config: support HeadersList

CHANGELOG.md

@@ -24,6 +24,7 @@ The next release will require at least [Go 1.23].
 - Support for the `OTEL_HTTP_CLIENT_COMPATIBILITY_MODE=http/dup` environment variable in `instrumentation/github.com/emicklei/go-restful/otelrestful` to emit attributes for both the v1.20.0 and v1.26.0 semantic conventions. (#6710)
 - Added metrics support, and emit all stable metrics from the [Semantic Conventions](https://github.com/open-telemetry/semantic-conventions/blob/main/docs/http/http-metrics.md) in `go.opentelemetry.io/contrib/instrumentation/github.com/gin-gonic/gin/otelgin`. (#6747)
 - Support [Go 1.24]. (#6765)
+- Add support for configuring `HeadersList` field for OTLP exporters in `go.opentelemetry.io/contrib/config`. (#6657)
 
 ### Changed
 

config/v0.3.0/config.go

@@ -13,6 +13,7 @@ import (
 
 	"gopkg.in/yaml.v3"
 
+	"go.opentelemetry.io/otel/baggage"
 	"go.opentelemetry.io/otel/log"
 	nooplog "go.opentelemetry.io/otel/log/noop"
 	"go.opentelemetry.io/otel/metric"
@@ -152,16 +153,6 @@ func ParseYAML(file []byte) (*OpenTelemetryConfiguration, error) {
 	return &cfg, nil
 }
 
-func toStringMap(pairs []NameStringValuePair) map[string]string {
-	output := make(map[string]string)
-	for _, v := range pairs {
-		if v.Value != nil && len(v.Name) > 0 {
-			output[v.Name] = *v.Value
-		}
-	}
-	return output
-}
-
 // createTLSConfig creates a tls.Config from certificate files.
 func createTLSConfig(caCertFile *string, clientCertFile *string, clientKeyFile *string) (*tls.Config, error) {
 	tlsConfig := &tls.Config{}
@@ -188,3 +179,27 @@ func createTLSConfig(caCertFile *string, clientCertFile *string, clientKeyFile *
 	}
 	return tlsConfig, nil
 }
+
+// createHeadersConfig combines the two header config fields. Headers take precedence over headersList.
+func createHeadersConfig(headers []NameStringValuePair, headersList *string) (map[string]string, error) {
+	result := make(map[string]string)
+	if headersList != nil {
+		// Parsing follows https://github.com/open-telemetry/opentelemetry-configuration/blob/568e5080816d40d75792eb754fc96bde09654159/schema/type_descriptions.yaml#L584.
+		headerslist, err := baggage.Parse(*headersList)
+		if err != nil {
+			return nil, fmt.Errorf("invalid headers list: %w", err)
+		}
+		for _, kv := range headerslist.Members() {
+			result[kv.Key()] = kv.Value()
+		}
+	}
+	// Headers take precedence over HeadersList, so this has to be after HeadersList is processed
+	if len(headers) > 0 {
+		for _, kv := range headers {
+			if kv.Value != nil {
+				result[kv.Name] = *kv.Value
+			}
+		}
+	}
+	return result, nil
+}

