Implement W3C Correlation Context propagator (#179)

* Implement W3C Correlation Context propagator

* PR comments

* PR comments

* Update test to inject context properly

* Fix merge

Author: Steven Karis

api/propagation/noop_propagator.go

@@ -18,6 +18,7 @@ import (
 	"context"
 
 	"go.opentelemetry.io/api/core"
+	dctx "go.opentelemetry.io/api/distributedcontext"
 )
 
 // NoopTextFormatPropagator implements TextFormatPropagator that does nothing.
@@ -30,8 +31,8 @@ func (np NoopTextFormatPropagator) Inject(ctx context.Context, supplier Supplier
 }
 
 // Extract does nothing and returns an empty SpanContext
-func (np NoopTextFormatPropagator) Extract(ctx context.Context, supplier Supplier) core.SpanContext {
-	return core.EmptySpanContext()
+func (np NoopTextFormatPropagator) Extract(ctx context.Context, supplier Supplier) (core.SpanContext, dctx.Map) {
+	return core.EmptySpanContext(), dctx.NewEmptyMap()
 }
 
 // GetAllKeys returns empty list of strings.

api/propagation/propagator.go

@@ -18,22 +18,25 @@ import (
 	"context"
 
 	"go.opentelemetry.io/api/core"
+	dctx "go.opentelemetry.io/api/distributedcontext"
 )
 
 // TextFormatPropagator is an interface that specifies methods to inject and extract SpanContext
-// into/from a carrier using Supplier interface.
+// and distributed context into/from a carrier using Supplier interface.
 // For example, HTTP Trace Context propagator would encode SpanContext into W3C Trace
 // Context Header and set the header into HttpRequest.
 type TextFormatPropagator interface {
 	// Inject method retrieves current SpanContext from the ctx, encodes it into propagator
 	// specific format and then injects the encoded SpanContext using supplier into a carrier
-	// associated with the supplier.
+	// associated with the supplier. It also takes a correlationCtx whose values will be
+	// injected into a carrier using the supplier.
 	Inject(ctx context.Context, supplier Supplier)
 
 	// Extract method retrieves encoded SpanContext using supplier from the associated carrier.
-	// It decodes the SpanContext and returns it. If no SpanContext was retrieved OR
-	// if the retrieved SpanContext is invalid then an empty SpanContext is returned.
-	Extract(ctx context.Context, supplier Supplier) core.SpanContext
+	// It decodes the SpanContext and returns it and a dctx of correlated context.
+	// If no SpanContext was retrieved OR if the retrieved SpanContext is invalid then
+	// an empty SpanContext is returned.
+	Extract(ctx context.Context, supplier Supplier) (core.SpanContext, dctx.Map)
 
 	// GetAllKeys returns all the keys that this propagator injects/extracts into/from a
 	// carrier. The use cases for this are

plugin/httptrace/httptrace.go

@@ -36,14 +36,20 @@ var (
 
 // Returns the Attributes, Context Entries, and SpanContext that were encoded by Inject.
 func Extract(ctx context.Context, req *http.Request) ([]core.KeyValue, []core.KeyValue, core.SpanContext) {
-	sc := propagator.Extract(ctx, req.Header)
+	sc, correlationCtx := propagator.Extract(ctx, req.Header)
 
 	attrs := []core.KeyValue{
 		URLKey.String(req.URL.String()),
 		// Etc.
 	}
 
-	return attrs, nil, sc
+	var correlationCtxKVs []core.KeyValue
+	correlationCtx.Foreach(func(kv core.KeyValue) bool {
+		correlationCtxKVs = append(correlationCtxKVs, kv)
+		return true
+	})
+
+	return attrs, correlationCtxKVs, sc
 }
 
 func Inject(ctx context.Context, req *http.Request) {

plugin/othttp/handler.go

@@ -143,7 +143,8 @@ func NewHandler(handler http.Handler, operation string, opts ...Option) http.Han
 func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	opts := append([]trace.SpanOption{}, h.spanOptions...) // start with the configured options
 
-	sc := h.prop.Extract(r.Context(), r.Header)
+	// TODO: do something with the correlation context
+	sc, _ := h.prop.Extract(r.Context(), r.Header)
 	if sc.IsValid() { // not a valid span context, so no link / parent relationship to establish
 		var opt trace.SpanOption
 		if h.public {

propagation/http_b3_propagator.go

@@ -24,6 +24,7 @@ import (
 	"go.opentelemetry.io/api/trace"
 
 	"go.opentelemetry.io/api/core"
+	dctx "go.opentelemetry.io/api/distributedcontext"
 	apipropagation "go.opentelemetry.io/api/propagation"
 )
 
@@ -84,11 +85,11 @@ func (b3 HTTPB3Propagator) Inject(ctx context.Context, supplier apipropagation.S
 }
 
