Response Validation Issue - "Cannot read property 'then' of undefined in modded.mung"

[spencerbn]

Hi,

It looks like response validation was just added a few days ago, so this could be a known issue or not. So far I really appreciate how straight-forward and friendly this library is. Thank you!

Now to the issue:

I have a simple example app using OpenApiValidator to validate requests and responses.

I am sending the request

http://localhost:3000/v1/progress?type=test

When I have the validateResponses flag set to false, my response is returned correctly (although not validated of course). However when I set validateResponses to true I get:

TypeError: Cannot read property 'then' of undefined
    at ServerResponse.json_async_hook (node_modules/express-openapi-validator/dist/middlewares/modded.express.mung.js:73:21)
    at app.ts:24:7
    at Layer.handle [as handle_request] (node_modules/express/lib/router/layer.js:95:5)
    at next (node_modules/express/lib/router/route.js:137:13)
    at Route.dispatch (node_modules/express/lib/router/route.js:112:3)
    at Layer.handle [as handle_request] (node_modules/express/lib/router/layer.js:95:5)
    at node_modules/express/lib/router/index.js:281:22
    at Function.process_params (node_modules/express/lib/router/index.js:335:12)
    at next (node_modules/express/lib/router/index.js:275:10)
    at node_modules/express-openapi-validator/dist/middlewares/modded.express.mung.js:94:17

Line 24 in my app.ts is pretty straightforward:

23 app.get('/v1/progress', function(req, res, next) {
24   res.json({id: 1, name: 'test'});
25 });

So I am trying to figure out if I mis-configured the project or if its existing issue.
I would really appreciate any feedback on how I can get this to work!

app.ts

const app = express();
app.use(express.json());
new OpenApiValidator({
  apiSpec: './workflow-tracker-openapi.yml',
  validateRequests: true,
  validateResponses: true,
}).install(app);

app.get('/v1/progress', function(req, res, next) {
  res.json({id: 1, name: 'test'});
});

const server = app.listen(3000);

yml spec

info:
  title: Example Service API
  version: '1.0'
servers:
  - url: http://localhost:3000/v1

paths:
  /progress:
    get:
      description: Get the progress of an event
      parameters:
        - name: type
          in: query
          required: true
          schema:
            type: string
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Progress'
          
components:
  schemas:
    Progress:
      properties:
        id:
          type: integer
          format: int64
        name:
          type: string
      required:
        - id
        - name

I really appreciate that you've made this library available and will keep digging through the source to see if I can fix it myself, but if you have any idea what might be wrong in the meantime, please let me know.

Thank you!

[cdimascio]

@SpencerLawrenceBrown thanks for the issue.
which version of express-openapi-validator are you using?

[spencerbn]

2.3.0

[spencerbn]

it seems to be related to how

try {
    fn(json, req, res)
} catch ...

is compiled to js. When its compiled it becomes:

 try {
                fn(json, req, res)
                    .then(json => {
                    if (res.headersSent)
                        return;
                    // If null, then 204 No Content
                    if (json === null)
                        return res.status(204).end();
                    // If munged scalar value, then text/plain
                    if (json !== originalJson && isScalar(json)) {
                        res.set('content-type', 'text/plain');
                        return res.send(String(json));
                    }
                    return original.call(this, json);
                })
                    .catch(e => mung.onError(e, req, res, next));
            }

[spencerbn]

^^ in modded.express.mung

[spencerbn]

I just downgraded to 2.1.5 and it works fine. Looks like a change between 2.1.5 and 2.3.0

[cdimascio]

Thanks @SpencerLawrenceBrown. I spotted the issue. It should be resolved in v2.3.1.