《Linux网络开发必学教程》18_网络通讯框架的完善

问题：如何扩展之前的通信框架，使其支持 UDP 通信，进而成为一个完善的网络通讯框架？

UDP 通讯扩展

UDP 通信实体概要设计

• 每个 UDP Point 地位对等（因为不必主动发起连接），可通过 ip 地址和 port 号进行通讯
• UDP Point 数据收发单位为： Message 或 Byte
• 在接受口设计上，与 TcpClient 保持一致（框架接口一致性）
• 目标：封装原生 socket 细节，关注 UDP 通信逻辑

UDP 通讯实体接口设计

typedef void UdpPoint;

UdpPoint *UdpPoint_New(int port);
UdpPoint *UdpPoint_From(int fd);
void UdpPoint_Del(UdpPoint *point);

int UdpPoint_SendMsg(UdpPoint *point, Message *msg, const char *remote, int port);
int UdpPoint_SendRaw(UdpPoint *point, const char *buf, int length, const char *remote, int port);
Message *UdpPoint_RecvMsg(UdpPoint *point, char *remote, int *port);
int UdpPoint_RecvRaw((UdpPoint *point, const char *buf, int length, char *remote, int *port);

int UdpPoint_Available(UdpPoint *point);
void UdpPoint_SetData(UdpPoint *point, void *data);
void *UdpPoint_GetData(UdpPoint *point);

int UdpPoint_SetOpt(UdpPoint *point, int levle, int optname, const void *optval, unsigned int optlen);
int UdpPoint_GetOpt(UdpPoint *point, int levle, int optname, void *optval, unsigned int *optlen);

关键代码实现

• 由于 UDP 是以数据报方式进行通讯（非数据流方式，报文间有明显边界）
• 因此，不能直接通过 MParser_ReadFd(...) 解析出消息
• 必须先将报文完整接收到内存中，再进行从内存中解析出消息
• 即通过 MParser_ReadMeme(...) 间接完成消息解析

关于上述的补充

UDP 套接字的收发报文要用 sendto 和 recvfrom（可以类比 TCP 套接字的 connect 和 accept），参数里面会标识要发往的对端，或者要接收的对端的 IP 地址和端口；

对 UDP 套接字 connect 的行为也只会告诉内核：”帮我做个过滤，我只关心这个对端的报文“，已”连接“的UDP套接字可以利用 read, write， recv, send 函数，通常如果确定了该实体只与一个对端进行通讯，那么就选择 connect；

[更重要的是 UDP 套接字的缓冲区是以一个个报文为单位进行排队的]，调用一次 recvfrom 表示提取一个报文，和基于 TCP 基于字节流的方式是不同的。基于这样的原因我们不能在 UDP 中先读取一定的应用层 header, 而后再根据头部长度字段来优雅的读取具体数量的数据，这样会出错，发生混乱，而在 TCP 中经常这么做。

编程实验： UDP 通讯端设计与实现

udp_point.h

#ifndef UDP_POINT_H
#define UDP_POINT_H

#include "message.h"

typedef void UdpPoint;

UdpPoint *UdpPoint_New(int port);
UdpPoint *UdpPoint_From(int fd);
void UdpPoint_Del(UdpPoint *point);

int UdpPoint_SendMsg(UdpPoint *point, Message *msg, const char *remote, int port);
int UdpPoint_SendRaw(UdpPoint *point, const char *buf, int length, const char *remote, int port);
Message *UdpPoint_RecvMsg(UdpPoint *point, char *remote, int *port);
int UdpPoint_RecvRaw(UdpPoint *point, char *buf, int length, char *remote, int *port);

int UdpPoint_Available(UdpPoint *point);
void UdpPoint_SetData(UdpPoint *point, void *data);
void *UdpPoint_GetData(UdpPoint *point);

int UdpPoint_SetOpt(UdpPoint *point, int levle, int optname, const void *optval, unsigned int optlen);
int UdpPoint_GetOpt(UdpPoint *point, int levle, int optname, void *optval, unsigned int *optlen);

#endif // UDP_POINT_H

udp_point.c

#include "udp_point.h"

#include "msg_parser.h"

