Work around Docker Desktop's macOS socket location change

Docker Desktop 4.13.0+ moved the socket from /var/run/docker.sock to
~/.docker/run/docker.sock on macOS, but the Docker client library still
defaults to the old location for all Unix systems.

Add platform-specific logic to use the correct default on macOS when
--daemon-host is not specified.

This makes skopeo work more reliable out of the box for new users.

Signed-off-by: Jacques Nadeau <jacques@apache.org>

cmd/skopeo/utils.go

@@ -6,6 +6,8 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"path/filepath"
+	"runtime"
 	"strings"
 	"time"
 
@@ -32,7 +34,20 @@ import (
 	"golang.org/x/term"
 )
 
-// errorShouldDisplayUsage is a subtype of error used by command handlers to indicate that the command’s help should be included.
+// getDefaultDockerSocket returns the platform-specific default Docker socket path
+func getDefaultDockerSocket() string {
+	if runtime.GOOS == "darwin" {
+		// On macOS, use the user-specific Docker socket location
+		if home := os.Getenv("HOME"); home != "" {
+			return "unix://" + filepath.Join(home, ".docker/run/docker.sock")
+		}
+	}
+	// For all other platforms or if HOME is not set, return empty string
+	// to use the default from the Docker client library
+	return ""
+}
+
+// errorShouldDisplayUsage is a subtype of error used by command handlers to indicate that the command's help should be included.
 type errorShouldDisplayUsage struct {
 	error
 }
@@ -204,6 +219,12 @@ func (opts *imageOptions) newSystemContext() (*types.SystemContext, error) {
 	ctx.OCISharedBlobDirPath = opts.sharedBlobDir
 	ctx.AuthFilePath = opts.shared.authFilePath
 	ctx.DockerDaemonHost = opts.dockerDaemonHost
+	// Set platform-specific default for Docker daemon host if not explicitly set
+	if ctx.DockerDaemonHost == "" {
+		if defaultSocket := getDefaultDockerSocket(); defaultSocket != "" {
+			ctx.DockerDaemonHost = defaultSocket
+		}
+	}
 	ctx.DockerDaemonCertPath = opts.dockerCertPath
 	if opts.authFilePath.Present() {
 		ctx.AuthFilePath = opts.authFilePath.Value()

cmd/skopeo/utils_darwin_test.go

@@ -0,0 +1,33 @@
+//go:build darwin
+
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestGetDefaultDockerSocketDarwin(t *testing.T) {
+	// Save original HOME
+	originalHome := os.Getenv("HOME")
+	defer func() {
+		os.Setenv("HOME", originalHome)
+	}()
+
+	// Test with HOME set
+	testHome := "/Users/test"
+	os.Setenv("HOME", testHome)
+	expected := "unix://" + filepath.Join(testHome, ".docker/run/docker.sock")
+	result := getDefaultDockerSocket()
+	if result != expected {
+		t.Errorf("Expected %s, got %s", expected, result)
+	}
+
+	// Test with HOME unset
+	os.Unsetenv("HOME")
+	result = getDefaultDockerSocket()
+	if result != "" {
+		t.Errorf("Expected empty string when HOME is unset, got %s", result)
+	}
+}

cmd/skopeo/utils_test.go

@@ -4,6 +4,8 @@ import (
 	"bytes"
 	"errors"
 	"os"
+	"path/filepath"
+	"runtime"
 	"testing"
 
 	"github.com/containers/image/v5/copy"
@@ -16,6 +18,21 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+// newExpectedSystemContext creates a SystemContext with expected defaults for tests,
+// accounting for platform-specific behavior like macOS Docker socket location
+func newExpectedSystemContext() *types.SystemContext {
+	ctx := &types.SystemContext{
+		DockerRegistryUserAgent: defaultUserAgent,
+	}
+	// On macOS, DockerDaemonHost gets set to the platform-specific default
+	if runtime.GOOS == "darwin" {
+		if home := os.Getenv("HOME"); home != "" {
+			ctx.DockerDaemonHost = "unix://" + filepath.Join(home, ".docker/run/docker.sock")
+		}
+	}
+	return ctx
+}
+
 func TestNoteCloseFailure(t *testing.T) {
 	const description = "description"
 
@@ -73,9 +90,7 @@ func TestImageOptionsNewSystemContext(t *testing.T) {
 	opts := fakeImageOptions(t, "dest-", true, []string{}, []string{})
 	res, err := opts.newSystemContext()
 	require.NoError(t, err)
-	assert.Equal(t, &types.SystemContext{
-		DockerRegistryUserAgent: defaultUserAgent,
-	}, res)
+	assert.Equal(t, newExpectedSystemContext(), res)
 
 	// Set everything to non-default values.
 	opts = fakeImageOptions(t, "dest-", true, []string{
@@ -148,9 +163,7 @@ func TestImageDestOptionsNewSystemContext(t *testing.T) {
 	opts := fakeImageDestOptions(t, "dest-", true, []string{}, []string{})
 	res, err := opts.newSystemContext()
 	require.NoError(t, err)
-	assert.Equal(t, &types.SystemContext{
-		DockerRegistryUserAgent: defaultUserAgent,
-	}, res)
+	assert.Equal(t, newExpectedSystemContext(), res)
 
 	authFile := "/tmp/auth.json"
 	// Make sure when REGISTRY_AUTH_FILE is set the auth file is used
@@ -162,10 +175,9 @@ func TestImageDestOptionsNewSystemContext(t *testing.T) {
 	})
 	res, err = opts.newSystemContext()
 	require.NoError(t, err)
-	assert.Equal(t, &types.SystemContext{
-		AuthFilePath:            authFile,
-		DockerRegistryUserAgent: defaultUserAgent,
-	}, res)
+	expected := newExpectedSystemContext()
+	expected.AuthFilePath = authFile
+	assert.Equal(t, expected, res)
 
 	// Set everything to non-default values.
 	opts = fakeImageDestOptions(t, "dest-", true, []string{
@@ -255,10 +267,9 @@ func TestImageOptionsUsernamePassword(t *testing.T) {
 			assert.Error(t, err)
 		} else {
 			require.NoError(t, err)
-			assert.Equal(t, &types.SystemContext{
-				DockerRegistryUserAgent: defaultUserAgent,
-				DockerAuthConfig:        command.expectedAuthConfig,
-			}, res)
+			expected := newExpectedSystemContext()
+			expected.DockerAuthConfig = command.expectedAuthConfig
+			assert.Equal(t, expected, res)
 		}
 	}
 }
@@ -508,9 +519,16 @@ func TestImageOptionsAuthfileOverride(t *testing.T) {
 		res, err := opts.newSystemContext()
 		require.NoError(t, err)
 
-		assert.Equal(t, &types.SystemContext{
+		expected := &types.SystemContext{
 			AuthFilePath:            testCase.expectedAuthfilePath,
 			DockerRegistryUserAgent: defaultUserAgent,
-		}, res)
+		}
+		// On macOS, DockerDaemonHost gets set to the platform-specific default
+		if runtime.GOOS == "darwin" {
+			if home := os.Getenv("HOME"); home != "" {
+				expected.DockerDaemonHost = "unix://" + filepath.Join(home, ".docker/run/docker.sock")
+			}
+		}
+		assert.Equal(t, expected, res)
 	}
 }