Add logic to translate metric descriptors and initial flow

exporter/collector/breaking-changes.md

@@ -3,6 +3,22 @@
 The new pdata based exporter has some breaking changes from the original OpenCensus stackdriver
 based `googlecloud` exporter:
 
+## Metric Names and Descriptors
+
+The previous collector exporter would default to sending metrics with the type:
+`custom.googleapis.com/OpenCensus/{metric_name}`.  This has been changed to
+`workload.googleapis.com/{metric_name}`.
+
+Additionally, the previous exporter had a hardcoded list of known metric domains
+where this "prefix" would not be used. The new exporter allows full configuration
+of this list via the `metric.known_domains` property.
+
+Additionally, the DisplayName for a metric used to be exactly the
+`{metric_name}`. Now, the metric name is chosen as the full-path after the
+domain name of the metric type.  E.g. if a metric called
+`workload.googleapis.com/nginx/latency` is created, the display name will
+be `nginx/latency` instead of `workload.googleapis.com/nginx/latency`.
+
 ## Labels
 
 Original label key mapping code is
@@ -18,3 +34,10 @@ In the old exporter, delta sums were converted into GAUGE points ([see test
 fixture](https://github.com/GoogleCloudPlatform/opentelemetry-operations-go/blob/9bc1f49ebe000b0b3b1aa5b7f201e7996effdcd8/exporter/collector/testdata/fixtures/delta_counter_metrics_expect.json#L15)).
 The new pdata exporter sends these as CUMULATIVE points with the same delta time window
 (reseting at each point) aka pseudo-cumulatives.
+
+## OTLP Summary
+
+The old exporter relied on upstream conversion of OTLP Summary into Gauge and
+Cumulative points.  The new exporter performas this conversion itself, which
+means summary metric descriptors will include label description for `percentile`
+labels.

exporter/collector/config.go

@@ -47,6 +47,8 @@ type Config struct {
 type MetricConfig struct {
 	Prefix                     string `mapstructure:"prefix"`
 	SkipCreateMetricDescriptor bool   `mapstructure:"skip_create_descriptor"`
+	// If a metric belongs to one of these domains it does not get a prefix.
+	KnownDomains []string `mapstructure:"known_domains"`
 }
 
 // ResourceMapping defines mapping of resources from source (OpenCensus) to target (Google Cloud).

exporter/collector/config_test.go

@@ -90,6 +90,9 @@ func TestLoadConfig(t *testing.T) {
 			MetricConfig: MetricConfig{
 				Prefix:                     "prefix",
 				SkipCreateMetricDescriptor: true,
+				KnownDomains: []string{
+					"googleapis.com", "kubernetes.io", "istio.io", "knative.dev",
+				},
 			},
 		})
 }

exporter/collector/factory.go

@@ -42,20 +42,24 @@ func NewFactory() component.ExporterFactory {
 
 	return exporterhelper.NewFactory(
 		typeStr,
-		createDefaultConfig,
+		func() config.Exporter { return createDefaultConfig() },
 		exporterhelper.WithTraces(createTracesExporter),
 		exporterhelper.WithMetrics(createMetricsExporter),
 	)
 }
 
 // createDefaultConfig creates the default configuration for exporter.
-func createDefaultConfig() config.Exporter {
+func createDefaultConfig() *Config {
 	return &Config{
 		ExporterSettings: config.NewExporterSettings(config.NewComponentID(typeStr)),
 		TimeoutSettings:  exporterhelper.TimeoutSettings{Timeout: defaultTimeout},
 		RetrySettings:    exporterhelper.DefaultRetrySettings(),
 		QueueSettings:    exporterhelper.DefaultQueueSettings(),
 		UserAgent:        "opentelemetry-collector-contrib {{version}}",
+		MetricConfig: MetricConfig{
+			KnownDomains: domains,
+			Prefix:       "workload.googleapis.com",
+		},
 	}
 }