Implement tracing package for toolkit (#193)

* add SpanContextAnnotator
SpanContextAnnotator retrieve current trace.Span from context.Context
or, in case there is no open trace.Span assemble trace.SpanContext from HTTP
headers

* Implement wrapper to extend ochttp.Handler

* Add options to configure what should be added to span

* Implement propogation of request/response headers, and body to span

* Implement wrapper to extend ocgrpc.ServerHandler

* Add options to configure what should be added to span

* Implement propogation of inbound/outbound metadata, and payload to span

* add util functions

* add grpc error into span

* implement simple exporter constructor

* implement obfuscation logic

* move obfuscation factor to constant

* Get lattest span value after calling wrapped handler

* Use library function to assemble span context

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 +1,39 @@
+package tracing
+
+import (
+	"context"
+	"net/http"
+
+	"go.opencensus.io/plugin/ochttp/propagation/b3"
+	"go.opencensus.io/trace"
+	"go.opencensus.io/trace/propagation"
+	"google.golang.org/grpc/metadata"
+)
+
+const (
+	traceContextKey = "grpc-trace-bin"
+)
+
+var defaultFormat propagation.HTTPFormat = &b3.HTTPFormat{}
+
+//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
+	}
+
+	sc, ok := defaultFormat.SpanContextFromRequest(req)
+	if ok {
+		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)
+}