e2e room has no timeline (indexeddb full, error handling incomplete)

[turt2live]

Error from the console (repeated several times):

rageshake.js:66 Error decrypting event (id=$1527REDACTEDHbo:matrix.org): TypeError: Cannot read property 'message' of undefined
    at MegolmDecryption._callee4$ (megolm.js:638)
    at tryCatch (runtime.js:62)
    at Generator.invoke [as _invoke] (runtime.js:296)
    at Generator.prototype.(/develop/anonymous function) [as throw] (https://riot.im/develop/bundles/59c5a97589583c924c54/bundle.js:260369:22)
    at Generator.tryCatcher (util.js:16)
    at PromiseSpawn._promiseRejected (generators.js:107)
    at Promise._settlePromise (promise.js:576)
    at Promise._settlePromise0 (promise.js:614)
    at Promise._settlePromises (promise.js:689)
    at Async._drainQueue (async.js:133)
    at Async._drainQueues (async.js:143)
    at Async.drainQueues (async.js:17)
    at run (es6.promise.js:75)
    at es6.promise.js:92
    at MutationObserver.flush (_microtask.js:18)

[turt2live]

The megolm test room has a similar fate:

[dbkr]

Looks like something is throwing undefined here. If you open chrome dev tools and brea on exceptions, you may be able to see what's throwing it.

[turt2live]

Windows restarted, causing Riot to update/refresh. I've now lost the ability to reproduce this :(

Closing due to being unable to reproduce. Will re-open if it happens again.

[turt2live]

I got this again. The issue at hand is indexeddb being full, again: #6120

I'm reopening it as "please fix the error so it fails semi-gracefully". Previously, the messages would show up as "Cannot decrypt: encryption not enabled" (as per #6120), but blank is a new failure mode.

The particular code block throwing the exception is:

try {
        res = await this._olmDevice.decryptGroupMessage(
            event.getRoomId(), content.sender_key, content.session_id, content.ciphertext,
            event.getId(), event.getTs(),
        );
    } catch (e) {
        if (e.message === 'OLM.UNKNOWN_MESSAGE_INDEX') {
            this._requestKeysForEvent(event);
        }
        throw new base.DecryptionError(
            e.toString(), {
                session: content.sender_key + '|' + content.session_id,
            },
        );
    }

In particular, it's mad about e.message being used in the catch. As expected, e is in fact undefined.

[lukebarnard1]

The offending code (amongst other cases in indexeddb-crypto-store.js) is:
https://github.com/matrix-org/matrix-js-sdk/blob/master/src/crypto/store/indexeddb-crypto-store.js#L85-L87

MDN doesn't say anything about event.target.error but does claim that event.target.errorCode is a thing: https://developer.mozilla.org/en-US/docs/Web/API/IndexedDB_API/Using_IndexedDB