 // Extract retrieves B3 Headers from the supplier
-func (b3 HTTPB3Propagator) Extract(ctx context.Context, supplier apipropagation.Supplier) core.SpanContext {
+func (b3 HTTPB3Propagator) Extract(ctx context.Context, supplier apipropagation.Supplier) (core.SpanContext, dctx.Map) {
 	if b3.SingleHeader {
-		return b3.extractSingleHeader(supplier)
+		return b3.extractSingleHeader(supplier), dctx.NewEmptyMap()
 	}
-	return b3.extract(supplier)
+	return b3.extract(supplier), dctx.NewEmptyMap()
 }
 
 func (b3 HTTPB3Propagator) GetAllKeys() []string {

propagation/http_b3_propagator_benchmark_test.go

@@ -65,7 +65,7 @@ func BenchmarkExtractB3(b *testing.B) {
 				b.ReportAllocs()
 				b.ResetTimer()
 				for i := 0; i < b.N; i++ {
-					_ = propagator.Extract(ctx, req.Header)
+					_, _ = propagator.Extract(ctx, req.Header)
 				}
 			})
 		}

propagation/http_b3_propagator_test.go

@@ -65,7 +65,7 @@ func TestExtractB3(t *testing.T) {
 				}
 
 				ctx := context.Background()
-				gotSc := propagator.Extract(ctx, req.Header)
+				gotSc, _ := propagator.Extract(ctx, req.Header)
 				if diff := cmp.Diff(gotSc, tt.wantSc); diff != "" {
 					t.Errorf("%s: %s: -got +want %s", tg.name, tt.name, diff)
 				}

propagation/http_trace_context_propagator.go

@@ -18,20 +18,23 @@ import (
 	"context"
 	"encoding/hex"
 	"fmt"
+	"net/url"
 	"regexp"
 	"strconv"
 	"strings"
 
-	"go.opentelemetry.io/api/trace"
-
 	"go.opentelemetry.io/api/core"
+	dctx "go.opentelemetry.io/api/distributedcontext"
+	"go.opentelemetry.io/api/key"
 	apipropagation "go.opentelemetry.io/api/propagation"
+	"go.opentelemetry.io/api/trace"
 )
 
 const (
-	supportedVersion  = 0
-	maxVersion        = 254
-	TraceparentHeader = "Traceparent"
+	supportedVersion         = 0
+	maxVersion               = 254
+	TraceparentHeader        = "Traceparent"
+	CorrelationContextHeader = "Correlation-Context"
 )
 
 // HTTPTraceContextPropagator propagates SpanContext in W3C TraceContext format.
@@ -51,9 +54,35 @@ func (hp HTTPTraceContextPropagator) Inject(ctx context.Context, supplier apipro
 			sc.TraceFlags&core.TraceFlagsSampled)
 		supplier.Set(TraceparentHeader, h)
 	}
+
+	correlationCtx := dctx.FromContext(ctx)
+	firstIter := true
+	var headerValueBuilder strings.Builder
+	correlationCtx.Foreach(func(kv core.KeyValue) bool {
+		if !firstIter {
+			headerValueBuilder.WriteRune(',')
+		}
+		firstIter = false
+		headerValueBuilder.WriteString(url.QueryEscape(strings.TrimSpace((string)(kv.Key))))
+		headerValueBuilder.WriteRune('=')
+		headerValueBuilder.WriteString(url.QueryEscape(strings.TrimSpace(kv.Value.Emit())))
+		return true
+	})
+	if headerValueBuilder.Len() > 0 {
+		headerString := headerValueBuilder.String()
+		supplier.Set(CorrelationContextHeader, headerString)
+	}
 }
 
-func (hp HTTPTraceContextPropagator) Extract(ctx context.Context, supplier apipropagation.Supplier) core.SpanContext {
+func (hp HTTPTraceContextPropagator) Extract(
+	ctx context.Context, supplier apipropagation.Supplier,
+) (core.SpanContext, dctx.Map) {
+	return hp.extractSpanContext(ctx, supplier), hp.extractCorrelationCtx(ctx, supplier)
+}
+
+func (hp HTTPTraceContextPropagator) extractSpanContext(
+	ctx context.Context, supplier apipropagation.Supplier,
+) core.SpanContext {
 	h := supplier.Get(TraceparentHeader)
 	if h == "" {
 		return core.EmptySpanContext()
@@ -128,6 +157,50 @@ func (hp HTTPTraceContextPropagator) Extract(ctx context.Context, supplier apipr
 	return sc
 }
 
+func (hp HTTPTraceContextPropagator) extractCorrelationCtx(ctx context.Context, supplier apipropagation.Supplier) dctx.Map {
+	correlationContext := supplier.Get(CorrelationContextHeader)
+	if correlationContext == "" {
+		return dctx.NewEmptyMap()
+	}
+
+	contextValues := strings.Split(correlationContext, ",")
+	keyValues := make([]core.KeyValue, 0, len(contextValues))
+	for _, contextValue := range contextValues {
+		valueAndProps := strings.Split(contextValue, ";")
+		if len(valueAndProps) < 1 {
+			continue
+		}
+		nameValue := strings.Split(valueAndProps[0], "=")
+		if len(nameValue) < 2 {
+			continue
+		}
+		name, err := url.QueryUnescape(nameValue[0])
+		if err != nil {
+			continue
+		}
+		trimmedName := strings.TrimSpace(name)
+		value, err := url.QueryUnescape(nameValue[1])
+		if err != nil {
+			continue
+		}
+		trimmedValue := strings.TrimSpace(value)
+
+		// TODO (skaris): properties defiend https://w3c.github.io/correlation-context/, are currently
+		// just put as part of the value.
+		var trimmedValueWithProps strings.Builder
+		trimmedValueWithProps.WriteString(trimmedValue)
+		for _, prop := range valueAndProps[1:] {
+			trimmedValueWithProps.WriteRune(';')
+			trimmedValueWithProps.WriteString(prop)
+		}
+
+		keyValues = append(keyValues, key.New(trimmedName).String(trimmedValueWithProps.String()))
+	}
+	return dctx.NewMap(dctx.MapUpdate{
+		MultiKV: keyValues,
+	})
+}
+
 func (hp HTTPTraceContextPropagator) GetAllKeys() []string {
-	return []string{TraceparentHeader}
+	return []string{TraceparentHeader, CorrelationContextHeader}
 }