NewShardingBlobAccess is an adapter for BlobAccess that partitions requests across backends by hashing the digest.

NewWeightedShardPermuter is a shard selection algorithm that generates a permutation of [0, len(weights)) for every hash, where every index i is returned weights[i] times.

ShardPermuter is an algorithm for turning a hash into a series of indices corresponding to backends capable of serving blobs corresponding with that hash.

ShardSelector is the callback type called by ShardPermuter.GetShard.