[Talk-GB] 'Can't load map'

Richard Fairhurst richard at systemed.net
Thu Sep 29 11:48:49 BST 2011

Peter Miller wrote:
> Correct. I think the actual message is 'couldn't load the map'. Sometimes 
> it will load the data eventually if one persists, but generally it is 
> better to give it a rest for a few hours and try later. It only occurs 
> using Potlatch 2 btw, Potlatch 1 still works fine and never fails to 
> get the data in my experience.

A bit of background:

"Couldn't load the map" is P2's general response for "I asked the API for
some data, and an error came back".

Because of limitations in Flash Player, historically that's all it's been
able to show. Flash Player is not able to differentiate between the various
error codes that the API might pass back. It basically just throws its hands
in the air and says "waaaaaah" and leaves Potlatch 2 to cope with it.

As a result, we built a workaround into the API. When P2 sends a request to
the API, it now says "if there's an error, send it back to me as XML, not as
an HTTP error code". That way, Flash Player doesn't balls it up, and P2 can
report the error.

This has been working well for uploads for a few months and was recently
added for downloads too. I'm not 100% sure whether we deployed the download
version at the time, or indeed whether it was working entirely correctly
(simulating errors is kinda hard to do ;) ) but half an hour ago we tweaked
it slightly and deployed the new version.

So now if you get a simple "Couldn't load the map" it means a 500 server
error genuinely came back from the API. This is the sort of thing that
basically shouldn't happen, but it can occur, AIUI, if the daemon restarts
halfway through the response; I've had that very occasionally.

If you get "Couldn't load the map: <some message>" then that's the API
saying "hey, there was a problem with your request". It might be that you've
downloaded too much data, or it might be that P2 sent an invalid request.

P1 doesn't use the same API so doesn't flake out in this way. It just flakes
out differently. :)


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