Implement Configuration V2 models (#549)

This commit adds configuration models and is the first in the series of
planned commits that implement Configuration V2 support. For full support
of config V2 I plan to submit several additional PRs after this one is
reviewed and merged.

The next planned PR is the implementation of V2 configuration loading.

For reference, the Configuration Format V2 design doc:
https://docs.google.com/document/d/1GWOzV0H0RTN1adiwo7fTmkjfCATDDFGuOB4jp3ldCc8/edit#

Author: tigrannajaryan

internal/configmodels/configmodels.go

@@ -0,0 +1,114 @@
+// 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 configmodels defines the data models for entities. This file defines the
+// models for V2 configuration format. The defined entities are:
+// ConfigV2 (the top-level structure), Receivers, Exporters, Processors, Pipelines.
+package configmodels
+
+/*
+Receivers, Exporters and Processors typically have common configuration settings, however
+sometimes specific implementations (e.g. StackDriver) will have extra configuration settings.
+This requires the configuration data for these entities to be polymorphic.
+
+To satisfy these requirements we declare interfaces Receiver, Exporter, Processor,
+which define the behavior. We also provide helper structs ReceiverSettings, ExporterSettings,
+ProcessorSettings, which define the common settings and un-marshaling from config files.
+
+Specific Receivers/Exporters/Processors are expected to at the minimum implement the
+corresponding interface and if they have additional settings they must also extend
+the corresponding common settings struct (the easiest approach is to embed the common struct).
+*/
+
+// ConfigV2 defines the configuration V2 for the various elements of collector or agent.
+type ConfigV2 struct {
+	Receivers  Receivers
+	Exporters  Exporters
+	Processors Processors
+	Pipelines  Pipelines
+}
+
+// Receiver is the configuration of a receiver. Specific receivers must implement this
+// interface and will typically embed ReceiverSettings struct or a struct that extends it.
+type Receiver interface {
+}
+
+// Receivers is a map of names to Receivers.
+type Receivers map[string]Receiver
+
+// Exporter is the configuration of an exporter. Specific exporters must implement this
+// interface and will typically embed ExporterSettings struct or a struct that extends it.
+type Exporter interface {
+}
+
+// Exporters is a map of names to Exporters.
+type Exporters map[string]Exporter
+
+// Processor is the configuration of a processor. Specific processors must implement this
+// interface and will typically embed ProcessorSettings struct or a struct that extends it.
+type Processor interface {
+}
+
+// Processors is a map of names to Processors.
+type Processors map[string]Processor
+
+// DataType is the data type that is supported for collection. We currently support
+// collecting metrics and traces, this can expand in the future (e.g. logs, events, etc).
+type DataType int
+
+// Currently supported data types. Add new data types here when new types are supported in the future.
+const (
+	_ DataType = iota // skip 0, start types from 1.
+
+	// TracesDataType is the data type tag for traces.
+	TracesDataType
+
+	// MetricsDataType is the data type tag for metrics.
+	MetricsDataType
+)
+
+// Pipeline defines a single pipeline.
+type Pipeline struct {
+	Name       string   `mapstructure:"-"`
+	InputType  DataType `mapstructure:"-"`
+	Receivers  []string `mapstructure:"receivers"`
+	Processors []string `mapstructure:"processors"`
+	Exporters  []string `mapstructure:"exporters"`
+}
+
+// Pipelines is a map of names to Pipelines.
+type Pipelines map[string]*Pipeline
+
+// Below are common setting structs for Receivers, Exporters and Processors.
+// These are helper structs which you can embed when implementing your specific
+// receiver/exporter/processor config storage.
+
+// ReceiverSettings defines common settings for a single-protocol receiver configuration.
+// Specific receivers can embed this struct and extend it with more fields if needed.
+type ReceiverSettings struct {
+	Enabled  bool   `mapstructure:"enabled"`
+	Endpoint string `mapstructure:"endpoint"`
+}
+
+// ExporterSettings defines common settings for an exporter configuration.
+// Specific exporters can embed this struct and extend it with more fields if needed.
+type ExporterSettings struct {
+	Enabled bool `mapstructure:"enabled"`
+}
+
+// ProcessorSettings defines common settings for a processor configuration.
+// Specific processors can embed this struct and extend it with more fields if needed.
+type ProcessorSettings struct {
+	Enabled bool `mapstructure:"enabled"`
+}

internal/configmodels/empty_test.go

@@ -0,0 +1,17 @@
+// 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 configmodels
+
+// Package with interfaces and structs only.