So we stumbled onto this problem with a new customer who was using a module called Techtwo_Mailplus. When trying to make a rest connection HHVM would cause the following exception to be thrown: Invalid chunk size “” unable to read chunked body. This did not happen with their old server which ran bog standard PHP DSO. Now, I was not looking forward to debugging it because it’s a complex module and the error eventually ended up in Zend_Rest_Client after tracing it through 4 other files and multiple functions in those files. However, I stumbled onto this post which gave me the solution: http://framework.zend.com/issues/browse/ZF-741

To fix the Techtwo_Mailplus module I edited app/code/community/Techtwo/Mailplus/Helper/Rest.php and around line 160 you will find:

This is the spot where you can add the fix from the Zend post. So just add it to the end of this part so it looks like this:

I don’t have time to figure out exactly why this happening but forcing HTTP version 1.0 seems to “walk a different path” in Zend Framework and doesn’t hit the part that causes the error.