Avoid replacing existing correlation map data in context when correla…

…tion context extractor does not find any valid data (#923)

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

CHANGELOG.md

@@ -61,6 +61,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - Add test for api.standard `HTTPClientAttributesFromHTTPRequest`. (#905)
 - Bump github.com/golangci/golangci-lint from 1.27.0 to 1.28.1 in /tools. (#901, #913)
 - Update otel-colector example to use the v0.5.0 collector. (#915)
+- Correlation Context extractor will no longer insert an empty map into the returned context when no valid values are extracted. (#923)
 
 ## [0.7.0] - 2020-06-26
 

api/correlation/correlation_context_propagator.go

@@ -65,7 +65,7 @@ func (CorrelationContext) Inject(ctx context.Context, supplier propagation.HTTPS
 func (CorrelationContext) Extract(ctx context.Context, supplier propagation.HTTPSupplier) context.Context {
 	correlationContext := supplier.Get(correlationContextHeader)
 	if correlationContext == "" {
-		return ContextWithMap(ctx, NewEmptyMap())
+		return ctx
 	}
 
 	contextValues := strings.Split(correlationContext, ",")
@@ -101,9 +101,15 @@ func (CorrelationContext) Extract(ctx context.Context, supplier propagation.HTTP
 
 		keyValues = append(keyValues, kv.Key(trimmedName).String(trimmedValueWithProps.String()))
 	}
-	return ContextWithMap(ctx, NewMap(MapUpdate{
-		MultiKV: keyValues,
-	}))
+
+	if len(keyValues) > 0 {
+		// Only update the context if valid values were found
+		return ContextWithMap(ctx, NewMap(MapUpdate{
+			MultiKV: keyValues,
+		}))
+	}
+
+	return ctx
 }
 
 // GetAllKeys implements HTTPPropagator.

api/correlation/correlation_context_propagator_test.go

@@ -123,24 +123,55 @@ func TestExtractInvalidDistributedContextFromHTTPReq(t *testing.T) {
 	tests := []struct {
 		name   string
 		header string
+		hasKVs []kv.KeyValue
 	}{
 		{
 			name:   "no key values",
 			header: "header1",
 		},
+		{
+			name:   "invalid header with existing context",
+			header: "header2",
+			hasKVs: []kv.KeyValue{
+				kv.Key("key1").String("val1"),
+				kv.Key("key2").String("val2"),
+			},
+		},
+		{
+			name:   "empty header value",
+			header: "",
+			hasKVs: []kv.KeyValue{
+				kv.Key("key1").String("val1"),
+				kv.Key("key2").String("val2"),
+			},
+		},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			req, _ := http.NewRequest("GET", "http://example.com", nil)
 			req.Header.Set("otcorrelations", tt.header)
 
-			ctx := context.Background()
+			ctx := correlation.NewContext(context.Background(), tt.hasKVs...)
+			wantCorCtx := correlation.MapFromContext(ctx)
 			ctx = propagation.ExtractHTTP(ctx, props, req.Header)
 			gotCorCtx := correlation.MapFromContext(ctx)
-			if gotCorCtx.Len() != 0 {
-				t.Errorf("Got and Want CorCtx are not the same size %d != %d", gotCorCtx.Len(), 0)
+			if gotCorCtx.Len() != wantCorCtx.Len() {
+				t.Errorf(
+					"Got and Want CorCtx are not the same size %d != %d",
+					gotCorCtx.Len(),
+					wantCorCtx.Len(),
+				)
 			}
+			totalDiff := ""
+			wantCorCtx.Foreach(func(keyValue kv.KeyValue) bool {
+				val, _ := gotCorCtx.Value(keyValue.Key)
+				diff := cmp.Diff(keyValue, kv.KeyValue{Key: keyValue.Key, Value: val}, cmp.AllowUnexported(value.Value{}))
+				if diff != "" {
+					totalDiff += diff + "\n"
+				}
+				return true
+			})
 		})
 	}
 }