Add support for resource detector option. (#70)

* Add support for resource detector option.

* fix copyright and remove setting reconnection period.

* rename WithResource to WithResourceDetector

go.mod

@@ -3,6 +3,7 @@ module contrib.go.opencensus.io/exporter/ocagent
 require (
 	github.com/census-instrumentation/opencensus-proto v0.2.0 // this is to match the version used in census-instrumentation/opencensus-service
 	github.com/golang/protobuf v1.3.1
+	github.com/google/go-cmp v0.3.0
 	github.com/grpc-ecosystem/grpc-gateway v1.8.5 // indirect
 	go.opencensus.io v0.22.0
 	google.golang.org/api v0.5.0

ocagent.go

@@ -70,6 +70,7 @@ type Exporter struct {
 	nodeInfo           *commonpb.Node
 	grpcClientConn     *grpc.ClientConn
 	reconnectionPeriod time.Duration
+	resourceDetector   resource.Detector
 	resource           *resourcepb.Resource
 	compressor         string
 	headers            map[string]string
@@ -125,7 +126,17 @@ func NewUnstartedExporter(opts ...ExporterOption) (*Exporter, error) {
 	viewDataBundler.BundleCountThreshold = 500 // TODO: (@odeke-em) make this configurable.
 	e.viewDataBundler = viewDataBundler
 	e.nodeInfo = NodeWithStartTime(e.serviceName)
-	e.resource = resourceProtoFromEnv()
+	if e.resourceDetector != nil {
+		res, err := e.resourceDetector(context.Background())
+		if err != nil {
+			panic(fmt.Sprintf("Error detecting resource. err:%v\n", err))
+		}
+		if res != nil {
+			e.resource = resourceToResourcePb(res)
+		}
+	} else {
+		e.resource = resourceProtoFromEnv()
+	}
 
 	return e, nil
 }
@@ -512,7 +523,10 @@ func resourceProtoFromEnv() *resourcepb.Resource {
 	if rs == nil {
 		return nil
 	}
+	return resourceToResourcePb(rs)
+}
 
+func resourceToResourcePb(rs *resource.Resource) *resourcepb.Resource {
 	rprs := &resourcepb.Resource{
 		Type: rs.Type,
 	}

options.go

@@ -17,6 +17,7 @@ package ocagent
 import (
 	"time"
 
+	"go.opencensus.io/resource"
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/credentials"
 )
@@ -30,6 +31,22 @@ type ExporterOption interface {
 	withExporter(e *Exporter)
 }
 
+type resourceDetector resource.Detector
+
+var _ ExporterOption = (*resourceDetector)(nil)
+
+func (rd resourceDetector) withExporter(e *Exporter) {
+	e.resourceDetector = resource.Detector(rd)
+}
+
+// WithResourceDetector allows one to register a resource detector. Resource Detector is used
+// to detect resources associated with the application. Detected resource is exported
+// along with the metrics. If the detector fails then it panics.
+// If a resource detector is not provided then by default it detects from the environment.
+func WithResourceDetector(rd resource.Detector) ExporterOption {
+	return resourceDetector(rd)
+}
+
 type insecureGrpcConnection int
 
 var _ ExporterOption = (*insecureGrpcConnection)(nil)

resource_detector_test.go

@@ -0,0 +1,54 @@
+// 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 ocagent
+
+import (
+	"context"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"go.opencensus.io/resource"
+
+	resourcepb "github.com/census-instrumentation/opencensus-proto/gen-go/resource/v1"
+)
+
+func TestResourceDetector(t *testing.T) {
+	ocexp, err := NewExporter(
+		WithInsecure(),
+		WithAddress(":0"),
+		WithResourceDetector(customResourceDetector),
+	)
+	if err != nil {
+		t.Fatalf("Failed to create the ocagent exporter: %v", err)
+	}
+	defer ocexp.Stop()
+
+	got := ocexp.resource
+	want := &resourcepb.Resource{
+		Type:   "foo",
+		Labels: map[string]string{},
+	}
+	if !cmp.Equal(got, want) {
+		t.Fatalf("Resource detection failed. got %v, want %v\n", got, want)
+	}
+}
+
+func customResourceDetector(context.Context) (*resource.Resource, error) {
+	res := &resource.Resource{
+		Type:   "foo",
+		Labels: map[string]string{},
+	}
+	return res, nil
+}