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xterm.js/src/common/input/KittyKeyboard.ts
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/**
* Copyright (c) 2025 The xterm.js authors. All rights reserved.
* @license MIT
*
* Kitty keyboard protocol implementation.
* @see https://sw.kovidgoyal.net/kitty/keyboard-protocol/
*/
import { IKeyboardEvent, IKeyboardResult, KeyboardResultType } from 'common/Types';
import { C0 } from 'common/data/EscapeSequences';
/**
* Kitty keyboard protocol enhancement flags (bitfield).
*/
export const enum KittyKeyboardFlags {
NONE = 0b00000,
/** Disambiguate escape codes - fixes ambiguous legacy encodings */
DISAMBIGUATE_ESCAPE_CODES = 0b00001,
/** Report event types - press/repeat/release */
REPORT_EVENT_TYPES = 0b00010,
/** Report alternate keys - shifted key and base layout key */
REPORT_ALTERNATE_KEYS = 0b00100,
/** Report all keys as escape codes - text-producing keys as CSI u */
REPORT_ALL_KEYS_AS_ESCAPE_CODES = 0b01000,
/** Report associated text - includes text codepoints in escape code */
REPORT_ASSOCIATED_TEXT = 0b10000,
}
/**
* Kitty keyboard event types.
*/
export const enum KittyKeyboardEventType {
PRESS = 1,
REPEAT = 2,
RELEASE = 3,
}
/**
* Kitty modifier bits (different from xterm modifier encoding).
* Value sent = 1 + modifier_bits
*/
export const enum KittyKeyboardModifiers {
SHIFT = 0b00000001,
ALT = 0b00000010,
CTRL = 0b00000100,
SUPER = 0b00001000,
HYPER = 0b00010000,
META = 0b00100000,
CAPS_LOCK = 0b01000000,
NUM_LOCK = 0b10000000,
}
/**
* Functional key codes for Kitty protocol.
* Keys that don't produce text have specific unicode codepoint mappings.
*/
const FUNCTIONAL_KEY_CODES: { [key: string]: number } = {
'Escape': 27,
'Enter': 13,
'Tab': 9,
'Backspace': 127,
'Insert': 2,
'Delete': 3,
'ArrowLeft': 57419,
'ArrowRight': 57421,
'ArrowUp': 57417,
'ArrowDown': 57420,
'PageUp': 57423,
'PageDown': 57424,
'Home': 57416,
'End': 57418,
'CapsLock': 57358,
'ScrollLock': 57359,
'NumLock': 57360,
'PrintScreen': 57361,
'Pause': 57362,
'ContextMenu': 57363,
// F1-F35
'F1': 57364,
'F2': 57365,
'F3': 57366,
'F4': 57367,
'F5': 57368,
'F6': 57369,
'F7': 57370,
'F8': 57371,
'F9': 57372,
'F10': 57373,
'F11': 57374,
'F12': 57375,
'F13': 57376,
'F14': 57377,
'F15': 57378,
'F16': 57379,
'F17': 57380,
'F18': 57381,
'F19': 57382,
'F20': 57383,
'F21': 57384,
'F22': 57385,
'F23': 57386,
'F24': 57387,
'F25': 57388,
// Keypad keys
'KP_0': 57399,
'KP_1': 57400,
'KP_2': 57401,
'KP_3': 57402,
'KP_4': 57403,
'KP_5': 57404,
'KP_6': 57405,
'KP_7': 57406,
'KP_8': 57407,
'KP_9': 57408,
'KP_Decimal': 57409,
'KP_Divide': 57410,
'KP_Multiply': 57411,
'KP_Subtract': 57412,
'KP_Add': 57413,
'KP_Enter': 57414,
'KP_Equal': 57415,
// Modifier keys
'ShiftLeft': 57441,
'ShiftRight': 57447,
'ControlLeft': 57442,
'ControlRight': 57448,
'AltLeft': 57443,
'AltRight': 57449,
'MetaLeft': 57444,
'MetaRight': 57450,
// Media keys
'MediaPlayPause': 57430,
'MediaStop': 57432,
'MediaTrackNext': 57435,
'MediaTrackPrevious': 57436,
'AudioVolumeDown': 57438,
'AudioVolumeUp': 57439,
'AudioVolumeMute': 57440
};
/**
* Map browser key codes to Kitty numpad codes.
*/
function getNumpadKeyCode(ev: IKeyboardEvent): number | undefined {
// Detect numpad via code property
if (ev.code.startsWith('Numpad')) {
const suffix = ev.code.slice(6);
if (suffix >= '0' && suffix <= '9') {
return 57399 + parseInt(suffix, 10);
}
switch (suffix) {
case 'Decimal': return 57409;
case 'Divide': return 57410;
case 'Multiply': return 57411;
case 'Subtract': return 57412;
case 'Add': return 57413;
case 'Enter': return 57414;
case 'Equal': return 57415;
}
}
return undefined;
}
/**
* Get modifier key code from code property.
*/
function getModifierKeyCode(ev: IKeyboardEvent): number | undefined {
switch (ev.code) {
case 'ShiftLeft': return 57441;
case 'ShiftRight': return 57447;
case 'ControlLeft': return 57442;
case 'ControlRight': return 57448;
case 'AltLeft': return 57443;
case 'AltRight': return 57449;
case 'MetaLeft': return 57444;
case 'MetaRight': return 57450;
}
return undefined;
}
/**
* Encode modifiers for Kitty protocol.
* Returns 1 + modifier bits, or 0 if no modifiers.
