element-web/docs/settings.md

Settings Reference

This document serves as developer documentation for using "Granular Settings". Granular Settings allow users to specify different values for a setting at particular levels of interest. For example, a user may say that in a particular room they want URL previews off, but in all other rooms they want them enabled. The SettingsStore helps mask the complexity of dealing with the different levels and exposes easy to use getters and setters.

Levels

Granular Settings rely on a series of known levels in order to use the correct value for the scenario. These levels, in order of priority, are:

• device - The current user's device
• room-device - The current user's device, but only when in a specific room
• room-account - The current user's account, but only when in a specific room
• account - The current user's account
• room - A specific room (setting for all members of the room)
• config - Values are defined by the setting_defaults key (usually) in config.json
• default - The hardcoded default for the settings

Individual settings may control which levels are appropriate for them as part of the defaults. This is often to ensure that room administrators cannot force account-only settings upon participants.

Settings

Settings are the different options a user may set or experience in the application. These are pre-defined in src/settings/Settings.tsx under the SETTINGS constant, and match the ISetting interface as defined there.

Settings that support the config level can be set in the config file under the setting_defaults key (note that some settings, like the "theme" setting, are special cased in the config file):

{
  ...
  "setting_defaults": {
    "settingName": true
  },
  ...
}

Getting values for a setting

After importing SettingsStore, simply make a call to SettingsStore.getValue. The roomId parameter should always be supplied where possible, even if the setting does not have a per-room level value. This is to ensure that the value returned is best represented in the room, particularly if the setting ever gets a per-room level in the future.

In settings pages it is often desired to have the value at a particular level instead of getting the calculated value. Call SettingsStore.getValueAt to get the value of a setting at a particular level, and optionally make it explicitly at that level. By default getValueAt will traverse the tree starting at the provided level; making it explicit means it will not go beyond the provided level. When using getValueAt, please be sure to use SettingLevel to represent the target level.

Setting values for a setting

Values are defined at particular levels and should be done in a safe manner. There are two checks to perform to ensure a clean save: is the level supported and can the user actually set the value. In most cases, neither should be an issue although there are circumstances where this changes. An example of a safe call is:

const isSupported = SettingsStore.isLevelSupported(SettingLevel.ROOM);
if (isSupported) {
  const canSetValue = SettingsStore.canSetValue("mySetting", "!curbf:matrix.org", SettingLevel.ROOM);
  if (canSetValue) {
    SettingsStore.setValue("mySetting", "!curbf:matrix.org", SettingLevel.ROOM, newValue);
  }
}

These checks may also be performed in different areas of the application to avoid the verbose example above. For instance, the component which allows changing the setting may be hidden conditionally on the above conditions.

SettingsFlag component

Where possible, the SettingsFlag component should be used to set simple "flip-a-bit" (true/false) settings. The SettingsFlag also supports simple radio button options, such as the theme the user would like to use.

<SettingsFlag name="theSettingId"
              level={SettingsLevel.ROOM}
              roomId="!curbf:matrix.org"
              label={_td("Your label here")} // optional, if falsey then the `SettingsStore` will be used
              onChange={function(newValue) { }} // optional, called after saving
              isExplicit={false} // this is passed along to `SettingsStore.getValueAt`, defaulting to false
              manualSave={false} // if true, saving is delayed. You will need to call .save() on this component

              // Options for radio buttons
              group="your-radio-group" // this enables radio button support
              value="yourValueHere" // the value for this particular option
/>

Getting the display name for a setting

Simply call SettingsStore.getDisplayName. The appropriate display name will be returned and automatically translated for you. If a display name cannot be found, it will return null.

Features

Feature flags are just like regular settings with some underlying semantics for how they are meant to be used. Usually a feature flag is used when a portion of the application is under development or not ready for full release yet, such as new functionality or experimental ideas. In these cases, the feature name should be named with the feature_* convention and must be tagged with isFeature: true in the setting definition. By doing so, the feature will automatically appear in the "labs" section of the user's settings.

Features can be controlled at the config level using the following structure:

"features": {
  "feature_lazyloading": true
}

When true, the user will see the feature as enabled. Similarly, when false the user will see the feature as disabled. The user will only be able to change/see these states if show_labs_settings: true is in the config.

Determining if a feature is enabled

Call SettingsStore.getValue() as you would for any other setting.

Enabling a feature

Call SettingsStore.setValue("feature_name", null, SettingLevel.DEVICE, true).

A note on UI features

UI features are a different concept to plain features. Instead of being representative of unstable or unpredicatable behaviour, they are logical chunks of UI which can be disabled by deployments for ease of understanding with users. They are simply represented as boring settings with a convention of being named as UIFeature.$location where $location is a rough descriptor of what is toggled, such as URLPreviews or Communities.

