网络服务器发送封包设计

接上篇，本文介绍发送封包的设计.

WPacket的构成与RPacket类似,实际数据都存放在buffer组成的链表中.发送时,如果一个WPacket的数据跨越了两个buffer,可通过WSASend提交
多个缓冲,一次性将数据发出去.


WPacket还提供了一个传入RPacket的构造函数,以方便网关类程序收到一个包就马上将其转发的需求.一般情况下,从一个RPacket构造的WPacket都
不需要向其写入新的数据,而是直接转发.所以.构造的这个WPacket和传入的RPacket是共享buffer的.这样大大减少了内存拷贝的次数.当第一次向这
个WPacket写入数据时,将会触发拷贝过程,将RPacket中的数据拷贝到一个生成的buffer之中,至此,WPacket与构造传入的RPacket将不再共享buffer,
所有的数据将会被写入到WPacket自己的buffer中.

代码如下:

const static unsigned short sizeOfLen = sizeof(unsigned short);
const static unsigned short cmdlen = sizeof(unsigned short);

#define MAX_PACKET_SIZE 65535

class WPacket
{
    friend class Connection;
public:
    WPacket(const RPacket &rpk):m_copyOnWrite(true),m_writePos(0),m_head(rpk.m_head)
    ,m_buf(rpk.m_buf),m_writeBuf(rpk.m_buf),m_len(rpk.m_len)
    {

    }

    WPacket():m_buf(0),m_writeBuf(0),m_head(0),m_writePos(sizeOfLen+cmdlen)
        ,m_len(sizeOfLen+cmdlen)
    {

    }

    WPacket(const WPacket &wpk):m_buf(wpk.m_buf),m_writeBuf(wpk.m_writeBuf),
        m_head(wpk.m_head),m_writePos(wpk.m_writePos),m_len(wpk.m_len),m_copyOnWrite(wpk.m_copyOnWrite)
    {

    }

    WPacket & operator = (const WPacket &other)
    {
        if(this == &other)
            return *this;
        m_head = other.m_head;
        m_len = other.m_len;
        m_buf = other.m_buf;
        m_writePos = other.m_writePos;
        m_copyOnWrite = other.m_copyOnWrite;
        return *this;
    }

    void WriteShort(unsigned short value)
    {
        Write<unsigned short>(value);
    }

    //.......其它Write

    void WriteString(const char *str)
    {
        unsigned short strLen = strlen(str) + 1;
        WriteBinary((const void *)str,strLen);
    }

    void WriteBinary(const void *bin,unsigned short len)
    {
        CopyOnWrite();
        CreateBuffer();
        //先写入长度
        WriteShort(len);
        unsigned short sizeRemain = m_writeBuf->m_bufSize - m_writePos;
        if(sizeRemain >=len)
        {
            memcpy(&m_writeBuf->m_buf[m_writePos],bin,len);
            m_writePos += len;
            m_writeBuf->m_dataSize += len;
        }
        else
        {
            const char *ptr = (const char *)bin;
            unsigned short copySize = sizeRemain;
            memcpy(&m_writeBuf->m_buf[m_writePos],ptr,copySize);
            ptr += copySize;
            m_writeBuf->m_dataSize += copySize;
            m_writePos = 0;
            copySize = len - copySize;
            rptr<buffer> newbuf = new buffer(copySize);
            m_writeBuf->m_next = newbuf;
            m_writeBuf = newbuf;
            memcpy(&m_writeBuf->m_buf[m_writePos],ptr,copySize);
            m_writePos += copySize;
            m_writeBuf->m_dataSize += copySize;
        }
        *(unsigned short*)&m_writeBuf->m_buf[m_head] += (len);
        m_len = *(unsigned short*)&m_writeBuf->m_buf[m_head];
    }

private:

    void CreateBuffer()
    {
        if(m_buf._nil())
        {
            m_buf = m_writeBuf = new buffer(4096);
        }
    }


    void CopyOnWrite()
    {

        if(!m_copyOnWrite)
            return;

        unsigned short totalSize = m_len;        
        rptr<buffer> tmp = new buffer(totalSize > 0 ? totalSize : 4096);
        if(totalSize > 0)
        {
            //复制数据
            unsigned short copySize = totalSize;
            rptr<buffer> cur = m_buf;
            while(copySize > 0)
            {
                unsigned short curDataRemian = cur->m_bufSize - m_head;
                if(curDataRemian >= copySize)
                {
                    memcpy(&tmp->m_buf[m_writePos],&cur->m_buf[m_head],copySize);
                    m_writePos += copySize;
                    m_buf = m_writeBuf = tmp;
                    m_head = 0;
                    copySize = 0;
                }
                else
                {
                    memcpy(&tmp->m_buf[m_writePos],&cur->m_buf[m_head],curDataRemian);
                    m_writePos += curDataRemian;
                    copySize -= curDataRemian;
                    cur = cur->m_next;
                    m_head = 0;
                }
            }
        }
        else
        {
            m_buf = m_writeBuf = tmp;
            m_head = 0;
            m_writePos = m_head + sizeOfLen + cmdlen;
            m_len = sizeOfLen + cmdlen;
        }
        m_buf->m_dataSize = m_len;
        m_copyOnWrite = false;
        
    }

    template <typename T>
    void Write(const T &value)
    {
        CopyOnWrite();
        CreateBuffer();
        unsigned short sizeRemain = m_writeBuf->m_bufSize - m_writePos;
        if(sizeRemain >= sizeof(T))
        {
            *(T*)&m_writeBuf->m_buf[m_writePos] = value;
            m_writePos += sizeof(T);
            m_writeBuf->m_dataSize += sizeof(T);
        }
        else
        {

            char *ptr = (char*)&value;
            unsigned short copySize = sizeRemain;
            memcpy(&m_writeBuf->m_buf[m_writePos],ptr,copySize);
            ptr += copySize;
            m_writeBuf->m_dataSize += copySize;
            m_writePos = 0;
            copySize = sizeof(T) - copySize;
            rptr<buffer> newbuf = new buffer(copySize);
            m_writeBuf->m_next = newbuf;
            m_writeBuf = newbuf;
            memcpy(&m_writeBuf->m_buf[m_writePos],ptr,copySize);
            m_writePos += copySize;
            m_writeBuf->m_dataSize += copySize;

        }
        *(T*)&m_writeBuf->m_buf[m_head] += sizeof(T);
        m_len = *(unsigned short*)&m_writeBuf->m_buf[m_head];
    }

private:
    bool           m_copyOnWrite;//是否需要写时拷贝
    unsigned short m_len;
    unsigned short m_writePos;
    unsigned short m_head; //在buf中的起始下标
    rptr<buffer> m_writeBuf;//当前writePos所在的buf
    rptr<buffer> m_buf;//存放packet的数据，可能由一组m_buf构成链表
};

项目的完整代码在这里:

http://download.csdn.net/detail/sniperhuangwei/4083117

尚未经过完整测试，Packet位移上的处理可能还有bug,后续会修正，整体结构基本不会改变，可能会加上组包和超时处理。

也就是当套接口要发送的数据量太小时暂时不发送，等待后续的写请求或触发超时才将数据写出去。