fetch
Synchronously fetches metadata about a resource from this ResourceProvider. The method returns when resource metadata is available, or throws an Exception on failure.
Relative URLs
If this ResourceProvider has a baseUrl, the implementation will use that baseUrl when resolving relative URLs. For example, If the ResourceProvider has the baseUrl "com.colibrio://xyz/", then the following URLs will target the same resource:
"index.html"
"com.colibrio://xyz/index.html"
If the ResourceProvider has no baseURL, then calling this method with a relative URL will cause InvalidUrlException to be thrown.
URL encoding
The passed url MAY contain URL encoded (percent-encoded) path segments using the UTF-8 character set. The implementation MUST normalize the path segment encoding so that it is insensitive to how it is encoded. For example, the following URLs MUST resolve to the same resource:
'cool movie.mp4'
'cool%20movie.mp4'
It is recommended that implementations use UriUtils.normalizePathnameEncoding to maximize compatibility with the framework.
Options
The options parameter configures how to fetch the resource. If an options parameter isn't defined, the implementation use the default values specified in ResourceRequestOptions.
Thread safety
This method may be called by multiple threads in parallel. As the method blocks until a Response is available, it should not be called on the Main thread.
Error handling and retry handling
Some data transport mediums are prone to errors. For example, a HTTP Resource Provider implementation fetching resource from the Internet SHOULD internally retry requests if the user temporarily loses internet connection. Once the data is successfully retrieved, the implementation returns a Response.
For longer interruptions (decided by the implementation), the implementation SHOULD throw an ResourceUnavailableException to indicate to the framework that the resource could be fetched sometime in the future.
Parameters
The url to the resource that should be fetched.
Options for how to perform the fetch request.
Throws
If the resource is currently unavailable but might be retrievable later.
Like for example if the resource cannot be fetched due to the user temporarily loosing the internet connection.
The caller MAY try to recover by fetching this resource again later.If `fetchMetadata()` fails for any other reason.