Add GCP resource detector

detectors/gcp/README.md

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+# GCP Resource detector
+
+Note: This is still a work in progress. Use the detector in opentelemetry-go-contrib for now: https://github.com/open-telemetry/opentelemetry-go-contrib/tree/main/detectors/gcp.
+
+## Usage
+
+```golang
+    ctx := context.Background()
+    // detect your resources
+    resource, err := resource.New(ctx,
+        resource.WithDetectors(
+            // Use this GCP resource detector!
+            gcp.NewDetector(), 
+            // Add other, default resource detectors.
+            resource.WithFromEnv(), 
+            resource.WithTelemetrySDK(),
+        ),
+        // Add your own custom attributes to identify your application
+        resource.WithAttributes(
+            semconv.ServiceNameKey.String("my-application"),
+            semconv.ServiceNamespaceKey.String("my-company-frontend-team"),
+        ),
+    )
+    // use the resource in your tracerprovider (or meterprovider)
+	tp := trace.NewTracerProvider(
+        // ... other options
+		trace.WithResource(resource),
+	)
+```
+
+## Setting Kubernetes attributes
+
+Previous iterations of GCP resource detection attempted to detect
+container.name, k8s.pod.name and k8s.namespace.name.  When using this detector,
+you should use this in your Pod Spec to set these using
+OTEL_RESOURCE_ATTRIBUTES:
+
+```yaml
+env:
+- name: POD_NAME
+   valueFrom:
+     fieldRef:
+       fieldPath: metadata.name
+- name: NAMESPACE_NAME
+  valueFrom:
+    fieldRef:
+      fieldPath: metadata.namespace
+- name: CONTAINER_NAME
+   value: 
+- name: OTEL_RESOURCE_ATTRIBUTES
+  value: k8s.pod.name=$(POD_NAME),k8s.namespace.name=$(NAMESPACE_NAME),k8s.container.name=$(CONTAINER_NAME)
+```

detectors/gcp/app_engine.go

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+// Copyright 2022 Google LLC
+//
+// 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
+//
+//      https://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 gcp
+
+import (
+	"go.opentelemetry.io/otel/attribute"
+	semconv "go.opentelemetry.io/otel/semconv/v1.10.0"
+)
+
+func (d *detector) onAppEngine() bool {
+	_, found := d.os.LookupEnv("GAE_SERVICE")
+	return found
+}
+
+// appEngineAttributes detects attributes available in app-engine environments:
+// https://cloud.google.com/appengine/docs/flexible/python/migrating#modules
+// This includes: faas name, faas version, faas id, and cloud region
+func (d *detector) appEngineAttributes() ([]attribute.KeyValue, []string) {
+	attributes, errs := d.zoneAndRegionAttributes()
+	if serviceName, found := d.os.LookupEnv("GAE_SERVICE"); !found {
+		errs = append(errs, "envvar GAE_SERVICE not found.")
+	} else {
+		attributes = append(attributes, semconv.FaaSNameKey.String(serviceName))
+	}
+	if serviceVersion, found := d.os.LookupEnv("GAE_VERSION"); !found {
+		errs = append(errs, "envvar GAE_VERSION contains empty string.")
+	} else {
+		attributes = append(attributes, semconv.FaaSVersionKey.String(serviceVersion))
+	}
+	if serviceInstance, found := d.os.LookupEnv("GAE_INSTANCE"); !found {
+		errs = append(errs, "envvar GAE_INSTANCE contains empty string.")
+	} else {
+		attributes = append(attributes, semconv.FaaSIDKey.String(serviceInstance))
+	}
+	return attributes, errs
+}

detectors/gcp/detector.go

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+// Copyright 2022 Google LLC
+//
+// 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
+//
+//      https://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 gcp
+
+import (
+	"context"
+	"fmt"
+	"os"
+
+	"cloud.google.com/go/compute/metadata"
+
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/sdk/resource"
+	semconv "go.opentelemetry.io/otel/semconv/v1.10.0"
+)
+
+// NewDetector returns a resource.Detector which performs OpenTelemetry resource
+// detection for GKE, Cloud Run, Cloud Functions, App Engine, and Compute Engine.
+func NewDetector() resource.Detector {
+	return &detector{metadata: metadata.NewClient(nil), os: realOSProvider{}}
+}
+
+func (d *detector) Detect(ctx context.Context) (*resource.Resource, error) {
+	if !metadata.OnGCE() {
+		return nil, nil
+	}
+	attributes := []attribute.KeyValue{semconv.CloudProviderGCP}
+	var errors []string
+
+	// Detect project attributes on all platforms
+	attrs, errs := d.projectAttributes()
+	attributes = append(attributes, attrs...)
+	errors = append(errors, errs...)
+
+	// Detect different resources depending on which platform we are on
+	switch {
+	case d.onGKE():
+		attributes = append(attributes, semconv.CloudPlatformGCPKubernetesEngine)
+		attrs, errs = d.gkeAttributes()
+		attributes = append(attributes, attrs...)
+		errors = append(errors, errs...)
+	case d.onCloudRun():
+		attributes = append(attributes, semconv.CloudPlatformGCPCloudRun)
+		attrs, errs = d.faasAttributes()
+		attributes = append(attributes, attrs...)
+		errors = append(errors, errs...)
+	case d.onCloudFunctions():
+		attributes = append(attributes, semconv.CloudPlatformGCPCloudFunctions)
+		attrs, errs = d.faasAttributes()
+		attributes = append(attributes, attrs...)
+		errors = append(errors, errs...)
+	case d.onAppEngine():
+		attributes = append(attributes, semconv.CloudPlatformGCPAppEngine)
+		attrs, errs = d.appEngineAttributes()
+		attributes = append(attributes, attrs...)
+		errors = append(errors, errs...)
+	default:
+		attributes = append(attributes, semconv.CloudPlatformGCPComputeEngine)
+		attrs, errs = d.gceAttributes()
+		attributes = append(attributes, attrs...)
+		errors = append(errors, errs...)
+	}
+	var aggregatedErr error
+	if len(errors) > 0 {
+		aggregatedErr = fmt.Errorf("detecting GCP resources: %s", errors)
+	}
+
+	return resource.NewWithAttributes(semconv.SchemaURL, attributes...), aggregatedErr
+}
+
+func (d *detector) projectAttributes() (attributes []attribute.KeyValue, errs []string) {
+	if projectID, err := d.metadata.ProjectID(); err != nil {
+		errs = append(errs, err.Error())
+	} else if projectID != "" {
+		attributes = append(attributes, semconv.CloudAccountIDKey.String(projectID))
+	}
+	return
+}
+
+// detector collects resource information for all GCP platforms
+type detector struct {
+	metadata metadataProvider
+	os       osProvider
+}
+
+// metadataProvider contains the subset of the metadata.Client functions used
+// by this resource detector to allow testing with a fake implementation.
+type metadataProvider interface {
+	ProjectID() (string, error)
+	InstanceID() (string, error)
+	Get(string) (string, error)
+	InstanceName() (string, error)
+	Zone() (string, error)
+	InstanceAttributeValue(string) (string, error)
+}
+
+// osProvider contains the subset of the os package functions used by
+type osProvider interface {
+	LookupEnv(string) (string, bool)
+}
+
+// realOSProvider uses the os package to lookup env vars
+type realOSProvider struct{}
+
+func (realOSProvider) LookupEnv(env string) (string, bool) {
+	return os.LookupEnv(env)
+}