images::check

Tag 11: a client names an image by repository and digest; the server sends exactly one response stating whether it can supply that image as the server variant of a container image, and the scope finishes.

A client opens the scope with a request whose payload is the tag byte 11 followed by the image’s name and digest. The server sends exactly one response, which is either the answer or an error. The response finish follows the response, and no frame follows the finish.

• The request. The request names a repository path and a manifest digest. It names no registry: the digest identifies the image, and the source from which the server obtains the image is the server’s own. Request states its form.
• The answer. The answer is exactly {"type":"available"} or exactly {"type":"unavailable"}. The available answer states that the server would supply the image as the server variant of a container request naming that name and digest, at the time of the answer. The unavailable answer states that it would not. Neither answer states more. Response states their form.
• The error. An error states that the server did not answer the question, and that nothing was determined about the image. An error is not an unavailable answer.