Implement tracing package for toolkit

Gopkg.toml

@@ -38,6 +38,10 @@
   name = "google.golang.org/grpc"
   version = ">=1.0.0"
 
+[[constraint]]
+   name = "go.opencensus.io"
+   version = ">=0.22.3"
+
 [prune]
   go-tests = true
   unused-packages = true

tracing/annotator.go

@@ -0,0 +1,78 @@
+package tracing
+
+import (
+	"context"
+	"encoding/hex"
+	"net/http"
+
+	"go.opencensus.io/trace"
+	"go.opencensus.io/trace/propagation"
+	"google.golang.org/grpc/metadata"
+)
+
+const (
+	traceContextKey = "grpc-trace-bin"
+
+	//ParentSpanIDKey is a header name for ParrentSpanId B3 header
+	ParentSpanIDKey = "X-B3-ParentSpanId"
+
+	//SpanIDKey is a header name for SpanId B3 header
+	SpanIDKey = "X-B3-SpanId"
+
+	//TraceIDKey is a header name for TraceId B3 header
+	TraceIDKey = "X-B3-TraceId"
+
+	//TraceSampledKey is a header name for Sampled B3 header
+	TraceSampledKey = "X-B3-Sampled"
+
+	//TODO: handle ParentSpanIDKey and TraceSampledKey as well
+	//TODO: check headers names
+)
+
+//SpanContextAnnotator retrieve information about current span from context or HTTP headers
+//and propogate in binary format to gRPC service
+func SpanContextAnnotator(ctx context.Context, req *http.Request) metadata.MD {
+	md := make(metadata.MD)
+
+	span := trace.FromContext(ctx)
+	if span != nil {
+		traceContextBinary := propagation.Binary(span.SpanContext())
+		md[traceContextKey] = []string{string(traceContextBinary)}
+
+		return md
+	}
+
+	//Fallback to assembling trace.SpanContext from headers
+	var sc trace.SpanContext
+
+	spanID := req.Header.Get(SpanIDKey)
+	if spanID == "" {
+		return md
+	}
+
+	buf, err := hex.DecodeString(spanID)
+	if err != nil {
+		return md
+	}
+
+	copy(sc.SpanID[:], buf)
+
+	traceID := req.Header.Get(TraceIDKey)
+	if traceID == "" {
+		return md
+	}
+
+	buf, err = hex.DecodeString(traceID)
+	if err != nil {
+		return md
+	}
+
+	copy(sc.TraceID[:], buf)
+
+	//TODO: check how to use TraceSampledKey and logTraceParentSpanID
+
+	traceContextBinary := propagation.Binary(sc)
+	md[traceContextKey] = []string{string(traceContextBinary)}
+
+	return md
+}

tracing/exporter.go

@@ -0,0 +1,31 @@
+package tracing
+
+import (
+	"time"
+
+	"contrib.go.opencensus.io/exporter/ocagent"
+	"go.opencensus.io/trace"
+)
+
+//Exporter creates a new OC Agent exporter and configure for tracing
+func Exporter(address string, serviceName string, sampler trace.Sampler) error {
+	// TRACE: Setup OC agent for tracing
+	exporter, err := ocagent.NewExporter(
+		ocagent.WithInsecure(),
+		ocagent.WithReconnectionPeriod(5*time.Second),
+		ocagent.WithAddress(address),
+		ocagent.WithServiceName(serviceName))
+	if err != nil {
+		return err
+	}
+
+	trace.RegisterExporter(exporter)
+	trace.ApplyConfig(trace.Config{DefaultSampler: sampler})
+
+	return nil
+}
+
+//SamplerForFraction init sampler for specified fraction
+func SamplerForFraction(fraction float64) trace.Sampler {
+	return trace.ProbabilitySampler(fraction)
+}