Ard Schrijvers napisał(a):
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Considering caching RSS feeds. Is there any option to configure cocoon
(maybe by using some source protocol?) to behave like proxy and do not
break the rest of cached content?
Any chance to do conditional gets? [1]
[1] http://fishbowl.pastiche.org/2002/10/21/http_conditional_get_for_rss_hackers
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I know there are some proxy generators around (see blocks/proxy for
GenericProxyGenerator.java, HttpProxyGenerator.java,
WebServiceProxyGenerator.java), though I haven't had a close look at them, but
I don't think they do what you want them to do, and probably you haven't
configured them anyway.
IMHO generator is not suitable for this task as it would lead to bogus
pipelines only for proxing. E.g. you want include your RSS via XInclude,
then you have to build
<map:generate type="someproxy"/>
<map:serialize type="xml"/>
And call this pipeline thought cocoon:/ protocol. Given that, it seems
that http scheme/Excalibur's source is more convenient.
Anyway, by default, when generating an external rss, you will probably have
something like:
<map:generate src="http://www.foo.org/rss"/>
Unless you have specified a specific source-factories for http in your
cocoon.xconf, this uri scheme will be managed by
org.apache.excalibur.source.impl.URLSourceFactory. I am not sure if this
URLSourceFactory delivers what you want, but I don't think so. Then again, I
think when working with external (http) sources like rss, one wants the
following behavior:
1) fetch the rss/xml only when modified
2) have the fetched content cached
3) have the fetched content cached with an expires (configurable)
4) have a configurable connection time out (we had cocoon apps completely
hanging on failing external rss feeds)
I think cocoon is particularly well suited for xml content aggregation of external sources, but I haven't found something that managed the above 4 (logical) demands for it (Anybody....is it in there already? Portal block? Do I miss something?)
For the last point, there was implementation[1] of Excalibur's source
which was meeting our expectations. Good explanation how to use it was
there[2]. However, this code was in 'scratchpad' block and was removed
in 2.1.7 release as no one was maintaining it. Valuable gems has been
lost, unfortunately.
I want this behavior to have the following behavior:
Fetching rss/xml only when modified is clear I suppose. Caching the content is
necessary to have the content available when you get a 304. You might have an
external rss that lacks proper headers, making your generator having to
regenerate the rss every time. Therefore, making the cache also expiring gives
you the possibility to only ask for the rss every X minutes. At last, quite an
important one, a failing external rss can make your cocoon app waiting very
long for the external source, resulting in a broken front end.
I think it is not very hard to make an external rss/xml generator that meets
these 4 points (or adding a http scheme to the source-factories with a
component-instance that behaves accordingly), but I am afraid that it must be
in cocoon somewhere already...
As for now I cannot work on this but in not-so-distant future I could
port and document cached source into 2.1.x's core of course question is
if patch would be accepted.
My gut feeling is that conditional gets are not implemented in
Cocoon/Excalibur and I have no idea if would be hard "fix" it.
Any hints greatly appreciated.
--
Grzegorz Kossakowski
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