region hacking generalization

gcp/lib/gcp.dart

@@ -22,18 +22,13 @@ export 'src/gcp_project.dart'
         gcpProjectIdEnvironmentVariables,
         projectIdFromEnvironment,
         projectIdFromMetadataServer;
-export 'src/gpc_region.dart'
-    show
-        computeRegion,
-        gcpRegionEnvironmentVariables,
-        regionFromEnvironment,
-        regionFromMetadataServer;
 export 'src/log_severity.dart' show LogSeverity, RequestLogger;
 export 'src/logging.dart'
     show
         badRequestMiddleware,
         cloudLoggingMiddleware,
         createLoggingMiddleware,
         currentLogger;
+export 'src/metadata.dart' show MetadataValue;
 export 'src/serve.dart' show listenPort, serveHandler;
 export 'src/terminate.dart' show waitForTerminate;

gcp/lib/src/gcp_project.dart

@@ -12,26 +12,16 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-import 'dart:io';
-
-import 'package:http/http.dart' as http;
-
 import 'bad_configuration_exception.dart';
+import 'metadata.dart';
 
 /// A convenience wrapper that first tries [projectIdFromEnvironment]
 /// then (if the value is `null`) tries [projectIdFromMetadataServer]
 ///
 /// Like [projectIdFromMetadataServer], if no value is found, a
 /// [BadConfigurationException] is thrown.
-Future<String> computeProjectId() async {
-  final localValue = projectIdFromEnvironment();
-  if (localValue != null) {
-    return localValue;
-  }
-  final result = await projectIdFromMetadataServer();
-
-  return result;
-}
+Future<String> computeProjectId() =>
+    MetadataValue.project.fromEnvironmentOrMetadata();
 
 /// Returns the
 /// [Project ID](https://cloud.google.com/resource-manager/docs/creating-managing-projects#identifying_projects)
@@ -41,14 +31,7 @@ Future<String> computeProjectId() async {
 /// The list is checked in order. This is useful for local development.
 ///
 /// If no matching variable is found, `null` is returned.
-String? projectIdFromEnvironment() {
-  for (var envKey in gcpProjectIdEnvironmentVariables) {
-    final value = Platform.environment[envKey];
-    if (value != null) return value;
-  }
-
-  return null;
-}
+String? projectIdFromEnvironment() => MetadataValue.project.fromEnvironment();
 
 /// Returns a [Future] that completes with the
 /// [Project ID](https://cloud.google.com/resource-manager/docs/creating-managing-projects#identifying_projects)
@@ -57,36 +40,8 @@ String? projectIdFromEnvironment() {
 ///
 /// If the metadata server cannot be contacted, a [BadConfigurationException] is
 /// thrown.
-Future<String> projectIdFromMetadataServer() async {
-  const host = 'http://metadata.google.internal/';
-  final url = Uri.parse('$host/computeMetadata/v1/project/project-id');
-
-  try {
-    final response = await http.get(
-      url,
-      headers: {'Metadata-Flavor': 'Google'},
-    );
-
-    if (response.statusCode != 200) {
-      throw HttpException(
-        '${response.body} (${response.statusCode})',
-        uri: url,
-      );
-    }
-
-    return response.body;
-  } on SocketException catch (e) {
-    throw BadConfigurationException(
-      '''
-Could not connect to $host.
-If not running on Google Cloud, one of these environment variables must be set
-to the target Google Project ID:
-${gcpProjectIdEnvironmentVariables.join('\n')}
-''',
-      details: e.toString(),
-    );
-  }
-}
+Future<String> projectIdFromMetadataServer() =>
+    MetadataValue.project.fromMetadataServer();
 
 /// A set of typical environment variables that are likely to represent the
 /// current Google Cloud project ID.
@@ -98,9 +53,5 @@ ${gcpProjectIdEnvironmentVariables.join('\n')}
 ///
 /// Note: these are ordered starting from the most current/canonical to least.
 /// (At least as could be determined at the time of writing.)
-const gcpProjectIdEnvironmentVariables = {
-  'GCP_PROJECT',
-  'GCLOUD_PROJECT',
-  'CLOUDSDK_CORE_PROJECT',
-  'GOOGLE_CLOUD_PROJECT',
-};
+Set<String> get gcpProjectIdEnvironmentVariables =>
+    MetadataValue.project.environmentValues;

