docker ps: allow formatting as JSON

With this patch:

    docker ps --format 'table {{.Names}}\t{{.Platform}}'
    NAMES                    PLATFORM
    optimistic_nightingale   linux/arm64
    mycontainer              linux/arm64/v8
    trusting_goldstine       linux/arm64

    docker ps --format '{{.Platform}}'
    linux/arm64
    linux/arm64/v8
    linux/arm64

    docker ps --format '{{json .Platform}}'
    {"architecture":"arm64","os":"linux"}
    {"architecture":"arm64","os":"linux","variant":"v8"}
    {"architecture":"arm64","os":"linux"}

    docker ps --format 'json'
    {"Command":"\"/bin/bash\"","CreatedAt":"2025-05-13 10:12:19 +0000 UTC","ID":"e8b3b2d604f1","Image":"docker-cli-dev","Labels":"desktop.docker.io/binds/0/Source=/Users/thajeztah/go/src/github.com/docker/cli,desktop.docker.io/binds/0/SourceKind=hostFile,desktop.docker.io/binds/0/Target=/go/src/github.com/docker/cli,desktop.docker.io/mounts/0/Source=/var/run/docker.sock,desktop.docker.io/mounts/0/SourceKind=dockerSocketProxied,desktop.docker.io/mounts/0/Target=/var/run/docker.sock,desktop.docker.io/ports.scheme=v2","LocalVolumes":"1","Mounts":"/host_mnt/User…,docker-cli-dev…,/run/host-serv…","Names":"optimistic_nightingale","Networks":"bridge","Platform":{"architecture":"arm64","os":"linux"},"Ports":"","RunningFor":"38 minutes ago","Size":"0B","State":"running","Status":"Up 38 minutes"}
    {"Command":"\"/docker-entrypoint.…\"","CreatedAt":"2025-05-13 09:58:01 +0000 UTC","ID":"c93b808dd54e","Image":"nginx:alpine","Labels":"desktop.docker.io/ports.scheme=v2,maintainer=NGINX Docker Maintainers \[email protected]\u003e","LocalVolumes":"0","Mounts":"","Names":"mycontainer","Networks":"bridge","Platform":{"architecture":"arm64","os":"linux","variant":"v8"},"Ports":"80/tcp","RunningFor":"53 minutes ago","Size":"0B","State":"running","Status":"Up 53 minutes"}
    {"Command":"\"/usr/bin/gotty --ti…\"","CreatedAt":"2025-05-13 07:31:18 +0000 UTC","ID":"cbb981b06e46","Image":"thajeztah/dockershell:latest","Labels":"desktop.docker.io/ports.scheme=v2,com.thajeztah.docker-shell=1","LocalVolumes":"0","Mounts":"","Names":"trusting_goldstine","Networks":"bridge","Platform":{"architecture":"arm64","os":"linux"},"Ports":"0.0.0.0:55000-\u003e8080/tcp","RunningFor":"3 hours ago","Size":"0B","State":"running","Status":"Up 3 hours"}

Signed-off-by: Sebastiaan van Stijn <[email protected]>

Author: thaJeztah

cli/command/formatter/container.go

@@ -16,6 +16,7 @@ import (
 	"github.com/docker/docker/api/types/container"
 	"github.com/docker/docker/pkg/stringid"
 	"github.com/docker/go-units"
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 )
 
 const (
@@ -30,6 +31,15 @@ const (
 	platformHeader   = "PLATFORM"
 )
 
+// Platform wraps a [ocispec.Platform] to implement the stringer interface.
+type Platform struct {
+	ocispec.Platform
+}
+
+func (p Platform) String() string {
+	return platforms.FormatAll(p.Platform)
+}
+
 // NewContainerFormat returns a Format for rendering using a Context
 func NewContainerFormat(source string, quiet bool, size bool) Format {
 	switch source {
@@ -213,11 +223,12 @@ func (c *ContainerContext) RunningFor() string {
 
 // Platform returns a human-readable representation of the container's
 // platform if it is available.
-func (c *ContainerContext) Platform() string {
-	if c.c.ImageManifestDescriptor != nil && c.c.ImageManifestDescriptor.Platform != nil {
-		return platforms.FormatAll(*c.c.ImageManifestDescriptor.Platform)
+func (c *ContainerContext) Platform() *Platform {
+	p := c.c.ImageManifestDescriptor
+	if p == nil || p.Platform == nil {
+		return nil
 	}
-	return ""
+	return &Platform{*p.Platform}
 }
 
 // Ports returns a comma-separated string representing open ports of the container

cli/command/formatter/container_test.go

@@ -464,7 +464,7 @@ func TestContainerContextWriteJSON(t *testing.T) {
 			"Mounts":       "",
 			"Names":        "foobar_baz",
 			"Networks":     "",
-			"Platform":     "",
+			"Platform":     nil,
 			"Ports":        "",
 			"RunningFor":   "About a minute ago",
 			"Size":         "0B",
@@ -481,7 +481,7 @@ func TestContainerContextWriteJSON(t *testing.T) {
 			"Mounts":       "",
 			"Names":        "foobar_bar",
 			"Networks":     "",
-			"Platform":     "linux/amd64",
+			"Platform":     map[string]any{"architecture": "amd64", "os": "linux"},
 			"Ports":        "",
 			"RunningFor":   "About a minute ago",
 			"Size":         "0B",
@@ -498,7 +498,7 @@ func TestContainerContextWriteJSON(t *testing.T) {
 			"Mounts":       "",
 			"Names":        "foobar_bar",
 			"Networks":     "",
-			"Platform":     "unknown",
+			"Platform":     map[string]any{"architecture": "", "os": ""},
 			"Ports":        "",
 			"RunningFor":   "About a minute ago",
 			"Size":         "0B",