WebAPI/BrowserAPI/KeyboardEvent

Dispatch KeyboardEvent across BrowserElements

This is a proposal to enable applications to handle/override the behavior of certain KeyboardEvent. For implementation, see bug 989198.

There are four scenarios which should be fulfilled:

Scenario	Description	Example Keys
SYSTEM-ONLY	For keys which should be handled by mozbrowser embedder iframe only.	'Power', 'DisplaySwap'
SYSTEM-FIRST	For keys which can be handled by mozbrowser embedder iframe first and can also be handled by mozbrowser embedded iframe then.	'Info', 'Settings'
APP-CANCELLED	For keys which should be handled by mozbrowser embedded iframe only.	'ColorF0Red', 'ColorF1Green', 'ColorF2Yellow', 'ColorF3Blue', 'ColorF4Grey'
APP-FIRST	For keys which keys can be handled by mozbrowser embedded iframe first and can also be handled by mozbrowser embedder iframe then.	'Info', 'Settings'

Note that some keys could be either SYSTEM-FIRST or APP-FIRST. The behavior is decided by the author of applications.

Proposal Concept

Four new events are proposed:

• mozbrowserbeforekeydown
• mozbrowserafterkeydown
• mozbrowserbeforekeyup
• mozbrowserafterkeyup

When a key is pressed down, the event sequence would be:

1. 'mozbrowserbeforekeydown' is dispatched to mozbrowser-embedder iframe
2. 'keydown' is dispatched to mozbrowser-embedded iframe
3. 'mozbrowserafterkeydown' is dispatched to mozbrowser-embedder iframe

Similarly, when a key is released, the event sequence would be:

1. 'mozbrowserbeforekeyup' is dispatched to mozbrowser-embedder iframe
2. 'keyup' is dispatched to mozbrowser-embedded iframe
3. 'mozbrowserafterkeyup' is dispatched to mozbrowser-embedder iframe

Nested mozbrowser iframes case

This proposal can be extended to nested mozbrowser iframes. The four new events will be dispatched to all mozbrowser-embedder iframes.

How to Fulfill Scenarios?

Here are some examples for each scenario.

Let's define some functions first.

function handleEvent(event) {
  dump("Receive event \'" + event.type + "\'.");
};

function handleEventAndPreventDefault(event) {
  dump("Receive event \'" + event.type + "\'.");
  event.preventDefault();
};

function checkAttrAndHandleEvent(event) {
  dump("Receive event \'" + event.type + "\' with embeddedCancelled equals to \'" + event.embeddedCancelled + "\'.");
  if (!event.embeddedCancelled) {
    // do something
  }
};

Scenario SYSTEM-ONLY

• mozbrowser-embedder iframe

   window.addEventListener('mozbrowserbeforekeydown', handleEventAndPreventDefault);
   window.addEventListener('mozbrowserbeforekeyup', handleEventAndPreventDefault);
   window.addEventListener('mozbrowserafterkeydown', function() { });
   window.addEventListener('mozbrowserafterkeyup', function() { });

• mozbrowser-embedded iframe

   window.addEventListener('keydown', handleEvent);
   window.addEventListener('keyup', handleEvent);

Order	mozbrowser-embedder iframe	mozbrowser-embedded iframe	Output
1	mozbrowserbeforekeydown		Receive event 'mozbrowserbeforekeydown'.
2	mozbrowserafterkeydown
3	mozbrowserbeforekeyup		Receive event 'mozbrowserbeforekeyup'.
4	mozbrowserafterkeyup

Scenario SYSTEM-FIRST

• mozbrowser-embedder iframe

   window.addEventListener('mozbrowserbeforekeydown', handleEvent);
   window.addEventListener('mozbrowserbeforekeyup', handleEvent);
   window.addEventListener('mozbrowserafterkeydown', function() { });
   window.addEventListener('mozbrowserafterkeyup', function() { });

• mozbrowser-embedded iframe

   window.addEventListener('keydown', handleEvent);
   window.addEventListener('keyup', handleEvent);

Order	mozbrowser-embedder iframe	mozbrowser-embedded iframe	Output
1	mozbrowserbeforekeydown		Receive event 'mozbrowserbeforekeydown'.
2		keydown	Receive event 'keydown'.
3	mozbrowserafterkeydown
4	mozbrowserbeforekeyup		Receive event 'mozbrowserbeforekeyup'.
5		keyup	Receive event 'keyup'.
6	mozbrowserafterkeyup

Scenario APP-CANCELLED

• mozbrowser-embedder iframe

   window.addEventListener('mozbrowserbeforekeydown', function() { });
   window.addEventListener('mozbrowserbeforekeyup', function() { });
   window.addEventListener('mozbrowserafterkeydown', checkAttrAndHandleEvent);
   window.addEventListener('mozbrowserafterkeyup', checkAttrAndHandleEvent);

• mozbrowser-embedded iframe

   window.addEventListener('keydown', handleEventAndPreventDefault);
   window.addEventListener('keyup', handleEventAndPreventDefault);

Order	mozbrowser-embedder iframe	mozbrowser-embedded iframe	Output
1	mozbrowserbeforekeydown
2		keydown	Receive event 'keydown'.
3	mozbrowserafterkeydown		Receive event 'mozbrowserafterkeydown' with embeddedCancelled equals to 'true'.
4	mozbrowserbeforekeyup
5		keyup	Receive event 'keyup'.
6	mozbrowserup		Receive event 'mozbrowserafterkeyup' with embeddedCancelled equals to 'true'.

