Add Keys() method to propagation.TextMapCarrier (open-telemetry#1544)

...and propagation.HeaderCarrier to adapt http.Header to this interface.

Co-authored-by: Tyler Yahn <[email protected]>

CHANGELOG.md

@@ -16,6 +16,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 ### Added
 
 - Added `resource.Default()` for use with meter and tracer providers. (#1507)
+- Added `Keys()` method to `propagation.TextMapCarrier` and `propagation.HeaderCarrier` to adapt `http.Header` to this interface. (#1544)
 
 ## [0.17.0] - 2020-02-12
 

bridge/opentracing/bridge.go

@@ -637,7 +637,7 @@ func (t *BridgeTracer) Inject(sm ot.SpanContext, format interface{}, carrier int
 	}
 	ctx := trace.ContextWithSpan(context.Background(), fs)
 	ctx = baggage.ContextWithMap(ctx, bridgeSC.baggageItems)
-	t.getPropagator().Inject(ctx, header)
+	t.getPropagator().Inject(ctx, propagation.HeaderCarrier(header))
 	return nil
 }
 
@@ -654,7 +654,7 @@ func (t *BridgeTracer) Extract(format interface{}, carrier interface{}) (ot.Span
 		return nil, ot.ErrInvalidCarrier
 	}
 	header := http.Header(hhcarrier)
-	ctx := t.getPropagator().Extract(context.Background(), header)
+	ctx := t.getPropagator().Extract(context.Background(), propagation.HeaderCarrier(header))
 	baggage := baggage.MapFromContext(ctx)
 	otelSC, _, _ := otelparent.GetSpanContextAndLinks(ctx, false)
 	bridgeSC := &bridgeSpanContext{

oteltest/text_map_propagator.go

@@ -46,6 +46,18 @@ func NewTextMapCarrier(data map[string]string) *TextMapCarrier {
 	return &TextMapCarrier{data: copied}
 }
 
+// Keys returns the keys for which this carrier has a value.
+func (c *TextMapCarrier) Keys() []string {
+	c.mtx.Lock()
+	defer c.mtx.Unlock()
+
+	result := make([]string, 0, len(c.data))
+	for k := range c.data {
+		result = append(result, k)
+	}
+	return result
+}
+
 // Get returns the value associated with the passed key.
 func (c *TextMapCarrier) Get(key string) string {
 	c.mtx.Lock()

oteltest/text_map_propagator_test.go

@@ -16,13 +16,22 @@ package oteltest
 
 import (
 	"context"
+	"reflect"
 	"testing"
 )
 
 var (
 	key, value = "test", "true"
 )
 
+func TestTextMapCarrierKeys(t *testing.T) {
+	tmc := NewTextMapCarrier(map[string]string{key: value})
+	expected, actual := []string{key}, tmc.Keys()
+	if !reflect.DeepEqual(actual, expected) {
+		t.Errorf("expected tmc.Keys() to be %v but it was %v", expected, actual)
+	}
+}
+
 func TestTextMapCarrierGet(t *testing.T) {
 	tmc := NewTextMapCarrier(map[string]string{key: value})
 	tmc.GotN(t, 0)

propagation/baggage_test.go

@@ -90,7 +90,7 @@ func TestExtractValidBaggageFromHTTPReq(t *testing.T) {
 			req.Header.Set("baggage", tt.header)
 
 			ctx := context.Background()
-			ctx = prop.Extract(ctx, req.Header)
+			ctx = prop.Extract(ctx, propagation.HeaderCarrier(req.Header))
 			gotBaggage := baggage.MapFromContext(ctx)
 			wantBaggage := baggage.NewMap(baggage.MapUpdate{MultiKV: tt.wantKVs})
 			if gotBaggage.Len() != wantBaggage.Len() {
@@ -152,7 +152,7 @@ func TestExtractInvalidDistributedContextFromHTTPReq(t *testing.T) {
 
 			ctx := baggage.NewContext(context.Background(), tt.hasKVs...)
 			wantBaggage := baggage.MapFromContext(ctx)
-			ctx = prop.Extract(ctx, req.Header)
+			ctx = prop.Extract(ctx, propagation.HeaderCarrier(req.Header))
 			gotBaggage := baggage.MapFromContext(ctx)
 			if gotBaggage.Len() != wantBaggage.Len() {
 				t.Errorf(
@@ -218,7 +218,7 @@ func TestInjectBaggageToHTTPReq(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			req, _ := http.NewRequest("GET", "http://example.com", nil)
 			ctx := baggage.ContextWithMap(context.Background(), baggage.NewMap(baggage.MapUpdate{MultiKV: tt.kvs}))
-			propagator.Inject(ctx, req.Header)
+			propagator.Inject(ctx, propagation.HeaderCarrier(req.Header))
 
 			gotHeader := req.Header.Get("baggage")
 			wantedLen := len(strings.Join(tt.wantInHeader, ","))

propagation/propagation.go

@@ -14,14 +14,41 @@
 
 package propagation // import "go.opentelemetry.io/otel/propagation"
 
-import "context"
+import (
+	"context"
+	"net/http"
+)
 
