Document payload returned by ImageBuild when using BuildKit

[cowwoc]

Is this a docs issue?

• My issue is about the documentation content or website

Type of issue

I can't find what I'm looking for

Description

Please document the payload format returned by https://docs.docker.com/reference/api/engine/version/v1.47/#tag/Image/operation/ImageBuild when "version" is set to "2" (meaning, when using BuildKit for the build). It seems to return base64-encoded protobuf messages but I can't find them documented anywhere.

Related discussion by someone else: moby/buildkit#5610

Location

https://docs.docker.com/reference/api/engine/version/v1.47/#tag/Image/operation/ImageBuild

Suggestion

No response

[cowwoc]

@tonistiigi Based on moby/buildkit#2429 (comment) it sounds like you are the right person to ask: how am I supposed to decode the contents of aux when BuildKit through https://docs.docker.com/reference/api/engine/version/v1.47/#tag/Image/operation/ImageBuild?

I downloaded and built classes from the protobuf files I found in the BuildKit repository, but it's not clear which of them I am supposed to use to decode aux. Please point me in the right direction.

PS: My library is written in Java, not Go, so I can't use your native libraries directly.