Scenario APP-FIRST

• mozbrowser-embedder iframe

   window.addEventListener('mozbrowserbeforekeydown', function() { });
   window.addEventListener('mozbrowserbeforekeyup', function() { });
   window.addEventListener('mozbrowserafterkeydown', checkAttrAndHandleEvent);
   window.addEventListener('mozbrowserafterkeyup', checkAttrAndHandleEvent);

• mozbrowser-embedded iframe

   window.addEventListener('keydown', handleEvent);
   window.addEventListener('keyup', handleEvent);

Order	mozbrowser-embedder iframe	mozbrowser-embedded iframe	Output
1	mozbrowserbeforekeydown
2		keydown	Receive event 'keydown'.
3	mozbrowserafterkeydown		Receive event 'mozbrowserafterkeyup' with embeddedCancelled equals to 'false'.
4	mozbrowserbeforekeyup
5		keyup	Receive event 'keyup'.
6	mozbrowserafterkeyup		Receive event 'mozbrowserafterkeyup' with embeddedCancelled equals to 'false'.

Proposal Details

mozbrowserbeforekeydown

Type	mozbrowserbeforekeydown
Interface	KeyboardEvent
Sync/Async	Sync
Bubbles	Yes
Target	Document, Element
Cancelable	Yes
Default action	keydown event

keydown

Type	keydown
Interface	KeyboardEvent
Sync/Async	Sync
Bubbles	Yes
Target	Document, Element
Cancelable	Yes
Default action	Set mozbrowserafterkeydown.embeddedCancelled to false; others defined in http://www.w3.org/TR/DOM-Level-3-Events/#event-type-keydown

mozbrowserafterkeydown

Type	mozbrowserkeydown
Interface	KeyboardEvent
Sync/Async	Sync
Bubbles	Yes
Target	Document, Element
Cancelable	Yes
Default action	None

mozbrowserbeforekeyup

Type	mozbrowserbeforekeyup
Interface	KeyboardEvent
Sync/Async	Sync
Bubbles	Yes
Target	Document, Element
Cancelable	Yes
Default action	keyup event

keyup

Type	keyup
Interface	KeyboardEvent
Sync/Async	Sync
Bubbles	Yes
Target	Document, Element
Cancelable	Yes
Default action	Set mozbrowserafterkeyup.embeddedCancelled to false; others defined in http://www.w3.org/TR/DOM-Level-3-Events/#event-type-keyup

mozbrowserafterkeyup

Type	mozbrowserafterkeyup
Interface	KeyboardEvent
Sync/Async	Sync
Bubbles	Yes
Target	Document, Element
Cancelable	Yes
Default action	None

Related Gaia Changes

Current Implementation

Currently, shell.js filters all hardware key event and wraps them in mozChromeEvent and then dispatch to Gaia System app. In Gaia System app, hardware_buttons.js listens for these low-level `mozChromeEvents`, processes them and generates higher-level events to handle autorepeat on the volume key long presses on Home and Sleep, and the Home+Sleep key combination. Other system app modules should listen for the high-level button events generated by this module.

The low level input events wrapped in mozChromeEvent are:

• home-button-press
• home-button-release
• sleep-button-press
• sleep-button-release
• volume-up-button-press
• volume-up-button-release
• volume-down-button-press
• volume-down-button-release

Hardware Buttons module (hardware_buttons.js) implements a state machine in it. Each state object has a mandatory `process()` method to process incoming low level input events and two optional `enter()` and `exit()` method when enter and exit state. Hardware Buttons module will listen to all low level input events and relay it to current state object to process. An all state transitions happen in `process()` or timer in `enter()` method.

Plan of Change

In patch of https://bugzilla.mozilla.org/show_bug.cgi?id=989198, Gina will keep both mozChromeEvents and new KeyboardEvents dispatching at the same time. But we only need to listen to one of them in Gaia.

Part 1 - Switch to new keyboard event

The state objects in hardware_buttons.js and software_button_manager.js all have dependency on low level input event names listed above. In this part, we stop listening to 'mozChromeEvent' and start listening to 'mozbrowserbeforekeydown', 'mozbrowserbeforekeyup', 'keydown', and 'keyup' event, and do a translation in handleEvent of hardware_buttons.js.

Translations are as follows:

This translation would make sure the original finite state machine in hardware_buttons.js and software_button_manager.js works as usual. All other outer module still listens to custom events generate in hardware_buttons.js (that is, home/sleep/home+sleep/holdhome/holdsleep/wake/volumeup/volumedown). In this part, these four events need to `preventDefault()`. Because we have not implement customization yet, and we should let hardware key handling process just as the same as before.

Part 2 - Key event handling customization

What needs to be customization?

1. System app should decide which key event would propagate to inner iframe or not
2. System app should decide how to handle key event when inner iframe did not handle it

Build time customization detail will be discussed later. Default Policy in System App for 'Power', 'Exit', 'VolumeUp', 'VolumeDown':

Key	Default Policy
Power	SYSTEM-ONLY
Exit	SYSTEM-ONLY
VolumeUp	APP-CANCELLED
VolumeDown	APP-CANCELLED

Default Policy for other keys are APP-CANCELLED.

There is one more thing to do in this part. We only handle 'Power', 'Exit', 'VolumeUp', 'VolumDown' in part 1. But there will be more 'keys' need to be handled. We'll have to create a key mapping and handling table with customization in this part.

Part 3 - Remove all translated low-level input events

In this part, we need to refactor both hardware_buttons.js and software_button_manager.js to remove all low-level input event names. In software_button_manager.js, we should dispatch events the same as new key event (such as mozbrowserbeforekeydown or keydown...etc)

Bugs

https://bugzilla.mozilla.org/show_bug.cgi?id=1014405

https://bugzilla.mozilla.org/show_bug.cgi?id=1014418

https://bugzilla.mozilla.org/show_bug.cgi?id=1103339

https://bugzilla.mozilla.org/show_bug.cgi?id=1094066