OCI has

Tag 2: the client asks the server whether it holds an image for the client, by digest; the server answers with exactly one channel response, the byte 0, or the byte 1 followed by a repository path, and the channel response finish; a finish that no response precedes states that the server does not hold it for the client.

The client opens this channel to ask whether the server holds an image for it, before it asks for anything of the image.

• The request. The tag byte 2 followed by the digest as JSON. Request states its form.
• The response. Exactly one channel response, the byte 0, or the byte 1 followed by the repository path the server holds the image under, and the channel response finish. Response states the sequence.
• Held for the client. The server answers 1 only for an image it holds for the client, as images::oci states: an image the client built on it. An image another client built, and an image the server holds on its own account, are answered 0.