to new util package
• Add end-of-message checking to GunzipOutputStream
• All new utilities unused in this checkin

changed milestone to %2.5.0

added i2ptunnel label

requested review from @idk

assigned to @zzz

Details:

To implement keepalive, the client must find the end of the response from the server, so it knows it can send the next request. There's 3 cases:

• known size (content-length)
• chunked
• x-i2p-gzip

This MR adds classes for the first two that do that, and adds support for it to the existing gunzipper class. The new classes are in a new util/ dir and the gunzipper is moved there for consistency.

This MR does not use the new classes or the support added to gunzipper. That will happen in followup MRs.

approved this merge request

Ack, thanks for the details, sorry for the long wait time on the review. Please merge when you're ready.

merged

mentioned in commit 37791e83

mentioned in merge request !176 (merged)