Propagate framework errors to user application

[gregorygaines]

Currently, errors that happen in the framework express layer are passed to the default express error handler. The default error handler returns the error to the client with a stack trace if in non-prod enviornments. It would be useful for certain cases for the user to have context of what happened during a request instead of the user being bypassed entirely. Instead, if the user has an error handler middleware installed in their application, we should pass the framework error to the user's error handler.

For example, if the framework gets a request with a bad json body.

const app = express():

app.post("/", (req, res) => {
 ...
});

// User error handler
app.use((err, req, res, next) => {
  logger.log(err);
  res.send("Caught error!");
});

functions.http("function, app);

// Post request with bad JSON
http.post("/", "{"id": "Hello}");

The framework responds with the following not very helpful message from the Express default error handler:

SyntaxError: Expected double-quoted property name in JSON at position 20 (line 3 column 1)
    at JSON.parse (<anonymous>)
    at parse (functions-framework-nodejs/node_modules/body-parser/lib/types/json.js:92:19)
    at functions-framework-nodejs/node_modules/body-parser/lib/read.js:128:18
    at AsyncResource.runInAsyncScope (node:async_hooks:211:14)
    at invokeCallback (functions-framework-nodejs/node_modules/raw-body/index.js:238:16)
    at done (functions-framework-nodejs/node_modules/raw-body/index.js:227:7)
    at IncomingMessage.onEnd (functions-framework-nodejs/node_modules/raw-body/index.js:287:7)
    at IncomingMessage.emit (node:events:518:28)
    at endReadableNT (node:internal/streams/readable:1698:12)
    at process.processTicksAndRejections (node:internal/process/task_queues:90:21)

There should be an option to propagate errors to the user client applcation, so their error handler is triggered and can preform logging, mitigations, or any other action the user wants instead of ignoring and leaving their application in the dust.

I've created #685 to address this issue.

[chatelgu]

Hi,

Facing the same issue : I need to handle json parsing errors in the way the specs I implement specify it.

Maybe, it would be easier just to have a way to deactivate the json parsing inside the framework and let the function code (express style) parse the body and handle potential errors.

Something like --disableMiddleware so in the server.js ligne 90, we can have :

  // Apply middleware
  if (options.disableMiddleware !== true) {
    app.use(bodyParser.json(cloudEventsBodySavingOptions));
    app.use(bodyParser.json(defaultBodySavingOptions));
    app.use(bodyParser.text(defaultBodySavingOptions));
    app.use(bodyParser.urlencoded(urlEncodedOptions));
  }

Is it something that can suit you @gregorygaines ?

Question to @jihuin, waiting for a integration, is it possible to deploy a function with a custom functions-framework-nodejs ?

[gregorygaines]

Let me think more on this. In my case, if I pass an error handler to my application its only triggered through certain situtations but not all since the parent application installs its own error handler. Let me see if your solution works.