Function parseDisplayString

http/unstable_structured_fields.ts:1032–1095

(state: ParserState)

}

function parseDisplayString(state: ParserState): BareItem {
  if (consume(state) !== "%") {
    throw new SyntaxError(
      `Invalid structured field: expected '%' at position ${state.pos - 1}`,
    );
  }
  if (consume(state) !== '"') {
    throw new SyntaxError(
      `Invalid structured field: expected '"' at position ${state.pos - 1}`,
    );
  }

  const bytes: number[] = [];
  while (!isEof(state)) {
    const c = consume(state);

    if (c === '"') {
      // Decode UTF-8 bytes to string
      try {
        const value = UTF8_DECODER.decode(new Uint8Array(bytes));
        return { type: "displaystring", value };
      } catch {
        throw new SyntaxError(
          "Invalid structured field: invalid UTF-8 in display string",
        );
      }
    } else if (c === "%") {
      // Percent-encoded byte
      const hex1 = consume(state);
      const hex2 = consume(state);
      if (!isLcHexDigit(hex1) || !isLcHexDigit(hex2)) {
        throw new SyntaxError(
          `Invalid structured field: invalid percent encoding at position ${
            state.pos - 2
          }`,
        );
      }
      bytes.push(parseInt(hex1 + hex2, 16));
    } else {
      // Must be allowed unescaped character per RFC 9651:
      // unescaped = %x20-21 / %x23-24 / %x26-5B / %x5D-7E
      // (space, !, #, $, &-[, ]-~)
      // Note: " (0x22) and % (0x25) must be percent-encoded
      // Note: Per conformance tests, \ (0x5C) is also allowed
      const code = c.charCodeAt(0);
      const isAllowed = code === 0x20 || code === 0x21 || // space, !
        code === 0x23 || code === 0x24 || // #, $
        (code >= 0x26 && code <= 0x5b) || // &-[
        (code >= 0x5c && code <= 0x7e); // \-~ (includes \ per conformance tests)
      if (!isAllowed) {
        throw new SyntaxError(
          `Invalid structured field: invalid character in display string at position ${
            state.pos - 1
          }`,
        );
      }
      bytes.push(code);
    }