Settings Refactoring

Major Tasks/Missing Features

The Admin Webapp Does Not Work.

On the one hand, Heritrix can now be controlled remotely via JMX, so anything you could do via the webapp can now be done via jconsole. Also, it is mostly trivial to add additional JMX operations per module (see kickUpdate thoughts below) if necessary.

But, that means the webapp needs to speak JMX in order to control Heritrix, as there is no longer another way. I'd prefer it if the webapp were its own standalone project in the source tree.

The Merge

Changes to trunk must be merged in with changes in my branch. Since so many packages/classes moved around, I think the easiest thing to do here would be to generate per-package diffs of trunk's code, merge them in to pjack_settings separately, then do an svn move to make pjack_settings the new trunk.

Intermittent BDB Corruption During CheckpointSelfTest.

One of my unit tests occassionally raises a DatabaseException trying to find the cap of a Frontier queue.

Missing/altered DecideRules Need to be Restored.

This is outstanding from previous discussions. I had modified DecideRule to include an "invert" setting, which was widely regarded as a bad move. I did this to eliminate as many DecideRules as possible, since there are many of them.

A different way to eliminate some DecideRules would be to add two rules that handle most operations on CrawlURI fields. So there would be a "CrawlURIFieldDecideRule" and a "NotCrawlURIFieldDecideRule" that would let an operator pick a CrawlURI field (or enter an arbitrary attribute name), pick an operation (is exactly, starts with, ends with, contains, matches regex...) and then enter a value for that operation. This may end up causing more work than not, though; I haven't really evaluated it.

No Cookie Support in FetchHTTP.

This was an oversight. I knew I was forgetting something. I had
factored out the cookie-handling code from FetchHTTP, intending to
create three separate implementations of a new CookieManager interface:
IgnoreCookieManager, BdbCookieManager, FileCookieManager. This change
greatly simplified FetchHTTP's code, but I never actually created those
implementations. This would be a simple process of copying the now
commented-out portions of FetchHTTP that used to deal with cookies into
new homes.

The ProcessorResult is Never Being Evaluated by ToeThread.

Again, an oversight on my part. Processors can return certain signals to
the ToeThread, which should tell the ToeThread to (for instance) skip ahead
to the postprocessing. These signals are never evaluated by the ToeThread,
though, so each CrawlURI always passes through each processor. The
processors were designed to not blow up in this case, but it's inefficient.

Review of Non-Default Modules

The only things that have been truly tested are modules that were listed
in the default configuration file for Heritrix. So, for instance,
AdaptiveRevisitFrontier was never tested. Additionally, certain features
(eg, kickUpdate) are not covered by any unit test.

I'd like to at least do a formal review of each module. I'd create a list
of "difficult" things to check for (eg, special checkpointing behavior)
and ensure the module has been altered to function properly in the new
system. Or, we can run a largeish crawl that is configured to use each
untested module and attempt to active/deactive those modules over time to
see if they function as expected.

Refactorings/Code Cleanup

Elimination of CandidateURI

This was regarded as a good idea, and now's the time to do it. This should
go quickly; merge the CandidateURI code into CrawlURI, replace all
references/constructions of CandidateURI with CrawlURI, ensure tests still
work.

Elimination of CrawlStatusListener

Of necessity, CrawlController is now an MBean. It emits an MBean
notification when the crawl status changes (eg, from RUNNING to PAUSED).

I simply layered this notification on top of the existing
CrawlStatusListener architecture. It doesn't make a lot of sense to
support to event notification systems for the same thing, though.

For that matter, CrawlURIDispositionListener should probably also change
to MBean notifications, for the sake of consistency (and to allow remote
applications to follow CrawlURI dispositions).

KickUpdate/Reporter

Rather than having components iterate over their own children and manually
invoking kickUpdate(), I think it makes more sense for the settings system
to track modules that provide a kickUpdate() implementations. Such modules
would implement a KickUpdateable interface; the CrawlController would expose
a JMX operation "kickUpdate"; that operation would iterate over all the
known KickUpdateable interface, invoking kickUpdate().

Yet another way to handle this would be to avoid the notion of a
kickUpdate altogether, and have the modules that require a kickUpdate to
expose their own method via JMX. That way an operator could kick just
one module at a time. Not sure which approach is best.

Interfaces for JMX Modules

CrawlController is now an open MBean. Standard practice for MBeans is to
create an interface X that defines the attributes/operations, then implement
that interface in a class named XImpl. It's an ugly convention but it is
standard. So, the existing CrawlController would become CrawlControllerImpl,
and it would implement a CrawlController interface. Modules that depend on
keeping a CrawlController reference handy would declare that reference as
the interface; that might help with unit testing.

Delete Commented-Out and Dead Code.

Self-explanatory. Large parts of FetchHTTP and CrawlController were moved
to other places, but the old code was just commented out for reference.
Now that I'm a bit more confident that these things work, the old code
should be removed for clarity's sake.

Documentation

At minimum I'd like the public API of org.archive.state and
org.archive.settings fully documented, as that would cover the core of
the new settings system.

Testing

Again, important things like AdaptiveRevisitFrontier need better test
coverage in general, but should be at least manually tested before we
think of release.

Old Notes

Still left to do before code review:

  1. Make unit test stubs for all modules to ensure they actually conform to new settings system. (Done)
  2. Integrate XML format into FileSheetManager. (Done)
  3. Change CrawlJobHandler so that it uses FileSheetManagers instead of XMLSettingsHandlers (Done)
  4. Change Heritrix to use new CrawlJobHandler (Done)
  5. Make selftest work again. (99% done)
  6. Make maven dist work again.

Stuff to do during code review but before merge: 

  1.  Restore deleted DecideRules, make unit test stubs for them too.

Stuff to do after merge:

  1. Bold new webapp -- either complete rewrite or minor tweaks, but either way it should be divorced from actual Heritrix instance (all webapp communication should occur over JMX).
  2. Split commons, processors and crawler into 3 separate subprojects to ensure that there's no cross-pollution (there are currently classes in archive-commons.jar that will will raise a LinkageError if loaded in apps other than Heritrix).
  3. Document the hell out of org.archive.state, org.archive.settings and org.archive.processors.
  4. Review modules to make sure their documentation is up-to-date.
  5. Turn unit test stubs into actual unit tests.
  6. Create src/test for testing code, create src/i18n for utf8 files.
  7. Clear warnings.

Other stuff that I'm just documenting so I don't forget:

  • Would be nice to have some sort of mechanism so that default values for Keys are allowed to violate the constraints for those Keys. In particular, it would be nice to have a non-null Constraint on most Keys, but still to specify null as the default value. Maybe some sort of @Required tag that the manager can use to enforce presence of things.
  • Some sort of object lifecycle tracking for objects within sheets -- would be groovy if JMXSheetManager could automatically register and deregister modules that implement DynamicMBean. (Done)

Ugly, ugly bits:

  • Handling of Lists and Maps follows old settings system model, which makes it difficult to predict.
  • Formal dependencies place extra burden on crawl operators. (Dealt with)
  • Full resolution of settings is too expensive, especially for maps and lists. A more efficient implementation of Sheet.get is possible.
  • Weird polymorphism since resolution depends on key type, and not the actual value of the Key. (Eg, Key<Object> whose value is a Map won't have Map resolution rules applied.) Also Map and List implementations cannot also be configuration modules (a Map implementation cannot define static Key fields).