Middleware can't intercept errors in case of async method's function

[stubbornick]

Here is an example of the issue:

const {
  JSONRPCServer, createJSONRPCErrorResponse, JSONRPCErrorCode, JSONRPC,
} = require('json-rpc-2.0');

const server = new JSONRPCServer();
server.applyMiddleware(async (next, request, serverParams) => {
  try {
    console.log('MIDDLEWARE');
    const res = await next(request, serverParams);
    console.log('MIDDLEWARE RESULT', res);
    return res;
  } catch (error) {
    console.log('MIDDLEWARE EXCEPT', error);
    return createJSONRPCErrorResponse(
      request.id,
      error.code || JSONRPCErrorCode.InternalError,
      error.message,
    );
  }
});

server.addMethod('myMethod', async () => {
  throw new Error('TEST ERROR');
});

const main = async () => {
  const result = await server
    .receive({
      jsonrpc: JSONRPC,
      id: 0,
      method: 'myMethod',
      params: {},
    });

  console.log('RESULT', result);
};

main();

The output is:

MIDDLEWARE
JSON-RPC method myMethod responded an error Error: TEST ERROR
   ... <stacktrace> ...
MIDDLEWARE RESULT { jsonrpc: '2.0', id: 0, error: { code: 0, message: 'TEST ERROR' } }
RESULT { jsonrpc: '2.0', id: 0, error: { code: 0, message: 'TEST ERROR' } }

Moreover, in such case the error is posted in console with console.warn which makes it impossible to control logging of errors by lib's user.

[Shogo Wada]

Oh, just noticed to this issue. Let me take a look at it by next week.

[Shogo Wada]

It looks like I already have a test case for this (and it's passing):

json-rpc-2.0/src/server.spec.ts

Lines 589 to 634 in 2b03a44

 describe("using middleware that catches exception", () => { 
   beforeEach(() => { 
     server.applyMiddleware(async (next, request, serverParams) => { 
       try { 
         return await next(request, serverParams); 
       } catch (error) { 
         return createJSONRPCErrorResponse( 
           request.id!, 
           error.code || JSONRPCErrorCode.InternalError, 
           error.message 
         ); 
       } 
     }); 
   }); 
  
   describe("throwing", () => { 
     let error: any; 
     let actualResponse: JSONRPCResponse; 
  
     beforeEach(() => { 
       server 
         .receive({ 
           jsonrpc: JSONRPC, 
           id: 0, 
           method: methodName, 
           params: {}, 
         }) 
         .then((response) => (actualResponse = response!)); 
  
       error = { code: 123, message: "test" }; 
  
       throwFromMethod(error); 
  
       return consumeAllEvents(); 
     }); 
  
     it("should catch the exception on middleware", () => { 
       const expected: JSONRPCErrorResponse = createJSONRPCErrorResponse( 
         0, 
         error.code, 
         error.message 
       ); 
       expect(actualResponse).to.deep.equal(expected); 
     }); 
   }); 
 }); 

Can you please tell what's missing from the test case?

[stubbornick]

Sure. In your test case echoMethod is a synchronous one. The problem arrives when you throw in asynchronous method like in example I posted above.

[stubbornick]

Ah, I see now that method is actually asynchronous... Maybe the reason is that method is defined by addMethodAdvanced instead of addMethod.

[Shogo Wada]

Thanks! I could reproduce it by using non-advanced method & async 😄

Both fix for the original issue and support for injecting custom error logger are published under v1.1.0:

• b91fc1f
• 5956627