Queue Versioning

A system comprising:

• one or more network interfaces;
• at least one processor;
• and
• at least one non-transitory computer-readable medium comprising program instructions that are executable by the at least one processor such that the system is configured to:
• send, via the one or more network interfaces to a playback device, one or more messages indicating a first version of a queue as represented by a queue version parameter indicating a current version of the queue, wherein the first version of the queue includes representations of one or more first audio streams, and wherein the queue is playable by the playback device;
• receive, via the one or more network interfaces, a request to add one or more second audio streams to the queue, the request including:
• (i) an indication of the one or more second audio streams, the one or more second audio streams including a particular second audio stream and (ii) a uniform resource identifier (URI) representing a location of the particular second audio stream at one or more servers of a streaming audio service;
• add representations of the one or more second audio streams to the queue;
• based on the addition of the one or more second audio streams to the queue, modify the queue version parameter indicating the current version of the queue to indicate a second version of the queue;
• receive, via the one or more network interfaces from the playback device, a request for a state of the queue, the request indicating an expected version of the queue;
• determine that the expected version of the queue differs from the second version of the queue represented by the queue version parameter;
• and
• based on the determination, cause at least a portion of a representation of the queue on the playback device to be replaced with a corresponding portion of the queue.