Image proxy

app/config/dartlang-pub-dev.yaml

@@ -71,3 +71,5 @@ rateLimits:
     scope: package
     burst: 10
     daily: 24
+imageProxyHmacKeyVersion: projects/dartlang-pub-dev/locations/us-central1/keyRings/image-proxy-key-ring/cryptoKeys/image-proxy-mac-key/cryptoKeyVersions/1
+imageProxyServiceBaseUrl: https://external-images-staging.pub.dev

app/lib/service/image_proxy/backend.dart

@@ -0,0 +1,98 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// 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:convert';
+
+import 'package:crypto/crypto.dart';
+import 'package:gcloud/service_scope.dart' as ss;
+import 'package:googleapis/cloudkms/v1.dart' as kms;
+import 'package:googleapis_auth/auth_io.dart';
+import 'package:pub_dev/shared/configuration.dart';
+import 'package:retry/retry.dart';
+
+import '../../shared/cached_value.dart';
+
+/// Sets the Image proxy backend service.
+void registerImageProxyBackend(ImageProxyBackend backend) =>
+    ss.register(#_imageProxyBackend, backend);
+
+/// The active Youtube backend service.
+ImageProxyBackend get imageProxyBackend =>
+    ss.lookup(#_imageProxyBackend) as ImageProxyBackend;
+
+/// Represents the backend for the Youtube handling and related utilities.
+class ImageProxyBackend {
+  ImageProxyBackend._();
+
+  static Future<ImageProxyBackend> create() async {
+    final instance = ImageProxyBackend._();
+    await instance._dailySecret.update();
+    return instance;
+  }
+
+  static Future<List<int>> _getDailySecret(
+    DateTime day,
+    AuthClient client,
+  ) async {
+    return await retry(() async {
+      final api = kms.CloudKMSApi(client);
+      final response = await api
+          .projects
+          .locations
+          .keyRings
+          .cryptoKeys
+          .cryptoKeyVersions
+          .macSign(
+            kms.MacSignRequest()
+              ..dataAsBytes = utf8.encode(
+                DateTime(
+                  day.year,
+                  day.month,
+                  day.day,
+                ).toUtc().toIso8601String(),
+              ),
+            activeConfiguration.imageProxyHmacKeyVersion!,
+          );
+      return response.macAsBytes;
+    });
+  }
+
+  final _dailySecret = CachedValue(
+    name: 'image-proxy-daily-secret',
+    interval: Duration(minutes: 15),
+    maxAge: Duration(hours: 12),
+    timeout: Duration(hours: 12),
+    updateFn: () async {
+      final now = DateTime.now().toUtc();
+      final today = DateTime(now.year, now.month, now.day);
+      return (
+        today,
+        await _getDailySecret(
+          today,
+          await clientViaApplicationDefaultCredentials(
+            scopes: [kms.CloudKMSApi.cloudPlatformScope],
+          ),
+        ),
+      );
+    },
+  );
+
+  String imageProxyUrl(Uri originalUrl) {
+    final dailySecret = _dailySecret.value;
+    // TODO handle the null case more gracefully.
+    if (dailySecret == null) {
+      throw StateError('Image proxy HMAC secret is not available.');
+    }
+    final (today, secret) = dailySecret;
+
+    final hmac = Hmac(
+      sha256,
+      secret,
+    ).convert(originalUrl.toString().codeUnits).bytes;
+    activeConfiguration.imageProxyServiceBaseUrl;
+
+    return '${activeConfiguration.imageProxyServiceBaseUrl}/${Uri.encodeComponent(base64Encode(hmac))}/${today.millisecondsSinceEpoch}/${Uri.encodeComponent(originalUrl.toString())}';
+  }
+}

app/lib/service/services.dart

@@ -20,6 +20,7 @@ import 'package:pub_dev/package/api_export/api_exporter.dart';
 import 'package:pub_dev/search/handlers.dart';
 import 'package:pub_dev/service/async_queue/async_queue.dart';
 import 'package:pub_dev/service/download_counts/backend.dart';
+import 'package:pub_dev/service/image_proxy/backend.dart';
 import 'package:pub_dev/service/security_advisories/backend.dart';
 import 'package:shelf/shelf.dart' as shelf;
 import 'package:shelf/shelf_io.dart';
@@ -319,6 +320,8 @@ Future<R> _withPubServices<R>(FutureOr<R> Function() fn) async {
         registerYoutubeBackend(YoutubeBackend());
         registerScopeExitCallback(youtubeBackend.close);
 
