Incompatibility between the Dart shelf and rpc packages? ('access-control-request-method' header)


There seems to be an incompatibility between the shelf and rpc packages.

In rpc [0.4.1] config/api.dart: The handleHttpOptionsRequest expects the
‘access-control-request-method’ header to be a List:

    Future<HttpApiResponse> handleHttpOptionsRequest(
          ParsedHttpApiRequest request) async {
        var requestedHttpMethods = request.headers['access-control-request-method'];
        List<String> allowed = [];
        assert('OPTIONS'.allMatches(request.methodKey).length == 1);
        if (requestedHttpMethods != null) {
          requestedHttpMethods.forEach((httpMethod) {
            var methodKey =
                request.methodKey.replaceFirst('OPTIONS', httpMethod);
            final List<ApiConfigMethod> methods = _methodMap[methodKey];
            if (methods != null) {
              for (var method in methods) {
                if (method.matches(request)) {

When using the shelf [0.5.7] package,
the ParsedHttpApiRequest which is passed to this method contains an
‘access-control-request-method’ header which is a String.

This generates an exception…

When using rpc with HttpServer, the code works fine and ParsedHttpApiRequest
has a List of Strings (with a single element) as value of the
‘access-control-request-method’ header.

Anyone uses dart rpc + shelf successfully? If so, any idea on how to avoid the

[update] After the rpc fix, the previously mentioned issue seems to be fixed. Thanks for that!
I now run into another issue, but I did not yet investigate in detail.
Stack trace is:

shelf [0.5.7] shelf_rpc [0.0.3] rpc [0.4.2]:

     Error thrown by handler.
     type 'List' is not a subtype of type 'String' of 'value'.
     package:collection/src/canonicalized_map.dart 66:30  CanonicalizedMap.[]=
     package:collection/src/canonicalized_map.dart 71:39  CanonicalizedMap.addAll.<fn>
     dart:collection                                      _CompactLinkedHashMap.forEach
     package:collection/src/canonicalized_map.dart 71:18  CanonicalizedMap.addAll
     package:collection/src/canonicalized_map.dart 57:11  CanonicalizedMap.CanonicalizedMap.from
     package:shelf/src/response.dart 215:9                Response.Response
     package:shelf_rpc/shelf_rpc.dart 18:24               createRpcHandler.<fn>.<fn>

=> see incompatibility when running dart rpc and shelf (with shelf_rpc) related to headers which are lists (and not Strings)


This is a bug in the RPC package. I will fix this ASAP and publish a new version of the RPC package.

You are welcome to file this kind of issue under github at:


Answered By – Gustav Wibling

Answer Checked By – Pedro (FlutterFixes Volunteer)

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