Make component interfaces uniform

This change fixes inconsistencies in component interfaces. Motivation:

- Uniformness results in reduction of code that currently has to
  deal with differences.
- Processor.Start is missing and is important for allowing processors
  to communicate with the Host.

What's changed:

- Introduced Component interface.
- Unified Host interface.
- Added a Start function to processors (via Component interface).
- Start/Shutdown is now called for Processors from service start/shutdown.
- Receivers, Exporters, Processors, Extensions now embed Component interface.
- Replaced StartTraceReception/StartMetricsReception by single Start function for receivers.
- Replaced StopTraceReception/StopMetricsReception by single Shutdown function for receivers.

Note: before merging this we need to announce the change in Gitter since it
breaks existing implementations in contrib (although the fix is easy).

Resolves #477
Resolves #262

component/component.go

@@ -0,0 +1,41 @@
+// Copyright 2019 OpenTelemetry 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 component
+
+import "context"
+
+// Component is either a receiver, exporter, processor or extension.
+type Component interface {
+	// Start tells the component to start. Host parameter can be used for communicating
+	// with the host after Start() has already returned. If error is returned by
+	// Start() then the collector startup will be aborted.
+	// If this is an exporter component it may prepare for exporting
+	// by connecting to the endpoint.
+	Start(host Host) error
+
+	// Shutdown is invoked during service shutdown.
+	Shutdown() error
+}
+
+type Host interface {
+	// ReportFatalError is used to report to the host that the extension
+	// encountered a fatal error (i.e.: an error that the instance can't recover
+	// from) after its start function had already returned.
+	ReportFatalError(err error)
+
+	// Context returns a context provided by the host to be used on the component
+	// operations.
+	Context() context.Context
+}

component/component_test.go

@@ -0,0 +1,15 @@
+// Copyright 2019 OpenTelemetry 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 component

receiver/receivertest/mock_host.go → component/mock_host.go

@@ -14,19 +14,17 @@
 
 // Package receivertest define types and functions used to help test packages
 // implementing the receiver package interfaces.
-package receivertest
+package component
 
 import (
 	"context"
-
-	"github.com/open-telemetry/opentelemetry-collector/receiver"
 )
 
 // MockHost mocks a receiver.ReceiverHost for test purposes.
 type MockHost struct {
 }
 
-var _ receiver.Host = (*MockHost)(nil)
+var _ Host = (*MockHost)(nil)
 
 // Context returns a context provided by the host to be used on the receiver
 // operations.
@@ -43,6 +41,6 @@ func (mh *MockHost) ReportFatalError(err error) {
 
 // NewMockHost returns a new instance of MockHost with proper defaults for most
 // tests.
-func NewMockHost() receiver.Host {
+func NewMockHost() Host {
 	return &MockHost{}
 }

receiver/receivertest/mock_host_test.go → component/mock_host_test.go

@@ -14,7 +14,7 @@
 
 // Package receivertest define types and functions used to help test packages
 // implementing the receiver package interfaces.
-package receivertest
+package component
 
 import (
 	"errors"

config/example_factories.go

@@ -20,6 +20,7 @@ import (
 
 	"go.uber.org/zap"
 
+	"github.com/open-telemetry/opentelemetry-collector/component"
 	"github.com/open-telemetry/opentelemetry-collector/config/configerror"
 	"github.com/open-telemetry/opentelemetry-collector/config/configmodels"
 	"github.com/open-telemetry/opentelemetry-collector/consumer"
@@ -82,7 +83,20 @@ func (f *ExampleReceiverFactory) CreateTraceReceiver(
 	if cfg.(*ExampleReceiver).FailTraceCreation {
 		return nil, configerror.ErrDataTypeIsNotSupported
 	}
-	return &ExampleReceiverProducer{TraceConsumer: nextConsumer}, nil
+
+	// There must be one receiver for both metrics and traces. We maintain a map of
+	// receivers per config.
+
+	// Check to see if there is already a receiver for this config.
+	receiver, ok := exampleReceivers[cfg]
+	if !ok {
+		receiver = &ExampleReceiverProducer{}
+		// Remember the receiver in the map
+		exampleReceivers[cfg] = receiver
+	}
+	receiver.TraceConsumer = nextConsumer
+
+	return receiver, nil
 }
 
 // CreateMetricsReceiver creates a metrics receiver based on this config.
@@ -94,33 +108,44 @@ func (f *ExampleReceiverFactory) CreateMetricsReceiver(
 	if cfg.(*ExampleReceiver).FailMetricsCreation {
 		return nil, configerror.ErrDataTypeIsNotSupported
 	}
-	return &ExampleReceiverProducer{MetricsConsumer: nextConsumer}, nil
+
+	// There must be one receiver for both metrics and traces. We maintain a map of
+	// receivers per config.
+
+	// Check to see if there is already a receiver for this config.
+	receiver, ok := exampleReceivers[cfg]
+	if !ok {
+		receiver = &ExampleReceiverProducer{}
+		// Remember the receiver in the map
+		exampleReceivers[cfg] = receiver
+	}
+	receiver.MetricsConsumer = nextConsumer
+
+	return receiver, nil
 }
 
 // ExampleReceiverProducer allows producing traces and metrics for testing purposes.
 type ExampleReceiverProducer struct {
 	TraceConsumer   consumer.TraceConsumer
-	TraceStarted    bool
-	TraceStopped    bool
+	Started         bool
+	Stopped         bool
 	MetricsConsumer consumer.MetricsConsumer
-	MetricsStarted  bool
-	MetricsStopped  bool
 }
 
 // TraceSource returns the name of the trace data source.
 func (erp *ExampleReceiverProducer) TraceSource() string {
 	return ""
 }
 
-// StartTraceReception tells the receiver to start its processing.
-func (erp *ExampleReceiverProducer) StartTraceReception(host receiver.Host) error {
-	erp.TraceStarted = true
+// Start tells the receiver to start its processing.
+func (erp *ExampleReceiverProducer) Start(host component.Host) error {
+	erp.Started = true
 	return nil
 }
 
-// StopTraceReception tells the receiver that should stop reception,
-func (erp *ExampleReceiverProducer) StopTraceReception() error {
-	erp.TraceStopped = true
+// Shutdown tells the receiver that should stop reception,
+func (erp *ExampleReceiverProducer) Shutdown() error {
+	erp.Stopped = true
 	return nil
 }
 
@@ -129,17 +154,11 @@ func (erp *ExampleReceiverProducer) MetricsSource() string {
 	return ""
 }
 
-// StartMetricsReception tells the receiver to start its processing.
-func (erp *ExampleReceiverProducer) StartMetricsReception(host receiver.Host) error {
-	erp.MetricsStarted = true
-	return nil
-}
-
-// StopMetricsReception tells the receiver that should stop reception,
-func (erp *ExampleReceiverProducer) StopMetricsReception() error {
-	erp.MetricsStopped = true
-	return nil
-}
+// This is the map of already created example receivers for particular configurations.
+// We maintain this map because the Factory is asked trace and metric receivers separately
+// when it gets CreateTraceReceiver() and CreateMetricsReceiver() but they must not
+// create separate objects, they must use one Receiver object per configuration.
+var exampleReceivers = map[configmodels.Receiver]*ExampleReceiverProducer{}
 
 // MultiProtoReceiver is for testing purposes. We are defining an example multi protocol
 // config and factory for "multireceiver" receiver type.
@@ -293,7 +312,7 @@ type ExampleExporterConsumer struct {
 // Start tells the exporter to start. The exporter may prepare for exporting
 // by connecting to the endpoint. Host parameter can be used for communicating
 // with the host after Start() has already returned.
-func (exp *ExampleExporterConsumer) Start(host exporter.Host) error {
+func (exp *ExampleExporterConsumer) Start(host component.Host) error {
 	exp.ExporterStarted = true
 	return nil
 }

exporter/exporter.go

@@ -16,28 +16,13 @@
 package exporter
 
 import (
+	"github.com/open-telemetry/opentelemetry-collector/component"
 	"github.com/open-telemetry/opentelemetry-collector/consumer"
 )
 
