Add request and response context to traces (#2162)

Automatically submitted.

Gopkg.lock

@@ -348,6 +348,7 @@
     ".",
     "ext",
     "log",
+    "mocktracer",
   ]
   pruneopts = ""
   revision = "1949ddbfd147afd4d964a9f00b24eb291e0e7c38"
@@ -812,9 +813,11 @@
     "github.com/grpc-ecosystem/grpc-opentracing/go/otgrpc",
     "github.com/matttproud/golang_protobuf_extensions/pbutil",
     "github.com/opentracing/opentracing-go",
+    "github.com/opentracing/opentracing-go/mocktracer",
     "github.com/openzipkin/zipkin-go-opentracing",
     "github.com/prometheus/client_model/go",
     "github.com/prometheus/common/expfmt",
+    "golang.org/x/sys/unix",
     "google.golang.org/grpc",
     "google.golang.org/grpc/credentials",
     "google.golang.org/grpc/grpclog",

plugin/trace/trace.go

@@ -10,8 +10,11 @@ import (
 
 	"github.com/coredns/coredns/plugin"
 	"github.com/coredns/coredns/plugin/metrics"
+	"github.com/coredns/coredns/plugin/pkg/dnstest"
+	"github.com/coredns/coredns/plugin/pkg/rcode"
 	// Plugin the trace package.
 	_ "github.com/coredns/coredns/plugin/pkg/trace"
+	"github.com/coredns/coredns/request"
 
 	ddtrace "github.com/DataDog/dd-trace-go/opentracing"
 	"github.com/miekg/dns"
@@ -19,6 +22,12 @@ import (
 	zipkin "github.com/openzipkin/zipkin-go-opentracing"
 )
 
+const (
+	tagName  = "coredns.io/name"
+	tagType  = "coredns.io/type"
+	tagRcode = "coredns.io/rcode"
+)
+
 type trace struct {
 	Next            plugin.Handler
 	Endpoint        string
@@ -94,10 +103,26 @@ func (t *trace) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg)
 			trace = true
 		}
 	}
-	if span := ot.SpanFromContext(ctx); span == nil && trace {
-		span := t.Tracer().StartSpan("servedns:" + metrics.WithServer(ctx))
-		defer span.Finish()
-		ctx = ot.ContextWithSpan(ctx, span)
+	span := ot.SpanFromContext(ctx)
+	if !trace || span != nil {
+		return plugin.NextOrFailure(t.Name(), t.Next, ctx, w, r)
 	}
-	return plugin.NextOrFailure(t.Name(), t.Next, ctx, w, r)
+
+	req := request.Request{W: w, Req: r}
+	span = t.Tracer().StartSpan(spanName(ctx, req))
+	defer span.Finish()
+
+	rw := dnstest.NewRecorder(w)
+	ctx = ot.ContextWithSpan(ctx, span)
+	status, err := plugin.NextOrFailure(t.Name(), t.Next, ctx, rw, r)
+
+	span.SetTag(tagName, req.Name())
+	span.SetTag(tagType, req.Type())
+	span.SetTag(tagRcode, rcode.ToString(rw.Rcode))
+
+	return status, err
+}
+
+func spanName(ctx context.Context, req request.Request) string {
+	return "servedns:" + metrics.WithServer(ctx) + " " + req.Name()
 }

plugin/trace/trace_test.go

@@ -1,20 +1,24 @@
 package trace
 
 import (
+	"context"
 	"testing"
 
+	"github.com/coredns/coredns/plugin"
+	"github.com/coredns/coredns/plugin/pkg/dnstest"
+	"github.com/coredns/coredns/plugin/pkg/rcode"
+	"github.com/coredns/coredns/plugin/test"
+	"github.com/coredns/coredns/request"
+
 	"github.com/mholt/caddy"
+	"github.com/miekg/dns"
+	"github.com/opentracing/opentracing-go/mocktracer"
 )
 
-// createTestTrace creates a trace plugin to be used in tests
-func createTestTrace(config string) (*caddy.Controller, *trace, error) {
-	c := caddy.NewTestController("dns", config)
-	m, err := traceParse(c)
-	return c, m, err
-}
+const server = "coolServer"
 
