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[Nigel Cunningham <nigelc@xxxxxxxxxxxxxxx>]

I've spent some time looking into this this afternoon. It seems to me
that some of the issue is already resolved:

If I set up my IDE to catch the invocation of an installation in
admin/upgrade.json.php, line 42 ($fun()) and just sit on the breakpoint
until the request times out, the spinner gets changed to "Failed to
upgrade".

The problem I saw was where the failure is not an failure of the ajax
call itself (like the above), but a successful completion of the request
which returns an error. The simplest way to reproduce this was to add

throw new Exception("Failure!");

prior to the $fun() invocation mentioned above. The ajax call thus completes, but neither the success or the failure handler passed to sendjsonrequest in line 145 of admin/upgrade.php get invoked. This is because sendjsonrequest uses its own success and
error handlers, and there is a path (which we're hitting) wherein neither of our handlers will be invoked by sendjsonrequest's handlers:

If an ajax request succeeds, but the data in the result indicates an
error (data.error = true), the code in lines 233-236 will be invoked,
calling globalErrorHandler. In this case, errtype has not been set, so
the successcallback function will rightly not be called, but neither
will the errorcallback.

My solution is to simply call errorcallback() after globalErrorHandler,
as well as after setting errortype = 'error' in the block above.

I'm not submitting it as a patch yet, though, because I'm aware that
sendjsonrequest is called from many other places, and I'd like to have a
discussion with others about it first. The code seems messy to me, and
I'm not sure I fully comprehend yet the implications of this change as
well as others might (particularly since you're all way more familiar
with the code!).

Thanks for any feedback!

Nigel

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https://bugs.launchpad.net/bugs/1318432

Title:
  Improve error reporting in Ajax installer/upgrader

Status in Mahara ePortfolio:
  Confirmed

Bug description:
  We use an Ajax-based page to install & upgrade Mahara. For each
  upgrade task it:

  - fires off a separate Ajax request to run the task
  - shows a "progress" spinner while it waits for a response
  - and then once it gets a response it updates the page and fires off the next task

  The problem is that this system doesn't handle errors well. If the
  Ajax script errors out, it continues showing the "progress" spinner
  forever. Consequently we get a LOT of error reports where people
  complain that "installation takes forever", when in fact it errored
  out after 30 seconds or whatever and it just never told them.

  We need to update this process so that it actually lets you know when
  it failed, and why.

  The simplest solution, suggested by Robert, is that we put a timeout
  on waiting for the Ajax response. Mahara sets max_execution_time
  itself, so we could:

  1. Make the ajax time out after max_execution_time
  2. Show an error icon
  3. Fire off a second ajax response to a script that gets any error messages from the session and displays those on the page.

  That should be pretty robust against any type of error.

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