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Updated Wsf previous policy (markdown)

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colin-adams
2013-08-14 02:22:22 -07:00
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Wsf-previous-policy.md
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# Implementing WSF_PREVIOUS_POLICY
# WSF_PREVIOUS_POLICY
This class provides routines which enable the programmer to encode knowledge about resources that have moved (either temporarily, or permanently), or have been permanently removed. There are four routines, but only one is actually deferred.
This class deals with resources that have moved or gone. The default assumes no such resources. It exists as a separate class, rather than have the routines directly in WSF_SKELETON_HANDLER, as sub-classing it may be convenient for an organisation.
## resource_previously_existed
By default, this routine says that currently doesn't exist, never has existed. You need to redefine this routine to return True for any URIs that you want to indicate used to exist, and either no longer do so, or have moved to another location.
Redefining this routine is always necessary if you want to deal with any previous resources.
## resource_moved_permanently
If you have indicated that a resource previously existed, then it may have moved permanently, temporarily, or just ceased to exist. In the first case, you need to redefine this routine to return True for such a resource.
Redefine this routine for any resources that have permanently changed location. The framework will generate a 301 Moved Permanently response, and the user agent will automatically redirect the request to (one of) the new location(s) you provide. The user agent will use the new URI for future requests.
## resource_moved_temporarily
If you have indicated that a resource previously existed, then it may have moved permanently, temporarily, or just ceased to exist. In the second case, you need to redefine this routine to return True for such a resource.
This is for resource that have only been moved for a short period. The framework will generate a 302 Found response. The only substantial difference between this and resource_moved_permanently, is that the agent will use the old URI for future requests.
## previous_location
You need to implement this routine. It should provide the locations where a resource has moved to. There must be at least one such location. If more than one is provided, then the first one is considered primary.
If the preconditions for this routine are never met (as is the case by default), then just return an empty list.
When you redefine resource_moved_permanently or resource_moved_temporarily, the framework will generate a Location header for the new URI, and a hypertext document to the new URI(s). You **must** redefine this routine to provide those locations (the first one you provide will be in the location header).