add APIs for traceoption and tracestate. (#60)

* add APIs for traceoption and tracestate.

* remove tracestate and refactor traceoptions.

api/core/span_context.go

@@ -23,9 +23,19 @@ type TraceID struct {
 	Low  uint64
 }
 
+const (
+	traceOptionBitMaskSampled = byte(0x01)
+	traceOptionBitMaskUnused  = byte(0xFE)
+
+	// TraceOptionSampled is a byte with sampled bit set. It is a convenient value initialize
+	// SpanContext when a trace is sampled.
+	TraceOptionSampled = traceOptionBitMaskSampled
+)
+
 type SpanContext struct {
-	TraceID TraceID
-	SpanID  uint64
+	TraceID      TraceID
+	SpanID       uint64
+	TraceOptions byte
 }
 
 var (
@@ -52,3 +62,7 @@ func (sc SpanContext) TraceIDString() string {
 	p2 := fmt.Sprintf("%.16x", sc.TraceID.Low)
 	return p1[0:3] + ".." + p2[13:16]
 }
+
+func (sc SpanContext) IsSampled() bool {
+	return sc.TraceOptions&traceOptionBitMaskSampled == traceOptionBitMaskSampled
+}

api/core/span_context_test.go

@@ -135,3 +135,45 @@ func TestTraceIDString(t *testing.T) {
 		})
 	}
 }
+
+func TestSpanContextIsSampled(t *testing.T) {
+	for _, testcase := range []struct {
+		name string
+		sc   SpanContext
+		want bool
+	}{
+		{
+			name: "sampled",
+			sc: SpanContext{
+				TraceID: TraceID{
+					High: uint64(42),
+					Low:  uint64(42),
+				},
+				TraceOptions: TraceOptionSampled,
+			},
+			want: true,
+		}, {
+			name: "sampled plus unused",
+			sc: SpanContext{
+				TraceID: TraceID{
+					High: uint64(42),
+					Low:  uint64(42),
+				},
+				TraceOptions: TraceOptionSampled | traceOptionBitMaskUnused,
+			},
+			want: true,
+		}, {
+			name: "not sampled/default",
+			sc:   SpanContext{TraceID: TraceID{}},
+			want: false,
+		},
+	} {
+		t.Run(testcase.name, func(t *testing.T) {
+			//proto: func (sc SpanContext) TraceIDString() string {}
+			have := testcase.sc.IsSampled()
+			if have != testcase.want {
+				t.Errorf("Want: %v, but have: %v", testcase.want, have)
+			}
+		})
+	}
+}

go.mod

@@ -7,7 +7,7 @@ require (
 	github.com/golang/mock v1.2.0 // indirect
 	github.com/golang/protobuf v1.3.1 // indirect
 	github.com/golangci/golangci-lint v1.17.1
-	github.com/google/go-cmp v0.3.0 // indirect
+	github.com/google/go-cmp v0.3.0
 	github.com/lightstep/tracecontext.go v0.0.0-20181129014701-1757c391b1ac
 	github.com/onsi/ginkgo v1.8.0 // indirect
 	github.com/onsi/gomega v1.5.0 // indirect
@@ -20,6 +20,7 @@ require (
 	golang.org/x/sys v0.0.0-20190614160838-b47fdc937951 // indirect
 	golang.org/x/text v0.3.2 // indirect
 	golang.org/x/tools v0.0.0-20190521203540-521d6ed310dd
+	google.golang.org/appengine v1.4.0 // indirect
 	google.golang.org/genproto v0.0.0-20190502173448-54afdca5d873 // indirect
 	google.golang.org/grpc v1.21.1
 )