-func TestTrace(t *testing.T) {
-	_, m, err := createTestTrace(`trace`)
+func TestStartup(t *testing.T) {
+	m, err := traceParse(caddy.NewTestController("dns", `trace`))
 	if err != nil {
 		t.Errorf("Error parsing test input: %s", err)
 		return
@@ -31,3 +35,65 @@ func TestTrace(t *testing.T) {
 		t.Errorf("Error, no tracer created")
 	}
 }
+
+func TestTrace(t *testing.T) {
+	cases := []struct {
+		name     string
+		rcode    int
+		question *dns.Msg
+		server   string
+	}{
+		{
+			name:     "NXDOMAIN",
+			rcode:    dns.RcodeNameError,
+			question: new(dns.Msg).SetQuestion("example.org.", dns.TypeA),
+		},
+		{
+			name:     "NOERROR",
+			rcode:    dns.RcodeSuccess,
+			question: new(dns.Msg).SetQuestion("example.net.", dns.TypeCNAME),
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			w := dnstest.NewRecorder(&test.ResponseWriter{})
+			m := mocktracer.New()
+			tr := &trace{
+				Next: test.HandlerFunc(func(_ context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+					m := new(dns.Msg)
+					m.SetRcode(r, tc.rcode)
+					w.WriteMsg(m)
+					return tc.rcode, nil
+				}),
+				every:  1,
+				tracer: m,
+			}
+			ctx := context.WithValue(context.TODO(), plugin.ServerCtx{}, server)
+			if _, err := tr.ServeDNS(ctx, w, tc.question); err != nil {
+				t.Fatalf("Error during tr.ServeDNS(ctx, w, %v): %v", tc.question, err)
+			}
+
+			fs := m.FinishedSpans()
+			// Each trace consists of two spans; the root and the Next function.
+			if len(fs) != 2 {
+				t.Fatalf("Unexpected span count: len(fs): want 2, got %v", len(fs))
+			}
+
+			rootSpan := fs[1]
+			req := request.Request{W: w, Req: tc.question}
+			if rootSpan.OperationName != spanName(ctx, req) {
+				t.Errorf("Unexpected span name: rootSpan.Name: want %v, got %v", spanName(ctx, req), rootSpan.OperationName)
+			}
+			if rootSpan.Tag(tagName) != req.Name() {
+				t.Errorf("Unexpected span tag: rootSpan.Tag(%v): want %v, got %v", tagName, req.Name(), rootSpan.Tag(tagName))
+			}
+			if rootSpan.Tag(tagType) != req.Type() {
+				t.Errorf("Unexpected span tag: rootSpan.Tag(%v): want %v, got %v", tagType, req.Type(), rootSpan.Tag(tagType))
+			}
+			if rootSpan.Tag(tagRcode) != rcode.ToString(tc.rcode) {
+				t.Errorf("Unexpected span tag: rootSpan.Tag(%v): want %v, got %v", tagRcode, rcode.ToString(tc.rcode), rootSpan.Tag(tagRcode))
+			}
+		})
+	}
+}

