ui/file_manager/image_loader/piex_loader.ts

// Copyright 2015 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

/**
 * Declares the piex-wasm Module interface. The Module has many interfaces
 * but only declare the parts required for PIEX work.
 */
export interface PiexWasmModule {
  calledRun: boolean;
  HEAP8: Uint8Array;
  _malloc: (size: number) => number;
  _free: (size: number) => void;
  image: (width: number, height: number) => PiexWasmImageResult;
}

interface VoidCallback {
  (): void;
}

/**
 * Subset of the Emscripten Module API required for initialization. See
 * https://emscripten.org/docs/api_reference/module.html#module.
 */
interface ModuleInitParams {
  onAbort: (result: Error|string) => void;
}

/**
 * Module defined by 'piex.js.wasm' script upon initialization.
 */
let PiexModule: PiexWasmModule;

declare global {
  function createPiexModule(params: ModuleInitParams): Promise<PiexWasmModule>;
}

/**
 * Module constructor defined by 'piex.js.wasm' script.
 */
const initPiexModule = globalThis.createPiexModule;

console.info(`[PiexLoader] available [init=${typeof initPiexModule}]`);

/**
 * Set true if the Module.onAbort() handler is called.
 */
let piexFailed = false;

const MODULE_SETTINGS = {
  /**
   * Installs an (Emscripten) Module.onAbort handler. Record that the
   * Module has failed in piexFailed and re-throw the error.
   *
   * @throws {!Error|string}
   */
  onAbort: (error: Error|string) => {
    piexFailed = true;
    throw error;
  },
};

let initPiexModulePromise: Promise<void>|null = null;

/**
 * Returns a promise that resolves once initialization is complete. PiexModule
 * may be undefined before this promise resolves.
 */
function piexModuleInitialized(): Promise<void> {
  if (!initPiexModulePromise) {
    initPiexModulePromise = new Promise(resolve => {
      initPiexModule(MODULE_SETTINGS).then(module => {
        PiexModule = module;
        console.info(`[PiexLoader] loaded [module=${typeof module}]`);
        resolve();
      });
    });
  }
  return initPiexModulePromise;
}

/**
 * Module failure recovery: if piexFailed is set via onAbort due to OOM in
 * the C++ for example, or the Module failed to load or call run, then the
 * Module is in a broken, non-functional state.
 *
 * Loading the entire page is the only reliable way to recover from broken
 * Module state. Log the error, and return true to tell caller to initiate
 * failure recovery steps.
 *
 */
function piexModuleFailed(): boolean {
  if (piexFailed || !PiexModule.calledRun) {
    console.error('[PiexLoader] piex wasm module failed');
    return true;
  }
  return false;
}

interface PiexPreviewImageData {
  thumbnail: ArrayBuffer;
  mimeType?: string;
  orientation: number;
  colorSpace: string;
  ifd: string|null;
}

class PiexLoaderResponse {
  readonly thumbnail: ArrayBuffer;
  readonly mimeType: string;

  /** JEITA EXIF image orientation being an integer in [1..8].  */
  readonly orientation: number;

  /** JEITA EXIF image color space: 'sRgb' or 'adobeRgb'.  */
  readonly colorSpace: string;

  /** JSON encoded RAW image photographic details.  */
  readonly ifd: string|null;

  /**
   * @param data The extracted preview image data.
   */
  constructor(data: PiexPreviewImageData) {
    this.thumbnail = data.thumbnail;
    this.mimeType = data.mimeType || 'image/jpeg';
    this.orientation = data.orientation;
    this.colorSpace = data.colorSpace;
    this.ifd = data.ifd || null;
  }
}

