Detect permission state of Local Network Access setting

[tresf]

Upstream question:

• Detect permission state WICG/local-network-access#69

We need a way to programmatically detect the presence of the Local Network Access (LNA) setting to better inform users when it's preventing a connection from succeeding.

navigator.permissions.query({ name: 'local-network-access'})
    .then(result => console.log("LNA permission state: ", result))
    .catch(err => console.error(err));

Firefox 147 Nightly:

TypeError: 'local-network-access' (value of 'name' member of PermissionDescriptor) is not a valid value for enumeration PermissionName.
    <anonymous> debugger eval code:1

Safari 18.6:

TypeError: Type error

TODO:

• Find a way to detect this reliably and add to qz-tray.js.

[tresf]

O.M.G. why can't we have usable APIs... 🤢🤢

[...] I would recommend against exposing more information in permissions.query(). It's a fingerprinting vector, and an API that's mostly been troublesome for Firefox (websites that use it tend to design around Chrome's persisted permission models which ends up creating slow lanes for Firefox users).

So is our only option is elaborate try/catch with inference around exception type?

[tresf]

    navigator.permissions.query({ name: 'local-network-access'})
    .then(result => console.log("LNA permission state: ", result))
    .catch(err => {
        if(err instanceof TypeError) {
            console.log("Permission 'local-network-access' is not supported by this browser")
        } else {
            throw err;
        }
    });

(We'll need much more guarding to detect of permissions are even supported, if we're in a browser, etc).

[tresf]

Note we can register the onchange event to attempt to reconnect.