Error: Callback was already called. du to race condition

[pixelshot91]

Have you checked that the bug is not already fixed?

Yes

Summary

markdown-link-check crashes somewhat randomly with Error: Callback was already called.

Affected version

3.13.7, commit b88c7e6

Steps to reproduce the bug

It seems it check the same link twice, calling a callback create by onlyOnce twice, causing a crash

Minimal example below:
For privacy reason, I cannot disclose the exact links, but they return a 200 statusCode.
I was not able to find a public link pairs that triggered the crash.

dir1/index.md

<https://link1.com>

dir2/index.md:

<https://link2.com>

$ docker run -it -v $HOME/dummy_doc/:/tmp:ro $(docker build -q .) --verbose /tmp/

FILE: /tmp/dir1/index.md
ERROR: XXX null LinkCheckResult {
  link: 'https://link1.com',
  statusCode: 200,
  err: null,
  status: 'alive'
}
  [✓] https://link1.com → Status: 200

  1 links checked.

FILE: /tmp/dir2/index.md
ERROR: XXX null LinkCheckResult {
  link: 'https://link1.com',
  statusCode: 200,
  err: null,
  status: 'alive'
}
/src/node_modules/async/dist/async.js:325
            if (fn === null) throw new Error("Callback was already called.");
                             ^

Error: Callback was already called.
    at /src/node_modules/async/dist/async.js:325:36
    at /src/node_modules/async/dist/async.js:249:17
    at /src/index.js:214:13
    at /src/node_modules/link-check/lib/proto/http.js:119:21
    at done (/src/node_modules/needle/lib/needle.js:474:14)
    at PassThrough.<anonymous> (/src/node_modules/needle/lib/needle.js:734:9)
    at PassThrough.emit (node:events:519:35)
    at endReadableNT (node:internal/streams/readable:1701:12)
    at process.processTicksAndRejections (node:internal/process/task_queues:90:21)

The error log comes from this line I added:

diff --git a/index.js b/index.js
index 167e9d4..5687ec2 100644
--- a/index.js
+++ b/index.js
@@ -209,6 +209,8 @@ module.exports = function markdownLinkCheck(markdown, opts, callback) {
                 result.status = 'error'; // custom status for errored links
             }
 
+            console.error("ERROR: XXX %s", err, result);
+
             callback(null, result);
         });
     }, callback);

Note that markdown-link-check believe the dir2/index.md contain a link to link1.com, which is false.
In other runs, markdown-link-check believed dir2/index.md contained the two links

To me it looks like a race condition

The problem only appear for some links

It is probably linked to: #222

Expected behavior

It should not crash and don't mix up links

Actual behavior

Additional context

No response

Can you fix it?

Yes

[github-actions]

This issue has been marked as stale because it has been open 60 days with no activity. It will be closed in 90 days unless the stale label is removed or someone adds a comment.

[cristiklein]

I believe I just hit this with version 3.14.1:

Markdown Link Check.....................................................................Failed
- hook id: markdown-link-check
- exit code: 1

/home/cklein/.cache/pre-commit/repon5a1wdl_/node_env-system/lib/node_modules/markdown-link-check/node_modules/async/dist/async.js:325
            if (fn === null) throw new Error("Callback was already called.");
                             ^

Error: Callback was already called.
    at /home/cklein/.cache/pre-commit/repon5a1wdl_/node_env-system/lib/node_modules/markdown-link-check/node_modules/async/dist/async.js:325:36
    at /home/cklein/.cache/pre-commit/repon5a1wdl_/node_env-system/lib/node_modules/markdown-link-check/node_modules/async/dist/async.js:249:17
    at /home/cklein/.cache/pre-commit/repon5a1wdl_/node_env-system/lib/node_modules/markdown-link-check/index.js:212:13
    at /home/cklein/.cache/pre-commit/repon5a1wdl_/node_env-system/lib/node_modules/markdown-link-check/node_modules/link-check/lib/proto/http.js:119:21
    at done (/home/cklein/.cache/pre-commit/repon5a1wdl_/node_env-system/lib/node_modules/markdown-link-check/node_modules/needle/lib/needle.js:474:14)
    at PassThrough.<anonymous> (/home/cklein/.cache/pre-commit/repon5a1wdl_/node_env-system/lib/node_modules/markdown-link-check/node_modules/needle/lib/needle.js:734:9)
    at PassThrough.emit (node:events:531:35)
    at endReadableNT (node:internal/streams/readable:1698:12)
    at process.processTicksAndRejections (node:internal/process/task_queues:90:21)

Node.js v22.21.0

[BaseMax]

I believe I just hit this with version 3.14.1

Thanks for reporting this. Do you have the ability to fix it by submitting a PR? We will review and merge it soon.
Best regards.

[cristiklein]

Hi. Thanks for the quick answer. I haven't yet managed to understand the issue. However, I managed to come up with a minimum viable example:

<https://imy.se>                                                          
<https://www.google.com/> 
<https://www.imy.se/>    

The first URL returns 302 FOUND and Location: https://www.imy.se/. That seems to be key to triggering this error.

I tried to add some console.log() in index.js, but don't quite understand which callback is called twice and why.

Any helpful pointers?

[cristiklein]

Thanks @BaseMax for the encouragement! I believe I found it: #540

[BaseMax]

Close - from #540

[BaseMax]

Please double check it and in case of any problem re-open it again.
@pixelshot91

Thanks.