fix: honor standard Docker host environment

pkg/app.go

@@ -154,7 +154,7 @@ func NewApp() *cli.Command {
 			},
 			&cli.StringFlag{
 				Name:    "host",
-				Sources: cli.EnvVars("DOCKLE_HOST"),
+				Sources: cli.EnvVars("DOCKLE_HOST", "DOCKER_HOST"),
 				Usage:   "docker daemon host",
 			},
 			&cli.StringFlag{

pkg/run_test.go

@@ -0,0 +1,88 @@
+package pkg
+
+import (
+	"context"
+	"os"
+	"testing"
+
+	"github.com/urfave/cli/v3"
+)
+
+func setOptionalEnv(t *testing.T, key, value string) {
+	t.Helper()
+	original, exists := os.LookupEnv(key)
+	if value == "" {
+		if err := os.Unsetenv(key); err != nil {
+			t.Fatalf("unset %s: %v", key, err)
+		}
+	} else if err := os.Setenv(key, value); err != nil {
+		t.Fatalf("set %s: %v", key, err)
+	}
+	t.Cleanup(func() {
+		if exists {
+			_ = os.Setenv(key, original)
+		} else {
+			_ = os.Unsetenv(key)
+		}
+	})
+}
+
+func TestGetDockerSockPath(t *testing.T) {
+	tests := []struct {
+		name       string
+		args       []string
+		dockleHost string
+		dockerHost string
+		xdgRuntime string
+		expected   string
+	}{
+		{
+			name:       "explicit host takes precedence",
+			args:       []string{"--host", "tcp://explicit:2375"},
+			dockerHost: "tcp://docker:2375",
+			expected:   "tcp://explicit:2375",
+		},
+		{
+			name:       "dockle host environment takes precedence",
+			dockleHost: "tcp://dockle:2375",
+			dockerHost: "tcp://docker:2375",
+			expected:   "tcp://dockle:2375",
+		},
+		{
+			name:       "standard docker host environment",
+			dockerHost: "tcp://docker:2375",
+			expected:   "tcp://docker:2375",
+		},
+		{
+			name:       "xdg socket",
+			args:       []string{"--use-xdg"},
+			xdgRuntime: "/run/user/1000",
+			expected:   "unix:///run/user/1000/docker.sock",
+		},
+		{
+			name:     "default socket",
+			expected: "unix:///var/run/docker.sock",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			setOptionalEnv(t, "DOCKLE_HOST", tt.dockleHost)
+			setOptionalEnv(t, "DOCKER_HOST", tt.dockerHost)
+			setOptionalEnv(t, "XDG_RUNTIME_DIR", tt.xdgRuntime)
+
+			var actual string
+			cmd := NewApp()
+			cmd.Action = func(_ context.Context, cmd *cli.Command) error {
+				actual = getDockerSockPath(cmd)
+				return nil
+			}
+			if err := cmd.Run(context.Background(), append([]string{"dockle"}, tt.args...)); err != nil {
+				t.Fatalf("run command: %v", err)
+			}
+			if actual != tt.expected {
+				t.Fatalf("getDockerSockPath() = %q, want %q", actual, tt.expected)
+			}
+		})
+	}
+}