Download file from Azure Blob Storage hangs when retrieving final 1-2 blocks about azure-functions-nodejs-worker HOT 7 CLOSED

No problem, glad you got it figured out!

There's some known issues around the timing/ordering of context.log. The host team made some changes recently to address this, but it'll be slow to roll out. The fix may or may not have helped in your case
Azure/azure-functions-nodejs-library#191
Azure/azure-functions-host#9238

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I wanted to add this as a separate comment rather than detract from the original, but I did notice this very odd bit of behavior. If I throw an error immediately after the file download, it looks like the file download completes in a reasonable amount of time:

  const fileBuffer = await blobClient.downloadToBuffer(0, undefined, {
    blockSize: Math.pow(2, 10) * 256,
    onProgress: function ({ loadedBytes }) {
      context.log(`progress! ${loadedBytes} of ${contentLength}`);
    },
  });
  throw new Error('blah');

This logs to the console:

[2024-01-19T22:39:25.925Z] progress! 262144 of 1311223
[2024-01-19T22:39:25.936Z] progress! 524288 of 1311223
[2024-01-19T22:39:25.938Z] progress! 524791 of 1311223
[2024-01-19T22:39:25.944Z] progress! 786935 of 1311223
[2024-01-19T22:39:25.952Z] progress! 1049079 of 1311223
[2024-01-19T22:39:25.961Z] progress! 1311223 of 1311223
[2024-01-19T22:39:25.961Z] Error: blah

Note the timestamps --- there is very little delay between retrieving all of the blocks. The whole download completes in ~36ms. Of course, throwing an error does me no good as it fails my function execution. Swallowing the error in a try/catch just reproduces the original behavior

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What version of @azure/storage-blob are you using? That being said, it's weird to me that it fails when you send an http.get request without even using the @azure/storage-blob package. That indicates the package theoretically isn't the problem

Could you share the files you're using to test? I'm curious if there's anything weird/unique about them. I used the command mkfile -n 2m 2m to make a 2mb file (not json though) and your code worked just fine for me locally.

from azure-functions-nodejs-worker.

Hi @ejizba,

We're using @azure/storage-blob ^12.17.0 which I believe is the latest version currently. But like you said, it doesn't appear to be related to that package considering a standard http get request hangs in the same way.

Here is a sample ~2mb file that I am having trouble downloading
Here is a sample 1.3mb file that I can download, but only after a 3.5 minute hang

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Also confirming I tried mkfile -n 2m 2m to generate a file, and I am able to download the file successfully without any hanging.

from azure-functions-nodejs-worker.

The sample file worked fine for me 🤷‍♂️. Maybe it's something unique about your storage account? You could try a fresh new storage account if you think that could be contributing

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@ejizba sorry for bothering you with this. I determined the root cause was in our function app code. After downloading from blob storage, we had a bit of poorly performing code that was taking a long time to operate on the downloaded blob.

It looked like the blob was never finished downloading because I couldn't log the progress to 100%, but it appears that has something to do with using context.log before a long and resource-intensive process is occurring? If I switched to console.log I could see that my code was still executing and stuck in a long-running loop. Fixed the long-running loop and the download appears to complete as it should! It also explains why throwing an error after download appeared to finish the download -- the function execution would complete before my long-running loop could start.

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