UDT源码剖析（十）之Channel

其他 2018-06-16 19:07:50 阅读次数: 5

封装UDP SOCKET，使其成为UDT数据的发送通道，所有的UDT SOCKET都通过这种类型来进行数据发送。为了完整性，咱们接着分析哈～

CChannel

  • 基础数据结构：
    ```
    class CChannel
    {
    private:
    int m_iIPversion; // IP version
    int m_iSockAddrSize; // socket address structure size (pre-defined to avoid run-time test)

UDPSOCKET m_iSocket; // socket descriptor

int m_iSndBufSize; // UDP sending buffer size
int m_iRcvBufSize; // UDP receiving buffer size
};

- 初始化：`CChannel::CChannel()`

CChannel::CChannel():
m_iIPversion(AF_INET),
m_iSockAddrSize(sizeof(sockaddr_in)),
m_iSocket(),
m_iSndBufSize(65536), //唯一能得到的信息就是将UDP SOCKET的Buffer设置为65536Byte
m_iRcvBufSize(65536)
{
}

CChannel::CChannel(int version):
m_iIPversion(version),
m_iSocket(),
m_iSndBufSize(65536),
m_iRcvBufSize(65536)
{
m_iSockAddrSize = (AF_INET == m_iIPversion) ? sizeof(sockaddr_in) : sizeof(sockaddr_in6);
}

- 打开通道：`void CChannel::open(const sockaddr* addr)`

void CChannel::open(const sockaddr* addr)
{
m_iSocket = ::socket(m_iIPversion, SOCK_DGRAM, 0); //创建一个UDP SOCKET

#ifdef WINDOWS
if (INVALID_SOCKET == m_iSocket)
#else
if (m_iSocket < 0)
#endif
throw CUDTException(1, 0, NET_ERROR);

if (NULL != addr) //如果提供地址,将创建的UDPSOCKET与Address关联
{
socklen_t namelen = m_iSockAddrSize;

  if (0 != ::bind(m_iSocket, addr, namelen))
     throw CUDTException(1, 3, NET_ERROR);

}
else //如果不提供地址,获取地址也要给UDP和Address关联在一起
{
//sendto or WSASendTo will also automatically bind the socket
addrinfo hints;
addrinfo* res;

  memset(&hints, 0, sizeof(struct addrinfo));

  hints.ai_flags = AI_PASSIVE;
  hints.ai_family = m_iIPversion;
  hints.ai_socktype = SOCK_DGRAM;

  if (0 != ::getaddrinfo(NULL, "0", &hints, &res))
     throw CUDTException(1, 3, NET_ERROR);

  if (0 != ::bind(m_iSocket, res->ai_addr, res->ai_addrlen))
     throw CUDTException(1, 3, NET_ERROR);

  ::freeaddrinfo(res);

}

setUDPSockOpt(); //根据初始化时提供的信息，设置这个UDP SOCKET的选项
}

- 关闭通道：`void CChannel::close() const`

void CChannel::close() const
{
#ifndef WINDOWS
::close(m_iSocket);
#else
::closesocket(m_iSocket);
#endif
}

- 设置UDP选项：`void CChannel::setUDPSockOpt()`

void CChannel::setUDPSockOpt()
{
//设置接收与发送缓冲区
#if defined(BSD) || defined(MACOSX)
// BSD system will fail setsockopt if the requested buffer size exceeds system maximum value
int maxsize = 64000;
if (0 != ::setsockopt(m_iSocket, SOL_SOCKET, SO_RCVBUF, (char)&m_iRcvBufSize, sizeof(int)))
::setsockopt(m_iSocket, SOL_SOCKET, SO_RCVBUF, (char)&maxsize, sizeof(int));
if (0 != ::setsockopt(m_iSocket, SOL_SOCKET, SO_SNDBUF, (char)&m_iSndBufSize, sizeof(int)))
::setsockopt(m_iSocket, SOL_SOCKET, SO_SNDBUF, (char)&maxsize, sizeof(int));
#else
// for other systems, if requested is greated than maximum, the maximum value will be automactally used
if ((0 != ::setsockopt(m_iSocket, SOL_SOCKET, SO_RCVBUF, (char)&m_iRcvBufSize, sizeof(int))) ||
(0 != ::setsockopt(m_iSocket, SOL_SOCKET, SO_SNDBUF, (char)&m_iSndBufSize, sizeof(int))))
throw CUDTException(1, 3, NET_ERROR);
#endif

timeval tv;
tv.tv_sec = 0;
#if defined (BSD) || defined (MACOSX)
// Known BSD bug as the day I wrote this code.
// A small time out value will cause the socket to block forever.
tv.tv_usec = 10000;
#else
tv.tv_usec = 100;
#endif

  //顺便将UDPSOCKET设置成非阻塞模式

#ifdef UNIX
// Set non-blocking I/O
// UNIX does not support SO_RCVTIMEO
int opts = ::fcntl(m_iSocket, F_GETFL);
if (-1 == ::fcntl(m_iSocket, F_SETFL, opts | O_NONBLOCK))
throw CUDTException(1, 3, NET_ERROR);
#elif WINDOWS
DWORD ot = 1; //milliseconds
if (0 != ::setsockopt(m_iSocket, SOL_SOCKET, SO_RCVTIMEO, (char )&ot, sizeof(DWORD)))
throw CUDTException(1, 3, NET_ERROR);
#else
// Set receiving time-out value
if (0 != ::setsockopt(m_iSocket, SOL_SOCKET, SO_RCVTIMEO, (char )&tv, sizeof(timeval)))
throw CUDTException(1, 3, NET_ERROR);
#endif
}

