Use new HTTP retry logic when fetching SDK's index.json + refactor

app/lib/search/backend.dart

@@ -87,7 +87,6 @@ void registerSearchIndex(SearchIndex index) =>
 class SearchBackend {
   final DatastoreDB _db;
   final VersionedJsonStorage _snapshotStorage;
-  final _http = httpRetryClient();
 
   SearchBackend(this._db, Bucket snapshotBucket)
       : _snapshotStorage = VersionedJsonStorage(snapshotBucket, 'snapshot/');
@@ -428,42 +427,6 @@ class SearchBackend {
     }
   }
 
-  /// Downloads the remote SDK content from [uri] and creates a cached file in the
-  /// `.dart_tool/pub-search-data/` directory.
-  ///
-  /// When a local file in `app/.dart_tool/pub-search-data/<reduced-uri>` exists,
-  /// its content will be loaded instead. URL reduction replaces slashes and other
-  /// non-characters with a single dash `-`, like:
-  /// - `https-api.dart.dev-stable-latest-index.json`
-  Future<String> loadOrFetchSdkIndexJsonAsString(
-    Uri uri, {
-    @visibleForTesting Duration? ttl,
-  }) async {
-    final fileName = uri.toString().replaceAll(RegExp(r'[^a-z0-9\.]+'), '-');
-    final file = File(p.join('.dart_tool', 'pub-search-data', fileName));
-    if (await file.exists()) {
-      var canUseCached = true;
-      if (ttl != null) {
-        final age = clock.now().difference(await file.lastModified());
-        if (age > ttl) {
-          canUseCached = false;
-        }
-      }
-      if (canUseCached) {
-        return await file.readAsString();
-      }
-    }
-
-    final rs = await _http.get(uri);
-    if (rs.statusCode != 200) {
-      throw Exception('Unexpected status code for $uri: ${rs.statusCode}');
-    }
-    final content = rs.body;
-    await file.parent.create(recursive: true);
-    await file.writeAsString(content);
-    return content;
-  }
-
   Future<List<PackageDocument>?> fetchSnapshotDocuments() async {
     try {
       final map = await _snapshotStorage.getContentAsJsonMap();
@@ -519,7 +482,6 @@ class SearchBackend {
 
   Future<void> close() async {
     _snapshotStorage.close();
-    _http.close();
   }
 }
 
@@ -615,6 +577,38 @@ List<ApiDocPage> apiDocPagesFromPubData(PubDartdocData pubData) {
   return results;
 }
 
+/// Downloads the remote SDK content from [uri] and creates a cached file in the
+/// `.dart_tool/pub-search-data/` directory.
+///
+/// When a local file in `app/.dart_tool/pub-search-data/<reduced-uri>` exists,
+/// its content will be loaded instead. URL reduction replaces slashes and other
+/// non-characters with a single dash `-`, like:
+/// - `https-api.dart.dev-stable-latest-index.json`
+Future<String> loadOrFetchSdkIndexJsonAsString(
+  Uri uri, {
+  @visibleForTesting Duration? ttl,
+}) async {
+  final fileName = uri.toString().replaceAll(RegExp(r'[^a-z0-9\.]+'), '-');
+  final file = File(p.join('.dart_tool', 'pub-search-data', fileName));
+  if (await file.exists()) {
+    var canUseCached = true;
+    if (ttl != null) {
+      final age = clock.now().difference(await file.lastModified());
+      if (age > ttl) {
+        canUseCached = false;
+      }
+    }
+    if (canUseCached) {
+      return await file.readAsString();
+    }
+  }
+
+  final content = await httpGetWithRetry(uri, responseFn: (rs) => rs.body);
+  await file.parent.create(recursive: true);
+  await file.writeAsString(content);
+  return content;
+}
+
 class _CombinedSearchIndex implements SearchIndex {
   const _CombinedSearchIndex();
 

app/lib/search/dart_sdk_mem_index.dart

@@ -38,8 +38,7 @@ SdkMemIndex? get dartSdkMemIndex =>
 Future<SdkMemIndex?> createDartSdkMemIndex() async {
   try {
     final index = await SdkMemIndex.dart();
-    final content =
-        await searchBackend.loadOrFetchSdkIndexJsonAsString(index.indexJsonUri);
+    final content = await loadOrFetchSdkIndexJsonAsString(index.indexJsonUri);
     await index.addDartdocIndex(DartdocIndex.parseJsonText(content));
     index.updateWeights(
       libraryWeights: dartSdkLibraryWeights,

