normalize MIME types for comparison

normalizeMime.js

function normalizeMime(string) {
  let pos = 0;
  let normalized = "";
  const consume = (regex) => {
    const match = string.match(regex);
    if (!match)
      throw new SyntaxError(
        "failed to match /" +
          regex.source +
          "/" +
          regex.flags +
          " at index " +
          pos,
      );
    const consumed = match[0];
    const length = consumed.length;
    pos += length;
    string = string.slice(length);
    return consumed;
  };
  const consumeQuoted = () => {
    let str = "";
    consume(/^"/);
    while (true) {
      if (string[0] === "\\") {
        str += consume(/^\\/);
        str += consume(/^[\x21-\x7E]/);
      } else if (string[0] === '"') {
        consume(/^"/);
        break;
      } else {
        str += consume(/^[\s\S]/);
      }
    }
    return str;
  };
  const ws = () => consume(/^\s*/);
  const token = /^[0-9A-Za-z!#$%&'*+.^_`|~-]+/;
  ws();
  normalized += consume(token);
  ws();
  normalized += consume(/^\//);
  ws();
  normalized += consume(token);
  ws();
  while (string.length > 0) {
    normalized += consume(/^;/);
    ws();
    normalized += consume(token);
    ws();
    normalized += consume(/^=/);
    ws();
    const value = string[0] === '"' ? consumeQuoted() : consume(token);
    const match = value.match(token);
    normalized +=
      match && match[0].length === value.length ? value : `"${value}"`;
    ws();
  }
  return normalized;
}