fix: container mount inspection logic

Author: kmendell

backend/pkg/dockerutil/mount_utils.go

@@ -20,14 +20,14 @@ func GetHostPathForContainerPath(ctx context.Context, dockerCli *client.Client,
 		return "", nil // No docker client, can't discover
 	}
 
-	// 1. Get current container ID (usually the short ID is the hostname)
-	hostname, err := os.Hostname()
+	// 1. Prefer robust current-container detection and fall back to hostname.
+	inspectTarget, err := getCurrentContainerInspectTargetInternal(GetCurrentContainerID, os.Hostname)
 	if err != nil {
 		return "", err
 	}
 
 	// 2. Inspect self
-	inspect, err := libarcane.ContainerInspectWithCompatibility(ctx, dockerCli, hostname, client.ContainerInspectOptions{})
+	inspect, err := libarcane.ContainerInspectWithCompatibility(ctx, dockerCli, inspectTarget, client.ContainerInspectOptions{})
 	if err != nil {
 		// Not running in a container or can't reach docker daemon
 		return "", err
@@ -70,6 +70,27 @@ func GetHostPathForContainerPath(ctx context.Context, dockerCli *client.Client,
 	return "", nil
 }
 
+func getCurrentContainerInspectTargetInternal(currentContainerID func() (string, error), hostname func() (string, error)) (string, error) {
+	if currentContainerID != nil {
+		if containerID, err := currentContainerID(); err == nil {
+			if containerID = strings.TrimSpace(containerID); containerID != "" {
+				return containerID, nil
+			}
+		}
+	}
+
+	if hostname == nil {
+		hostname = os.Hostname
+	}
+
+	value, err := hostname()
+	if err != nil {
+		return "", err
+	}
+
+	return strings.TrimSpace(value), nil
+}
+
 // MountForDestination returns a Mount suitable for container creation that mirrors an
 // existing container mount at the given destination.
 //

backend/pkg/dockerutil/mount_utils_test.go

@@ -1,13 +1,57 @@
 package docker
 
 import (
+	"errors"
 	"testing"
 
 	containertypes "github.com/moby/moby/api/types/container"
 	mounttypes "github.com/moby/moby/api/types/mount"
 	"github.com/stretchr/testify/require"
 )
 
+func TestGetCurrentContainerInspectTargetInternal(t *testing.T) {
+	t.Run("prefers detected container id over hostname", func(t *testing.T) {
+		target, err := getCurrentContainerInspectTargetInternal(
+			func() (string, error) { return "0123456789ab", nil },
+			func() (string, error) { return "rpi4", nil },
+		)
+
+		require.NoError(t, err)
+		require.Equal(t, "0123456789ab", target)
+	})
+
+	t.Run("falls back to hostname when container id unavailable", func(t *testing.T) {
+		target, err := getCurrentContainerInspectTargetInternal(
+			func() (string, error) { return "", errors.New("no container id found") },
+			func() (string, error) { return "rpi4", nil },
+		)
+
+		require.NoError(t, err)
+		require.Equal(t, "rpi4", target)
+	})
+
+	t.Run("trims whitespace from detected container id", func(t *testing.T) {
+		target, err := getCurrentContainerInspectTargetInternal(
+			func() (string, error) { return "  0123456789ab  ", nil },
+			func() (string, error) { return "rpi4", nil },
+		)
+
+		require.NoError(t, err)
+		require.Equal(t, "0123456789ab", target)
+	})
+
+	t.Run("returns hostname error when fallback fails", func(t *testing.T) {
+		target, err := getCurrentContainerInspectTargetInternal(
+			func() (string, error) { return "", errors.New("no container id found") },
+			func() (string, error) { return "", errors.New("hostname unavailable") },
+		)
+
+		require.Error(t, err)
+		require.Contains(t, err.Error(), "hostname unavailable")
+		require.Equal(t, "", target)
+	})
+}
+
 func TestMountForDestination(t *testing.T) {
 	tests := []struct {
 		name       string