vendor/github.com/opentracing/opentracing-go/mocktracer/mocklogrecord.go

@@ -0,0 +1,105 @@
+package mocktracer
+
+import (
+	"fmt"
+	"reflect"
+	"time"
+
+	"github.com/opentracing/opentracing-go/log"
+)
+
+// MockLogRecord represents data logged to a Span via Span.LogFields or
+// Span.LogKV.
+type MockLogRecord struct {
+	Timestamp time.Time
+	Fields    []MockKeyValue
+}
+
+// MockKeyValue represents a single key:value pair.
+type MockKeyValue struct {
+	Key string
+
+	// All MockLogRecord values are coerced to strings via fmt.Sprint(), though
+	// we retain their type separately.
+	ValueKind   reflect.Kind
+	ValueString string
+}
+
+// EmitString belongs to the log.Encoder interface
+func (m *MockKeyValue) EmitString(key, value string) {
+	m.Key = key
+	m.ValueKind = reflect.TypeOf(value).Kind()
+	m.ValueString = fmt.Sprint(value)
+}
+
+// EmitBool belongs to the log.Encoder interface
+func (m *MockKeyValue) EmitBool(key string, value bool) {
+	m.Key = key
+	m.ValueKind = reflect.TypeOf(value).Kind()
+	m.ValueString = fmt.Sprint(value)
+}
+
+// EmitInt belongs to the log.Encoder interface
+func (m *MockKeyValue) EmitInt(key string, value int) {
+	m.Key = key
+	m.ValueKind = reflect.TypeOf(value).Kind()
+	m.ValueString = fmt.Sprint(value)
+}
+
+// EmitInt32 belongs to the log.Encoder interface
+func (m *MockKeyValue) EmitInt32(key string, value int32) {
+	m.Key = key
+	m.ValueKind = reflect.TypeOf(value).Kind()
+	m.ValueString = fmt.Sprint(value)
+}
+
+// EmitInt64 belongs to the log.Encoder interface
+func (m *MockKeyValue) EmitInt64(key string, value int64) {
+	m.Key = key
+	m.ValueKind = reflect.TypeOf(value).Kind()
+	m.ValueString = fmt.Sprint(value)
+}
+
+// EmitUint32 belongs to the log.Encoder interface
+func (m *MockKeyValue) EmitUint32(key string, value uint32) {
+	m.Key = key
+	m.ValueKind = reflect.TypeOf(value).Kind()
+	m.ValueString = fmt.Sprint(value)
+}
+
+// EmitUint64 belongs to the log.Encoder interface
+func (m *MockKeyValue) EmitUint64(key string, value uint64) {
+	m.Key = key
+	m.ValueKind = reflect.TypeOf(value).Kind()
+	m.ValueString = fmt.Sprint(value)
+}
+
+// EmitFloat32 belongs to the log.Encoder interface
+func (m *MockKeyValue) EmitFloat32(key string, value float32) {
+	m.Key = key
+	m.ValueKind = reflect.TypeOf(value).Kind()
+	m.ValueString = fmt.Sprint(value)
+}
+
+// EmitFloat64 belongs to the log.Encoder interface
+func (m *MockKeyValue) EmitFloat64(key string, value float64) {
+	m.Key = key
+	m.ValueKind = reflect.TypeOf(value).Kind()
+	m.ValueString = fmt.Sprint(value)
+}
+
+// EmitObject belongs to the log.Encoder interface
+func (m *MockKeyValue) EmitObject(key string, value interface{}) {
+	m.Key = key
+	m.ValueKind = reflect.TypeOf(value).Kind()
+	m.ValueString = fmt.Sprint(value)
+}
+
+// EmitLazyLogger belongs to the log.Encoder interface
+func (m *MockKeyValue) EmitLazyLogger(value log.LazyLogger) {
+	var meta MockKeyValue
+	value(&meta)
+	m.Key = meta.Key
+	m.ValueKind = meta.ValueKind
+	m.ValueString = meta.ValueString
+}

