bug:Merge custom labels with default

container.go

@@ -392,7 +392,10 @@ func (c *ContainerRequest) BuildOptions() (types.ImageBuildOptions, error) {
 	}
 
 	if !c.ShouldKeepBuiltImage() {
-		buildOptions.Labels = core.DefaultLabels(core.SessionID())
+		err := core.MergeCustomLabels(buildOptions.Labels, core.DefaultLabels(core.SessionID()))
+		if err != nil {
+			panic(fmt.Errorf("Unable to merge custom labels"))
+		}
 	}
 
 	// Do this as late as possible to ensure we don't leak the context on error/panic.

container_test.go

@@ -17,6 +17,7 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"github.com/testcontainers/testcontainers-go"
+	"github.com/testcontainers/testcontainers-go/internal/core"
 	"github.com/testcontainers/testcontainers-go/wait"
 )
 
@@ -489,6 +490,53 @@ func TestShouldStartContainersInParallel(t *testing.T) {
 	}
 }
 
+func TestLabelBuilding(t *testing.T) {
+	labels := core.DefaultLabels("session-id")
+	assert.NotNil(t, labels)
+	assert.Len(t, labels, 4)
+	goodCustomLabels := map[string]string{
+		"org.custom.label1": "foo",
+		"org.custom.label2": "bar",
+	}
+	err := core.MergeCustomLabels(goodCustomLabels, labels)
+	require.NoError(t, err)
+	assert.NotNil(t, goodCustomLabels)
+	assert.Contains(t, goodCustomLabels, core.LabelLang)
+	assert.Len(t, goodCustomLabels, 6)
+
+	badCustomLabels := map[string]string{
+		core.LabelLang:      "python",
+		core.LabelSessionID: "invalid",
+	}
+	err = core.MergeCustomLabels(badCustomLabels, labels)
+	require.Error(t, err)
+}
+
+func TestLabelsForContainer(t *testing.T) {
+	ctx := context.Background()
+
+	customLabel := "org.company.environment"
+	container, err := testcontainers.GenericContainer(ctx, testcontainers.GenericContainerRequest{
+		ContainerRequest: testcontainers.ContainerRequest{
+			Image:  "alpine:latest",
+			Labels: map[string]string{customLabel: "test"},
+		},
+	})
+	require.NoError(t, err)
+
+	containerJson, err := container.Inspect(ctx)
+	require.NoError(t, err)
+	assert.Contains(t, containerJson.Config.Labels, core.LabelLang)
+	assert.Contains(t, containerJson.Config.Labels, customLabel)
+
+	defer func() {
+		err := container.Terminate(ctx)
+		if err != nil {
+			log.Fatalf("could not terminate container: %v", err)
+		}
+	}()
+}
+
 func ExampleGenericContainer_withSubstitutors() {
 	ctx := context.Background()
 

internal/core/labels.go

@@ -1,6 +1,9 @@
 package core
 
 import (
+	"fmt"
+	"strings"
+
 	"github.com/testcontainers/testcontainers-go/internal"
 )
 
@@ -13,6 +16,7 @@ const (
 	LabelVersion   = LabelBase + ".version"
 )
 
+// DefaultLabels returns the default map of Labels for a container
 func DefaultLabels(sessionID string) map[string]string {
 	return map[string]string{
 		LabelBase:      "true",
@@ -21,3 +25,20 @@ func DefaultLabels(sessionID string) map[string]string {
 		LabelVersion:   internal.Version,
 	}
 }
+
+// MergeCustomLabels merges default labels in-place to the custom labels.
+//
+// It is an error to use "org.testcontainers" as a prefix to custom labels.
+func MergeCustomLabels(customLabels map[string]string, defaultLabels map[string]string) error {
+	for customLabelKey := range customLabels {
+		_, present := defaultLabels[customLabelKey]
+		if present || strings.HasPrefix(customLabelKey, LabelBase) {
+			return fmt.Errorf("custom labels cannot begin with %s or already be present", LabelBase)
+		}
+	}
+	for defaultLabel, defaultValue := range defaultLabels {
+		customLabels[defaultLabel] = defaultValue
+	}
+
+	return nil
+}