config/v0.3.0/config_test.go

@@ -568,10 +568,97 @@ func TestCreateTLSConfig(t *testing.T) {
 	}
 }
 
-func TestToStringMap(t *testing.T) {
-	require.Equal(t, map[string]string{}, toStringMap([]NameStringValuePair{}))
-	require.Equal(t, map[string]string{}, toStringMap([]NameStringValuePair{{Name: "test"}}))
-	require.Equal(t, map[string]string{}, toStringMap([]NameStringValuePair{{Value: ptr("test")}}))
+func TestCreateHeadersConfig(t *testing.T) {
+	tests := []struct {
+		name        string
+		headers     []NameStringValuePair
+		headersList *string
+		wantHeaders map[string]string
+		wantErr     string
+	}{
+		{
+			name:        "no headers",
+			headers:     []NameStringValuePair{},
+			headersList: nil,
+			wantHeaders: map[string]string{},
+		},
+		{
+			name:        "headerslist only",
+			headers:     []NameStringValuePair{},
+			headersList: ptr("a=b,c=d"),
+			wantHeaders: map[string]string{
+				"a": "b",
+				"c": "d",
+			},
+		},
+		{
+			name: "headers only",
+			headers: []NameStringValuePair{
+				{
+					Name:  "a",
+					Value: ptr("b"),
+				},
+				{
+					Name:  "c",
+					Value: ptr("d"),
+				},
+			},
+			headersList: nil,
+			wantHeaders: map[string]string{
+				"a": "b",
+				"c": "d",
+			},
+		},
+		{
+			name: "both headers and headerslist",
+			headers: []NameStringValuePair{
+				{
+					Name:  "a",
+					Value: ptr("b"),
+				},
+			},
+			headersList: ptr("c=d"),
+			wantHeaders: map[string]string{
+				"a": "b",
+				"c": "d",
+			},
+		},
+		{
+			name: "headers supersedes headerslist",
+			headers: []NameStringValuePair{
+				{
+					Name:  "a",
+					Value: ptr("b"),
+				},
+				{
+					Name:  "c",
+					Value: ptr("override"),
+				},
+			},
+			headersList: ptr("c=d"),
+			wantHeaders: map[string]string{
+				"a": "b",
+				"c": "override",
+			},
+		},
+		{
+			name:        "invalid headerslist",
+			headersList: ptr("==="),
+			wantErr:     "invalid headers list: invalid key: \"\"",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			headersMap, err := createHeadersConfig(tt.headers, tt.headersList)
+			if tt.wantErr != "" {
+				require.Error(t, err)
+				require.Equal(t, tt.wantErr, err.Error())
+			} else {
+				require.NoError(t, err)
+			}
+			require.Equal(t, tt.wantHeaders, headersMap)
+		})
+	}
 }
 
 func ptr[T any](v T) *T {

config/v0.3.0/log.go

@@ -152,8 +152,12 @@ func otlpHTTPLogExporter(ctx context.Context, otlpConfig *OTLP) (sdklog.Exporter
 	if otlpConfig.Timeout != nil && *otlpConfig.Timeout > 0 {
 		opts = append(opts, otlploghttp.WithTimeout(time.Millisecond*time.Duration(*otlpConfig.Timeout)))
 	}
-	if len(otlpConfig.Headers) > 0 {
-		opts = append(opts, otlploghttp.WithHeaders(toStringMap(otlpConfig.Headers)))
+	headersConfig, err := createHeadersConfig(otlpConfig.Headers, otlpConfig.HeadersList)
+	if err != nil {
+		return nil, err
+	}
+	if len(headersConfig) > 0 {
+		opts = append(opts, otlploghttp.WithHeaders(headersConfig))
 	}
 
 	tlsConfig, err := createTLSConfig(otlpConfig.Certificate, otlpConfig.ClientCertificate, otlpConfig.ClientKey)
@@ -200,8 +204,12 @@ func otlpGRPCLogExporter(ctx context.Context, otlpConfig *OTLP) (sdklog.Exporter
 	if otlpConfig.Timeout != nil && *otlpConfig.Timeout > 0 {
 		opts = append(opts, otlploggrpc.WithTimeout(time.Millisecond*time.Duration(*otlpConfig.Timeout)))
 	}
-	if len(otlpConfig.Headers) > 0 {
-		opts = append(opts, otlploggrpc.WithHeaders(toStringMap(otlpConfig.Headers)))
+	headersConfig, err := createHeadersConfig(otlpConfig.Headers, otlpConfig.HeadersList)
+	if err != nil {
+		return nil, err
+	}
+	if len(headersConfig) > 0 {
+		opts = append(opts, otlploggrpc.WithHeaders(headersConfig))
 	}
 
 	tlsConfig, err := createTLSConfig(otlpConfig.Certificate, otlpConfig.ClientCertificate, otlpConfig.ClientKey)