libcurl internals suddenly become a lot cleaner and neater to work with when we made all code assume and work with the multi interface!
libcurl was initially created slightly after the birth of the curl tool. After the tool started to get some traction and use out in the world, requests and queries about a library with its powers started to drop in. Soon enough, in the year 2000 we shipped the first release of libcurl and it featured a synchronous API (the "easy" interface) that performs the complete operation and then returns.Â I think we can now say that the blocking easy interface was successful and its ease of use has been very popular and appreciated by many users.
During 2002 the need for a non-blocking API had been identified and we introduced the multi interface. The multi interface is kind of a super-set as it re-uses the same handles as is used with the easy interface, so it cleverly makes it fairly easy for a standard application to move from the easy interface to the multi.
Basically since that day, we've struggled in the source code structure to handle the fact that we have both a blocking and a non-blocking API. In lots of places we've had different code paths and choices done depending on which API that was used. It made the source code hard to follow and it occasionally introduced hard to track bugs which could lead to the multi and easy interface not behaving the same way to the underlying network or protocol behavior. It was clear very early on that it wasn't an ideal design choice, but it was a design choice that was spread out among the code and it stuck.
During November 2012 I finally took on the code that we've had #ifdef'ed since around 2005 which makes the blocking easy interface operation a wrapper function around the non-blocking multi interface functions. Using this method, all internals should be considered non-blocking and there is no need left to treat things differently depending on which API that was used because everything is now multi interface == non-blocking.
On January 17th 2013 the big patch was committed. 400 added lines, 800 removed over 54 modified files...