gcp/lib/src/metadata.dart

@@ -0,0 +1,138 @@
+// 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
+//
+//     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.
+
+import 'dart:io';
+
+import 'package:http/http.dart' as http;
+
+import 'bad_configuration_exception.dart';
+
+enum MetadataValue {
+  /// A set of typical environment variables that are likely to represent the
+  /// current Google Cloud instance region.
+  ///
+  /// For context, see:
+  /// * https://cloud.google.com/functions/docs/env-var
+  /// * https://cloud.google.com/compute/docs/gcloud-compute#default_project
+  /// * https://github.com/GoogleContainerTools/gcp-auth-webhook/blob/08136ca171fe5713cc70ef822c911fbd3a1707f5/server.go#L38-L44
+  ///
+  /// Note: these are ordered starting from the most current/canonical to least.
+  /// (At least as could be determined at the time of writing.)
+  project(
+    path: 'project/project-id',
+    environmentValues: {
+      'GCP_PROJECT',
+      'GCLOUD_PROJECT',
+      'CLOUDSDK_CORE_PROJECT',
+      'GOOGLE_CLOUD_PROJECT',
+    },
+  ),
+
+  /// A set of typical environment variables that are likely to represent the
+  /// current Google Cloud instance region.
+  ///
+  /// For context, see:
+  /// * https://cloud.google.com/functions/docs/env-var
+  /// * https://cloud.google.com/compute/docs/gcloud-compute#default_project
+  /// * https://github.com/GoogleContainerTools/gcp-auth-webhook/blob/08136ca171fe5713cc70ef822c911fbd3a1707f5/server.go#L38-L44
+  ///
+  /// Note: these are ordered starting from the most current/canonical to least.
+  /// (At least as could be determined at the time of writing.)
+  region(
+    path: 'instance/region',
+    environmentValues: {
+      'FUNCTION_REGION',
+      'CLOUDSDK_COMPUTE_REGION',
+    },
+  );
+
+  const MetadataValue({
+    required this.path,
+    required this.environmentValues,
+  });
+
+  final String path;
+
+  final Set<String> environmentValues;
+
+  /// A convenience wrapper that first tries [fromEnvironment]
+  /// then (if the value is `null`) tries [fromMetadataServer]
+  ///
+  /// Like [fromMetadataServer], if no value is found, a
+  /// [BadConfigurationException] is thrown.
+  Future<String> fromEnvironmentOrMetadata() async {
+    final localValue = fromEnvironment();
+    if (localValue != null) {
+      return localValue;
+    }
+    final result = await fromMetadataServer();
+
+    return result;
+  }
+
+  /// Returns the
+  /// [Region](https://cloud.google.com/compute/docs/regions-zones#identifying_a_region_or_zone)
+  /// for the current instance by checking the environment variables in
+  /// [environmentValues].
+  ///
+  /// The list is checked in order. This is useful for local development.
+  ///
+  /// If no matching variable is found, `null` is returned.
+  String? fromEnvironment() {
+    for (var envKey in environmentValues) {
+      final value = Platform.environment[envKey];
+      if (value != null) return value;
+    }
+
+    return null;
+  }
+
+  /// Returns a [Future] that completes with the
+  /// [Region](https://cloud.google.com/compute/docs/regions-zones#identifying_a_region_or_zone)
+  /// for the current instance by checking
+  /// [instance metadata](https://cloud.google.com/compute/docs/metadata/default-metadata-values#vm_instance_metadata).
+  ///
+  /// If the metadata server cannot be contacted, a [BadConfigurationException]
+  /// is thrown.
+  Future<String> fromMetadataServer() async {
+    const host = 'http://metadata.google.internal/';
+    final url = Uri.parse('$host/computeMetadata/v1/$path');
+
+    try {
+      final response = await http.get(
+        url,
+        headers: {'Metadata-Flavor': 'Google'},
+      );
+
+      if (response.statusCode != 200) {
+        throw HttpException(
+          '${response.body} (${response.statusCode})',
+          uri: url,
+        );
+      }
+
+      return response.body;
+    } on SocketException catch (e) {
+      throw BadConfigurationException(
+        '''
+Could not connect to $host.
+If not running on Google Cloud, one of these environment variables must be set
+to the target region:
+${environmentValues.join('\n')}
+''',
+        details: e.toString(),
+      );
+    }
+  }
+}

gcp/test/gcp_test.dart

@@ -142,7 +142,7 @@ void main() {
 
       await expectLater(
         errorOut,
-        containsAll(gcpRegionEnvironmentVariables),
+        containsAll(MetadataValue.region.environmentValues),
       );
       await expectLater(proc.stdout, emitsDone);
 
@@ -152,7 +152,9 @@ void main() {
     test('environment set', () async {
       final proc = await _run(
         regionPrint,
-        environment: {gcpRegionEnvironmentVariables.first: 'us-central1'},
+        environment: {
+          MetadataValue.region.environmentValues.first: 'us-central1',
+        },
       );
 
       await expectLater(proc.stdout, emits('us-central1'));

gcp/test/src/region_print.dart

@@ -14,5 +14,5 @@
 import 'package:gcp/gcp.dart';
 
 Future<void> main() async {
-  print(await computeRegion());
+  print(await MetadataValue.region.fromEnvironmentOrMetadata());
 }