app/lib/search/flutter_sdk_mem_index.dart

@@ -55,8 +55,7 @@ SdkMemIndex? get flutterSdkMemIndex =>
 Future<SdkMemIndex?> createFlutterSdkMemIndex() async {
   try {
     final index = SdkMemIndex.flutter();
-    final content =
-        await searchBackend.loadOrFetchSdkIndexJsonAsString(index.indexJsonUri);
+    final content = await loadOrFetchSdkIndexJsonAsString(index.indexJsonUri);
     await index.addDartdocIndex(DartdocIndex.parseJsonText(content),
         allowedLibraries: _allowedLibraries);
     index.updateWeights(

app/test/search/backend_test.dart

@@ -14,8 +14,7 @@ void main() {
   group('search backend', () {
     testWithProfile('fetch SDK library description', fn: () async {
       final index = await SdkMemIndex.dart();
-      final content = await searchBackend
-          .loadOrFetchSdkIndexJsonAsString(index.indexJsonUri);
+      final content = await loadOrFetchSdkIndexJsonAsString(index.indexJsonUri);
       await index.addDartdocIndex(DartdocIndex.parseJsonText(content));
       expect(
         index.getLibraryDescription('dart:async'),

app/test/search/dartdoc_index_parsing_test.dart

@@ -13,7 +13,7 @@ import '../shared/test_services.dart';
 void main() {
   group('dartdoc index.json parsing', () {
     testWithProfile('parse Dart SDK index.json', fn: () async {
-      final textContent = await searchBackend.loadOrFetchSdkIndexJsonAsString(
+      final textContent = await loadOrFetchSdkIndexJsonAsString(
         Uri.parse('https://api.dart.dev/stable/latest/index.json'),
         ttl: Duration(days: 1),
       );
@@ -35,7 +35,7 @@ void main() {
     });
 
     testWithProfile('parse Flutter SDK index.json', fn: () async {
-      final textContent = await searchBackend.loadOrFetchSdkIndexJsonAsString(
+      final textContent = await loadOrFetchSdkIndexJsonAsString(
         Uri.parse('https://api.flutter.dev/flutter/index.json'),
         ttl: Duration(days: 1),
       );

pkg/_pub_shared/lib/utils/http.dart

@@ -2,10 +2,12 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'dart:async';
 import 'dart:io';
 
 import 'package:http/http.dart' as http;
 import 'package:http/retry.dart';
+import 'package:retry/retry.dart';
 
 final _transientStatusCodes = {
   // See: https://cloud.google.com/storage/docs/xml-api/reference-status
@@ -35,3 +37,45 @@ http.Client httpRetryClient({
     whenError: (e, st) => lenient || e is SocketException,
   );
 }
+
+/// Creates a HTTP client and executes a GET request to the specified [uri],
+/// making sure that the HTTP resources are freed after the [responseFn]
+/// callback finishes.
+/// The HTTP GET and the [responseFn] callback is retried on the transient
+/// network errors.
+Future<K> httpGetWithRetry<K>(
+  Uri uri, {
+  required FutureOr<K> Function(http.Response response) responseFn,
+  int maxAttempts = 3,
+}) async {
+  return await retry(
+    () async {
+      final client = http.Client();
+      try {
+        final rs = await client.get(uri);
+        if (rs.statusCode == 200) {
+          return responseFn(rs);
+        }
+        throw http.ClientException(
+            'Unexpected status code for $uri: ${rs.statusCode}.');
+      } finally {
+        client.close();
+      }
+    },
+    maxAttempts: maxAttempts,
+    retryIf: _retryIf,
+  );
+}
+
+bool _retryIf(Exception e) {
+  if (e is TimeoutException) {
+    return true; // Timeouts we can retry
+  }
+  if (e is IOException) {
+    return true; // I/O issues are worth retrying
+  }
+  if (e is http.ClientException) {
+    return true; // HTTP issues are worth retrying
+  }
+  return false;
+}

pkg/_pub_shared/pubspec.yaml

@@ -13,6 +13,7 @@ dependencies:
   logging: ^1.2.0
   meta: ^1.3.0
   pub_semver: ^2.0.0
+  retry: ^3.1.2
   sanitize_html: ^2.1.0
   api_builder: