Add Unified factory interfaces (#428)

This changes adds three factory interfaces, one for each type of generic component that can be added.

`*DataExporterFactory ` creates a new `*DataExporter` which is a thin extension of `*DataProcessor`. By inheriting this interface, we can use an Exporter as a *DataProcessor, while still getting strong-typing guarantees when evaluating whether or not a pipeline is valid (it should end in an exporter).

`*DataProcessorFactory` creates a new `*DataProcessor` which can be used as an intermediate step in the processing workflow.

`*ReceiverFactory` creates a new `*Receiver` which listens for traffic and passes along data it receives to the next `*DataProcessor`

Author: Steven Karis

exporter/factory.go

@@ -0,0 +1,67 @@
+// Copyright 2019, OpenCensus 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 exporter
+
+import (
+	"github.com/spf13/viper"
+
+	"github.com/census-instrumentation/opencensus-service/processor"
+)
+
+// TraceDataExporter composes TraceDataProcessor with some additional
+// exporter-specific functions. This helps the service core to identify which
+// TraceDataProcessors are Exporters and which are internal processing
+// components, so that better validation of pipelines can be done.
+type TraceDataExporter interface {
+	processor.TraceDataProcessor
+
+	// ExportFormat gets the name of the format in which this exporter sends its data.
+	ExportFormat() string
+}
+
+// TraceDataExporterFactory is an interface that builds a new TraceDataExporter based on
+// some viper.Viper configuration.
+type TraceDataExporterFactory interface {
+	// Type gets the type of the TraceDataExporter created by this factory.
+	Type() string
+	// NewFromViper takes a viper.Viper config and creates a new TraceDataExporter.
+	NewFromViper(cfg *viper.Viper) (TraceDataExporter, error)
+	// DefaultConfig returns the default configuration for TraceDataExporter
+	// created by this factory.
+	DefaultConfig() *viper.Viper
+}
+
+// MetricsDataExporter composes MetricsDataProcessor with some additional
+// exporter-specific functions. This helps the service core to identify which
+// MetricsDataProcessors are Exporters and which are internal processing
+// components, so that better validation of pipelines can be done.
+type MetricsDataExporter interface {
+	processor.MetricsDataProcessor
+
+	// ExportFormat gets the name of the format in which this exporter sends its data.
+	ExportFormat() string
+}
+
+// MetricsDataExporterFactory is an interface that builds a new MetricsDataExporter based on
+// some viper.Viper configuration.
+type MetricsDataExporterFactory interface {
+	// Type gets the type of the MetricsDataExporter created by this factory.
+	Type() string
+	// NewFromViper takes a viper.Viper config and creates a new MetricsDataExporter.
+	NewFromViper(cfg *viper.Viper) (MetricsDataExporter, error)
+	// DefaultConfig returns the default configuration for MetricsDataExporter
+	// created by this factory.
+	DefaultConfig() *viper.Viper
+}

processor/factory.go

@@ -0,0 +1,43 @@
+// Copyright 2019, OpenCensus 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 processor
+
+import "github.com/spf13/viper"
+
+// TraceDataProcessorFactory is an interface that builds a new TraceDataProcessor based on
+// some viper.Viper configuration.
+type TraceDataProcessorFactory interface {
+	// Type gets the type of the TraceDataProcessor created by this factory.
+	Type() string
+	// NewFromViper takes a viper.Viper config and creates a new TraceDataProcessor which uses next as
+	// the next TraceDataProcessor in the pipeline.
+	NewFromViper(cfg *viper.Viper, next TraceDataProcessor) (TraceDataProcessor, error)
+	// DefaultConfig returns the default configuration for TraceDataProcessors
+	// created by this factory.
+	DefaultConfig() *viper.Viper
+}
+
+// MetricsDataProcessorFactory is an interface that builds a new MetricsDataProcessor based on
+// some viper.Viper configuration.
+type MetricsDataProcessorFactory interface {
+	// Type gets the type of the MetricsDataProcessor created by this factory.
+	Type() string
+	// NewFromViper takes a viper.Viper config and creates a new MetricsDataProcessor which uses next as
+	// the next MetricsDataProcessor in the pipeline.
+	NewFromViper(cfg *viper.Viper, next MetricsDataProcessor) (MetricsDataProcessor, error)
+	// DefaultConfig returns the default configuration for MetricsDataProcessors
+	// created by this factory.
+	DefaultConfig() *viper.Viper
+}

receiver/factory.go

@@ -0,0 +1,46 @@
+// Copyright 2019, OpenCensus 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 receiver
+
+import (
+	"github.com/census-instrumentation/opencensus-service/processor"
+	"github.com/spf13/viper"
+)
+
+// TraceReceiverFactory is an interface that builds a new TraceReceiver based on
+// some viper.Viper configuration.
+type TraceReceiverFactory interface {
+	// Type gets the type of the TraceReceiver created by this factory.
+	Type() string
+	// NewFromViper takes a viper.Viper config and creates a new TraceReceiver which uses next as the
+	// next TraceDataProcessor in the pipeline.
+	NewFromViper(cfg *viper.Viper, next processor.TraceDataProcessor) (TraceReceiver, error)
+	// DefaultConfig returns the default configuration for TraceReceivers
+	// created by this factory.
+	DefaultConfig() *viper.Viper
+}
+
+// MetricsReceiverFactory is an interface that builds a new MetricsReceiver based on
+// some viper.Viper configuration.
+type MetricsReceiverFactory interface {
+	// Type gets the type of the MetricsReceiver created by this factory.
+	Type() string
+	// NewFromViper takes a viper.Viper config and creates a new MetricsReceiver which uses next as the
+	// next MetricsDataProcessor in the pipeline.
+	NewFromViper(cfg *viper.Viper, next processor.MetricsDataProcessor) (MetricsReceiver, error)
+	// DefaultConfig returns the default configuration for MetricsReceivers
+	// created by this factory.
+	DefaultConfig() *viper.Viper
+}