如何在 Dart 中从服务器 API 代码中抛出异常？

Question

我正在用 Dart 开发客户端-服务器应用程序，并且一直在关注 tutorial。我的服务器代码大致是基于它。

在我的服务器API代码中，当出错的时候，我想抛出一个异常，例如：

void checkEverything() {
  if(somethingWrong)
    throw new RpcError(400, "Something Wrong", "Something went wrong!");
}

@ApiMethod(path: 'myservice/{arg}')
Future<String> myservice(String arg) async {
  checkEverything();
  // ...
  return myServiceResponse;
}

并且该异常应该在主服务器中处理，例如

// ...
var apiResponse;
try {
  var apiRequest = new HttpApiRequest.fromHttpRequest(request);
  apiResponse = await _apiServer.handleHttpApiRequest(apiRequest);
} catch (error, stack) {
  var exception = error is Error ? new Exception(error.toString()) : error;
  if((error is RpcError && error.statusCode==400) {
    // My code for creating the HTTP response
    apiResponse = new HttpApiResponse.error(
        HttpStatus.BAD_REQUEST, "Something went wrong", exception, stack);
  }
  else {
    // standard error processing from the Dart tutorial
    apiResponse = new HttpApiResponse.error(
        HttpStatus.INTERNAL_SERVER_ERROR, exception.toString(),
        exception, stack);
  }
}

（片段，请参阅 tutorial 了解完整代码，但没有我的错误处理）。

但是，我的异常从来没有达到上面的catch子句。相反，它似乎陷入了 _apiServer.handleHttpApiRequest(apiRequest);，而后者又抛出了 INTERNAL_SERVER_ERROR (500):

[WARNING] rpc: Method myservice returned null instead of valid return value
[WARNING] rpc:
Response
  Status Code: 500
  Headers:
    access-control-allow-credentials: true
    access-control-allow-origin: *
    cache-control: no-cache, no-store, must-revalidate
    content-type: application/json; charset=utf-8
    expires: 0
    pragma: no-cache
  Exception:
    RPC Error with status: 500 and message: Method with non-void return type returned 'null'

Unhandled exception:
RPC Error with status: 400 and message: Something went wrong!
#0      MyApi.myservice (package:mypackage/server/myapi.dart:204:24)
[...]

这对客户来说不是很具体。我想传达发生了错误，而不是 return 一个好看的回应。那么在 Dart 中处理服务器端异常并将该信息传递给客户端的正确方法是什么？

Answer 1

好的，我想我解决了问题。 throw 子句显然必须在 API 方法本身中，而不是在从属方法中。即：

@ApiMethod(path: 'myservice/{arg}')
Future<String> myservice(String arg) async {
  if(somethingWrong)
    throw new RpcError(400, "Something Wrong", "Something went wrong!");
  // ...
  return myServiceResponse;
}

而不是：

void checkEverything() {
  if(somethingWrong)
    throw new RpcError(400, "Something Wrong", "Something went wrong!");
}

@ApiMethod(path: 'myservice/{arg}')
Future<String> myservice(String arg) async {
  checkEverything();
  // ...
  return myServiceResponse;
}

如何在 Dart 中从服务器 API 代码中抛出异常？

How to throw an exception from a server API code in Dart?

rpc

dart