Grain events

[synchrone]

Sometimes apps would like to get notified about user actions done in sandstorm.
For example, user changing the grain name.

I would like to propose a way for web apps in grains to register for updates:

window.parent.postMessage({subscribeToEvents:['grainNameUpdate']}, "*");

and then get notified when the user changes it:

window.addEventListener("message", function(e) {
    if(e.data.sandstormEventName == 'grainNameUpdate'){
         var newName = e.data.grainName;
         // to what the app needs
    }
});

The same mechanism can be used to have the apps subscribe for other user-generated web events, like: app permissions changed, access token revoked, user name changed, grain list collapsed, etc.

[synchrone]

Relates to synchrone/sandstorm-radicale#14

[kentonv]

Seems reasonable. Note that there's a funny property of grain titles right now in that each person to whom the grain is shared can potentially set their own title which only they see. See #1087. So this is kind of unexpectedly complicated.

[mitar]

Hm, it might be that app misses such an event. It would be great if server-side could ask Sandstorm for current state if it feels it is behind.

Furthermore, I think it would be better if events would go to the server-side, not client-side. Client-side is still not trusted.

[synchrone]

Currently the only way an app can "ask" about anything is via window.parent.postMessage and get a response via message listeners, checking the same "code" was returned.

Server-side communication is currently harder to handle. App devs need to use captn-proto bindings to their language, or engage in exec()ing custom-built binaries due to lack thereof.

This whole grain communication kind of needs to be rethinked, cause currently it feels we're trying to re-purpose a mechanism not intended for doing this.

[mitar]

At least for Meteor apps: maybe Meteor app could just create a server-side DDP connection to some Sandstorm endpoint and get those events?

[paulproteus]

Hi all,

Another way to think about this is that the UiView capnproto interface could grow methods that Sandstorm would call to notify it of changes. Then sandstorm-http-bridge would be responsible for passing those into apps. One way to do so is over Meteor/DDP as @mitar suggests. Another is over a HTTP POST.