/** JFIF APP2 ICC_PROFILE segment containing an AdobeRGB1998 Color Profile. */
const adobeProfile = new Uint8Array([
  // clang-format off
  // APP2 ICC_PROFILE\0 segment header.
  0xff, 0xe2, 0x02, 0x40, 0x49, 0x43, 0x43, 0x5f, 0x50, 0x52, 0x4f, 0x46,
  0x49, 0x4c, 0x45, 0x00, 0x01, 0x01,
  // AdobeRGB1998 ICC Color Profile data.
  0x00, 0x00, 0x02, 0x30, 0x41, 0x44, 0x42, 0x45, 0x02, 0x10, 0x00, 0x00,
  0x6d, 0x6e, 0x74, 0x72, 0x52, 0x47, 0x42, 0x20, 0x58, 0x59, 0x5a, 0x20,
  0x07, 0xd0, 0x00, 0x08, 0x00, 0x0b, 0x00, 0x13, 0x00, 0x33, 0x00, 0x3b,
  0x61, 0x63, 0x73, 0x70, 0x41, 0x50, 0x50, 0x4c, 0x00, 0x00, 0x00, 0x00,
  0x6e, 0x6f, 0x6e, 0x65, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xf6, 0xd6,
  0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0xd3, 0x2d, 0x41, 0x44, 0x42, 0x45,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0a,
  0x63, 0x70, 0x72, 0x74, 0x00, 0x00, 0x00, 0xfc, 0x00, 0x00, 0x00, 0x32,
  0x64, 0x65, 0x73, 0x63, 0x00, 0x00, 0x01, 0x30, 0x00, 0x00, 0x00, 0x6b,
  0x77, 0x74, 0x70, 0x74, 0x00, 0x00, 0x01, 0x9c, 0x00, 0x00, 0x00, 0x14,
  0x62, 0x6b, 0x70, 0x74, 0x00, 0x00, 0x01, 0xb0, 0x00, 0x00, 0x00, 0x14,
  0x72, 0x54, 0x52, 0x43, 0x00, 0x00, 0x01, 0xc4, 0x00, 0x00, 0x00, 0x0e,
  0x67, 0x54, 0x52, 0x43, 0x00, 0x00, 0x01, 0xd4, 0x00, 0x00, 0x00, 0x0e,
  0x62, 0x54, 0x52, 0x43, 0x00, 0x00, 0x01, 0xe4, 0x00, 0x00, 0x00, 0x0e,
  0x72, 0x58, 0x59, 0x5a, 0x00, 0x00, 0x01, 0xf4, 0x00, 0x00, 0x00, 0x14,
  0x67, 0x58, 0x59, 0x5a, 0x00, 0x00, 0x02, 0x08, 0x00, 0x00, 0x00, 0x14,
  0x62, 0x58, 0x59, 0x5a, 0x00, 0x00, 0x02, 0x1c, 0x00, 0x00, 0x00, 0x14,
  0x74, 0x65, 0x78, 0x74, 0x00, 0x00, 0x00, 0x00, 0x43, 0x6f, 0x70, 0x79,
  0x72, 0x69, 0x67, 0x68, 0x74, 0x20, 0x32, 0x30, 0x30, 0x30, 0x20, 0x41,
  0x64, 0x6f, 0x62, 0x65, 0x20, 0x53, 0x79, 0x73, 0x74, 0x65, 0x6d, 0x73,
  0x20, 0x49, 0x6e, 0x63, 0x6f, 0x72, 0x70, 0x6f, 0x72, 0x61, 0x74, 0x65,
  0x64, 0x00, 0x00, 0x00, 0x64, 0x65, 0x73, 0x63, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x11, 0x41, 0x64, 0x6f, 0x62, 0x65, 0x20, 0x52, 0x47,
  0x42, 0x20, 0x28, 0x31, 0x39, 0x39, 0x38, 0x29, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x58, 0x59, 0x5a, 0x20, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0xf3, 0x51, 0x00, 0x01, 0x00, 0x00, 0x00, 0x01, 0x16, 0xcc,
  0x58, 0x59, 0x5a, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x63, 0x75, 0x72, 0x76,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x02, 0x33, 0x00, 0x00,
  0x63, 0x75, 0x72, 0x76, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01,
  0x02, 0x33, 0x00, 0x00, 0x63, 0x75, 0x72, 0x76, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x01, 0x02, 0x33, 0x00, 0x00, 0x58, 0x59, 0x5a, 0x20,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x9c, 0x18, 0x00, 0x00, 0x4f, 0xa5,
  0x00, 0x00, 0x04, 0xfc, 0x58, 0x59, 0x5a, 0x20, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x34, 0x8d, 0x00, 0x00, 0xa0, 0x2c, 0x00, 0x00, 0x0f, 0x95,
  0x58, 0x59, 0x5a, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x26, 0x31,
  0x00, 0x00, 0x10, 0x2f, 0x00, 0x00, 0xbe, 0x9c,
  // clang-format on
]);

