gongxiangp2/lib/performance-survey-image-source-guard.ts

export const PERFORMANCE_SURVEY_BROWSER_SOURCE_LIMITS = {
  maxWidth: 12_000,
  // 视觉评分的源图通常是 1600px 左右的长图。这里允许 1600×75,000 这类长图，
  // 但仍在浏览器解码前挡住会显著拖垮员工设备的超大像素文件。
  maxPixels: 120_000_000,
  maxOutputWidth: 1_600,
  sliceHeight: 1_500,
  maxSlicesPerCase: 60,
  headerReadBytes: 256 * 1024,
} as const

export type PerformanceSurveySourceImageDimensions = {
  width: number
  height: number
}

export class PerformanceSurveySourceImageError extends Error {}

function readUInt16BE(bytes: Uint8Array, offset: number) {
  return (bytes[offset] << 8) | bytes[offset + 1]
}

function readUInt16LE(bytes: Uint8Array, offset: number) {
  return bytes[offset] | (bytes[offset + 1] << 8)
}

function readUInt24LE(bytes: Uint8Array, offset: number) {
  return bytes[offset] | (bytes[offset + 1] << 8) | (bytes[offset + 2] << 16)
}

function startsWithAscii(bytes: Uint8Array, text: string, offset = 0) {
  if (bytes.length < offset + text.length) return false
  return Array.from(text).every((character, index) => bytes[offset + index] === character.charCodeAt(0))
}

function readPngDimensions(bytes: Uint8Array): PerformanceSurveySourceImageDimensions | null {
  const pngSignature = [0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a]
  if (bytes.length < 24 || !pngSignature.every((value, index) => bytes[index] === value)) return null
  const view = new DataView(bytes.buffer, bytes.byteOffset, bytes.byteLength)
  return { width: view.getUint32(16), height: view.getUint32(20) }
}

function readGifDimensions(bytes: Uint8Array): PerformanceSurveySourceImageDimensions | null {
  if (bytes.length < 10 || (!startsWithAscii(bytes, 'GIF87a') && !startsWithAscii(bytes, 'GIF89a'))) return null
  return { width: readUInt16LE(bytes, 6), height: readUInt16LE(bytes, 8) }
}

function readWebpDimensions(bytes: Uint8Array): PerformanceSurveySourceImageDimensions | null {
  if (bytes.length < 30 || !startsWithAscii(bytes, 'RIFF') || !startsWithAscii(bytes, 'WEBP', 8)) return null
  const chunkType = String.fromCharCode(bytes[12], bytes[13], bytes[14], bytes[15])
  if (chunkType === 'VP8X') {
    return { width: readUInt24LE(bytes, 24) + 1, height: readUInt24LE(bytes, 27) + 1 }
  }
  if (chunkType === 'VP8L' && bytes.length >= 25 && bytes[20] === 0x2f) {
    const b1 = bytes[21]
    const b2 = bytes[22]
    const b3 = bytes[23]
    const b4 = bytes[24]
    return {
      width: 1 + (b1 | ((b2 & 0x3f) << 8)),
      height: 1 + ((b2 >> 6) | (b3 << 2) | ((b4 & 0x0f) << 10)),
    }
  }
  if (chunkType === 'VP8 ' && bytes.length >= 30 && bytes[23] === 0x9d && bytes[24] === 0x01 && bytes[25] === 0x2a) {
    return { width: readUInt16LE(bytes, 26) & 0x3fff, height: readUInt16LE(bytes, 28) & 0x3fff }
  }
  return null
}

function readJpegDimensions(bytes: Uint8Array): PerformanceSurveySourceImageDimensions | null {
  if (bytes.length < 4 || bytes[0] !== 0xff || bytes[1] !== 0xd8) return null
  let offset = 2
  while (offset + 9 < bytes.length) {
    if (bytes[offset] !== 0xff) {
      offset += 1
      continue
    }
    while (bytes[offset] === 0xff) offset += 1
    const marker = bytes[offset]
    offset += 1
    if (marker === 0xd8 || marker === 0xd9 || (marker >= 0xd0 && marker <= 0xd7) || marker === 0x01) continue
    if (offset + 1 >= bytes.length) return null
    const segmentLength = readUInt16BE(bytes, offset)
    if (segmentLength < 2 || offset + segmentLength > bytes.length) return null
    const isStartOfFrame = marker >= 0xc0 && marker <= 0xcf && ![0xc4, 0xc8, 0xcc].includes(marker)
    if (isStartOfFrame) {
      return {
        height: readUInt16BE(bytes, offset + 3),
        width: readUInt16BE(bytes, offset + 5),
      }
    }
    offset += segmentLength
  }
  return null
}

export function readPerformanceSurveySourceImageDimensions(bytes: Uint8Array) {
  return readPngDimensions(bytes)
    || readJpegDimensions(bytes)
    || readGifDimensions(bytes)
    || readWebpDimensions(bytes)
}

export function assertPerformanceSurveyBrowserSourceImageDimensions(
  dimensions: PerformanceSurveySourceImageDimensions | null,
  sourceName: string,
) {
  if (!dimensions || !Number.isInteger(dimensions.width) || !Number.isInteger(dimensions.height)
    || dimensions.width <= 0 || dimensions.height <= 0) {
    throw new PerformanceSurveySourceImageError(
      `图片「${sourceName}」无法在解码前读取尺寸，请使用 PNG、JPG、GIF 或 WebP 格式`,
    )
  }
  if (dimensions.width > PERFORMANCE_SURVEY_BROWSER_SOURCE_LIMITS.maxWidth) {
    throw new PerformanceSurveySourceImageError(
      `图片「${sourceName}」宽度超过 ${PERFORMANCE_SURVEY_BROWSER_SOURCE_LIMITS.maxWidth}px`,
    )
  }
  if (dimensions.width * dimensions.height > PERFORMANCE_SURVEY_BROWSER_SOURCE_LIMITS.maxPixels) {
    throw new PerformanceSurveySourceImageError(
      `图片「${sourceName}」像素总量超过 ${PERFORMANCE_SURVEY_BROWSER_SOURCE_LIMITS.maxPixels.toLocaleString()}，请先压缩或切图`,
    )
  }
  const outputScale = Math.min(1, PERFORMANCE_SURVEY_BROWSER_SOURCE_LIMITS.maxOutputWidth / dimensions.width)
  const outputHeight = Math.max(1, Math.round(dimensions.height * outputScale))
  const sliceCount = Math.ceil(outputHeight / PERFORMANCE_SURVEY_BROWSER_SOURCE_LIMITS.sliceHeight)
  if (sliceCount > PERFORMANCE_SURVEY_BROWSER_SOURCE_LIMITS.maxSlicesPerCase) {
    throw new PerformanceSurveySourceImageError(
      `图片「${sourceName}」处理后需要 ${sliceCount} 张切片，单个案例最多支持 ${PERFORMANCE_SURVEY_BROWSER_SOURCE_LIMITS.maxSlicesPerCase} 张`,
    )
  }
}