Unhandled Promise Rejection

[michielbdejong]

I edited the example from the readme to wrap https://github.com/RubenVerborgh/LDflex#looking-up-data-on-the-web in a try-catch, and change the domain name to a non-existing one ending in .orgz:

const { PathFactory } = require('ldflex');
const { default: ComunicaEngine } = require('ldflex-comunica');
const { namedNode } = require('@rdfjs/data-model');

const profileDoc = 'https://ruben.verborgh.orgz/profile/';
const webId = `${profileDoc}#me`;

// The JSON-LD context for resolving properties
const context = {
  "@context": {
    "@vocab": "http://xmlns.com/foaf/0.1/",
    "friends": "knows",
    "label": "http://www.w3.org/2000/01/rdf-schema#label",
  }
};
// The query engine and its source
const queryEngine = new ComunicaEngine(profileDoc);
// The object that can create new paths
const path = new PathFactory({ context, queryEngine });

async function showPerson(person) {
  console.log(`This person is ${await person.name}`);

  console.log(`${await person.givenName} is interested in:`);
  for await (const name of person.interest.label)
    console.log(`- ${name}`);

  console.log(`${await person.givenName} is friends with:`);
  for await (const name of person.friends.givenName)
    console.log(`- ${name}`);
}


(async () => {
  try {
    const ruben = path.create({ subject: namedNode(webId) });
    await showPerson(ruben);
  } catch(e) {
    console.error(e);
  }
  console.log('success');
})();

The result is as follows:

(node:3188) UnhandledPromiseRejectionWarning: FetchError: request to https://ruben.verborgh.orgz/profile/ failed, reason: getaddrinfo ENOTFOUND ruben.verborgh.orgz
    at ClientRequest.<anonymous> (/Users/michiel/gh/solid/query-ldflex/node_modules/node-fetch/index.js:133:11)
    at ClientRequest.emit (events.js:203:13)
    at TLSSocket.socketErrorListener (_http_client.js:399:9)
    at TLSSocket.emit (events.js:203:13)
    at emitErrorNT (internal/streams/destroy.js:91:8)
    at emitErrorAndCloseNT (internal/streams/destroy.js:59:3)
    at processTicksAndRejections (internal/process/task_queues.js:77:11)
(node:3188) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 8)
(node:3188) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
(node:3188) PromiseRejectionHandledWarning: Promise rejection was handled asynchronously (rejection id: 8)
(node:3188) UnhandledPromiseRejectionWarning: FetchError: request to https://ruben.verborgh.orgz/profile/ failed, reason: getaddrinfo ENOTFOUND ruben.verborgh.orgz
    at ClientRequest.<anonymous> (/Users/michiel/gh/solid/query-ldflex/node_modules/node-fetch/index.js:133:11)
    at ClientRequest.emit (events.js:203:13)
    at TLSSocket.socketErrorListener (_http_client.js:399:9)
    at TLSSocket.emit (events.js:203:13)
    at emitErrorNT (internal/streams/destroy.js:91:8)
    at emitErrorAndCloseNT (internal/streams/destroy.js:59:3)
    at processTicksAndRejections (internal/process/task_queues.js:77:11)
(node:3188) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 9)

Am I doing something wrong? Could this be related to LDflex/Query-Solid#30 ?
This code works correctly when you change 'rubenverborgh.orgz' back to 'rubenverborgh.org'.

[RubenVerborgh]

Am I doing something wrong?

Nope, LDflex does 🙂 Thanks for the testcase.

[michielbdejong]

OK! I'm diving in to fix this. The code is quite hard to read for me so far, but making progress. https://github.com/RubenVerborgh/LDflex/blob/master/src/defaultHandlers.js#L25 seems to be what is adding the Promise behaviour, so maybe that gives me a route to where I can add some error handling for this.

[RubenVerborgh]

My suspicion is that the error will actually be down in Comunica (given that Comunica is the one doing the fetching, and that we are not getting back a Comunica error). It might be this module: https://github.com/comunica/actor-http-solid-auth-fetch

[RubenVerborgh]

Upon closer inspection, this issue is indeed a duplicate of LDflex/Query-Solid#30. The root cause is comunica/comunica#565.

[rubensworks]

Should be fixed in Comunica 1.14.0