GH-643: provide interfaces for caching file attributes on paths#645
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Remote file systems may have a need to cache file attributes on Path instances. A typical use case is iterating over all files in a directory: the directory listing returns paths, but the underlying remote listing operation may also return file attributes for each entry. This is the case in Sftp, but may also occur for other file systems, for instance a file system wrapping Amazon S3. It would be unfortunate and inefficient if iterating through the paths returned and doing something with the attributes would have to re-fetch the attributes again if they were already available. By implementing WithFileAttributes of its Paths, a file system can associate file attributes with a path instance, and client code can access them. If a file system also makes its paths implement the second interface WithFileAttributeCache, then the SftpSubsystem uses it internally to avoid making repeated remote calls to get file attributes.
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Remote file systems may have a need to cache file attributes on Path instances. A typical use case is iterating over all files in a directory: the directory listing returns paths, but the underlying remote listing operation may also return file attributes for each entry. This is the case in Sftp, but may also occur for other file systems, for instance a file system wrapping Amazon S3.
It would be unfortunate and inefficient if iterating through the paths returned and doing something with the attributes would have to re-fetch the attributes again if they were already available.
By implementing WithFileAttributes on its Paths, a file system can associate file attributes with a path instance, and client code can access them. If a file system also makes its paths implement the second interface WithFileAttributeCache, then the SftpSubsystem uses it internally to avoid making repeated remote calls to get file attributes.