/**
 * Piex-wasm extracts the "preview image" from a RAW image. The preview image
 * |format| is either 0 (JPEG), or 1 (RGB), and has a JEITA EXIF |colorSpace|
 * (sRGB or AdobeRGB1998) and a JEITA EXIF image |orientation|.
 *
 * An RGB format preview image has both |width| and |height|, but JPEG format
 * previews have neither (piex-wasm C++ does not parse/decode JPEG).
 *
 * The |offset| to, and |length| of, the preview image relative to the source
 * data is indicated by those fields. They are positive > 0. Note: the values
 * are controlled by a third-party and are untrustworthy (Security).
 */
interface PiexWasmPreviewImageMetadata {
  /** Ether 0 (JPEG), or 1 (RGB). */
  format: number;

  /** JEITA EXIF: sRGB or AdobeRGB1998. */
  colorSpace: string;

  /** JEITA EXIF image orientation.  */
  orientation: number;

  /** Only available for RGB format preview image. */
  width?: number;

  /** Only available for RGB format preview image. */
  height?: number;

  /**
   * The offset of the preview image relative to the source data. They are
   * positive > 0. Note: ths value is controlled by a third-party and are
   * untrustworthy (Security).
   */
  offset: number;

  /**
   * The length of the preview image relative to the source data. They are
   * positive > 0. Note: ths value is controlled by a third-party and are
   * untrustworthy (Security).
   */
  length: number;
}

/**
 * The piex-wasm Module.image(<RAW image source>,...) API returns `error`, or
 * else the source `preview` and/or `thumbnail` image metadata along with the
 * photographic `details` derived from the RAW image EXIF.
 */
interface PiexWasmImageResult {
  error: string|null;

  /** The `preview` images are JPEG.*/
  preview: PiexWasmPreviewImageMetadata|null;

  /**
   * The `thumbnail` images are smaller, lower  quality, JPEG or RGB format
   * images.
   */
  thumbnail: PiexWasmPreviewImageMetadata|null;

  /** The photographic `details` derived from the RAW image EXIF. */
  details: Record<string, any>|null;
}

/**
 * Preview Image EXtractor (PIEX).
 */
class ImageBuffer {
  private readonly source: Uint8Array;
  private readonly length: number;
  private memory = 0;

  /**
   * @param buffer - RAW image source data.
   */
  constructor(buffer: ArrayBuffer) {
    this.source = new Uint8Array(buffer);
    this.length = buffer.byteLength;
  }

  /**
   * Calls Module.image() to process |this.source| and return the result.
   *
   * @throws {!Error} Memory allocation error.
   */
  process(): PiexWasmImageResult {
    this.memory = PiexModule._malloc(this.length);
    if (!this.memory) {
      throw new Error('Image malloc failed: ' + this.length + ' bytes');
    }

    PiexModule.HEAP8.set(this.source, this.memory);
    const result = PiexModule.image(this.memory, this.length);
    if (result.error) {
      throw new Error(result.error);
    }

    return result;
  }

  /**
   * Returns the preview image data. If no preview image was found, returns
   * the thumbnail image.
   *
   * @throws {!Error} Data access security error.
   */
  preview(result: PiexWasmImageResult): PiexPreviewImageData {
    const preview = result.preview;
    if (!preview) {
      return this.thumbnail_(result);
    }

    const offset = preview.offset;
    const length = preview.length;
    if (offset > this.length || (this.length - offset) < length) {
      throw new Error('Preview image access failed');
    }

    const view = new Uint8Array(this.source.buffer, offset, length);
    return {
      thumbnail: this.createImageDataArray_(view, preview).buffer,
      mimeType: 'image/jpeg',
      ifd: this.details_(result, preview.orientation),
      orientation: preview.orientation,
      colorSpace: preview.colorSpace,
    };
  }