vendor/github.com/opentracing/opentracing-go/mocktracer/mockspan.go

@@ -0,0 +1,282 @@
+package mocktracer
+
+import (
+	"fmt"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"github.com/opentracing/opentracing-go"
+	"github.com/opentracing/opentracing-go/ext"
+	"github.com/opentracing/opentracing-go/log"
+)
+
+// MockSpanContext is an opentracing.SpanContext implementation.
+//
+// It is entirely unsuitable for production use, but appropriate for tests
+// that want to verify tracing behavior in other frameworks/applications.
+//
+// By default all spans have Sampled=true flag, unless {"sampling.priority": 0}
+// tag is set.
+type MockSpanContext struct {
+	TraceID int
+	SpanID  int
+	Sampled bool
+	Baggage map[string]string
+}
+
+var mockIDSource = uint32(42)
+
+func nextMockID() int {
+	return int(atomic.AddUint32(&mockIDSource, 1))
+}
+
+// ForeachBaggageItem belongs to the SpanContext interface
+func (c MockSpanContext) ForeachBaggageItem(handler func(k, v string) bool) {
+	for k, v := range c.Baggage {
+		if !handler(k, v) {
+			break
+		}
+	}
+}
+
+// WithBaggageItem creates a new context with an extra baggage item.
+func (c MockSpanContext) WithBaggageItem(key, value string) MockSpanContext {
+	var newBaggage map[string]string
+	if c.Baggage == nil {
+		newBaggage = map[string]string{key: value}
+	} else {
+		newBaggage = make(map[string]string, len(c.Baggage)+1)
+		for k, v := range c.Baggage {
+			newBaggage[k] = v
+		}
+		newBaggage[key] = value
+	}
+	// Use positional parameters so the compiler will help catch new fields.
+	return MockSpanContext{c.TraceID, c.SpanID, c.Sampled, newBaggage}
+}
+
+// MockSpan is an opentracing.Span implementation that exports its internal
+// state for testing purposes.
+type MockSpan struct {
+	sync.RWMutex
+
+	ParentID int
+
+	OperationName string
+	StartTime     time.Time
+	FinishTime    time.Time
+
+	// All of the below are protected by the embedded RWMutex.
+	SpanContext MockSpanContext
+	tags        map[string]interface{}
+	logs        []MockLogRecord
+	tracer      *MockTracer
+}
+
+func newMockSpan(t *MockTracer, name string, opts opentracing.StartSpanOptions) *MockSpan {
+	tags := opts.Tags
+	if tags == nil {
+		tags = map[string]interface{}{}
+	}
+	traceID := nextMockID()
+	parentID := int(0)
+	var baggage map[string]string
+	sampled := true
+	if len(opts.References) > 0 {
+		traceID = opts.References[0].ReferencedContext.(MockSpanContext).TraceID
+		parentID = opts.References[0].ReferencedContext.(MockSpanContext).SpanID
+		sampled = opts.References[0].ReferencedContext.(MockSpanContext).Sampled
+		baggage = opts.References[0].ReferencedContext.(MockSpanContext).Baggage
+	}
+	spanContext := MockSpanContext{traceID, nextMockID(), sampled, baggage}
+	startTime := opts.StartTime
+	if startTime.IsZero() {
+		startTime = time.Now()
+	}
+	return &MockSpan{
+		ParentID:      parentID,
+		OperationName: name,
+		StartTime:     startTime,
+		tags:          tags,
+		logs:          []MockLogRecord{},
+		SpanContext:   spanContext,
+
+		tracer: t,
+	}
+}
+
+// Tags returns a copy of tags accumulated by the span so far
+func (s *MockSpan) Tags() map[string]interface{} {
+	s.RLock()
+	defer s.RUnlock()
+	tags := make(map[string]interface{})
+	for k, v := range s.tags {
+		tags[k] = v
+	}
+	return tags
+}
+
+// Tag returns a single tag
+func (s *MockSpan) Tag(k string) interface{} {
+	s.RLock()
+	defer s.RUnlock()
+	return s.tags[k]
+}
+
+// Logs returns a copy of logs accumulated in the span so far
+func (s *MockSpan) Logs() []MockLogRecord {
+	s.RLock()
+	defer s.RUnlock()
+	logs := make([]MockLogRecord, len(s.logs))
+	copy(logs, s.logs)
+	return logs
+}
+
+// Context belongs to the Span interface
+func (s *MockSpan) Context() opentracing.SpanContext {
+	return s.SpanContext
+}
+
+// SetTag belongs to the Span interface
