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/internal/spanlog/json.go

@@ -0,0 +1,81 @@
+// 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 spanlog
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"github.com/opentracing/opentracing-go/log"
+)
+
+type fieldsAsMap map[string]string
+
+// MaterializeWithJSON converts log Fields into JSON string
+// TODO refactor into pluggable materializer
+func MaterializeWithJSON(logFields []log.Field) ([]byte, error) {
+	fields := fieldsAsMap(make(map[string]string, len(logFields)))
+	for _, field := range logFields {
+		field.Marshal(fields)
+	}
+	if event, ok := fields["event"]; ok && len(fields) == 1 {
+		return []byte(event), nil
+	}
+	return json.Marshal(fields)
+}
+
+func (ml fieldsAsMap) EmitString(key, value string) {
+	ml[key] = value
+}
+
+func (ml fieldsAsMap) EmitBool(key string, value bool) {
+	ml[key] = fmt.Sprintf("%t", value)
+}
+
+func (ml fieldsAsMap) EmitInt(key string, value int) {
+	ml[key] = fmt.Sprintf("%d", value)
+}
+
+func (ml fieldsAsMap) EmitInt32(key string, value int32) {
+	ml[key] = fmt.Sprintf("%d", value)
+}
+
+func (ml fieldsAsMap) EmitInt64(key string, value int64) {
+	ml[key] = fmt.Sprintf("%d", value)
+}
+
+func (ml fieldsAsMap) EmitUint32(key string, value uint32) {
+	ml[key] = fmt.Sprintf("%d", value)
+}
+
+func (ml fieldsAsMap) EmitUint64(key string, value uint64) {
+	ml[key] = fmt.Sprintf("%d", value)
+}
+
+func (ml fieldsAsMap) EmitFloat32(key string, value float32) {
+	ml[key] = fmt.Sprintf("%f", value)
+}
+
+func (ml fieldsAsMap) EmitFloat64(key string, value float64) {
+	ml[key] = fmt.Sprintf("%f", value)
+}
+
+func (ml fieldsAsMap) EmitObject(key string, value interface{}) {
+	ml[key] = fmt.Sprintf("%+v", value)
+}
+
+func (ml fieldsAsMap) EmitLazyLogger(value log.LazyLogger) {
+	value(ml)
+}