Function parseString

http/unstable_structured_fields.ts:857–929

(state: ParserState)

}

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

  const { input } = state;
  const startPos = state.pos;

  // Fast path: find first special character (\ or ")
  let firstSpecial = startPos;
  while (firstSpecial < input.length) {
    const c = input[firstSpecial]!;
    if (c === '"' || c === "\\") break;
    // Validate printable ASCII
    const code = c.charCodeAt(0);
    if (code < 0x20 || code > 0x7e) {
      throw new SyntaxError(
        `Invalid structured field: invalid character in string at position ${firstSpecial}`,
      );
    }
    firstSpecial++;
  }

  // If we hit end of string without finding closing quote
  if (firstSpecial >= input.length) {
    throw new SyntaxError("Invalid structured field: unterminated string");
  }

  // Fast path: no escapes, just a closing quote
  if (input[firstSpecial] === '"') {
    state.pos = firstSpecial + 1;
    return { type: "string", value: input.slice(startPos, firstSpecial) };
  }

  // Slow path: has escapes, need to process character by character
  let value = input.slice(startPos, firstSpecial);
  state.pos = firstSpecial;

  while (!isEof(state)) {
    const c = consume(state);

    if (c === "\\") {
      const escaped = consume(state);
      if (escaped !== '"' && escaped !== "\\") {
        throw new SyntaxError(
          `Invalid structured field: invalid escape sequence at position ${
            state.pos - 1
          }`,
        );
      }
      value += escaped;
    } else if (c === '"') {
      return { type: "string", value };
    } else {
      // Must be printable ASCII (0x20-0x7E) excluding 0x22 (") and 0x5C (\)
      const code = c.charCodeAt(0);