+func (s *MockSpan) SetTag(key string, value interface{}) opentracing.Span {
+	s.Lock()
+	defer s.Unlock()
+	if key == string(ext.SamplingPriority) {
+		if v, ok := value.(uint16); ok {
+			s.SpanContext.Sampled = v > 0
+			return s
+		}
+		if v, ok := value.(int); ok {
+			s.SpanContext.Sampled = v > 0
+			return s
+		}
+	}
+	s.tags[key] = value
+	return s
+}
+
+// SetBaggageItem belongs to the Span interface
+func (s *MockSpan) SetBaggageItem(key, val string) opentracing.Span {
+	s.Lock()
+	defer s.Unlock()
+	s.SpanContext = s.SpanContext.WithBaggageItem(key, val)
+	return s
+}
+
+// BaggageItem belongs to the Span interface
+func (s *MockSpan) BaggageItem(key string) string {
+	s.RLock()
+	defer s.RUnlock()
+	return s.SpanContext.Baggage[key]
+}
+
+// Finish belongs to the Span interface
+func (s *MockSpan) Finish() {
+	s.Lock()
+	s.FinishTime = time.Now()
+	s.Unlock()
+	s.tracer.recordSpan(s)
+}
+
+// FinishWithOptions belongs to the Span interface
+func (s *MockSpan) FinishWithOptions(opts opentracing.FinishOptions) {
+	s.Lock()
+	s.FinishTime = opts.FinishTime
+	s.Unlock()
+
+	// Handle any late-bound LogRecords.
+	for _, lr := range opts.LogRecords {
+		s.logFieldsWithTimestamp(lr.Timestamp, lr.Fields...)
+	}
+	// Handle (deprecated) BulkLogData.
+	for _, ld := range opts.BulkLogData {
+		if ld.Payload != nil {
+			s.logFieldsWithTimestamp(
+				ld.Timestamp,
+				log.String("event", ld.Event),
+				log.Object("payload", ld.Payload))
+		} else {
+			s.logFieldsWithTimestamp(
+				ld.Timestamp,
+				log.String("event", ld.Event))
+		}
+	}
+
+	s.tracer.recordSpan(s)
+}
+
+// String allows printing span for debugging
+func (s *MockSpan) String() string {
+	return fmt.Sprintf(
+		"traceId=%d, spanId=%d, parentId=%d, sampled=%t, name=%s",
+		s.SpanContext.TraceID, s.SpanContext.SpanID, s.ParentID,
+		s.SpanContext.Sampled, s.OperationName)
+}
+
+// LogFields belongs to the Span interface
+func (s *MockSpan) LogFields(fields ...log.Field) {
+	s.logFieldsWithTimestamp(time.Now(), fields...)
+}
+
+// The caller MUST NOT hold s.Lock
+func (s *MockSpan) logFieldsWithTimestamp(ts time.Time, fields ...log.Field) {
+	lr := MockLogRecord{
+		Timestamp: ts,
+		Fields:    make([]MockKeyValue, len(fields)),
+	}
+	for i, f := range fields {
+		outField := &(lr.Fields[i])
+		f.Marshal(outField)
+	}
+
+	s.Lock()
+	defer s.Unlock()
+	s.logs = append(s.logs, lr)
+}
+
+// LogKV belongs to the Span interface.
+//
+// This implementations coerces all "values" to strings, though that is not
+// something all implementations need to do. Indeed, a motivated person can and
+// probably should have this do a typed switch on the values.
+func (s *MockSpan) LogKV(keyValues ...interface{}) {
+	if len(keyValues)%2 != 0 {
+		s.LogFields(log.Error(fmt.Errorf("Non-even keyValues len: %v", len(keyValues))))
+		return
+	}
+	fields, err := log.InterleavedKVToFields(keyValues...)
+	if err != nil {
+		s.LogFields(log.Error(err), log.String("function", "LogKV"))
+		return
+	}
+	s.LogFields(fields...)
+}
+
+// LogEvent belongs to the Span interface
+func (s *MockSpan) LogEvent(event string) {
+	s.LogFields(log.String("event", event))
+}
+
+// LogEventWithPayload belongs to the Span interface
+func (s *MockSpan) LogEventWithPayload(event string, payload interface{}) {
+	s.LogFields(log.String("event", event), log.Object("payload", payload))
+}
+
+// Log belongs to the Span interface
+func (s *MockSpan) Log(data opentracing.LogData) {
+	panic("MockSpan.Log() no longer supported")
+}
+
+// SetOperationName belongs to the Span interface
+func (s *MockSpan) SetOperationName(operationName string) opentracing.Span {
+	s.Lock()
+	defer s.Unlock()
+	s.OperationName = operationName
+	return s
+}
+
+// Tracer belongs to the Span interface
+func (s *MockSpan) Tracer() opentracing.Tracer {
+	return s.tracer
+}

