Send chunked responses if body size is unknown.
Apply HTTP chunked transfer encoding to the response body if all of the
following conditions are met:
* client claims HTTP version 1.1 or later support
* response does not have a Content-Length header already
* response does not use multipart/byteranges encoding
* connection is persistent
If we decide to send chunked reply, chunked_reply flag is set. Chunked
encoding is done in ClientSocketContext::packChunk(). The last-chunk is
sent only when clientReplyContext complete flag is set.
--------
This feature was requested to make Squid work with HTTP/1.1 clients that
can handle chunked responses but cannot handle connection closures in
the middle of a transaction sequence. The earlier version of the patch
(for Squid v3.1) was tested in production.
N.B. A bug in Squid may result in server-side code not treating
premature server-side connection termination as an error. That bug
results in Squid client-side sending a complete chunked response to the
client instead of omitting the last-chunk to indicate a truncated
response. Fixing that bug is outside this project scope (but we might
have a patch for it somewhere, I need to check).
