Add option to specify propagators to use with grpctrace Extract and Inject

instrumentation/grpctrace/grpctrace.go

@@ -26,6 +26,29 @@ import (
 	"go.opentelemetry.io/otel/api/trace"
 )
 
+// Option is a function that allows configuration of the grpctrace Extract()
+// and Inject() functions
+type Option func(*config)
+
+type config struct {
+	propagators propagation.Propagators
+}
+
+func newConfig(opts []Option) *config {
+	c := &config{propagators: global.Propagators()}
+	for _, o := range opts {
+		o(c)
+	}
+	return c
+}
+
+// WithPropagators sets the propagators to use for Extraction and Injection
+func WithPropagators(props propagation.Propagators) Option {
+	return func(c *config) {
+		c.propagators = props
+	}
+}
+
 type metadataSupplier struct {
 	metadata *metadata.MD
 }
@@ -45,8 +68,9 @@ func (s *metadataSupplier) Set(key string, value string) {
 // Inject injects correlation context and span context into the gRPC
 // metadata object. This function is meant to be used on outgoing
 // requests.
-func Inject(ctx context.Context, metadata *metadata.MD) {
-	propagation.InjectHTTP(ctx, global.Propagators(), &metadataSupplier{
+func Inject(ctx context.Context, metadata *metadata.MD, opts ...Option) {
+	c := newConfig(opts)
+	propagation.InjectHTTP(ctx, c.propagators, &metadataSupplier{
 		metadata: metadata,
 	})
 }
@@ -54,8 +78,9 @@ func Inject(ctx context.Context, metadata *metadata.MD) {
 // Extract returns the correlation context and span context that
 // another service encoded in the gRPC metadata object with Inject.
 // This function is meant to be used on incoming requests.
-func Extract(ctx context.Context, metadata *metadata.MD) ([]kv.KeyValue, trace.SpanContext) {
-	ctx = propagation.ExtractHTTP(ctx, global.Propagators(), &metadataSupplier{
+func Extract(ctx context.Context, metadata *metadata.MD, opts ...Option) ([]kv.KeyValue, trace.SpanContext) {
+	c := newConfig(opts)
+	ctx = propagation.ExtractHTTP(ctx, c.propagators, &metadataSupplier{
 		metadata: metadata,
 	})