node-web-gpio/index.ts

import { EventEmitter } from 'events';
import { promises as fs } from 'fs';
import * as path from 'path';

/**
 * Interval of file system polling, in milliseconds.
 */
const PollingInterval = 100;

const SysfsGPIOPath = '/sys/class/gpio';

const GPIOPortMapSizeMax = 1024;

const Uint16Max = 65535;

function parseUint16(parseString: string) {
  const n = Number.parseInt(parseString, 10);
  if (0 <= n && n <= Uint16Max) return n;
  else throw new RangeError(`Must be between 0 and ${Uint16Max}.`);
}

type PortNumber = number;
type PortName = string;
type PinName = string;

type DirectionMode = 'in' | 'out';

type GPIOValue = 0 | 1;

interface GPIOChangeEvent {
  readonly value: GPIOValue;
  readonly port: GPIOPort;
}

interface GPIOChangeEventHandler {
  (event: GPIOChangeEvent): void;
}

export class GPIOAccess extends EventEmitter {
  private readonly _ports: GPIOPortMap;
  onchange: GPIOChangeEventHandler | undefined;

  constructor(ports?: GPIOPortMap) {
    super();

    this._ports = ports == null ? new GPIOPortMap() : ports;
    this._ports.forEach((port) =>
      port.on('change', (event) => {
        this.emit('change', event);
      })
    );

    this.on('change', (event: GPIOChangeEvent): void => {
      if (this.onchange !== undefined) this.onchange(event);
    });
  }

  get ports(): GPIOPortMap {
    return this._ports;
  }

  /**
   * Unexport all exported GPIO ports.
   */
  async unexportAll(): Promise<void> {
    await Promise.all(
      [...this.ports.values()].map((port) =>
        port.exported ? port.unexport() : undefined
      )
    );
  }
}

/**
 * Different from Web GPIO API specification.
 */
export class GPIOPortMap extends Map<PortNumber, GPIOPort> {}

export class GPIOPort extends EventEmitter {
  private readonly _portNumber: PortNumber;
  private readonly _pollingInterval: number;
  private _direction: DirectionMode | OperationError;
  private _exported: boolean | OperationError;
  private _exportRetry: number;
  private _value: GPIOValue | undefined;
  private _timeout: ReturnType<typeof setInterval> | undefined;
  onchange: GPIOChangeEventHandler | undefined;

  constructor(portNumber: PortNumber) {
    super();

    this._portNumber = parseUint16(portNumber.toString());
    this._pollingInterval = PollingInterval;
    this._direction = new OperationError('Unknown direction.');
    this._exported = new OperationError('Unknown export.');
    this._exportRetry = 0;

    this.on('change', (event: GPIOChangeEvent): void => {
      if (this.onchange !== undefined) this.onchange(event);
    });
  }

  get portNumber(): PortNumber {
    return this._portNumber;
  }

  get portName(): PortName {
    return `gpio${this.portNumber}`;
  }

  get pinName(): PinName {
    // NOTE: Unknown pinName.
    return '';
  }

  get direction(): DirectionMode {
    if (this._direction instanceof OperationError) throw this._direction;
    return this._direction;
  }

  get exported(): boolean {
    if (this._exported instanceof OperationError) throw this._exported;
    return this._exported;
  }

  async export(direction: DirectionMode): Promise<void> {
    if (!/^(in|out)$/.test(direction)) {
      throw new InvalidAccessError(`Must be "in" or "out".`);
    }

    try {
      await fs.access(path.join(SysfsGPIOPath, this.portName));
      this._exported = true;
    } catch {
      this._exported = false;
    }

    try {
      clearInterval(this._timeout as ReturnType<typeof setInterval>);
      if (!this.exported) {
        await fs.writeFile(
          path.join(SysfsGPIOPath, 'export'),
          String(this.portNumber)
        );
      }
      await fs.writeFile(
        path.join(SysfsGPIOPath, this.portName, 'direction'),
        direction
      );
      if (direction === 'in') {
        this._timeout = setInterval(
          // eslint-disable-next-line
          this.read.bind(this),
          this._pollingInterval
        );
      }
    } catch (error: any) {
      if (this._exportRetry == 0) {
        await sleep(100);
        console.warn('May be the first time port access. Retry..');
        ++this._exportRetry;
        await this.export(direction);
      } else {
        throw new OperationError(error);
      }
    }

    this._direction = direction;
    this._exported = true;
  }

  async unexport(): Promise<void> {
    clearInterval(this._timeout as ReturnType<typeof setInterval>);

    try {
      await fs.writeFile(
        path.join(SysfsGPIOPath, 'unexport'),
        String(this.portNumber)
      );
    } catch (error: any) {
      throw new OperationError(error);
    }

    this._exported = false;
  }

  async read(): Promise<GPIOValue> {
    if (!(this.exported && this.direction === 'in')) {
      throw new InvalidAccessError(
        `The exported must be true and value of direction must be "in".`
      );
    }

    try {
      const buffer = await fs.readFile(
        path.join(SysfsGPIOPath, this.portName, 'value')
      );

      const value = parseUint16(buffer.toString()) as GPIOValue;

      if (this._value !== value) {
        this._value = value;
        this.emit('change', { value, port: this });
      }

      return value;
    } catch (error: any) {
      throw new OperationError(error);
    }
  }

  async write(value: GPIOValue): Promise<void> {
    if (!(this.exported && this.direction === 'out')) {
      throw new InvalidAccessError(
        `The exported must be true and value of direction must be "out".`
      );
    }

    try {
      await fs.writeFile(
        path.join(SysfsGPIOPath, this.portName, 'value'),
        parseUint16(value.toString()).toString()
      );
    } catch (error: any) {
      throw new OperationError(error);
    }
  }
}

export class InvalidAccessError extends Error {
  constructor(message: string) {
    super(message);
    this.name = this.constructor.name;
  }
}

export class OperationError extends Error {
  constructor(message: string) {
    super(message);
    this.name = this.constructor.name;
  }
}

// Web GPIOの仕様に基づく意図的なasync関数の使用なので、ルールを無効化
// eslint-disable-next-line
export async function requestGPIOAccess(): Promise<GPIOAccess> {
  const ports = new GPIOPortMap(
    [...Array(GPIOPortMapSizeMax).keys()].map((portNumber) => [
      portNumber,
      new GPIOPort(portNumber),
    ])
  );

  return new GPIOAccess(ports);
}

function sleep(ms: number) {
  return new Promise((resolve) => {
    return setTimeout(resolve, ms);
  });
}