xterm.js/src/common/parser/ApcParser.ts

/**
 * Copyright (c) 2025 The xterm.js authors. All rights reserved.
 * @license MIT
 */

import { IApcHandler, IHandlerCollection, ApcFallbackHandlerType, IApcParser, ISubParserStackState } from 'common/parser/Types';
import { ParserConstants } from 'common/parser/Constants';
import { utf32ToString } from 'common/input/TextDecoder';
import { IDisposable } from 'common/Types';
import { LimitedStringBuilder } from 'common/StringBuilder';

const EMPTY_HANDLERS: IApcHandler[] = [];

/**
 * APC Parser for handling Application Program Command sequences.
 * APC sequences use the format: ESC _ <identifier><data> ESC \
 *
 * Unlike OSC which uses numeric identifiers (e.g., OSC 1337),
 * APC uses the first character as the identifier (e.g., 'G' for Kitty graphics).
 * The identifier is the character code of the first byte after ESC _.
 */
export class ApcParser implements IApcParser {
  private _handlers: IHandlerCollection<IApcHandler> = Object.create(null);
  private _active = EMPTY_HANDLERS;
  private _ident: number = 0;
  private _handlerFb: ApcFallbackHandlerType = () => { };
  private _stack: ISubParserStackState = {
    paused: false,
    loopPosition: 0,
    fallThrough: false
  };

  /**
   * Register an APC handler for a specific identifier.
   * @param ident The character code of the first byte (e.g., 0x47 for 'G')
   * @param handler The handler to register
   */
  public registerHandler(ident: number, handler: IApcHandler): IDisposable {
    this._handlers[ident] ??= [];
    const handlerList = this._handlers[ident];
    handlerList.push(handler);
    return {
      dispose: () => {
        const handlerIndex = handlerList.indexOf(handler);
        if (handlerIndex !== -1) {
          handlerList.splice(handlerIndex, 1);
        }
      }
    };
  }

  public clearHandler(ident: number): void {
    if (this._handlers[ident]) delete this._handlers[ident];
  }

  public setHandlerFallback(handler: ApcFallbackHandlerType): void {
    this._handlerFb = handler;
  }

  public dispose(): void {
    this._handlers = Object.create(null);
    this._handlerFb = () => { };
    this._active = EMPTY_HANDLERS;
  }

  public reset(): void {
    // force cleanup handlers
    if (this._active.length) {
      for (let j = this._stack.paused ? this._stack.loopPosition - 1 : this._active.length - 1; j >= 0; --j) {
        this._active[j].end(false);
      }
    }
    this._stack.paused = false;
    this._active = EMPTY_HANDLERS;
    this._ident = 0;
  }

  public start(ident: number): void {
    // always reset leftover handlers
    this.reset();
    this._ident = ident;
    this._active = this._handlers[ident] || EMPTY_HANDLERS;
    if (!this._active.length) {
      this._handlerFb(this._ident, 'START');
    } else {
      for (let j = this._active.length - 1; j >= 0; j--) {
        this._active[j].start();
      }
    }
  }

  public put(data: Uint32Array, start: number, end: number): void {
    if (!this._active.length) {
      this._handlerFb(this._ident, 'PUT', utf32ToString(data, start, end));
    } else {
      for (let j = this._active.length - 1; j >= 0; j--) {
        this._active[j].put(data, start, end);
      }
    }
  }

  /**
   * Indicates end of an APC command.
   * Whether the APC got aborted or finished normally
   * is indicated by `success`.
   */
  public end(success: boolean, promiseResult: boolean = true): void | Promise<boolean> {
    if (!this._active.length) {
      this._handlerFb(this._ident, 'END', success);
    } else {
      let handlerResult: boolean | Promise<boolean> = false;
      let j = this._active.length - 1;
      let fallThrough = false;
      if (this._stack.paused) {
        j = this._stack.loopPosition - 1;
        handlerResult = promiseResult;
        fallThrough = this._stack.fallThrough;
        this._stack.paused = false;
      }
      if (!fallThrough && handlerResult === false) {
        for (; j >= 0; j--) {
          handlerResult = this._active[j].end(success);
          if (handlerResult === true) {
            break;
          } else if (handlerResult instanceof Promise) {
            this._stack.paused = true;
            this._stack.loopPosition = j;
            this._stack.fallThrough = false;
            return handlerResult;
          }
        }
        j--;
      }
      // cleanup left over handlers (fallThrough for async)
      for (; j >= 0; j--) {
        handlerResult = this._active[j].end(false);
        if (handlerResult instanceof Promise) {
          this._stack.paused = true;
          this._stack.loopPosition = j;
          this._stack.fallThrough = true;
          return handlerResult;
        }
      }
    }
    this._active = EMPTY_HANDLERS;
    this._ident = 0;
  }
}

/**
 * Convenient class to allow attaching string based handler functions
 * as APC handlers.
 */
export class ApcHandler implements IApcHandler {
  private static _payloadLimit = ParserConstants.PAYLOAD_LIMIT;

  private _data = new LimitedStringBuilder(ApcHandler._payloadLimit);
  private _hitLimit: boolean = false;

  constructor(private _handler: (data: string) => boolean | Promise<boolean>) { }

  public start(): void {
    this._data.reset();
    this._hitLimit = false;
  }

  public put(data: Uint32Array, start: number, end: number): void {
    if (this._hitLimit) {
      return;
    }
    if (this._data.append(utf32ToString(data, start, end))) {
      this._hitLimit = true;
    }
  }

  public end(success: boolean): boolean | Promise<boolean> {
    let ret: boolean | Promise<boolean> = false;
    if (this._hitLimit) {
      ret = false;
    } else if (success) {
      ret = this._handler(this._data.toString());
      if (ret instanceof Promise) {
        // need to hold data until `ret` got resolved
        // dont care for errors, data will be freed anyway on next start
        return ret.then(res => {
          this._data.reset();
          this._hitLimit = false;
          return res;
        });
      }
    }
    this._data.reset();
    this._hitLimit = false;
    return ret;
  }
}