Add support for tracing via OpenCencus

This adds a few flags for configuring the tracer.
Includes support for jaeger tracing (built into OC).

vendor/go.opencensus.io/plugin/ocgrpc/trace_common.go

@@ -0,0 +1,107 @@
+// Copyright 2017, OpenCensus Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package ocgrpc
+
+import (
+	"strings"
+
+	"google.golang.org/grpc/codes"
+
+	"go.opencensus.io/trace"
+	"go.opencensus.io/trace/propagation"
+	"golang.org/x/net/context"
+	"google.golang.org/grpc/metadata"
+	"google.golang.org/grpc/stats"
+	"google.golang.org/grpc/status"
+)
+
+const traceContextKey = "grpc-trace-bin"
+
+// TagRPC creates a new trace span for the client side of the RPC.
+//
+// It returns ctx with the new trace span added and a serialization of the
+// SpanContext added to the outgoing gRPC metadata.
+func (c *ClientHandler) traceTagRPC(ctx context.Context, rti *stats.RPCTagInfo) context.Context {
+	name := strings.TrimPrefix(rti.FullMethodName, "/")
+	name = strings.Replace(name, "/", ".", -1)
+	ctx, span := trace.StartSpan(ctx, name,
+		trace.WithSampler(c.StartOptions.Sampler),
+		trace.WithSpanKind(trace.SpanKindClient)) // span is ended by traceHandleRPC
+	traceContextBinary := propagation.Binary(span.SpanContext())
+	return metadata.AppendToOutgoingContext(ctx, traceContextKey, string(traceContextBinary))
+}
+
+// TagRPC creates a new trace span for the server side of the RPC.
+//
+// It checks the incoming gRPC metadata in ctx for a SpanContext, and if
+// it finds one, uses that SpanContext as the parent context of the new span.
+//
+// It returns ctx, with the new trace span added.
+func (s *ServerHandler) traceTagRPC(ctx context.Context, rti *stats.RPCTagInfo) context.Context {
+	md, _ := metadata.FromIncomingContext(ctx)
+	name := strings.TrimPrefix(rti.FullMethodName, "/")
+	name = strings.Replace(name, "/", ".", -1)
+	traceContext := md[traceContextKey]
+	var (
+		parent     trace.SpanContext
+		haveParent bool
+	)
+	if len(traceContext) > 0 {
+		// Metadata with keys ending in -bin are actually binary. They are base64
+		// encoded before being put on the wire, see:
+		// https://github.com/grpc/grpc-go/blob/08d6261/Documentation/grpc-metadata.md#storing-binary-data-in-metadata
+		traceContextBinary := []byte(traceContext[0])
+		parent, haveParent = propagation.FromBinary(traceContextBinary)
+		if haveParent && !s.IsPublicEndpoint {
+			ctx, _ := trace.StartSpanWithRemoteParent(ctx, name, parent,
+				trace.WithSpanKind(trace.SpanKindServer),
+				trace.WithSampler(s.StartOptions.Sampler),
+			)
+			return ctx
+		}
+	}
+	ctx, span := trace.StartSpan(ctx, name,
+		trace.WithSpanKind(trace.SpanKindServer),
+		trace.WithSampler(s.StartOptions.Sampler))
+	if haveParent {
+		span.AddLink(trace.Link{TraceID: parent.TraceID, SpanID: parent.SpanID, Type: trace.LinkTypeChild})
+	}
+	return ctx
+}
+
+func traceHandleRPC(ctx context.Context, rs stats.RPCStats) {
+	span := trace.FromContext(ctx)
+	// TODO: compressed and uncompressed sizes are not populated in every message.
+	switch rs := rs.(type) {
+	case *stats.Begin:
+		span.AddAttributes(
+			trace.BoolAttribute("Client", rs.Client),
+			trace.BoolAttribute("FailFast", rs.FailFast))
+	case *stats.InPayload:
+		span.AddMessageReceiveEvent(0 /* TODO: messageID */, int64(rs.Length), int64(rs.WireLength))
+	case *stats.OutPayload:
+		span.AddMessageSendEvent(0, int64(rs.Length), int64(rs.WireLength))
+	case *stats.End:
+		if rs.Error != nil {
+			s, ok := status.FromError(rs.Error)
+			if ok {
+				span.SetStatus(trace.Status{Code: int32(s.Code()), Message: s.Message()})
+			} else {
+				span.SetStatus(trace.Status{Code: int32(codes.Internal), Message: rs.Error.Error()})
+			}
+		}
+		span.End()
+	}
+}