Display error messages from GCS

lib/src/authentication/client.dart

@@ -11,6 +11,7 @@ import 'package:http_parser/http_parser.dart';
 import '../http.dart';
 import '../log.dart' as log;
 import '../system_cache.dart';
+import '../utils.dart';
 import 'credential.dart';
 
 /// This client authenticates requests by injecting `Authentication` header to
@@ -83,11 +84,7 @@ class _AuthenticatedClient extends http.BaseClient {
       }
     }
     if (serverMessage != null) {
-      // Only allow printable ASCII, map anything else to whitespace, take
-      // at-most 1024 characters.
-      serverMessage = String.fromCharCodes(
-        serverMessage.runes.map((r) => 32 <= r && r <= 127 ? r : 32).take(1024),
-      );
+      serverMessage = sanitizeForTerminal(serverMessage);
     }
     throw AuthenticationException(response.statusCode, serverMessage);
   }

lib/src/command/lish.dart

@@ -179,9 +179,7 @@ class LishCommand extends PubCommand {
     } on PubHttpResponseException catch (error) {
       var url = error.response.request!.url;
       if (url == cloudStorageUrl) {
-        // TODO(nweiz): the response may have XML-formatted information about
-        // the error. Try to parse that out once we have an easily-accessible
-        // XML parser.
+        handleGCSError(error.response);
         fail(log.red('Failed to upload the package.'));
       } else if (Uri.parse(url.origin) == Uri.parse(host.origin)) {
         handleJsonError(error.response);

lib/src/http.dart

@@ -211,6 +211,40 @@ void handleJsonError(http.BaseResponse response) {
   fail(log.red(error['message'] as String));
 }
 
+/// Handles an unsuccessful XML-formatted response from google cloud storage.
+///
+/// Assumes messages are of the form in
+/// https://cloud.google.com/storage/docs/xml-api/reference-status.
+///
+/// This is a poor person's XML parsing with regexps, but this should be
+/// sufficient for the specified messages.
+void handleGCSError(http.BaseResponse response) {
+  if (response is http.Response) {
+    final responseBody = response.body;
+    if (responseBody.contains('<?xml')) {
+      String? getTagText(String tag) {
+        final result = RegExp('<$tag>(.*)</$tag>').firstMatch(responseBody)?[1];
+        if (result == null) return null;
+        return sanitizeForTerminal(result);
+      }
+
+      final code = getTagText('Code');
+      final message = getTagText('Message');
+      // `Details` are not specified in the doc above, but have been observed in actual responses.
+      final details = getTagText('Details');
+      if (code != null) {
+        log.error('Server error code: $code');
+      }
+      if (message != null) {
+        log.error('Server message: $message');
+      }
+      if (details != null) {
+        log.error('Server details: $details');
+      }
+    }
+  }
+}
+
 /// Parses a response body, assuming it's JSON-formatted.
 ///
 /// Throws a user-friendly error if the response body is invalid JSON, or if

lib/src/utils.dart

@@ -767,3 +767,13 @@ extension RetrieveFlags on ArgResults {
   String option(String name) => this[name] as String;
   String? optionWithoutDefault(String name) => this[name] as String?;
 }
+
+/// Limits the range of characters and length.
+///
+/// Useful for displaying externally provided strings.
+///
+/// Only allowd printable ASCII, map anything else to whitespace, take at-most
+/// 1024 characters.
+String sanitizeForTerminal(String input) => String.fromCharCodes(
+      input.runes.map((r) => 32 <= r && r <= 127 ? r : 32).take(1024),
+    );

test/lish/cloud_storage_upload_provides_an_error_test.dart

@@ -22,14 +22,30 @@ void main() {
     globalServer.expect('POST', '/upload', (request) {
       return request.read().drain().then((_) {
         return shelf.Response.notFound(
-          '<Error><Message>Your request sucked.</Message></Error>',
+          // Actual example of an error code we get from GCS
+          "<?xml version='1.0' encoding='UTF-8'?><Error><Code>EntityTooLarge</Code><Message>Your proposed upload is larger than the maximum object size specified in your Policy Document.</Message><Details>Content-length exceeds upper bound on range</Details></Error>",
           headers: {'content-type': 'application/xml'},
         );
       });
     });
 
-    // TODO(nweiz): This should use the server's error message once the client
-    // can parse the XML.
+    expect(
+      pub.stderr,
+      emits(
+        'Server error code: EntityTooLarge',
+      ),
+    );
+    expect(
+      pub.stderr,
+      emits(
+        'Server message: Your proposed upload is larger than the maximum object size specified in your Policy Document.',
+      ),
+    );
+    expect(
+      pub.stderr,
+      emits('Server details: Content-length exceeds upper bound on range'),
+    );
+
     expect(pub.stderr, emits('Failed to upload the package.'));
     await pub.shouldExit(1);
   });