Datasource Fallbacks (simplestreams)

[Jeroen Vermeulen]

On 04/10/13 12:26, John Arbash Meinel wrote:

> We came to this because the Azure provider was adding the "daily"
> stream to the search path. Which meant that we would find the daily
> stream, parse it, not find anything and then stop. Without falling
> back to the releases stream which has the actual entries we are
> looking for. (We "solved" this by just removing the daily stream,
> which was also for other reasons.)

I did that, IIRC at a time when only the daily images worked yet but 
releases were the obvious long-term way to go.

The implied contract for the imagemetadata package seemed to be that it 
would consider only the selected stream, and ignore any other streams it 
found in the search path.  From what you say, that's what Andrew 
implemented.  Otherwise, what's the point of supporting a search path 
consisting of multiple URLs?

With the fallback, having both the daily and the release stream in the 
path allows users to select one or the other by setting just a stream 
name — no messing with simplestreams URLs in the most common case.



Jeroen