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/zpages/zpages.go

@@ -0,0 +1,70 @@
+// 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 zpages implements a collection of HTML pages that display RPC stats
+// and trace data, and also functions to write that same data in plain text to
+// an io.Writer.
+//
+// Users can also embed the HTML for stats and traces in custom status pages.
+//
+// zpages are currrently work-in-process and cannot display minutely and
+// hourly stats correctly.
+//
+// Performance
+//
+// Installing the zpages has a performance overhead because additional traces
+// and stats will be collected in-process. In most cases, we expect this
+// overhead will not be significant but it depends on many factors, including
+// how many spans your process creates and how richly annotated they are.
+package zpages // import "go.opencensus.io/zpages"
+
+import (
+	"net/http"
+	"path"
+	"sync"
+
+	"go.opencensus.io/internal"
+)
+
+// TODO(ramonza): Remove Handler to make initialization lazy.
+
+// Handler is deprecated: Use Handle.
+var Handler http.Handler
+
+func init() {
+	mux := http.NewServeMux()
+	Handle(mux, "/")
+	Handler = mux
+}
+
+// Handle adds the z-pages to the given ServeMux rooted at pathPrefix.
+func Handle(mux *http.ServeMux, pathPrefix string) {
+	enable()
+	if mux == nil {
+		mux = http.DefaultServeMux
+	}
+	mux.HandleFunc(path.Join(pathPrefix, "rpcz"), rpczHandler)
+	mux.HandleFunc(path.Join(pathPrefix, "tracez"), tracezHandler)
+	mux.Handle(path.Join(pathPrefix, "public/"), http.FileServer(fs))
+}
+
+var enableOnce sync.Once
+
+func enable() {
+	enableOnce.Do(func() {
+		internal.LocalSpanStoreEnabled = true
+		registerRPCViews()
+	})
+}