Daily Archives: 30 June, 2005

One of the things that pisses me off about gweather is that it occasionally hangs and stops updating. It is a bit easier to tell when this has occurred these days, since it is quite obvious something’s wrong if gweather thinks it is night time when it clearly isn’t.

The current code uses gnome-vfs, which isn’t the best choice for this sort of thing. The code is the usual mess you get when turning an algoithm inside out to work through callbacks in C:

1. One function opens the URL with gnome_vfs_async_open().
2. The callback that gets triggered on completion of the open calls gnome_vfs_async_read().
3. The callback that gets triggered on the end of the read checks the status. If it is at the end of the stream, then process the data and close the stream. Otherwise, perform another read (which will loop back to this step).

This logic is repeated 5 times for the different weather data sources. To clean this up, I started looking at libsoup which doesn’t try to be a full file system abstraction, but provides a better API for the kind of things gweather does.

I put together a simple HttpResource class that wraps the relevant parts of libsoup for apps like gweather. It can be used like so:

1. Create an HttpResource instance for the given URI.
2. Connect a handler to the resource’s updated signal.
3. Call the _set_update_interval() method to say how often the resource should be checked.
4. Call the _refresh() method to kick off periodic freshness checks.
5. When new data arrives, the updated signal is emitted.

Since the code is designed for periodic updates, I added some simple caching behaviour. If the server reports that the resource hasn’t been modified, we don’t need to emit the updated signal.

There are a few things that still need doing:

• Some code to keep a SoupSession instance up to date with the proxy configuration settings in GConf.
• Correct handling of the Expires: response header. If we are checking for updates every 30 minutes, but the server says the current weather report is current for the next hour, then we shouldn’t check again til then.
• Support gzip and/or deflate content transfer encoding to reduce bandwidth.

This code should be pretty trivial to integrate into gweather when it is done, and should simplify the logic. I guess it would be useful for other applets too, such as gtik. The current code is available in my Bazaar archive:

baz get http://www.gnome.org/~jamesh/arch/james@jamesh.id.au/http-resource--devel--0