repo_description: Promise based HTTP client for the browser and node.js
repo_topics: hacktoberfest http-client javascript nodejs promise
code: /**
   * Estimate decoded byte length of a data:// URL *without* allocating large buffers.
   * - For base64: compute exact decoded size using length and padding;
   *               handle %XX at the character-count level (no string allocation).
   * - For non-base64: use UTF-8 byteLength of the encoded body as a safe upper bound.
   *
   * @param {string} url
   * @returns {number}
   */
  export default function estimateDataURLDecodedBytes(url) {
    if (!url || typeof url !== 'string') return 0;
    if (!url.startsWith('data:')) return 0;
  
    const comma = url.indexOf(',');
    if (comma < 0) return 0;
  
    const meta = url.slice(5, comma);
    const body = url.slice(comma + 1);
    const isBase64 = /;base64/i.test(meta);
  
    if (isBase64) {
      let effectiveLen = body.length;
      const len = body.length; // cache length
  
      for (let i = 0; i < len; i++) {
        if (body.charCodeAt(i) === 37 /* '%' */ && i + 2 < len) {
          const a = body.charCodeAt(i + 1);
          const b = body.charCodeAt(i + 2);
          const isHex =
            ((a >= 48 && a <= 57) || (a >= 65 && a <= 70) || (a >= 97 && a <= 102)) &&
            ((b >= 48 && b <= 57) || (b >= 65 && b <= 70) || (b >= 97 && b <= 102));
  
          if (isHex) {
            effectiveLen -= 2;
            i += 2;
          }
        }
      }
  
      let pad = 0;
      let idx = len - 1;
  
      const tailIsPct3D = (j) =>
        j >= 2 &&
        body.charCodeAt(j - 2) === 37 && // '%'
        body.charCodeAt(j - 1) === 51 && // '3'
        (body.charCodeAt(j) === 68 || body.charCodeAt(j) === 100); // 'D' or 'd'
  
      if (idx >= 0) {
        if (body.charCodeAt(idx) === 61 /* '=' */) {
          pad++;
          idx--;
        } else if (tailIsPct3D(idx)) {
          pad++;
          idx -= 3;
        }
      }
  
      if (pad === 1 && idx >= 0) {
        if (body.charCodeAt(idx) === 61 /* '=' */) {
          pad++;
        } else if (tailIsPct3D(idx)) {
          pad++;
        }
      }
  
      const groups = Math.floor(effectiveLen / 4);
      const bytes = groups * 3 - (pad || 0);
      return bytes > 0 ? bytes : 0;
    }
  
    if (typeof Buffer !== 'undefined' && typeof Buffer.byteLength === 'function') {
      return Buffer.byteLength(body, 'utf8');
    }
  
    // Compute UTF-8 byte length directly from UTF-16 code units without allocating
    // a byte buffer (TextEncoder.encode would defeat the DoS guard on large bodies).
    // Using body.length here would undercount non-ASCII (e.g. '€' is 1 code unit
    // but 3 UTF-8 bytes).
    let bytes = 0;
    for (let i = 0, len = body.length; i < len; i++) {
      const c = body.charCodeAt(i);
      if (c < 0x80) {
        bytes += 1;
      } else if (c < 0x800) {
        bytes += 2;
      } else if (c >= 0xd800 && c <= 0xdbff && i + 1 < len) {
        const next = body.charCodeAt(i + 1);
        if (next >= 0xdc00 && next <= 0xdfff) {
          bytes += 4;
          i++;
        } else {
          bytes += 3;
        }
      } else {
        bytes += 3;
      }
    }
    return bytes;
  }
  