swarm: integrate OpenTracing; propagate ctx to internal APIs (#17169)

* swarm: propagate ctx, enable opentracing

* swarm/tracing: log error when tracing is misconfigured

vendor/github.com/uber/jaeger-client-go/interop.go

@@ -0,0 +1,55 @@
+// Copyright (c) 2017 Uber Technologies, Inc.
+//
+// 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 jaeger
+
+import (
+	"github.com/opentracing/opentracing-go"
+)
+
+// TODO this file should not be needed after TChannel PR.
+
+type formatKey int
+
+// SpanContextFormat is a constant used as OpenTracing Format.
+// Requires *SpanContext as carrier.
+// This format is intended for interop with TChannel or other Zipkin-like tracers.
+const SpanContextFormat formatKey = iota
+
+type jaegerTraceContextPropagator struct {
+	tracer *Tracer
+}
+
+func (p *jaegerTraceContextPropagator) Inject(
+	ctx SpanContext,
+	abstractCarrier interface{},
+) error {
+	carrier, ok := abstractCarrier.(*SpanContext)
+	if !ok {
+		return opentracing.ErrInvalidCarrier
+	}
+
+	carrier.CopyFrom(&ctx)
+	return nil
+}
+
+func (p *jaegerTraceContextPropagator) Extract(abstractCarrier interface{}) (SpanContext, error) {
+	carrier, ok := abstractCarrier.(*SpanContext)
+	if !ok {
+		return emptyContext, opentracing.ErrInvalidCarrier
+	}
+	ctx := new(SpanContext)
+	ctx.CopyFrom(carrier)
+	return *ctx, nil
+}