Thursday, March 01, 2007

SOAP on Jetty

A common way for non-Java users to access Mulgara is through the iTQL client jar, using SOAP. This is very bad, as the iTQL jar uses RMI to talk to the server. This is OK if you're in a JVM and accessing the objects directly, since we put a bit of effort into making objects stream intelligently, but if you're going to chunk up the streamed results into XML, then you'll be introducing a whole series of problems. Not to mention that you now move all the data over sockets twice.

Unfortunately, there hasn't been an alternative to this approach before. There are some options with the descriptors interface, but this is designed for providing results for specific queries. Besides that, I hear it's broken at the moment. Trying to run it seemed to bear this out, but at least the SOAP endpoint is there. I believe Brian is looking into this bug at the moment.

The main problem with putting SOAP (or any other kind of access point, such as the RESTful options being considered) on the server is that the iTQL interpreter is supposed to be on the client. If ItqlInterpreter is naively accessed on the server, then some of its internal session data will not be set up correctly.

Fortunately, the main reason the ItqlInterpreter has internal session data is so that it knows which server to send the query to. If I want a non-RMI service on a Mulgara server, then it won't need to work out which server to go to, since it's already there!

However, this isn't a drop in replacement for the RMI service, as I need to find the appropriate references to Sessions and the like. A cursory inspection suggestions I will only need to change a couple of lines, but I want to be sure I get them right, so I'm going through the code line-by-line to make sure I have a correct understanding of all that is going on. It's a little strange, as I know I wrote some of it. There's a sense of familiarity there, and I even remember some things, but in many ways it also looks like completely new code. I'm probably taking longer than I need to in some of these classes, but I'm using the opportunity to get completely familiar with this code again.

One area I need to spend some time in is the Jetty configuration. It looks relatively straightforward, but I wanted to read the documentation for what certain method calls are doing... and that was when I discovered a problem.

The Jetty we are using is version 4.2.19. It turns out that this is ancient. Jetty is now up to version 6.1. This has a few implications.
  • No online Javadoc.
  • Difficult to track down the cvs revision for sourcecode.
  • Not Java 1.5 compiler-compatible (uses enum as a label).
  • Only supports Servlets 2.3, not 2.5.
  • Only supports JSP 1.2, not 2.1.
  • No longer maintained.
I'm sure there's a lot more, but you get the idea.

My initial reaction is to update to the latest Jetty. Unfortunately, I note that a lot of the interfaces have changed, and this will need learning how Jetty needs to be configured. I should also learn how it WAS put together, so I can work out what I'm updating.

The thing that led me here was trying to find out what an HttpContext is exactly, since a group of these gets set in the Jetty server in Mulgara. However, they don't exist anymore, and neither does the the more generic Context class. So I'll have to work out what these things were in order to make sure I can configure the same functionality in Jetty 6.1.

Fortunately, The download site has old versions, including 4.2.27. This should only involve bug fixes from 4.2.19, so the documentation will stay the same.

Frankly, I hate these distractions. The whole way down these side roads you question the value of the effort of learning a new part of the system just so you can replace something that is currently working. There's no denying the value and enjoyment of learning something new, but it really takes the focus off important things.

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