  /**
   * Returns the thumbnail image. If no thumbnail image was found, returns
   * an empty thumbnail image.
   *
   * @throws {!Error} Data access security error.
   */
  private thumbnail_(result: PiexWasmImageResult): PiexPreviewImageData {
    const thumbnail = result.thumbnail;
    if (!thumbnail) {
      return {
        thumbnail: new ArrayBuffer(0),
        colorSpace: 'sRgb',
        orientation: 1,
        ifd: null,
      };
    }

    if (thumbnail.format) {
      return this.rgb_(result);
    }

    const offset = thumbnail.offset;
    const length = thumbnail.length;
    if (offset > this.length || (this.length - offset) < length) {
      throw new Error('Thumbnail image access failed');
    }

    const view = new Uint8Array(this.source.buffer, offset, length);
    return {
      thumbnail: this.createImageDataArray_(view, thumbnail).buffer,
      mimeType: 'image/jpeg',
      ifd: this.details_(result, thumbnail.orientation),
      orientation: thumbnail.orientation,
      colorSpace: thumbnail.colorSpace,
    };
  }

  /**
   * Returns the RGB thumbnail. If no RGB thumbnail was found, returns
   * an empty thumbnail image.
   *
   * @throws {!Error} Data access security error.
   */
  private rgb_(result: PiexWasmImageResult): PiexPreviewImageData {
    const thumbnail = result.thumbnail;
    if (!thumbnail || thumbnail.format !== 1) {
      return {
        thumbnail: new ArrayBuffer(0),
        colorSpace: 'sRgb',
        orientation: 1,
        ifd: null,
      };
    }

    // Expect a width and height.
    if (!thumbnail.width || !thumbnail.height) {
      throw new Error('invalid image width or height');
    }

    const offset = thumbnail.offset;
    const length = thumbnail.length;
    if (offset > this.length || (this.length - offset) < length) {
      throw new Error('Thumbnail image access failed');
    }

    const view = new Uint8Array(this.source.buffer, offset, length);

    // Compute output image width and height.
    const usesWidthAsHeight = thumbnail.orientation >= 5;
    const height = usesWidthAsHeight ? thumbnail.width : thumbnail.height;
    const width = usesWidthAsHeight ? thumbnail.height : thumbnail.width;

    // Compute pixel row stride.
    const rowPad = width & 3;
    const rowStride = 3 * width + rowPad;

    // Create bitmap image.
    const pixelDataOffset = 14 + 108;
    const fileSize = pixelDataOffset + rowStride * height;
    const bitmap = new DataView(new ArrayBuffer(fileSize));

    // BITMAPFILEHEADER 14 bytes.
    bitmap.setUint8(0, 'B'.charCodeAt(0));
    bitmap.setUint8(1, 'M'.charCodeAt(0));
    bitmap.setUint32(2, fileSize /* bytes */, true);
    bitmap.setUint32(6, /* Reserved */ 0, true);
    bitmap.setUint32(10, pixelDataOffset, true);

    // DIB BITMAPV4HEADER 108 bytes.
    bitmap.setUint32(14, /* HeaderSize */ 108, true);
    bitmap.setInt32(18, width, true);
    bitmap.setInt32(22, -height /* top-down DIB */, true);
    bitmap.setInt16(26, /* ColorPlanes */ 1, true);
    bitmap.setInt16(28, /* BitsPerPixel BI_RGB */ 24, true);
    bitmap.setUint32(30, /* Compression: BI_RGB none */ 0, true);
    bitmap.setUint32(34, /* ImageSize: 0 not compressed */ 0, true);
    bitmap.setInt32(38, /* XPixelsPerMeter */ 0, true);
    bitmap.setInt32(42, /* YPixelPerMeter */ 0, true);
    bitmap.setUint32(46, /* TotalPalletColors */ 0, true);
    bitmap.setUint32(50, /* ImportantColors */ 0, true);

    bitmap.setUint32(54, /* RedMask */ 0, true);
    bitmap.setUint32(58, /* GreenMask */ 0, true);
    bitmap.setUint32(62, /* BlueMask */ 0, true);
    bitmap.setUint32(66, /* AlphaMask */ 0, true);

    let rx = 0;
    let ry = 0;
    let gx = 0;
    let gy = 0;
    let bx = 0;
    let by = 0;
    let zz = 0;
    let gg = 0;

