Add CryptoApi.encryptToDeviceMessages() and deprecate Crypto.encryptAndSendToDevices()

[hughns]

Fixes #3304

• Adds CryptoApi.encryptToDeviceMessages with rust and libolm implementations.
• Deprecates Crypto.encryptAndSendToDevices.

Depends on matrix-org/matrix-rust-sdk-crypto-wasm#140 and #4396

Checklist

• Tests written for new code (and old code if feasible).
• New or updated public/exported symbols have accurate TSDoc documentation.
• Linter and other CI checks pass.
• Sign-off given on the changes (see CONTRIBUTING.md).

[richvdh]

looks like the right general direction to me

[richvdh]

BTW it looks like the description in the PR is a bit outdated -- could you give it a refresh?

[hughns]

@richvdh I've had a go at adding an integration test in a87a29f.

However, whilst it passes on libolm it doesn't pass on rust SDK. It appears that getMissingSessions() is always returning null. Any idea what might be happening or missing?

[richvdh]

It appears that getMissingSessions() is always returning null. Any idea what might be happening or missing?

Well, that means that there are Olm Sessions already established for all the devices that the rust layer knows about. In this case, it probably means that the rust layer doesn't know about any of the target user's devices.

We only fetch the device list when we are told by the homeserver that our cached device list for a given user might be outdated. And that only happens if we share at least one room with the offending user. (Is that likely to be a problem in practice, for this application?)

Try something like:

        const syncResponder = new SyncResponder(homeserverUrl);
        syncResponder.sendOrQueueSyncResponse(getSyncResponse([testData.BOB_TEST_USER_ID]));
        await syncPromise(aliceClient);

I think that will probably do the job, though you might have to do something else to trigger the /keys/query request. (As long as there is a /keys/query request pending, getMissingSessions should block until it happens.)

[hughns]

Thanks, @richvdh. I think this is now ready for re-review.

[richvdh]

LGTM