Improve rate limit handling (Closes #37)

CHANGELOG.md

@@ -1,6 +1,10 @@
 # Changelog
 
-## [Unreleased]
+## [Unreleased] 0.4.0-alpha
+
+- Improve error handling
+  - RateLimitingException now contains the duration after which a retry should be done
+  - Not attempt is made to decode rate limiting error responses (they're not JSON)
 
 ### Breaking Changes
 

lib/src/api/core.dart

@@ -58,15 +58,25 @@ class CoreApi implements SpotifyWebApi {
 
   void checkErrors(Response response) {
     if (!response.isSuccessful) {
-      final body = response.body.decodeJson(ErrorResponse.fromJson);
       switch (response.statusCode) {
         case 401:
           throw AuthenticationException();
         case 403:
           throw AuthorizationException();
         case 429:
-          throw RateLimitException();
+          final retryAfterSeconds = response.header('Retry-After');
+
+          if (retryAfterSeconds == null) {
+            throw RateLimitException(null);
+          }
+
+          throw RateLimitException(
+            DateTime.now()
+                .toUtc()
+                .add(Duration(seconds: int.parse(retryAfterSeconds))),
+          );
         default:
+          final body = response.body.decodeJson(ErrorResponse.fromJson);
           throw SpotifyApiException(body.error.message);
       }
     }

lib/src/exceptions.dart

@@ -18,4 +18,8 @@ class AuthenticationException extends SpotifyApiException {}
 
 class AuthorizationException extends SpotifyApiException {}
 
-class RateLimitException extends SpotifyApiException {}
+class RateLimitException extends SpotifyApiException {
+  final DateTime? retryAfter;
+
+  RateLimitException(this.retryAfter);
+}

lib/src/requests.dart

@@ -61,6 +61,8 @@ class Response {
 
   bool get isSuccessful => statusCode >= 200 && statusCode < 300;
 
+  String? header(String headerName) => _response.headers[headerName];
+
   ResponseBody get body => ResponseBody(_response.bodyBytes);
 }