vendor/github.com/opentracing/opentracing-go/mocktracer/mocktracer.go

@@ -0,0 +1,105 @@
+package mocktracer
+
+import (
+	"sync"
+
+	"github.com/opentracing/opentracing-go"
+)
+
+// New returns a MockTracer opentracing.Tracer implementation that's intended
+// to facilitate tests of OpenTracing instrumentation.
+func New() *MockTracer {
+	t := &MockTracer{
+		finishedSpans: []*MockSpan{},
+		injectors:     make(map[interface{}]Injector),
+		extractors:    make(map[interface{}]Extractor),
+	}
+
+	// register default injectors/extractors
+	textPropagator := new(TextMapPropagator)
+	t.RegisterInjector(opentracing.TextMap, textPropagator)
+	t.RegisterExtractor(opentracing.TextMap, textPropagator)
+
+	httpPropagator := &TextMapPropagator{HTTPHeaders: true}
+	t.RegisterInjector(opentracing.HTTPHeaders, httpPropagator)
+	t.RegisterExtractor(opentracing.HTTPHeaders, httpPropagator)
+
+	return t
+}
+
+// MockTracer is only intended for testing OpenTracing instrumentation.
+//
+// It is entirely unsuitable for production use, but appropriate for tests
+// that want to verify tracing behavior in other frameworks/applications.
+type MockTracer struct {
+	sync.RWMutex
+	finishedSpans []*MockSpan
+	injectors     map[interface{}]Injector
+	extractors    map[interface{}]Extractor
+}
+
+// FinishedSpans returns all spans that have been Finish()'ed since the
+// MockTracer was constructed or since the last call to its Reset() method.
+func (t *MockTracer) FinishedSpans() []*MockSpan {
+	t.RLock()
+	defer t.RUnlock()
+	spans := make([]*MockSpan, len(t.finishedSpans))
+	copy(spans, t.finishedSpans)
+	return spans
+}
+
+// Reset clears the internally accumulated finished spans. Note that any
+// extant MockSpans will still append to finishedSpans when they Finish(),
+// even after a call to Reset().
+func (t *MockTracer) Reset() {
+	t.Lock()
+	defer t.Unlock()
+	t.finishedSpans = []*MockSpan{}
+}
+
+// StartSpan belongs to the Tracer interface.
+func (t *MockTracer) StartSpan(operationName string, opts ...opentracing.StartSpanOption) opentracing.Span {
+	sso := opentracing.StartSpanOptions{}
+	for _, o := range opts {
+		o.Apply(&sso)
+	}
+	return newMockSpan(t, operationName, sso)
+}
+
+// RegisterInjector registers injector for given format
+func (t *MockTracer) RegisterInjector(format interface{}, injector Injector) {
+	t.injectors[format] = injector
+}
+
+// RegisterExtractor registers extractor for given format
+func (t *MockTracer) RegisterExtractor(format interface{}, extractor Extractor) {
+	t.extractors[format] = extractor
+}
+
+// Inject belongs to the Tracer interface.
+func (t *MockTracer) Inject(sm opentracing.SpanContext, format interface{}, carrier interface{}) error {
+	spanContext, ok := sm.(MockSpanContext)
+	if !ok {
+		return opentracing.ErrInvalidCarrier
+	}
+	injector, ok := t.injectors[format]
+	if !ok {
+		return opentracing.ErrUnsupportedFormat
+	}
+	return injector.Inject(spanContext, carrier)
+}
+
+// Extract belongs to the Tracer interface.
+func (t *MockTracer) Extract(format interface{}, carrier interface{}) (opentracing.SpanContext, error) {
+	extractor, ok := t.extractors[format]
+	if !ok {
+		return nil, opentracing.ErrUnsupportedFormat
+	}
+	return extractor.Extract(carrier)
+}
+
+func (t *MockTracer) recordSpan(span *MockSpan) {
+	t.Lock()
+	defer t.Unlock()
+	t.finishedSpans = append(t.finishedSpans, span)
+}

