ws/lib/extension.js

'use strict';

//
// Allowed token characters:
//
// '!', '#', '$', '%', '&', ''', '*', '+', '-',
// '.', 0-9, A-Z, '^', '_', '`', a-z, '|', '~'
//
// tokenChars[32] === 0 // ' '
// tokenChars[33] === 1 // '!'
// tokenChars[34] === 0 // '"'
// ...
//
const tokenChars = [
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 0 - 15
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 16 - 31
  0, 1, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 0, 1, 1, 0, // 32 - 47
  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, // 48 - 63
  0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 64 - 79
  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 1, 1, // 80 - 95
  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 96 - 111
  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 0, 1, 0 // 112 - 127
];

/**
 * Adds an offer to the map of extension offers or a parameter to the map of
 * parameters.
 *
 * @param {Object} dest The map of extension offers or parameters
 * @param {String} name The extension or parameter name
 * @param {(Object|Boolean|String)} elem The extension parameters or the
 *     parameter value
 * @private
 */
function push (dest, name, elem) {
  if (Object.prototype.hasOwnProperty.call(dest, name)) dest[name].push(elem);
  else dest[name] = [elem];
}

/**
 * Parses the `Sec-WebSocket-Extensions` header into an object.
 *
 * @param {String} header The field value of the header
 * @return {Object} The parsed object
 * @public
 */
function parse (header) {
  const offers = {};

  if (header === undefined || header === '') return offers;

  var params = {};
  var mustUnescape = false;
  var isEscaping = false;
  var inQuotes = false;
  var extensionName;
  var paramName;
  var start = -1;
  var end = -1;

  for (var i = 0; i < header.length; i++) {
    const code = header.charCodeAt(i);

    if (extensionName === undefined) {
      if (end === -1 && tokenChars[code] === 1) {
        if (start === -1) start = i;
      } else if (code === 0x20/* ' ' */ || code === 0x09/* '\t' */) {
        if (end === -1 && start !== -1) end = i;
      } else if (code === 0x3b/* ';' */ || code === 0x2c/* ',' */) {
        if (start === -1) {
          throw new SyntaxError(`Unexpected character at index ${i}`);
        }

        if (end === -1) end = i;
        const name = header.slice(start, end);
        if (code === 0x2c) {
          push(offers, name, params);
          params = {};
        } else {
          extensionName = name;
        }

        start = end = -1;
      } else {
        throw new SyntaxError(`Unexpected character at index ${i}`);
      }
    } else if (paramName === undefined) {
      if (end === -1 && tokenChars[code] === 1) {
        if (start === -1) start = i;
      } else if (code === 0x20 || code === 0x09) {
        if (end === -1 && start !== -1) end = i;
      } else if (code === 0x3b || code === 0x2c) {
        if (start === -1) {
          throw new SyntaxError(`Unexpected character at index ${i}`);
        }

        if (end === -1) end = i;
        push(params, header.slice(start, end), true);
        if (code === 0x2c) {
          push(offers, extensionName, params);
          params = {};
          extensionName = undefined;
        }

        start = end = -1;
      } else if (code === 0x3d/* '=' */ && start !== -1 && end === -1) {
        paramName = header.slice(start, i);
        start = end = -1;
      } else {
        throw new SyntaxError(`Unexpected character at index ${i}`);
      }
    } else {
      //
      // The value of a quoted-string after unescaping must conform to the
      // token ABNF, so only token characters are valid.
      // Ref: https://tools.ietf.org/html/rfc6455#section-9.1
      //
      if (isEscaping) {
        if (tokenChars[code] !== 1) {
          throw new SyntaxError(`Unexpected character at index ${i}`);
        }
        if (start === -1) start = i;
        else if (!mustUnescape) mustUnescape = true;
        isEscaping = false;
      } else if (inQuotes) {
        if (tokenChars[code] === 1) {
          if (start === -1) start = i;
        } else if (code === 0x22/* '"' */ && start !== -1) {
          inQuotes = false;
          end = i;
        } else if (code === 0x5c/* '\' */) {
          isEscaping = true;
        } else {
          throw new SyntaxError(`Unexpected character at index ${i}`);
        }
      } else if (code === 0x22 && header.charCodeAt(i - 1) === 0x3d) {
        inQuotes = true;
      } else if (end === -1 && tokenChars[code] === 1) {
        if (start === -1) start = i;
      } else if (start !== -1 && (code === 0x20 || code === 0x09)) {
        if (end === -1) end = i;
      } else if (code === 0x3b || code === 0x2c) {
        if (start === -1) {
          throw new SyntaxError(`Unexpected character at index ${i}`);
        }

        if (end === -1) end = i;
        var value = header.slice(start, end);
        if (mustUnescape) {
          value = value.replace(/\\/g, '');
          mustUnescape = false;
        }
        push(params, paramName, value);
        if (code === 0x2c) {
          push(offers, extensionName, params);
          params = {};
          extensionName = undefined;
        }

        paramName = undefined;
        start = end = -1;
      } else {
        throw new SyntaxError(`Unexpected character at index ${i}`);
      }
    }
  }

  if (start === -1 || inQuotes) {
    throw new SyntaxError('Unexpected end of input');
  }

  if (end === -1) end = i;
  const token = header.slice(start, end);
  if (extensionName === undefined) {
    push(offers, token, {});
  } else {
    if (paramName === undefined) {
      push(params, token, true);
    } else if (mustUnescape) {
      push(params, paramName, token.replace(/\\/g, ''));
    } else {
      push(params, paramName, token);
    }
    push(offers, extensionName, params);
  }

  return offers;
}

/**
 * Builds the `Sec-WebSocket-Extensions` header field value.
 *
 * @param {Object} extensions The map of extensions and parameters to format
 * @return {String} A string representing the given object
 * @public
 */
function format (extensions) {
  return Object.keys(extensions).map((extension) => {
    var configurations = extensions[extension];
    if (!Array.isArray(configurations)) configurations = [configurations];
    return configurations.map((params) => {
      return [extension].concat(Object.keys(params).map((k) => {
        var values = params[k];
        if (!Array.isArray(values)) values = [values];
        return values.map((v) => v === true ? k : `${k}=${v}`).join('; ');
      })).join('; ');
    }).join(', ');
  }).join(', ');
}

module.exports = { format, parse };