- 获取与设置UDP信息：`int CChannel::getSndBufSize()`，`int CChannel::getRcvBufSize()`，`void CChannel::setSndBufSize(int size)`，`void CChannel::setRcvBufSize(int size)`，`void CChannel::getSockAddr(sockaddr* addr) const`，`void CChannel::getPeerAddr(sockaddr* addr) const`

int CChannel::getSndBufSize()
{
socklen_t size = sizeof(socklen_t);
::getsockopt(m_iSocket, SOL_SOCKET, SO_SNDBUF, (char *)&m_iSndBufSize, &size);
return m_iSndBufSize;
}

int CChannel::getRcvBufSize()
{
socklen_t size = sizeof(socklen_t);
::getsockopt(m_iSocket, SOL_SOCKET, SO_RCVBUF, (char *)&m_iRcvBufSize, &size);
return m_iRcvBufSize;
}

void CChannel::setSndBufSize(int size)
{
m_iSndBufSize = size;
}

void CChannel::setRcvBufSize(int size)
{
m_iRcvBufSize = size;
}

void CChannel::getSockAddr(sockaddr* addr) const
{
socklen_t namelen = m_iSockAddrSize;
::getsockname(m_iSocket, addr, &namelen);
}

void CChannel::getPeerAddr(sockaddr* addr) const
{
socklen_t namelen = m_iSockAddrSize;
::getpeername(m_iSocket, addr, &namelen);
}

- 发送数据包：`int CChannel::sendto(const sockaddr* addr, CPacket& packet) const`

int CChannel::sendto(const sockaddr* addr, CPacket& packet) const
{
// 先确定是数据包还是控制包,如果是控制包,将控制信息转换为网络字节序
if (packet.getFlag())
for (int i = 0, n = packet.getLength() / 4; i < n; ++ i)
((uint32_t )packet.m_pcData + i) = htonl(((uint32_t )packet.m_pcData + i));

// 将packet的header转换为网络字节序
uint32_t* p = packet.m_nHeader;
for (int j = 0; j < 4; ++ j)
{
p = htonl(p);
++ p;
}

#ifndef WINDOWS
msghdr mh; //使用这种方式将数据重组,然后发送
mh.msg_name = (sockaddr)addr;
mh.msg_namelen = m_iSockAddrSize;
mh.msg_iov = (iovec)packet.m_PacketVector;
mh.msg_iovlen = 2;
mh.msg_control = NULL;
mh.msg_controllen = 0;
mh.msg_flags = 0;

  int res = ::sendmsg(m_iSocket, &mh, 0);

#else
DWORD size = CPacket::m_iPktHdrSize + packet.getLength();
int addrsize = m_iSockAddrSize;
int res = ::WSASendTo(m_iSocket, (LPWSABUF)packet.m_PacketVector, 2, &size, 0, addr, addrsize, NULL, NULL);
res = (0 == res) ? size : -1;
#endif

//在发送结束之后,将头部的信息转化为local字节序
p = packet.m_nHeader;
for (int k = 0; k < 4; ++ k)
{
p = ntohl(p);
++ p;
}

//如果是控制包,将额外的控制信息的打data转化为loacl字节序
if (packet.getFlag())
{
for (int l = 0, n = packet.getLength() / 4; l < n; ++ l)
((uint32_t )packet.m_pcData + l) = ntohl(((uint32_t )packet.m_pcData + l));
}

return res;
}


- 接收数据包：`int CChannel::recvfrom(sockaddr* addr, CPacket& packet) const`

int CChannel::recvfrom(sockaddr* addr, CPacket& packet) const
{
#ifndef WINDOWS
msghdr mh;
mh.msg_name = addr;
mh.msg_namelen = m_iSockAddrSize;
mh.msg_iov = packet.m_PacketVector;
mh.msg_iovlen = 2;
mh.msg_control = NULL;
mh.msg_controllen = 0;
mh.msg_flags = 0;

  #ifdef UNIX
     fd_set set;
     timeval tv;
     FD_ZERO(&set);
     FD_SET(m_iSocket, &set);
     tv.tv_sec = 0;
     tv.tv_usec = 10000;
     ::select(m_iSocket+1, &set, NULL, &set, &tv);
  #endif

  int res = ::recvmsg(m_iSocket, &mh, 0);

#else
DWORD size = CPacket::m_iPktHdrSize + packet.getLength();
DWORD flag = 0;
int addrsize = m_iSockAddrSize;

  int res = ::WSARecvFrom(m_iSocket, (LPWSABUF)packet.m_PacketVector, 2, &size, &flag, addr, &addrsize, NULL, NULL);
  res = (0 == res) ? size : -1;

#endif

  //如果报文的读取错误,将报文的长度设置为-1

if (res <= 0)
{
packet.setLength(-1);
return -1;
}

//否则,将报文的长度设置为减去头部长度(-16)
packet.setLength(res - CPacket::m_iPktHdrSize);

// convert back into local host order
//for (int i = 0; i < 4; ++ i)
// packet.m_nHeader[i] = ntohl(packet.m_nHeader[i]);
uint32_t* p = packet.m_nHeader;
for (int i = 0; i < 4; ++ i) //转化报文的头部的信息为loacl字节序
{
p = ntohl(p);
++ p;
}

//如果是控制包,将控制信息转化为local字节序
if (packet.getFlag())
{
for (int j = 0, n = packet.getLength() / 4; j < n; ++ j)
((uint32_t )packet.m_pcData + j) = ntohl(((uint32_t )packet.m_pcData + j));
}

return packet.getLength();
}
```

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