Synchronizes database events between multiple clients

[kettanaito]

GitHub

• Relates to Persistency layer #49

Changes

• Adds a synchronization middleware that syncs database events (create/update/delete) between multiple open tabs.
• Each Database instance (internal) now has a unique reproducible MD5 hash to identify this instance among multiple database instances. This way a single broadcast channel applies events to proper databases based on the database ID of the source event.
  • MD5 hash is generated based on the following data:
    • Database invocation order.
    • Database invocation location (a stack trace to where factory() is called. Factory creates an internal Database instance).

Motivation

Client-side sync allows the database to feel like an actual external database you're working with, as its updates you provision in one tab are synced with the other tabs as if they are requesting the same database. In reality, each tab has its own runtime and creates its own database from a clean slate.

Roadmap

• Ensure that multiple db instances sync their updates independently.

[kettanaito]

I'm using an invocation order and database location to identify a single database instance.
The order of factory() calls is unlikely to change on runtime. Two first-created databases across clients aren't necessarily the same instances, as each client may load a different module, while the same BroadcastChannel controls the entire host. To account for that, I'm adding a module location to the hash salt.

Two database instances on multiple pages are equal if:

1. They were called in the same order.
2. They were created in the same module.

[kettanaito]

Ignoring unrelated events

It's possible to have multiple factory() calls (and thus, Database instances) on a single page. The sync extension should understand that db has issued an update, and apply that update to the respective db in another client. This comes down to two possible solutions:

1. Create a unique BroadcastChannel per db instance.
2. Assign a unique reproducible ID to each db instance.

Unfortunately, BroadcastChannel is applied to the entire host and is discerned by channel name, not reference. Even if each db creates its own channel, it must still assign it a unique name, which is, effectively, a unique ID.

[marcosvega91]

it looks very good :) nice 💯