vendor/github.com/opentracing/opentracing-go/mocktracer/propagation.go

@@ -0,0 +1,120 @@
+package mocktracer
+
+import (
+	"fmt"
+	"net/url"
+	"strconv"
+	"strings"
+
+	"github.com/opentracing/opentracing-go"
+)
+
+const mockTextMapIdsPrefix = "mockpfx-ids-"
+const mockTextMapBaggagePrefix = "mockpfx-baggage-"
+
+var emptyContext = MockSpanContext{}
+
+// Injector is responsible for injecting SpanContext instances in a manner suitable
+// for propagation via a format-specific "carrier" object. Typically the
+// injection will take place across an RPC boundary, but message queues and
+// other IPC mechanisms are also reasonable places to use an Injector.
+type Injector interface {
+	// Inject takes `SpanContext` and injects it into `carrier`. The actual type
+	// of `carrier` depends on the `format` passed to `Tracer.Inject()`.
+	//
+	// Implementations may return opentracing.ErrInvalidCarrier or any other
+	// implementation-specific error if injection fails.
+	Inject(ctx MockSpanContext, carrier interface{}) error
+}
+
+// Extractor is responsible for extracting SpanContext instances from a
+// format-specific "carrier" object. Typically the extraction will take place
+// on the server side of an RPC boundary, but message queues and other IPC
+// mechanisms are also reasonable places to use an Extractor.
+type Extractor interface {
+	// Extract decodes a SpanContext instance from the given `carrier`,
+	// or (nil, opentracing.ErrSpanContextNotFound) if no context could
+	// be found in the `carrier`.
+	Extract(carrier interface{}) (MockSpanContext, error)
+}
+
+// TextMapPropagator implements Injector/Extractor for TextMap and HTTPHeaders formats.
+type TextMapPropagator struct {
+	HTTPHeaders bool
+}
+
+// Inject implements the Injector interface
+func (t *TextMapPropagator) Inject(spanContext MockSpanContext, carrier interface{}) error {
+	writer, ok := carrier.(opentracing.TextMapWriter)
+	if !ok {
+		return opentracing.ErrInvalidCarrier
+	}
+	// Ids:
+	writer.Set(mockTextMapIdsPrefix+"traceid", strconv.Itoa(spanContext.TraceID))
+	writer.Set(mockTextMapIdsPrefix+"spanid", strconv.Itoa(spanContext.SpanID))
+	writer.Set(mockTextMapIdsPrefix+"sampled", fmt.Sprint(spanContext.Sampled))
+	// Baggage:
+	for baggageKey, baggageVal := range spanContext.Baggage {
+		safeVal := baggageVal
+		if t.HTTPHeaders {
+			safeVal = url.QueryEscape(baggageVal)
+		}
+		writer.Set(mockTextMapBaggagePrefix+baggageKey, safeVal)
+	}
+	return nil
+}
+
+// Extract implements the Extractor interface
+func (t *TextMapPropagator) Extract(carrier interface{}) (MockSpanContext, error) {
+	reader, ok := carrier.(opentracing.TextMapReader)
+	if !ok {
+		return emptyContext, opentracing.ErrInvalidCarrier
+	}
+	rval := MockSpanContext{0, 0, true, nil}
+	err := reader.ForeachKey(func(key, val string) error {
+		lowerKey := strings.ToLower(key)
+		switch {
+		case lowerKey == mockTextMapIdsPrefix+"traceid":
+			// Ids:
+			i, err := strconv.Atoi(val)
+			if err != nil {
+				return err
+			}
+			rval.TraceID = i
+		case lowerKey == mockTextMapIdsPrefix+"spanid":
+			// Ids:
+			i, err := strconv.Atoi(val)
+			if err != nil {
+				return err
+			}
+			rval.SpanID = i
+		case lowerKey == mockTextMapIdsPrefix+"sampled":
+			b, err := strconv.ParseBool(val)
+			if err != nil {
+				return err
+			}
+			rval.Sampled = b
+		case strings.HasPrefix(lowerKey, mockTextMapBaggagePrefix):
+			// Baggage:
+			if rval.Baggage == nil {
+				rval.Baggage = make(map[string]string)
+			}
+			safeVal := val
+			if t.HTTPHeaders {
+				// unescape errors are ignored, nothing can be done
+				if rawVal, err := url.QueryUnescape(val); err == nil {
+					safeVal = rawVal
+				}
+			}
+			rval.Baggage[lowerKey[len(mockTextMapBaggagePrefix):]] = safeVal
+		}
+		return nil
+	})
+	if rval.TraceID == 0 || rval.SpanID == 0 {
+		return emptyContext, opentracing.ErrSpanContextNotFound
+	}
+	if err != nil {
+		return emptyContext, err
+	}
+	return rval, nil
+}