 // TextMapCarrier is the storage medium used by a TextMapPropagator.
 type TextMapCarrier interface {
 	// Get returns the value associated with the passed key.
 	Get(key string) string
 	// Set stores the key-value pair.
 	Set(key string, value string)
+	// Keys lists the keys stored in this carrier.
+	Keys() []string
+}
+
+// HeaderCarrier adapts http.Header to satisfy the TextMapCarrier interface.
+type HeaderCarrier http.Header
+
+// Get returns the value associated with the passed key.
+func (hc HeaderCarrier) Get(key string) string {
+	return http.Header(hc).Get(key)
+}
+
+// Set stores the key-value pair.
+func (hc HeaderCarrier) Set(key string, value string) {
+	http.Header(hc).Set(key, value)
+}
+
+// Keys lists the keys stored in this carrier.
+func (hc HeaderCarrier) Keys() []string {
+	keys := make([]string, 0, len(hc))
+	for k := range hc {
+		keys = append(keys, k)
+	}
+	return keys
 }
 
 // TextMapPropagator propagates cross-cutting concerns as key-value text

propagation/propagation_test.go

@@ -30,6 +30,8 @@ var (
 
 type carrier []string
 
+func (c *carrier) Keys() []string { return nil }
+
 func (c *carrier) Get(string) string { return "" }
 
 func (c *carrier) Set(setter, _ string) {

propagation/propagators_test.go

@@ -79,6 +79,10 @@ type nilCarrier struct{}
 
 var _ propagation.TextMapCarrier = nilCarrier{}
 
+func (nilCarrier) Keys() []string {
+	return nil
+}
+
 func (nilCarrier) Get(key string) string {
 	return ""
 }

propagation/trace_context_benchmark_test.go

@@ -31,7 +31,7 @@ func BenchmarkInject(b *testing.B) {
 		req, _ := http.NewRequest("GET", "http://example.com", nil)
 		b.ResetTimer()
 		for i := 0; i < b.N; i++ {
-			t.Inject(ctx, req.Header)
+			t.Inject(ctx, propagation.HeaderCarrier(req.Header))
 		}
 	})
 }
@@ -66,7 +66,7 @@ func BenchmarkExtract(b *testing.B) {
 		ctx := context.Background()
 		b.ResetTimer()
 		for i := 0; i < b.N; i++ {
-			propagator.Extract(ctx, req.Header)
+			propagator.Extract(ctx, propagation.HeaderCarrier(req.Header))
 		}
 	})
 }

propagation/trace_context_test.go

@@ -112,7 +112,7 @@ func TestExtractValidTraceContextFromHTTPReq(t *testing.T) {
 			req.Header.Set("traceparent", tt.header)
 
 			ctx := context.Background()
-			ctx = prop.Extract(ctx, req.Header)
+			ctx = prop.Extract(ctx, propagation.HeaderCarrier(req.Header))
 			gotSc := trace.RemoteSpanContextFromContext(ctx)
 			if diff := cmp.Diff(gotSc, tt.wantSc, cmp.AllowUnexported(trace.TraceState{})); diff != "" {
 				t.Errorf("Extract Tracecontext: %s: -got +want %s", tt.name, diff)
@@ -200,7 +200,7 @@ func TestExtractInvalidTraceContextFromHTTPReq(t *testing.T) {
 			req.Header.Set("traceparent", tt.header)
 
 			ctx := context.Background()
-			ctx = prop.Extract(ctx, req.Header)
+			ctx = prop.Extract(ctx, propagation.HeaderCarrier(req.Header))
 			gotSc := trace.RemoteSpanContextFromContext(ctx)
 			if diff := cmp.Diff(gotSc, wantSc, cmp.AllowUnexported(trace.TraceState{})); diff != "" {
 				t.Errorf("Extract Tracecontext: %s: -got +want %s", tt.name, diff)
@@ -257,7 +257,7 @@ func TestInjectTraceContextToHTTPReq(t *testing.T) {
 				ctx = trace.ContextWithRemoteSpanContext(ctx, tt.sc)
 				ctx, _ = mockTracer.Start(ctx, "inject")
 			}
-			prop.Inject(ctx, req.Header)
+			prop.Inject(ctx, propagation.HeaderCarrier(req.Header))
 
 			gotHeader := req.Header.Get("traceparent")
 			if diff := cmp.Diff(gotHeader, tt.wantHeader); diff != "" {
@@ -337,7 +337,7 @@ func TestTraceStatePropagation(t *testing.T) {
 				inReq.Header.Add(hk, hv)
 			}
 
-			ctx := prop.Extract(context.Background(), inReq.Header)
+			ctx := prop.Extract(context.Background(), propagation.HeaderCarrier(inReq.Header))
 			if diff := cmp.Diff(
 				trace.RemoteSpanContextFromContext(ctx),
 				tt.wantSc,
@@ -351,7 +351,7 @@ func TestTraceStatePropagation(t *testing.T) {
 				mockTracer := oteltest.DefaultTracer()
 				ctx, _ = mockTracer.Start(ctx, "inject")
 				outReq, _ := http.NewRequest(http.MethodGet, "http://www.example.com", nil)
-				prop.Inject(ctx, outReq.Header)
+				prop.Inject(ctx, propagation.HeaderCarrier(outReq.Header))
 
 				if diff := cmp.Diff(outReq.Header.Get(stateHeader), tt.headers[stateHeader]); diff != "" {
 					t.Errorf("Propagated tracestate: -got +want %s", diff)