RFC5764/STUN

struct STUNHeader
{
  uint16_t     type;
  uint16_t     length;
  uint8_t      magicCookie[4];
  uint8_t      transactionId[12];
  struct Attribute attr;
}

struct Attribute
{
  uint16_t     attrType;
  uint16_t     attrLength;
  uint8_t      attrValue[N]; // N=attrLength
}

• type 消息类型。type[0]<3，type细节详解下面代码段
• length 消息长度，不包含消息头的长度
• magicCookie 魔法数字0x2112A442，用来确定一定是STUN消息
• transactionId 发送，返回的id是一致的

/* STUNHeader.type 图解，前两个bit一定是0，下面就没列出来
 0                 1
 2  3  4 5 6 7 8 9 0 1 2 3 4 5
+--+--+-+-+-+-+-+-+-+-+-+-+-+-+
|M |M |M|M|M|C|M|M|M|C|M|M|M|M|
|11|10|9|8|7|1|6|5|4|0|3|2|1|0|
+--+--+-+-+-+-+-+-+-+-+-+-+-+-+
*/

enum klass
{
  REQUEST          = 0,  // 绑定请求消息。C1=0，C0=0；type=0x0001
  INDICATION       = 1,  // 表示标志。C1=0，C0=1
  SUCCESS_RESPONSE = 2,  // 表示请求成功的响应。C1=1，C0=0；type=0x0101
  ERROR_RESPONSE   = 3   // 表示请求错误的响应。C1=1，C0=1；type=0x0111
};

enum method
{
  BINDING = 1  // 绑定消息，M0=1
};

STUN body

struct Attribute
{
  uint16_t     attrType; // attrType=attr
  uint16_t     attrLength;
  uint8_t      attrValue[N]; // N=attrLength
}

enum attr
{
  MAPPED_ADDRESS     = 0x0001,  // 获取客户端映射地址
  RESPONSE_ADDRESS   = 0x0002,  // 表示响应的目的地址
  CHANGE_REQUEST     = 0x0003,  // 请求服务器使用不同的ip或端口号来发送响应
  SOURCE_ADDRESS     = 0x0004,  // 指定服务器的ip和端口
  CHANGED_ADDRESS    = 0x0005,  // CHASNGE_REQUEST请求的响应
  USERNAME           = 0x0006,  // 用于安全验证
  PASSWORD           = 0x0007,  // 用于安全验证
  MESSAGE_INTEGRITY  = 0x0008,  // 消息完整性验证
  ERROR_CODE         = 0x0009,  // 错误码
  UNKNOWN_ATTRIBUTES = 0x000A,  // 未知属性
  REFLECTED_FROM     = 0x000B,  // 拒约
  REALM              = 0x0014,
  NONCE              = 0x0015,
  XOR_MAPPED_ADDRESS = 0x0020,
  PRIORITY           = 0x0024,
  USE_CANDIDATE      = 0x0025,
  SOFTWARE           = 0x8022,
  ALTERNATE_SERVER   = 0x8023,
  FINGERPRINT        = 0x8028,
  ICE_CONTROLLED     = 0x8029,
  ICE_CONTROLLING    = 0x802A
};
// Authentication result.
enum class Authentication
{
  OK           = 0,
  UNAUTHORIZED = 1,
  BAD_REQUEST  = 2
};