+        registerImageProxyBackend(await ImageProxyBackend.create());
+
         // depends on previously registered services
         registerPackageBackend(
           PackageBackend(

app/lib/shared/configuration.dart

@@ -218,6 +218,10 @@ final class Configuration {
   /// The rate limits for auditable operations.
   final List<RateLimit>? rateLimits;
 
+  /// The Cloud KMS HMAC key version used to sign image proxy URLs.
+  final String? imageProxyHmacKeyVersion;
+  final String? imageProxyServiceBaseUrl;
+
   /// Load [Configuration] from YAML file at [path] substituting `{{ENV}}` for
   /// the value of environment variable `ENV`.
   factory Configuration.fromYamlFile(final String path) {
@@ -285,6 +289,8 @@ final class Configuration {
     required this.defaultServiceBaseUrl,
     required this.tools,
     required this.rateLimits,
+    required this.imageProxyHmacKeyVersion,
+    required this.imageProxyServiceBaseUrl,
   });
 
   /// Load configuration from `app/config/<projectId>.yaml` where `projectId`
@@ -356,6 +362,8 @@ final class Configuration {
       ],
       tools: null,
       rateLimits: null,
+      imageProxyHmacKeyVersion: null,
+      imageProxyServiceBaseUrl: null,
     );
   }
 
@@ -406,6 +414,8 @@ final class Configuration {
       ],
       tools: null,
       rateLimits: null,
+      imageProxyHmacKeyVersion: null,
+      imageProxyServiceBaseUrl: null,
     );
   }
 

app/lib/shared/markdown.dart

@@ -2,12 +2,16 @@
 // 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:convert';
+
+import 'package:googleapis/cloudkms/v1.dart' as kms;
 import 'package:html/dom.dart' as html;
 import 'package:html/dom_parsing.dart' as html_parsing;
 import 'package:html/parser.dart' as html_parser;
 import 'package:logging/logging.dart';
 import 'package:markdown/markdown.dart' as m;
 import 'package:pub_dev/frontend/static_files.dart';
+import 'package:pub_dev/service/image_proxy/backend.dart';
 import 'package:pub_dev/shared/changelog.dart';
 import 'package:sanitize_html/sanitize_html.dart';
 
@@ -124,6 +128,7 @@ String _postProcessHtml(
   var root = html_parser.parseFragment(rawHtml);
 
   _RelativeUrlRewriter(urlResolverFn, relativeFrom).visit(root);
+  _ImageProxyRewriter().visit(root);
 
   if (isChangelog) {
     final oldNodes = [...root.nodes];
@@ -203,6 +208,27 @@ class _UnsafeUrlFilter extends html_parsing.TreeVisitor {
   }
 }
 
+class _ImageProxyRewriter extends html_parsing.TreeVisitor {
+  @override
+  void visitElement(html.Element element) {
+    super.visitElement(element);
+
+    if (element.localName == 'img') {
+      final src = element.attributes['src'];
+      final uri = Uri.tryParse(src ?? '');
+      if (uri == null || uri.isInvalid) {
+        // TODO: consider removing the element entirely
+        return;
+      }
+      if ((uri.isScheme('http') || uri.isScheme('https')) &&
+          !uri.isTrustedHost) {
+        final proxiedUrl = imageProxyBackend.imageProxyUrl(uri);
+        element.attributes['src'] = proxiedUrl;
+      }
+    }
+  }
+}
+
 /// Rewrites relative URLs with the provided [urlResolverFn].
 class _RelativeUrlRewriter extends html_parsing.TreeVisitor {
   final UrlResolverFn? urlResolverFn;