-// Host represents the entity where the exporter is being hosted. It is used to
-// allow communication between the exporter and its host.
-type Host interface {
-	// ReportFatalError is used to report to the host that the exporter encountered
-	// a fatal error (i.e.: an error that the instance can't recover from) after
-	// its start function has already returned.
-	ReportFatalError(err error)
-}
-
 // Exporter defines functions that trace and metric exporters must implement.
 type Exporter interface {
-	// Start tells the exporter to start. The exporter may prepare for exporting
-	// by connecting to the endpoint. Host parameter can be used for communicating
-	// with the host after Start() has already returned. If error is returned by
-	// Start() then the collector startup will be aborted.
-	Start(host Host) error
-
-	// Shutdown is invoked during service shutdown.
-	Shutdown() error
+	component.Component
 }
 
 // TraceExporter composes TraceConsumer with some additional exporter-specific functions.

exporter/exporterhelper/metricshelper.go

@@ -19,6 +19,7 @@ import (
 
 	"go.opencensus.io/trace"
 
+	"github.com/open-telemetry/opentelemetry-collector/component"
 	"github.com/open-telemetry/opentelemetry-collector/config/configmodels"
 	"github.com/open-telemetry/opentelemetry-collector/consumer/consumerdata"
 	"github.com/open-telemetry/opentelemetry-collector/exporter"
@@ -37,7 +38,7 @@ type metricsExporter struct {
 
 var _ (exporter.MetricsExporter) = (*metricsExporter)(nil)
 
-func (me *metricsExporter) Start(host exporter.Host) error {
+func (me *metricsExporter) Start(host component.Host) error {
 	return nil
 }
 

exporter/exporterhelper/tracehelper.go

@@ -19,6 +19,7 @@ import (
 
 	"go.opencensus.io/trace"
 
+	"github.com/open-telemetry/opentelemetry-collector/component"
 	"github.com/open-telemetry/opentelemetry-collector/config/configmodels"
 	"github.com/open-telemetry/opentelemetry-collector/consumer/consumerdata"
 	"github.com/open-telemetry/opentelemetry-collector/exporter"
@@ -37,7 +38,7 @@ type traceExporter struct {
 
 var _ (exporter.TraceExporter) = (*traceExporter)(nil)
 
-func (te *traceExporter) Start(host exporter.Host) error {
+func (te *traceExporter) Start(host component.Host) error {
 	return nil
 }
 

exporter/exportertest/nop_exporter.go

@@ -17,6 +17,7 @@ package exportertest
 import (
 	"context"
 
+	"github.com/open-telemetry/opentelemetry-collector/component"
 	"github.com/open-telemetry/opentelemetry-collector/consumer/consumerdata"
 	"github.com/open-telemetry/opentelemetry-collector/exporter"
 )
@@ -32,7 +33,7 @@ type nopExporter struct {
 var _ exporter.TraceExporter = (*nopExporter)(nil)
 var _ exporter.MetricsExporter = (*nopExporter)(nil)
 
-func (ne *nopExporter) Start(host exporter.Host) error {
+func (ne *nopExporter) Start(host component.Host) error {
 	return nil
 }
 

exporter/exportertest/sink_exporter.go

@@ -18,6 +18,7 @@ import (
 	"context"
 	"sync"
 
+	"github.com/open-telemetry/opentelemetry-collector/component"
 	"github.com/open-telemetry/opentelemetry-collector/consumer/consumerdata"
 	"github.com/open-telemetry/opentelemetry-collector/exporter"
 )
@@ -33,7 +34,7 @@ var _ exporter.TraceExporter = (*SinkTraceExporter)(nil)
 // Start tells the exporter to start. The exporter may prepare for exporting
 // by connecting to the endpoint. Host parameter can be used for communicating
 // with the host after Start() has already returned.
-func (ste *SinkTraceExporter) Start(host exporter.Host) error {
+func (ste *SinkTraceExporter) Start(host component.Host) error {
 	return nil
 }
 
@@ -76,7 +77,7 @@ var _ exporter.MetricsExporter = (*SinkMetricsExporter)(nil)
 // Start tells the exporter to start. The exporter may prepare for exporting
 // by connecting to the endpoint. Host parameter can be used for communicating
 // with the host after Start() has already returned.
-func (sme *SinkMetricsExporter) Start(host exporter.Host) error {
+func (sme *SinkMetricsExporter) Start(host component.Host) error {
 	return nil
 }
 

exporter/opencensusexporter/factory_test.go

@@ -23,12 +23,12 @@ import (
 	"github.com/stretchr/testify/require"
 	"go.uber.org/zap"
 
+	"github.com/open-telemetry/opentelemetry-collector/component"
 	"github.com/open-telemetry/opentelemetry-collector/compression"
 	"github.com/open-telemetry/opentelemetry-collector/config/configcheck"
 	"github.com/open-telemetry/opentelemetry-collector/config/configgrpc"
 	"github.com/open-telemetry/opentelemetry-collector/exporter/exportertest"
 	"github.com/open-telemetry/opentelemetry-collector/receiver/opencensusreceiver"
-	"github.com/open-telemetry/opentelemetry-collector/receiver/receivertest"
 	"github.com/open-telemetry/opentelemetry-collector/testutils"
 )
 
@@ -66,8 +66,8 @@ func TestCreateTraceExporter(t *testing.T) {
 		new(exportertest.SinkTraceExporter))
 	require.NotNil(t, rcv)
 	require.Nil(t, err)
-	require.Nil(t, rcv.StartTraceReception(receivertest.NewMockHost()))
-	defer rcv.StopTraceReception()
+	require.Nil(t, rcv.Start(component.NewMockHost()))
+	defer rcv.Shutdown()
 
 	tests := []struct {
 		name     string

exporter/prometheusexporter/prometheus.go

@@ -22,9 +22,9 @@ import (
 	// official census-ecosystem location, update this import path.
 	"github.com/orijtech/prometheus-go-metrics-exporter"
 
+	"github.com/open-telemetry/opentelemetry-collector/component"
 	"github.com/open-telemetry/opentelemetry-collector/consumer"
 	"github.com/open-telemetry/opentelemetry-collector/consumer/consumerdata"
-	"github.com/open-telemetry/opentelemetry-collector/exporter"
 	"github.com/open-telemetry/opentelemetry-collector/exporter/exporterhelper"
 )
 
@@ -38,7 +38,7 @@ type prometheusExporter struct {
 
 var _ consumer.MetricsConsumer = (*prometheusExporter)(nil)
 
-func (pe *prometheusExporter) Start(host exporter.Host) error {
+func (pe *prometheusExporter) Start(host component.Host) error {
 	return nil
 }
 

exporter/zipkinexporter/zipkin.go

@@ -29,9 +29,9 @@ import (
 	zipkinhttp "github.com/openzipkin/zipkin-go/reporter/http"
 	"go.opencensus.io/trace"
 
+	"github.com/open-telemetry/opentelemetry-collector/component"
 	"github.com/open-telemetry/opentelemetry-collector/consumer/consumerdata"
 	"github.com/open-telemetry/opentelemetry-collector/consumer/consumererror"
-	"github.com/open-telemetry/opentelemetry-collector/exporter"
 	"github.com/open-telemetry/opentelemetry-collector/observability"
 	tracetranslator "github.com/open-telemetry/opentelemetry-collector/translator/trace"
 	spandatatranslator "github.com/open-telemetry/opentelemetry-collector/translator/trace/spandata"
@@ -160,7 +160,7 @@ func extractStringAttribute(
 	return value, ok
 }
 
-func (ze *zipkinExporter) Start(host exporter.Host) error {
+func (ze *zipkinExporter) Start(host component.Host) error {
 	return nil
 }