`retryOptions.retryableErrorFn` called with 200 ok for resumable upload

[benogle]

Environment details

• OS: node14.18.2-alpine3.12 (docker)
• Node.js version: 14.18.2
• npm version: 6.14.15
• @google-cloud/storage version: 5.18.3

Steps to reproduce

retryOptions.retryableErrorFn is often called with a plain object containing code: 200.

const storage = new Storage({
  retryOptions: {
    autoRetry: true,
    retryDelayMultiplier: 2,
    totalTimeout: 600,
    maxRetryDelay: 60,
    maxRetries: 10,
    idempotencyStrategy: IdempotencyStrategy.RetryAlways,
    retryableErrorFn: (err) => {
      console.log(err)

      // !!
      // err is often a plain object:
      // { code: 200, message: 'OK', name: 'OK' }

      return true
    },
  },
})
const cloudFile = storage.bucket('our-bucket').file('somename.zip')
const result = await cloudFile.save(buffer, {
  // `resumable: true` seems to be the key to triggering this.
  // We only set `resumable: true` with files > 10mb.
  resumable: true,

  gzip: true,
  metadata: {
    cacheControl: 'no-cache',
  },
  predefinedAcl: 'projectPrivate',
})

If we ignore the 200s in retryableErrorFn, cloudFile.save ultimately succeeds, but it took a while for us to discover we could safely ignore them as we could only reproduce this in production. retryableErrorFn is called in the upload stream's error event, obviously extremely confusing that it's called with a code 200.

If we retry the 200s, it retries until it eventually fails with:

The offset is lower than the number of bytes written. The server has 0 bytes and while XXXX bytes has been uploaded - thus XXXX bytes are missing. Stopping as this could result in data loss. Initiate a new upload to continue.

[shaffeeullah]

Hi @benogle ,

This is happening here

nodejs-storage/src/gcs-resumable-upload.ts

Lines 1014 to 1031 in 72f7992

	/**
	* @return {bool} is the request good?
	*/
	private onResponse(resp: GaxiosResponse) {
	if (
	this.retryOptions.retryableErrorFn!({
	code: resp.status,
	message: resp.statusText,
	name: resp.statusText,
	})
	) {
	this.attemptDelayedRetry(resp);
	return false;
	}
	this.emit('response', resp);
	return true;
	}

We check all responses and if the retry function returns true, we retry the request. I've confirmed that for the default retry function, the 200 response is not retried.

nodejs-storage/src/storage.ts

Lines 258 to 285 in 72f7992

	/**
	* Returns true if the API request should be retried, given the error that was
	* given the first time the request was attempted.
	* @const
	* @param {error} err - The API error to check if it is appropriate to retry.
	* @return {boolean} True if the API request should be retried, false otherwise.
	*/
	export const RETRYABLE_ERR_FN_DEFAULT = function (err?: ApiError) {
	if (err) {
	if ([408, 429, 500, 502, 503, 504].indexOf(err.code!) !== -1) {
	return true;
	}
	if (err.errors) {
	for (const e of err.errors) {
	const reason = e?.reason?.toString().toLowerCase();
	if (
	(reason && reason.includes('eai_again')) || //DNS lookup error
	reason === 'econnreset' ||
	reason === 'unexpected connection closure'
	) {
	return true;
	}
	}
	}
	}
	return false;
	};

The custom function you've passed in here returns true for every type of response, so it will keep attempting to retry the request. Since 200 is a success response, it should never be retried. Is there a reason you're passing in a custom function instead of using the default?

[benogle]

Since 200 is a success response, it should never be retried.

Right, this is the issue. It feels like the retry function shouldn't be called at all for success responses, and it isn't when resumable: false, which added to the confusion when we started seeing these in the logs. Everything around this indicates it will be called on errors only, the function name, function arg type, etc.

Is there a reason you're passing in a custom function instead of using the default?

Basically to track when it is retrying, what errors it's retrying, and to ensure it did actually retry if the upload results in an error.

For more context, Google storage has been pretty unreliable on upload for us lately. We've been getting a number of 502s and 408s that come out as promise rejections / errors. We had the default retry configuration, but it was unclear if the lib was actually retrying the uploads. After digging into the code, it looks like you possibly need to specify a generation-related param or two to get the lib to actually retry with the default IdempotencyStrategy.RetryConditional. We weren't totally clear how that worked, and it's tough to repeatably test this against a real failure, so we set the strategy to RetryAlways and added the function to log retries for traceability.

[shaffeeullah]

I understand that this can be confusing. Thank you for calling it out and explaining a little bit. I've opened a PR that will prevent an accidental retry of a 200 response.

As for IdempotencyStrategy, the default behavior prevents data corruption by only retrying operations that are idempotent. An upload without a generation number is not idempotent. Retrying this operation could result in data corruption. For more information on preconditions, see the request preconditions documentation page. For more information on which operations are idempotent, see the retry strategy documentation page.