src/lib/qoder/encoding.js

/**
 * Qoder body encoding ported from qoder2api's QoderEncoding.java (via the
 * CLIProxyAPIPlus qoder-provider branch).
 *
 * Algorithm:
 *   1. base64-encode the plaintext bytes (standard alphabet).
 *   2. Rearrange: split into thirds, reorder as [tail][mid][head].
 *   3. Substitute each character via a custom alphabet mapping.
 *
 * The encoded body must be sent with `&Encode=1` appended to the URL so the
 * server decodes in reverse. The obfuscation prevents Alibaba Cloud WAF from
 * pattern-matching the plaintext request body.
 */

const QODER_STD_ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
const QODER_CUSTOM_ALPHABET = "_doRTgHZBKcGVjlvpC,@aFSx#DPuNJme&i*MzLOEn)sUrthbf%Y^w.(kIQyXqWA!";

const QODER_S2C = (() => {
  const table = new Int16Array(128).fill(-1);
  for (let i = 0; i < 64; i++) {
    table[QODER_STD_ALPHABET.charCodeAt(i)] = QODER_CUSTOM_ALPHABET.charCodeAt(i);
  }
  table["=".charCodeAt(0)] = "$".charCodeAt(0);
  return table;
})();

/**
 * Encode plaintext bytes/string using Qoder's WAF-bypass scheme.
 * @param {Buffer|Uint8Array|string} plaintext
 * @returns {string} encoded string
 */
export function qoderEncodeBody(plaintext) {
  const buf = Buffer.isBuffer(plaintext)
    ? plaintext
    : typeof plaintext === "string"
      ? Buffer.from(plaintext, "utf8")
      : Buffer.from(plaintext);

  const std = buf.toString("base64");
  const n = std.length;
  const a = Math.floor(n / 3);
  // [tail][mid][head]
  const rearranged = std.slice(n - a) + std.slice(a, n - a) + std.slice(0, a);

  const out = Buffer.alloc(n);
  for (let i = 0; i < n; i++) {
    const c = rearranged.charCodeAt(i);
    if (c < 128 && QODER_S2C[c] >= 0) {
      out[i] = QODER_S2C[c];
    } else {
      out[i] = c;
    }
  }
  return out.toString("latin1");
}