add options to configure logger by interface

This commit provides users of this library with the ability to configure
any logger of their choosing to be passed into the various components of
this library. Doing so allows use cases such as using other open source
logging packages, e.g. logrus or zap, in conjunction with this library.

Closes #37

logger.go

@@ -0,0 +1,27 @@
+// Copyright 2019 The OpenZipkin 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 zipkin
+
+import "log"
+
+// Verify that the Logger interface is implemented by the stdlib logger.
+var _ Logger = (*log.Logger)(nil)
+
+// Logger provides an interface defining the needed behavior for
+// loggers passed into various components.
+type Logger interface {
+	Print(v ...interface{})
+	Printf(format string, v ...interface{})
+}

middleware/http/transport.go

@@ -56,7 +56,7 @@ type transport struct {
 	defaultTags       map[string]string
 	errHandler        ErrHandler
 	errResponseReader *ErrResponseReader
-	logger            *log.Logger
+	logger            zipkin.Logger
 	requestSampler    RequestSamplerFunc
 	remoteEndpoint    *model.Endpoint
 }
@@ -115,6 +115,13 @@ func TransportLogger(l *log.Logger) TransportOption {
 	}
 }
 
+// TransportZipkinLogger allows to plug a logger into the transport
+func TransportZipkinLogger(l zipkin.Logger) TransportOption {
+	return func(t *transport) {
+		t.logger = l
+	}
+}
+
 // TransportRequestSampler allows one to set the sampling decision based on
 // the details found in the http.Request. It has preference over the existing
 // sampling decision contained in the context. The function returns a *bool,

reporter/amqp/amqp.go

@@ -11,6 +11,7 @@ import (
 
 	"github.com/streadway/amqp"
 
+	"github.com/openzipkin/zipkin-go"
 	"github.com/openzipkin/zipkin-go/model"
 	"github.com/openzipkin/zipkin-go/reporter"
 )
@@ -29,7 +30,7 @@ type rmqReporter struct {
 	conn     *amqp.Connection
 	exchange string
 	queue    string
-	logger   *log.Logger
+	logger   zipkin.Logger
 }
 
 // ReporterOption sets a parameter for the rmqReporter
@@ -43,6 +44,14 @@ func Logger(logger *log.Logger) ReporterOption {
 	}
 }
 
+// GenericLogger sets the logger used to report errors in the collection
+// process.
+func GenericLogger(logger zipkin.Logger) ReporterOption {
+	return func(c *rmqReporter) {
+		c.logger = logger
+	}
+}
+
 // Exchange sets the Exchange used to send messages (
 // see https://github.com/openzipkin/zipkin/tree/master/zipkin-collector/rabbitmq
 // if want to change default routing key or exchange

reporter/http/http.go

@@ -26,6 +26,7 @@ import (
 	"sync"
 	"time"
 
+	"github.com/openzipkin/zipkin-go"
 	"github.com/openzipkin/zipkin-go/model"
 	"github.com/openzipkin/zipkin-go/reporter"
 )
@@ -47,7 +48,7 @@ type HTTPDoer interface {
 type httpReporter struct {
 	url           string
 	client        HTTPDoer
-	logger        *log.Logger
+	logger        zipkin.Logger
 	batchInterval time.Duration
 	batchSize     int
 	maxBacklog    int
@@ -233,6 +234,12 @@ func Logger(l *log.Logger) ReporterOption {
 	return func(r *httpReporter) { r.logger = l }
 }
 
+// GenericLogger sets the logger used to report errors in the collection
+// process.
+func GenericLogger(l zipkin.Logger) ReporterOption {
+	return func(r *httpReporter) { r.logger = l }
+}
+
 // Serializer sets the serialization function to use for sending span data to
 // Zipkin.
 func Serializer(serializer reporter.SpanSerializer) ReporterOption {

reporter/kafka/kafka.go

@@ -22,6 +22,7 @@ import (
 	"os"
 
 	"github.com/Shopify/sarama"
+	"github.com/openzipkin/zipkin-go"
 	"github.com/openzipkin/zipkin-go/model"
 	"github.com/openzipkin/zipkin-go/reporter"
 )
@@ -35,7 +36,7 @@ const defaultKafkaTopic = "zipkin"
 // broker.
 type kafkaReporter struct {
 	producer   sarama.AsyncProducer
-	logger     *log.Logger
+	logger     zipkin.Logger
 	topic      string
 	serializer reporter.SpanSerializer
 }
@@ -51,6 +52,14 @@ func Logger(logger *log.Logger) ReporterOption {
 	}
 }
 
+// GenericLogger sets the logger used to report errors in the collection
+// process.
+func GenericLogger(logger zipkin.Logger) ReporterOption {
+	return func(c *kafkaReporter) {
+		c.logger = logger
+	}
+}
+
 // Producer sets the producer used to produce to Kafka. For tweaking
 // the reporting settings (e.g. reporting timeout or authentication)
 // check the sarama.Config struct.