Michael J. Radwin

Tales of a software engineer who keeps kosher and hates the web.

ApacheCon: Waka: a replacement for HTTP

waka.jpg Ok, I was a little misguided when I wrote earlier that XML/I18N was off-topic for an Apache conference. While not about the Apache server itself, these technologies are in fact widely used in today’s environment of HTTP and Apache.

But how about something completely different: a brand new protocol to replace HTTP? Whoa. (This is why it’s great to go to conferences. You get exposed to all of these neat ideas that you don’t always have time to think about as you’re doing your day job.)

Fielding covered a lot of ground in his 60 minutes. He started off discussing how Web Services is yet another example of how to solve the general problem of Enterprise Application Integration. What’s important about Web Services, Fielding points out, is that it helps to solve the integration problem. Ideally, once you have web services, you don’t have to do N^2 integrations for N corporate applications.

(Editorial comment: even though Web Services lets a bunch of different applications speak the same protocol, it doesn’t mean they understand the same stuff. PeopleSoft’s concept of what an Employee means is going to be different from what SAP thinks it means. Web Services can get the two applications in the same room as each other, but it can’t get them speaking the same language.)

Fielding went on to explain what’s great about HTTP as a protocol, and also pointed out some of the difficulties it presents. He described the REST architecture’s influence on the HTTP/1.1 spec, and then gave some further background on the HTTP protocol. He pointed out a few important limitations of HTTP/1.1:

  1. Overhead of MIME-style message syntax
  2. Head-of-line blocking on interactions
  3. Metadata unable to come after data
  4. Server can’t send unsolicited responses
  5. Low-power and bandwidth sensitive devices more severely impacted by verbosity

Fielding suggests that a new protocol standard could solve HTTP’s current problems in a generic way. “It’s not like we’re all going to keel over and die if we don’t get a replacement for HTTP, but it would be really valuable in some communities.” He proposes waka, which one could evision as a sort of HTTP/2.0. In fact, it takes advantage of the HTTP protocol upgrade feature that was implemented in HTTP/1.1. Waka is designed to match the efficiency of the REST architectural style.

Waka adds a handful of new verbs (methods) to HTTP:

  • RENDER – explicit support for transcoding content (display/print/speak)
  • MONITOR – notify me when resource state changes
  • Authoring methods (a la DAV)
  • Request control data – for asynchronicity, transactional support, and QoS

Fielding went on in much more detail about all of these cool features of waka. One of my favorites was the ability for clients to define macros. You could use this feature to define a macro for a User-Agent string, then avoid sending all of those bytes on future interactions. I also like the fact that due to the asynchronicity of the protocol, you can interleave data and metadata. This could be pretty handy if you realized that you needed to issue a Set-Cookie header in the middle of a response.

The transactional support is also pretty important. Imagine that you’re trying to make an online payment of a non-trivial amount of money, and your flaky internet connection drops in the middle of the request. Did the payment go through? These days we get things like email confirmation messages, or you can log back on when your internet connection comes back up later and see if the transaction is mentioned in the transaction history. Waka could provide more protocol-level support.

Lastly, Fielding points out that waka is very much a work in progress. It hasn’t been fully spec’d or implemented, but he’s working actively on it. Expect to hear more about it in the coming year or so.

[Update: Apparently I misunderstood Fielding’s comments about the N vs. N^2 integration problem. According to Jeff Bone, “The basic argument is that type-specific interfaces lead to O(N^2) integrations, while generic interfaces lead to O(N) integrations. Web Services as cast today (SOAP as RPC, etc.) have type-specific interfaces and O(N^2) integration complexity; truly RESTful Web Services would in contrast use generic interfaces, and have integration complexity O(N).”]