    if (thumbnail.colorSpace !== 'adobeRgb') {
      bitmap.setUint8(70, 's'.charCodeAt(0));
      bitmap.setUint8(71, 'R'.charCodeAt(0));
      bitmap.setUint8(72, 'G'.charCodeAt(0));
      bitmap.setUint8(73, 'B'.charCodeAt(0));
    } else {
      bitmap.setUint32(70, /* adobeRgb LCS_CALIBRATED_RGB */ 0);
      rx = Math.round(0.6400 * (1 << 30));
      ry = Math.round(0.3300 * (1 << 30));
      gx = Math.round(0.2100 * (1 << 30));
      gy = Math.round(0.7100 * (1 << 30));
      bx = Math.round(0.1500 * (1 << 30));
      by = Math.round(0.0600 * (1 << 30));
      zz = Math.round(1.0000 * (1 << 30));
      gg = Math.round(2.1992187 * (1 << 16));
    }

    // RGB CIEXYZ.
    bitmap.setUint32(74, /* R CIEXYZ x */ rx, true);
    bitmap.setUint32(78, /* R CIEXYZ y */ ry, true);
    bitmap.setUint32(82, /* R CIEXYZ z */ zz, true);
    bitmap.setUint32(86, /* G CIEXYZ x */ gx, true);
    bitmap.setUint32(90, /* G CIEXYZ y */ gy, true);
    bitmap.setUint32(94, /* G CIEXYZ z */ zz, true);
    bitmap.setUint32(98, /* B CIEXYZ x */ bx, true);
    bitmap.setUint32(102, /* B CIEXYZ y */ by, true);
    bitmap.setUint32(106, /* B CIEXYZ z */ zz, true);

    // RGB gamma.
    bitmap.setUint32(110, /* R Gamma */ gg, true);
    bitmap.setUint32(114, /* G Gamma */ gg, true);
    bitmap.setUint32(118, /* B Gamma */ gg, true);

    // Write RGB row pixels in top-down DIB order.
    const h = thumbnail.height - 1;
    const w = thumbnail.width - 1;
    let dx = 0;

    for (let input = 0, y = 0; y <= h; ++y) {
      let output = pixelDataOffset;

      /**
       * Compute affine(a,b,c,d,tx,ty) transform of pixel (x,y)
       *   { x': a * x + c * y + tx, y': d * y + b * x + ty }
       * a,b,c,d in [-1,0,1], to apply the image orientation at
       * (0,y) to find the output location of the input row.
       * The transform derivative in x is used to calculate the
       * relative output location of adjacent input row pixels.
       */
      switch (thumbnail.orientation) {
        case 1:  // affine(+1, 0, 0, +1, 0, 0)
          output += y * rowStride;
          dx = 3;
          break;
        case 2:  // affine(-1, 0, 0, +1, w, 0)
          output += y * rowStride + 3 * w;
          dx = -3;
          break;
        case 3:  // affine(-1, 0, 0, -1, w, h)
          output += (h - y) * rowStride + 3 * w;
          dx = -3;
          break;
        case 4:  // affine(+1, 0, 0, -1, 0, h)
          output += (h - y) * rowStride;
          dx = 3;
          break;
        case 5:  // affine(0, +1, +1, 0, 0, 0)
          output += 3 * y;
          dx = rowStride;
          break;
        case 6:  // affine(0, +1, -1, 0, h, 0)
          output += 3 * (h - y);
          dx = rowStride;
          break;
        case 7:  // affine(0, -1, -1, 0, h, w)
          output += w * rowStride + 3 * (h - y);
          dx = -rowStride;
          break;
        case 8:  // affine(0, -1, +1, 0, 0, w)
          output += w * rowStride + 3 * y;
          dx = -rowStride;
          break;
      }

      for (let x = 0; x <= w; ++x, input += 3, output += dx) {
        bitmap.setUint8(output + 0, view[input + 2]!);  // B
        bitmap.setUint8(output + 1, view[input + 1]!);  // G
        bitmap.setUint8(output + 2, view[input + 0]!);  // R
      }
    }

