Image inspect API (images/{name}/json) returns null RepoDigests

[NS-TomYang]

Description

Image inspect API (images/{name}/json) returns null RepoDigests

#45068 changed the behavior of RepoDigests, but is the null object expected?

Reproduce

curl --unix-socket /var/run/docker.sock "http://localhost/images/25cd1848987f/json" | json_pp

Result from Docker 3.0.6 (API v1.42)

   "Os" : "linux",
   "Parent" : "sha256:b599b8a799458fa7495dac80ed387bac8993b2bf3e7f5994ff1ef354033bee28",
   "RepoDigests" : [],

Result from Docker 4.0.0 (API v1.43)

   "Os" : "linux",
   "Parent" : "sha256:b599b8a799458fa7495dac80ed387bac8993b2bf3e7f5994ff1ef354033bee28",
   "RepoDigests" : null,

Expected behavior

At least from API v1.42 document https://docs.docker.com/engine/api/v1.42/#tag/Image/operation/ImageCreate

The format of the RepoDigests should be the array of the string.

docker version

Client: Docker Engine - Community
 Version:           24.0.0
 API version:       1.43
 Go version:        go1.20.4
 Git commit:        98fdcd7
 Built:             Mon May 15 18:48:35 2023
 OS/Arch:           linux/amd64
 Context:           default

Server: Docker Engine - Community
 Engine:
  Version:          24.0.0
  API version:      1.43 (minimum version 1.12)
  Go version:       go1.20.4
  Git commit:       1331b8c
  Built:            Mon May 15 18:48:35 2023
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.6.19
  GitCommit:        1e1ea6e986c6c86565bc33d52e34b81b3e2bc71f
 runc:
  Version:          1.1.4
  GitCommit:        v1.1.4-0-g5fd4c4d
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

docker info

Client: Docker Engine - Community
 Version:    24.0.0
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc.)
    Version:  v0.10.4
    Path:     /usr/libexec/docker/cli-plugins/docker-buildx
  compose: Docker Compose (Docker Inc.)
    Version:  v2.17.2
    Path:     /usr/libexec/docker/cli-plugins/docker-compose
  scan: Docker Scan (Docker Inc.)
    Version:  v0.23.0
    Path:     /usr/libexec/docker/cli-plugins/docker-scan

Server:
 Containers: 1
  Running: 1
  Paused: 0
  Stopped: 0
 Images: 2
 Server Version: 24.0.0
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Using metacopy: false
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: cgroupfs
 Cgroup Version: 1
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 1e1ea6e986c6c86565bc33d52e34b81b3e2bc71f
 runc version: v1.1.4-0-g5fd4c4d
 init version: de40ad0
 Security Options:
  apparmor
  seccomp
   Profile: builtin
 Kernel Version: 5.4.0-146-generic
 Operating System: Ubuntu 20.04.6 LTS
 OSType: linux
 Architecture: x86_64
 CPUs: 2
 Total Memory: 3.84GiB
 Name: npa-publisher
 ID: a9648b36-5329-4a53-9e90-28ebd6b900a8
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 Experimental: false
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false

WARNING: No swap limit support
WARNING: bridge-nf-call-iptables is disabled
WARNING: bridge-nf-call-ip6tables is disabled

Additional Info

No response

[thaJeztah]

/cc @vvoland

[vvoland]

It's a "regression" introduced in: #43883
Opened a PR: #45563