receiver/prometheus/internal: add createNodeAndResourcePdata for Prometheus->OTLP Pdata

Starts the progressive effort to convert directly from
    Prometheus->OTLPPdata

directly instead of

    Prometheus->OpenCensusProto->OTLPPdata

by adding a converter for node+resource -> pdata.Resource.

Updates #3137

Author: odeke-em

receiver/prometheusreceiver/internal/prom_to_otlp.go

@@ -0,0 +1,40 @@
+// Copyright The 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 internal
+
+import (
+	"net"
+
+	"go.opentelemetry.io/collector/consumer/pdata"
+	"go.opentelemetry.io/collector/translator/conventions"
+)
+
+func createNodeAndResourcePdata(job, instance, scheme string) pdata.Resource {
+	host, port, err := net.SplitHostPort(instance)
+	if err != nil {
+		host = instance
+	}
+	resource := pdata.NewResource()
+	attrs := resource.Attributes()
+	attrs.UpsertString(conventions.AttributeServiceName, job)
+	attrs.UpsertString(conventions.AttributeHostName, host)
+	attrs.UpsertString(jobAttr, job)
+	attrs.UpsertString(instanceAttr, instance)
+	attrs.UpsertString(portAttr, port)
+	attrs.UpsertString(schemeAttr, scheme)
+
+
+	return resource
+}

receiver/prometheusreceiver/internal/prom_to_otlp_test.go

@@ -0,0 +1,75 @@
+// Copyright The 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 internal
+
+import (
+	"sort"
+	"testing"
+	"unsafe"
+
+	metricspb "github.com/census-instrumentation/opencensus-proto/gen-go/metrics/v1"
+	"github.com/google/go-cmp/cmp"
+	"google.golang.org/protobuf/testing/protocmp"
+
+	"go.opentelemetry.io/collector/consumer/pdata"
+	otlpresource "go.opentelemetry.io/collector/internal/data/protogen/resource/v1"
+	"go.opentelemetry.io/collector/translator/internaldata"
+)
+
+func TestCreateNodeAndResourceConversion(t *testing.T) {
+	job, instance, scheme := "converter", "ocmetrics", "http"
+	ocNode, ocResource := createNodeAndResource(job, instance, scheme)
+	mdFromOC := internaldata.OCToMetrics(internaldata.MetricsData{
+		Node:     ocNode,
+		Resource: ocResource,
+		// We need to pass in a dummy set of metrics
+		// just to populate and allow for full conversion.
+		Metrics: []*metricspb.Metric{
+			{
+				MetricDescriptor: &metricspb.MetricDescriptor{
+					Name:        "m1",
+					Description: "d1",
+					Unit:        "By",
+				},
+			},
+		},
+	})
+
+	fromOCResource := protoResource(mdFromOC.ResourceMetrics().At(0).Resource())
+	byDirectOTLPResource := protoResource(createNodeAndResourcePdata(job, instance, scheme))
+
+	if diff := cmp.Diff(byDirectOTLPResource, fromOCResource, protocmp.Transform()); diff != "" {
+		t.Fatalf("Resource mismatch: got: - want: +\n%s", diff)
+	}
+}
+
+// Unfortunately pdata doesn't expose a way for us to retrieve the underlying resource,
+// yet we need
+func protoResource(presource pdata.Resource) *otlpresource.Resource {
+	type extract struct {
+		orig *otlpresource.Resource
+	}
+
+	extracted := (*extract)(unsafe.Pointer(&presource))
+	if extracted == nil {
+		return nil
+	}
+	// Ensure that the attributes are sorted.
+	resource := extracted.orig
+	sort.Slice(resource.Attributes, func(i, j int) bool {
+		return resource.Attributes[i].Key < resource.Attributes[j].Key
+	})
+	return resource
+}