    // Write pixel row padding bytes if needed.
    if (rowPad) {
      let paddingOffset = pixelDataOffset + 3 * width;

      for (let y = 0; y < height; ++y) {
        let output = paddingOffset;

        switch (rowPad) {
          case 1:
            bitmap.setUint8(output++, 0);
            break;
          case 2:
            bitmap.setUint8(output++, 0);
            bitmap.setUint8(output++, 0);
            break;
          case 3:
            bitmap.setUint8(output++, 0);
            bitmap.setUint8(output++, 0);
            bitmap.setUint8(output++, 0);
            break;
        }

        paddingOffset += rowStride;
      }
    }

    return {
      thumbnail: bitmap.buffer,
      mimeType: 'image/bmp',
      ifd: this.details_(result, thumbnail.orientation),
      colorSpace: thumbnail.colorSpace,
      orientation: 1,
    };
  }

  /**
   * Converts a |view| of the "preview image" to Uint8Array data. Embeds an
   * AdobeRGB1998 ICC Color Profile in that data if the preview is JPEG and
   * it has 'adodeRgb' color space.
   *
   */
  private createImageDataArray_(
      view: Uint8Array,
      preview: PiexWasmPreviewImageMetadata): Uint8Array<ArrayBuffer> {
    const jpeg = view.byteLength > 2 && view[0] === 0xff && view[1] === 0xd8;

    if (jpeg && preview.colorSpace === 'adobeRgb') {
      const data = new Uint8Array(view.byteLength + adobeProfile.byteLength);
      data.set(view.subarray(2), 2 + adobeProfile.byteLength);
      data.set(adobeProfile, 2);
      data.set([0xff, 0xd8], 0);
      return data;
    }

    return new Uint8Array(view);
  }

  /**
   * Returns the RAW image photographic |details| in a JSON-encoded string.
   * Only number and string values are retained, and they are formatted for
   * presentation to the user.
   *
   * @param orientation - image EXIF orientation
   */
  private details_(result: PiexWasmImageResult, orientation: number): null
      |string {
    const details = result.details;
    if (!details) {
      return null;
    }

    const format: Record<string, string|number> = {};
    for (const [key, value] of Object.entries(details)) {
      if (typeof value === 'string') {
        format[key] = value.replace(/\0+$/, '').trim();
      } else if (typeof value === 'number') {
        if (!Number.isInteger(value)) {
          format[key] = Number(value.toFixed(3).replace(/0+$/, ''));
        } else {
          format[key] = value;
        }
      }
    }

    const usesWidthAsHeight = orientation >= 5;
    if (usesWidthAsHeight) {
      const width = format['width']!;
      format['width'] = format['height']!;
      format['height'] = width;
    }

    return JSON.stringify(format);
  }

  /**
   * Release resources.
   */
  close() {
    const memory = this.memory;
    if (memory) {
      PiexModule._free(memory);
      this.memory = 0;
    }
  }
}

/**
 * PiexLoader: is a namespace.
 */
export const PiexLoader = {

  /**
   * Loads a RAW image. Returns the image metadata and the image thumbnail in a
   * PiexLoaderResponse.
   *
   * piexModuleFailed() returns true if the Module is in an unrecoverable error
   * state. This is rare, but possible, and the only reliable way to recover is
   * to reload the page. Callback |onPiexModuleFailed| is used to indicate that
   * the caller should initiate failure recovery steps.
   *
   */
  load(buffer: ArrayBuffer, onPiexModuleFailed: VoidCallback):
      Promise<PiexLoaderResponse> {
        let imageBuffer: ImageBuffer|null;

        return piexModuleInitialized()
            .then(() => {
              if (piexModuleFailed()) {
                throw new Error('piex wasm module failed');
              }
              imageBuffer = new ImageBuffer(buffer);
              return imageBuffer.process();
            })
            .then((result: PiexWasmImageResult) => {
              return new PiexLoaderResponse(imageBuffer!.preview(result));
            })
            .catch((error) => {
              if (piexModuleFailed()) {
                setTimeout(onPiexModuleFailed, 0);
                return Promise.reject('piex wasm module failed');
              }
              console.warn('[PiexLoader] ' + error);
              return Promise.reject(error);
            })
            .finally(() => {
              imageBuffer && imageBuffer.close();
            });
      },
};

export const PIEX_LOADER_TEST_ONLY = {
  getModule: () => PiexModule,
};