Working subtotal rtcp length and network byte order

最近在看zlMediaKit RTCP部分
RFC 5760 RTCP https://rfc2cn.com/rfc5760.html

Length: 16 bits As defined in [1], the length of the RTCP packet in 32-bit words minus one, including the header and any padding.

length的长度是32-bit下(Just a few lines) - 1(Minus the1是通用头 32 bit 4字节)
下图中length长度即为5

zl中解析rtcp长度：（ 转换字节序+1(加头) ）* 4 (32bitMeasurement into8bit) Access to the number of bytes of the packet

size_t RtcpHeader::getSize() const {
    
    //加上rtcp头长度
    size_t a = ntohs(length);
    return (1 + a) << 2;
}

另外debug时,看到length长度=1536,ntohs后转化为6.最终结果7*4=28,And we expect the results of the same28Bytes long onertcp包

Cooperate with the calculator+ntohs源码可以看到 After conversion 0000 0000 0000 0110 = 6（Network turn big end little endian,bitTurn order no,The network card to do）

0xAB --> 0xBA

unsigned short ntohs (unsigned short x)
{
    
x = (x << 8) | (x >> 8);
    return x;
}

0xABCD --> 0xDCBA

unsigned long ntohl(unsigned long x)
{
    
return (x >> 24) | ((x & 0xff0000) >> 8) | ((x & 0xff00) << 8) | (x << 24);
}