make carrier as interface instead of http.Request.

api/propagation/propagator.go

@@ -17,8 +17,6 @@
 package propagation // import "go.opentelemetry.io/api/propagation"
 
 import (
-	"net/http"
-
 	"go.opentelemetry.io/api/core"
 	"go.opentelemetry.io/api/tag"
 )
@@ -31,8 +29,8 @@ import (
 // Typically, a plugin for transport like HTTP uses this interface to allow user
 // to configure appropriate propagators.
 type TextFormatPropagator interface {
-	Extractor(req *http.Request) Extractor
-	Injector(req *http.Request) Injector
+	Extractor(carrier interface{}) Extractor
+	Injector(carrier interface{}) Injector
 }
 
 type Injector interface {

propagation/http_textformat_propagator.go

@@ -35,26 +35,46 @@ const (
 	traceparentHeader = "traceparent"
 )
 
-type textFormatPropagator struct{}
+type httpTraceContextPropagator struct{}
 
-var _ apipropagation.TextFormatPropagator = textFormatPropagator{}
+var _ apipropagation.TextFormatPropagator = httpTraceContextPropagator{}
 
-func (t textFormatPropagator) Extractor(req *http.Request) apipropagation.Extractor {
-	return textFormatExtractor{req: req}
+// Extractor implements Extractor method of TextFormatPropagator interface.
+//
+// It creates Extractor object and binds carrier to the object. The carrier
+// is expected to be *http.Request. If the carrier type is not *http.Request
+// then an empty extractor is returned which will extract nothing.
+func (t httpTraceContextPropagator) Extractor(carrier interface{}) apipropagation.Extractor {
+	req, ok := carrier.(*http.Request)
+	if ok {
+		return textFormatExtractor{req: req}
+	}
+	return textFormatExtractor{}
 }
 
-func (t textFormatPropagator) Injector(req *http.Request) apipropagation.Injector {
-	return textFormatInjector{req: req}
+// Injector implements Injector method of TextFormatPropagator interface.
+//
+// It creates Injector object and binds carrier to the object. The carrier
+// is expected to be of type *http.Request. If the carrier type is not *http.Request
+// then an empty injector is returned which will inject nothing.
+func (t httpTraceContextPropagator) Injector(carrier interface{}) apipropagation.Injector {
+	req, ok := carrier.(*http.Request)
+	if ok {
+		return textFormatInjector{req: req}
+	}
+	return textFormatInjector{}
 }
 
-// TextFormatPropagator creates a new propagator. The propagator is then used
-// to create Injector and Extrator associated with a specific request. Injectors
-// and Extractors respectively provides method to inject and extract SpanContext
-// into/from the http request. Inject method encodes SpanContext into W3C
-// TraceContext Header and injects the header in the request. Extract extracts
-// the header and decodes SpanContext.
-func TextFormatPropagator() textFormatPropagator {
-	return textFormatPropagator{}
+// HttpTraceContextPropagator creates a new propagator that propagates SpanContext
+// in W3C TraceContext format.
+//
+// The propagator is then used to create Injector and Extractor associated with a
+// specific request. Injectors and Extractors respectively provides method to
+// inject and extract SpanContext into/from the http request. Inject method encodes
+// SpanContext into W3C TraceContext Header and injects the header in the request.
+// Extract extracts the header and decodes SpanContext.
+func HttpTraceContextPropagator() httpTraceContextPropagator {
+	return httpTraceContextPropagator{}
 }
 
 type textFormatExtractor struct {
@@ -66,6 +86,9 @@ var _ apipropagation.Extractor = textFormatExtractor{}
 // Extract implements Extract method of trace.Extractor interface. It extracts
 // W3C TraceContext Header and decodes SpanContext from the Header.
 func (tfe textFormatExtractor) Extract() (sc core.SpanContext, tm tag.Map) {
+	if tfe.req == nil {
+		return core.EmptySpanContext(), tag.NewEmptyMap()
+	}
 	h, ok := getRequestHeader(tfe.req, traceparentHeader, false)
 	if !ok {
 		return core.EmptySpanContext(), tag.NewEmptyMap()
@@ -136,10 +159,13 @@ type textFormatInjector struct {
 
 var _ apipropagation.Injector = textFormatInjector{}
 
-// Inject implements Inject method of trace.Injector interface. It encodes
+// Inject implements Inject method of propagation.Injector interface. It encodes
 // SpanContext into W3C TraceContext Header and injects the header into
 // the associated request.
 func (tfi textFormatInjector) Inject(sc core.SpanContext, tm tag.Map) {
+	if tfi.req == nil {
+		return
+	}
 	if sc.IsValid() {
 		h := fmt.Sprintf("%.2x-%.16x%.16x-%.16x-%.2x",
 			supportedVersion,

propagation/http_textformat_propagator_test.go

@@ -31,7 +31,7 @@ var (
 )
 
 func TestExtractTraceContextFromHTTPReq(t *testing.T) {
-	propagator := propagation.TextFormatPropagator()
+	propagator := propagation.HttpTraceContextPropagator()
 	tests := []struct {
 		name   string
 		header string
@@ -86,8 +86,33 @@ func TestExtractTraceContextFromHTTPReq(t *testing.T) {
 	}
 }
 
+func TestExtractTraceContextFromInvalidCarrier(t *testing.T) {
+	propagator := propagation.HttpTraceContextPropagator()
+	tests := []struct {
+		name   string
+		header string
+		wantSc core.SpanContext
+	}{
+		{
+			name:   "valid header on invalid carrier",
+			header: "00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-01",
+			wantSc: core.EmptySpanContext(),
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			e := propagator.Extractor(tt.header)
+			gotSc, _ := e.Extract()
+			if diff := cmp.Diff(gotSc, tt.wantSc); diff != "" {
+				t.Errorf("Extract Tracecontext: %s: -got +want %s", tt.name, diff)
+			}
+		})
+	}
+}
+
 func TestInjectTraceContextToHTTPReq(t *testing.T) {
-	propagator := propagation.TextFormatPropagator()
+	propagator := propagation.HttpTraceContextPropagator()
 	tests := []struct {
 		name       string
 		sc         core.SpanContext
@@ -129,3 +154,26 @@ func TestInjectTraceContextToHTTPReq(t *testing.T) {
 		})
 	}
 }
+
+func TestInjectTraceContextToInvalidCarrier(t *testing.T) {
+	propagator := propagation.HttpTraceContextPropagator()
+	tests := []struct {
+		name string
+		sc   core.SpanContext
+	}{
+		{
+			name: "valid spancontext to invalid carrier",
+			sc: core.SpanContext{
+				TraceID:      traceID,
+				SpanID:       spanID,
+				TraceOptions: core.TraceOptionSampled,
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			i := propagator.Injector("")
+			i.Inject(tt.sc, tag.NewEmptyMap())
+		})
+	}
+}