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/log/logger.go

@@ -0,0 +1,90 @@
+// 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 log
+
+import (
+	"bytes"
+	"fmt"
+	"log"
+	"sync"
+)
+
+// Logger provides an abstract interface for logging from Reporters.
+// Applications can provide their own implementation of this interface to adapt
+// reporters logging to whatever logging library they prefer (stdlib log,
+// logrus, go-logging, etc).
+type Logger interface {
+	// Error logs a message at error priority
+	Error(msg string)
+
+	// Infof logs a message at info priority
+	Infof(msg string, args ...interface{})
+}
+
+// StdLogger is implementation of the Logger interface that delegates to default `log` package
+var StdLogger = &stdLogger{}
+
+type stdLogger struct{}
+
+func (l *stdLogger) Error(msg string) {
+	log.Printf("ERROR: %s", msg)
+}
+
+// Infof logs a message at info priority
+func (l *stdLogger) Infof(msg string, args ...interface{}) {
+	log.Printf(msg, args...)
+}
+
+// NullLogger is implementation of the Logger interface that is no-op
+var NullLogger = &nullLogger{}
+
+type nullLogger struct{}
+
+func (l *nullLogger) Error(msg string)                      {}
+func (l *nullLogger) Infof(msg string, args ...interface{}) {}
+
+// BytesBufferLogger implements Logger backed by a bytes.Buffer.
+type BytesBufferLogger struct {
+	mux sync.Mutex
+	buf bytes.Buffer
+}
+
+// Error implements Logger.
+func (l *BytesBufferLogger) Error(msg string) {
+	l.mux.Lock()
+	l.buf.WriteString(fmt.Sprintf("ERROR: %s\n", msg))
+	l.mux.Unlock()
+}
+
+// Infof implements Logger.
+func (l *BytesBufferLogger) Infof(msg string, args ...interface{}) {
+	l.mux.Lock()
+	l.buf.WriteString("INFO: " + fmt.Sprintf(msg, args...) + "\n")
+	l.mux.Unlock()
+}
+
+// String returns string representation of the underlying buffer.
+func (l *BytesBufferLogger) String() string {
+	l.mux.Lock()
+	defer l.mux.Unlock()
+	return l.buf.String()
+}
+
+// Flush empties the underlying buffer.
+func (l *BytesBufferLogger) Flush() {
+	l.mux.Lock()
+	defer l.mux.Unlock()
+	l.buf.Reset()
+}