Function getEncoding

src/pkg/utils/istextorbinary.ts:35–97

* Get the encoding of a buffer. * Checks the start, middle, and end of the buffer for characters that are unrecognized within UTF8 encoding. * History has shown that inspection at all three locations is necessary. * @returns Will be `null` if `buffer` was not provided. Otherwise will be either `'

(buffer: Uint8Array, opts?: EncodingOpts)

 * @returns Will be `null` if `buffer` was not provided. Otherwise will be either `'utf8'` or `'binary'`
 */
function getEncoding(buffer: Uint8Array, opts?: EncodingOpts): "utf8" | "binary" | null {
  // Check
  if (!buffer) return null;

  // Prepare
  const textEncoding = "utf8";
  const binaryEncoding = "binary";
  const chunkLength = opts?.chunkLength ?? 24;
  let chunkBegin = opts?.chunkBegin ?? 0;

  // Discover
  if (opts?.chunkBegin === undefined) {
    // Start
    let encoding = getEncoding(buffer, { chunkLength, chunkBegin });
    if (encoding === textEncoding) {
      // Middle
      chunkBegin = Math.max(0, Math.floor(buffer.length / 2) - chunkLength);
      encoding = getEncoding(buffer, {
        chunkLength,
        chunkBegin,
      });
      if (encoding === textEncoding) {
        // End
        chunkBegin = Math.max(0, buffer.length - chunkLength);
        encoding = getEncoding(buffer, {
          chunkLength,
          chunkBegin,
        });
      }
    }

    // Return
    return encoding;
  } else {
    // Extract
    chunkBegin = getChunkBegin(buffer, chunkBegin);
    if (chunkBegin === -1) {
      return binaryEncoding;
    }

    const chunkEnd = getChunkEnd(buffer, Math.min(buffer.length, chunkBegin + chunkLength));

    if (chunkEnd > buffer.length) {
      return binaryEncoding;
    }

    const contentChunkUTF8 = buffer.slice(chunkBegin, chunkEnd);

    // Detect encoding
    for (let i = 0; i < contentChunkUTF8.length; ++i) {
      const charCode = contentChunkUTF8[i];
      if (charCode === 65533 || charCode <= 8) {
        // 8 and below are control characters (e.g. backspace, null, eof, etc.)
        // 65533 is the unknown character
        // console.log(charCode, contentChunkUTF8[i])
        return binaryEncoding;
      }
    }