diffusion/src/node_modules/util/message-encoding.js

Diffusion JavaScript client

/*eslint valid-jsdoc: "off"*/
var MESSAGE_TYPE_MASK = 0xA7D8C0;
var ZLIB_TYPE_FLAGS = 0x80;

/**
 * The "message type flags" allow a subset of MessageEncodings to be encoded
 * in the upper two bits of the message type byte. Only NO_ENCODING and
 * ZLIB are supported.
 * @param {Number} - encodingByte.
 * @param {Number} - messageTypeFlags.
 * @return {MessageEncoding} - The MessageEncoding.
 */
function MessageEncoding(encodingByte, messageTypeFlags) {
    return {
        encodingByte : encodingByte,
        messageTypeFlags : messageTypeFlags
    };
}

/**
 * Decode the message type from a byte combining the message type and flags.
 * @return {Number} The message type.
 */
function extractMessageType(typeAndEncoding) {
    return typeAndEncoding & ~MESSAGE_TYPE_MASK;
}
/**
 * Decode the message encoding from a byte combining the message type and
 * flags.
 * @return {MessageEncoding} either ZLIB or NO_ENCODING.
 */
function extractMessageEncoding(typeAndEncoding) {
    var encoding = typeAndEncoding & MESSAGE_TYPE_MASK;
    if (encoding === ZLIB_TYPE_FLAGS) {
        return EncodingType.ZLIB;
    }
    else {
        return EncodingType.NO_ENCODING;
    }
}

var EncodingType = {
    NO_ENCODING : MessageEncoding(0x00, 0x00),
    ZLIB : MessageEncoding(0x12, 0x01)
};

module.exports = {
    extractMessageEncoding : extractMessageEncoding,
    extractMessageType : extractMessageType,
    EncodingType : EncodingType
};