Dropbox's `filesGetTemporaryLink` throws an uncatchable `UnhandledPromiseRejectionWarning` and terminates Node.js

Question

To get a download link to the file hosted on Dropbox, I'm using a Dropbox JavaScript API (7.0.0):

export const fileDownload = async function fileDownload(fileUUID) {

    let isSucceeded;
    let message;
    let file;
    const dbx = _dropboxFactory();

    try {
        const operationResult = await dbx.filesGetTemporaryLink({
            path: `/${CONFIG_STORAGE.uploader.assetsPath}/${fileUUID}`
        });

        if ("OK" === http.STATUS_CODES[operationResult.status].toUpperCase()) {

            file = Object.freeze({
                length: operationResult?.result?.metadata?.size,
                link: operationResult?.result?.link,
                mime: mime.lookup(operationResult?.result?.metadata?.name),
                name: operationResult?.result?.metadata?.name
            });
            isSucceeded = true;
            message = SYS_MESSAGES.storageFileDownloadSucceeded.code;

        } else {
            isSucceeded = false;
            message = SYS_MESSAGES.storageFileDownloadFailed.code;
        }
    } catch (err) {
        file = "error";
        isSucceeded = false;
        message = "FIL_NOT_FOUND";
    }

    const downloadResult = Object.freeze({
        file,
        isSucceeded,
        message
    });

    return downloadResult;

};

The problem is that when the path to the file is wrong, I get a Node.js exception:

(node:9156) UnhandledPromiseRejectionWarning: #<Object>

(node:9156) 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(). To terminate the node process on unhandled promise rejection, use the CLI flag --unhandled-rejections=strict (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 2)

(node:9156) [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.

I've tested several options and came to conclusion that the issue is in:

const operationResult = await dbx.filesGetTemporaryLink({
    path: `/${CONFIG_STORAGE.uploader.assetsPath}/${fileUUID}`
});

My questions:

Why does Node.js claim «unhandled promise rejection» or «promise which was not handled with .catch()» and throws an UnhandledPromiseRejectionWarning exception if the code, which generates it is wrapped by try-catch?
Starting Node.js 15.x.x, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code. Therefore, how to avoid UnhandledPromiseRejectionWarning?

A temporal workaround:

To run Node.js with a flag --unhandled-rejections=warn.
This will prevent the termination of the Node.js process with a non-zero exit code upon UnhandledPromiseRejectionWarning.

you wouldn't await on the server response. You are maybe getting mixed up with `fetch` json response, which you would `await` — Rezaa91, Oct 08 '20 at 20:26
@Rezaa91, I've investigated the case and adjusted the question according to my findings. — Mike, Oct 10 '20 at 14:28
_handleFileOperationException in your catch handler has no handler if it results in an exception, if it's actually something `await`able. Is it possible that's where the actual unhandled exception is coming from? — Joe, Oct 10 '20 at 14:35
@Joe, I've completely removed `_handleFileOperationException` but the problem still persists. I've simplified the code snippet. — Mike, Oct 10 '20 at 14:40

Mike · Accepted Answer · 2020-10-13T06:08:58.547

1

The problem was in the Dropbox library and has been solved by the Dropbox team with the release of 7.1.0. After upgrading the code in the question works correctly.

edited Oct 13 '20 at 06:08

answered Oct 12 '20 at 23:22

Mike

14,010
29
101
161

score 0 · Answer 2 · edited Oct 11 '20 at 08:51

0

try changing your fileResponse function to something like this. You are mixing up async/await with .then().catch() style syntax.

Just wrap your function in a try-catch

async function getDocument() {
  try {
    const response = await fetch(`${http() + ip}/downloadDocument`, {
      body: JSON.stringify({fileUUID: oModel.oData[0].documentFile}),
      cache: "no-cache",
      credentials: "same-origin",
      headers: {
        "Content-Type": "application/json"
      },
      method: "POST",
      mode: "cors"
    });

    const data = await response.json();
    
    return data;
  } catch(err) {
    console.log(err);
  }
}

edited Oct 11 '20 at 08:51

Mike

14,010
29
101
161

answered Oct 08 '20 at 20:35

Rezaa91

500
2
10

I've rollbacked a code snippet to my initial code version, which is actually very similar to your. But still the problem persists. – Mike Oct 08 '20 at 20:46
Cheers, and is that try...catch wrapped in an async function too? – Rezaa91 Oct 08 '20 at 20:49

Dropbox's `filesGetTemporaryLink` throws an uncatchable `UnhandledPromiseRejectionWarning` and terminates Node.js

A temporal workaround:

2 Answers2