Users may modify the chunk yielded to them in Net::HTTPResponse#read_body.
This will allow users to reduce memory usage by calling
String#clear on the buffer once they're done using it.
* lib/net/protocol.rb (read): increment read_bytes earlier
(read_all): ditto
* test/net/http/test_httpresponse.rb (test_read_body_block_mod): new test
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58846 b2dd03c8-39d4-4d8f-98ff-823fe69b080e