an application protocol monster

During the autumn 2009 I was sponsored by a company to work on some new protocols for libcurl to support – IMAP, POP3, SMTP and their TLS-powered versions. It took me a little while to get things working the way I’d like them to due work load elsewhere and other irrelevant distractions.

In the next curl and libcurl release, to be called version 7.20.0, which if everything runs fine and according to plan might happen at the end of January 2010 or possibly a little later, libcurl will truly have converted from a file transfer library into a full fledged application protocol layer monster.

The current incarnation of my development libcurl supports the following 18(!) protocols:

tftp ftp telnet dict ldap ldaps http file https ftps scp sftp imap imaps pop3 pop3s smtp smtps

While SSL versions of protocols are arguably not separate protocols, the 12 protocols in the list without SSL are still many in my view.

The fundamentals of libcurl remain the same though: specify a URL to operate against. Send or receive data. Sometimes both send and receive in the same request.

Internally in libcurl, I converted a big portion of the FTP-specific code into a more generic “pingpong”-generic code which is now designed to work similarly with all these new protocols that share many similarities with FTP. They are all sending commands to the server and get responses back, in similar ways.

As before, the ability to disable specific protocols when building libcurl remains so for those who don’t particularly care about these new ones and want to maintain building a library that is as small and lean as possible, there should be little extra weight due to this recent development. I’ve been pondering but I’ve not yet figured out the most perfect way to deal with such build options in the code so they are still a bit too #if and #ifdef intensive for my taste…

Meanwhile, Chris Conroy has been busy in his end implementing support for RTSP that also soon might be ripe for inclusion in the main code.

Not too surprisingly perhaps, the curl tool also then gets these protocol abilities so it becomes even more than before the Swiss army knife tool for internet protocols and then of course explicitly application layer ones.


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