UI features also tend to have their own setting controller (see below) to manipulate settings which might be affected by the UI feature being disabled. For example, if URL previews are disabled as a UI feature then the URL preview options will use the UIFeatureController to ensure they remain disabled while the UI feature is disabled.

Setting controllers

Settings may have environmental factors that affect their value or need additional code to be called when they are modified. A setting controller is able to override the calculated value for a setting and react to changes in that setting. Controllers are not a replacement for the level handlers and should only be used to ensure the environment is kept up to date with the setting where it is otherwise not possible. An example of this is the notification settings: they can only be considered enabled if the platform supports notifications, and enabling notifications requires additional steps to actually enable notifications.

For more information, see src/settings/controllers/SettingController.ts.

Local echo

SettingsStore will perform local echo on all settings to ensure that immediately getting values does not cause a split-brain scenario. As mentioned in the "Setting values for a setting" section, the appropriate checks should be done to ensure that the user is allowed to set the value. The local echo system assumes that the user has permission and that the request will go through successfully. The local echo only takes effect until the request to save a setting has completed (either successfully or otherwise).

SettingsStore.setValue(...).then(() => {
  // The value has actually been stored at this point.
});
SettingsStore.getValue(...); // this will return the value set in `setValue` above.

Watching for changes

Most use cases do not need to set up a watcher because they are able to react to changes as they are made, or the changes which are made are not significant enough for it to matter. Watchers are intended to be used in scenarios where it is important to react to changes made by other logged in devices. Typically, this would be done within the component itself, however the component should not be aware of the intricacies of setting inversion or remapping to particular data structures. Instead, a generic watcher interface is provided on SettingsStore to watch (and subsequently unwatch) for changes in a setting.

An example of a watcher in action would be:

class MyComponent extends React.Component {

    settingWatcherRef = null;

    componentWillMount() {
        const callback = (settingName, roomId, level, newValAtLevel, newVal) => {
            this.setState({color: newVal});
        };
        this.settingWatcherRef = SettingsStore.watchSetting("roomColor", "!example:matrix.org", callback);
    }

    componentWillUnmount() {
        SettingsStore.unwatchSetting(this.settingWatcherRef);
    }
}

Maintainers Reference

The granular settings system has a few complex parts to power it. This section is to document how the SettingsStore is supposed to work.

General information

The SettingsStore uses the hardcoded LEVEL_ORDER constant to ensure that it is using the correct override procedure. The array is checked from left to right, simulating the behaviour of overriding values from the higher levels. Each level should be defined in this array, including default.

Handlers (src/settings/handlers/SettingsHandler.ts) represent a single level and are responsible for getting and setting values at that level. Handlers also provide additional information to the SettingsStore such as if the level is supported or if the current user may set values at the level. The SettingsStore will use the handler to enforce checks and manipulate settings. Handlers are also responsible for dealing with migration patterns or legacy settings for their level (for example, a setting being renamed or using a different key from other settings in the underlying store). Handlers are provided to the SettingsStore via the LEVEL_HANDLERS constant. SettingsStore will optimize lookups by only considering handlers that are supported on the platform.

Local echo is achieved through src/settings/handlers/LocalEchoWrapper.ts which acts as a wrapper around a given handler. This is automatically applied to all defined LEVEL_HANDLERS and proxies the calls to the wrapped handler where possible. The echo is achieved by a simple object cache stored within the class itself. The cache is invalidated immediately upon the proxied save call succeeding or failing.

Controllers are notified of changes by the SettingsStore, and are given the opportunity to override values after the SettingsStore has deemed the value calculated. Controllers are invoked as the last possible step in the code.

Features

See above for feature reference.

Watchers

Watchers can appear complicated under the hood: there is a central WatchManager which handles the actual invocation of callbacks, and callbacks are managed by the SettingsStore by redirecting the caller's callback to a dedicated callback. This is done so that the caller can reuse the same function as their callback without worrying about whether or not it'll unsubscribe all watchers.

Setting changes are emitted into the default WatchManager, which calculates the new value for the setting. Ideally, we'd also try and suppress updates which don't have a consequence on this value, however there's not an easy way to do this. Instead, we just dispatch an update for all changes and leave it up to the consumer to deduplicate.

In practice, handlers which rely on remote changes (account data, room events, etc) will always attach a listener to the MatrixClient. They then watch for changes to events they care about and send off appropriate updates to the generalized WatchManager - a class specifically designed to deduplicate the logic of managing watchers. The handlers which are localized to the local client (device) generally just trigger the WatchManager when they manipulate the setting themselves as there's nothing to really 'watch'.