*/
function encodeModifiers(ev: IKeyboardEvent): number {
let mods = 0;
if (ev.shiftKey) mods |= KittyKeyboardModifiers.SHIFT;
if (ev.altKey) mods |= KittyKeyboardModifiers.ALT;
if (ev.ctrlKey) mods |= KittyKeyboardModifiers.CTRL;
if (ev.metaKey) mods |= KittyKeyboardModifiers.SUPER;
// Note: getModifierState would be needed for CAPS_LOCK/NUM_LOCK but not in IKeyboardEvent
return mods > 0 ? mods + 1 : 0;
}
/**
* Get the unicode key code for a keyboard event.
*/
function getKeyCode(ev: IKeyboardEvent): number | undefined {
// Check for numpad first
const numpadCode = getNumpadKeyCode(ev);
if (numpadCode !== undefined) {
return numpadCode;
}
// Check for modifier keys
const modifierCode = getModifierKeyCode(ev);
if (modifierCode !== undefined) {
return modifierCode;
}
// Check functional keys
const funcCode = FUNCTIONAL_KEY_CODES[ev.key];
if (funcCode !== undefined) {
return funcCode;
}
// For regular keys, use the key character's codepoint
if (ev.key.length === 1) {
return ev.key.codePointAt(0);
}
return undefined;
}
/**
* Check if a key is a modifier key.
*/
function isModifierKey(ev: IKeyboardEvent): boolean {
return ev.key === 'Shift' || ev.key === 'Control' || ev.key === 'Alt' || ev.key === 'Meta';
}
/**
* Evaluate a keyboard event using Kitty keyboard protocol.
*
* @param ev The keyboard event.
* @param flags The active Kitty keyboard enhancement flags.
* @param eventType The event type (press, repeat, release).
* @returns The keyboard result with the encoded key sequence.
*/
export function evaluateKeyboardEventKitty(
ev: IKeyboardEvent,
flags: number,
eventType: KittyKeyboardEventType = KittyKeyboardEventType.PRESS
): IKeyboardResult {
const result: IKeyboardResult = {
type: KeyboardResultType.SEND_KEY,
cancel: false,
key: undefined
};
// Get the key code
const keyCode = getKeyCode(ev);
if (keyCode === undefined) {
return result;
}
const modifiers = encodeModifiers(ev);
const isFunc = FUNCTIONAL_KEY_CODES[ev.key] !== undefined || getNumpadKeyCode(ev) !== undefined;
const isMod = isModifierKey(ev);
// Determine if we should use CSI u encoding or can use legacy
let useCsiU = false;
if (flags & KittyKeyboardFlags.REPORT_ALL_KEYS_AS_ESCAPE_CODES) {
// All keys use CSI u
useCsiU = true;
} else if (flags & KittyKeyboardFlags.REPORT_EVENT_TYPES) {
// When reporting event types, use CSI u for all keys
useCsiU = true;
} else if (flags & KittyKeyboardFlags.DISAMBIGUATE_ESCAPE_CODES) {
// Use CSI u for:
// - Modifier-only keys when reporting event types
// - Keys that would be ambiguous in legacy encoding
// - Escape key
// - Backspace
// - Tab (when shifted)
// - Enter
if (isMod && (flags & KittyKeyboardFlags.REPORT_EVENT_TYPES)) {
useCsiU = true;
} else if (keyCode === 27 || keyCode === 127 || keyCode === 13) {
// Escape, Backspace, Enter
useCsiU = true;
} else if (keyCode === 9 && ev.shiftKey) {
// Shift+Tab
useCsiU = true;
} else if (isFunc) {
useCsiU = true;
} else if (modifiers > 0) {
// Any modified key
useCsiU = true;
}
}
// Determine if we should report this event type
const reportEventTypes = !!(flags & KittyKeyboardFlags.REPORT_EVENT_TYPES);
if (!reportEventTypes && eventType === KittyKeyboardEventType.RELEASE) {
// Don't report release events unless flag is set
return result;
}
if (useCsiU) {
// Build CSI u sequence: CSI keycode ; modifiers:event-type u
// Format: CSI <keycode>[:<shifted>][:<base>] ; <modifiers>[:<event>] u
let seq = C0.ESC + '[' + keyCode;
// Add modifiers and event type
if (modifiers > 0 || (reportEventTypes && eventType !== KittyKeyboardEventType.PRESS)) {
seq += ';';
if (modifiers > 0) {
seq += modifiers;
}
if (reportEventTypes && eventType !== KittyKeyboardEventType.PRESS) {
seq += ':' + eventType;
}
}
// Add associated text if requested and available
if ((flags & KittyKeyboardFlags.REPORT_ASSOCIATED_TEXT) && ev.key.length === 1 && !isFunc && !isMod) {
const textCode = ev.key.codePointAt(0);
if (textCode !== undefined && textCode !== keyCode) {
// Append text as ; text u
if (!seq.includes(';')) {
seq += ';';
}
seq += ';' + textCode;
}
}
seq += 'u';
result.key = seq;
result.cancel = true;
} else {
// Legacy-compatible encoding for text keys without modifiers
if (ev.key.length === 1 && !ev.ctrlKey && !ev.altKey && !ev.metaKey) {
result.key = ev.key;
}
// Otherwise no key sequence (will fall through to legacy handling)
}
return result;
}
/**
* Check if a keyboard event should be handled by Kitty protocol.
* Returns true if Kitty flags are active and the event should use Kitty encoding.
*/
export function shouldUseKittyProtocol(flags: number): boolean {
return flags > 0;
}