web installer should _wrapReq and return promise for idb transaction in saveFile

[turbocrime]

problem

the installer page's BlobStore.download function awaits the return of async function BlobStore.saveFile,

grapheneos.org/static/js/web-install.js

Line 144 in 3547d7c

await this.saveFile(filename, blob);

but saveFile performs no async operation:

grapheneos.org/static/js/web-install.js

Lines 115 to 120 in 3547d7c

	async saveFile(name, blob) {
	this.db.transaction(["files"], "readwrite").objectStore("files").add({
	name: name,
	blob: blob,
	});
	}

analysis

other locations using idb use the BlobStore._wrapReq helper to promisify transaction results, but saveFile does not use this helper.

so, saveFile effectively performs the synchronous operation of creating the transaction, and then returns immediately. this means the success or failure of this transaction does not resolve before return, and the download function proceeds with execution immediately regardless of the transaction state. the download function will proceed despite a transaction that is still pending or has failed.

specifically, if the saveFile transaction fails, the failure is not reported to the user or logged to the console. in this case, the web installer indicates a successful download of the factory image. the next step to flash the factory image will fail to retrieve the blob and instruct the user to download the factory image (which may fail again).

in my case, this was caused by a configuration to restrict all sites from storing data.

fix

use _wrapReq in saveFile so that download may await the resolution of the transaction as seems to be intended. this would surface failures, and actually await completion of the saving transaction.

suggestions

these additional things may be nice to have:

• in the case of a QuotaExceededError, prompt the user to configure the appropriate site permission.
• configure eslint rule require-await https://eslint.org/docs/latest/rules/require-await
• use an eslint plugin to disallow floating promises
  • https://www.npmjs.com/package/eslint-plugin-no-floating-promise
  • https://typescript-eslint.io/rules/no-floating-promises/
• possibly, avoid storing the blob in idb.
  • it may be held in-memory, as it must be anyways to perform flashing operations.
  • alternatively, it may be downloaded as a file, and then accessed via file selection dialog.