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

typedef struct udp_point {
    int fd;
    MParser *parser;
    void *data;
}Point;

static char g_temp[1024 * 4] = {0};

static void ParserAddr(struct sockaddr_in addr, char *ip, int *port)
{
    if (ip) {
        strcpy(ip, inet_ntoa(addr.sin_addr));
    }

    if (port) {
        *port = ntohs(addr.sin_port);
    }
}

UdpPoint *UdpPoint_New(int port)
{
    Point *ret = malloc(sizeof(Point));
    struct sockaddr_in addr = {0};
    int ok = !! ret;

    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = htonl(INADDR_ANY);
    addr.sin_port = htons(port);

    ok = ok && ((ret->parser = MParser_New()) != NULL);
    ok = ok && ((ret->fd = socket(PF_INET, SOCK_DGRAM, 0)) != -1);
    ok = ok && (bind(ret->fd, (struct sockaddr*)&addr, sizeof(addr)) != -1);

    if (ok) {
        ret->data = NULL;
    } else {
        ret ? (MParser_Del(ret->parser), NULL) : NULL;
        ret ? close(ret->fd) : -1;

        free(ret);

        ret = NULL;
    }

    return ret;
}

UdpPoint *UdpPoint_From(int fd)
{
    Point *ret = malloc(sizeof(Point));

    if (ret) {
        ret->fd = fd;
        ret->parser = MParser_New();
        ret->data = NULL;
    }

    return (ret && ret->parser) ? ret : (free(ret), NULL);
}

void UdpPoint_Del(UdpPoint *point)
{
    Point *c = (Point*)point;

    if (c) {
        close(c->fd);
        MParser_Del(c->parser);
        free(c);
    }
}

int UdpPoint_SendMsg(UdpPoint *point, Message *msg, const char *remote, int port)
{
    int ret = 0;
    Point *c = (Point*)point; 

    if (c && msg && remote) {
        int len = Message_Size(msg);
        char *data = (char*)Message_H2N(msg);

        ret = UdpPoint_SendRaw(point, data, len, remote, port);

        Message_N2H(msg);
    }

    return ret;   
}

int UdpPoint_SendRaw(UdpPoint *point, const char *buf, int length, const char *remote, int port)
{
    int ret = 0;
    Point *c = (Point*)point; 

    if (c && buf && remote) {
        struct sockaddr_in raddr = {0};
        int addrlen = sizeof(raddr);

        raddr.sin_family = AF_INET;
        raddr.sin_addr.s_addr = inet_addr(remote);
        raddr.sin_port = htons(port);

        ret = (sendto(c->fd, buf, length, 0, (struct sockaddr*)&raddr, addrlen) != -1);
    }

    return ret;
}

Message *UdpPoint_RecvMsg(UdpPoint *point, char *remote, int *port)
{   
    Message *ret = NULL;
    Point *c = (Point*)point; 

    if (c) {
        struct sockaddr_in raddr = {0};
        int addrlen = sizeof(raddr);
        int length = recvfrom(c->fd, g_temp, sizeof(g_temp), MSG_PEEK, (struct sockaddr*)&raddr, &addrlen);
        char *buf = (length > 0) ? malloc(length) : NULL;

        length = recvfrom(c->fd, buf, length, 0, (struct sockaddr*)&raddr, &addrlen);

        if (length > 0) {
            ret = MParser_ReadMem(c->parser, buf, length);
        }

        if (ret) {
            ParserAddr(raddr, remote, port);
        }

        free(buf);
    }
    
    return ret;
}

int UdpPoint_RecvRaw(UdpPoint *point, char *buf, int length, char *remote, int *port)
{
    int ret = 0;
    Point *c = (Point*)point; 

    if (c && buf) {
        struct sockaddr_in raddr = {0};
        int addrlen = sizeof(raddr);

        printf("===============================\n");

        ret = recvfrom(c->fd, buf, length, 0, (struct sockaddr*)&raddr, &addrlen);

        printf("===============================\n");

        if (ret != -1) {
            ParserAddr(raddr, remote, port);
        }
    }

    return ret;
}

int UdpPoint_Available(UdpPoint *point)
{
    int ret = -1;
    Point *c = (Point*)point; 

    if (c) {
        struct sockaddr_in raddr = {0};
        int len = sizeof(raddr);
        ret = recvfrom(c->fd, g_temp, sizeof(g_temp), MSG_PEEK | MSG_DONTWAIT, (struct sockaddr*)&raddr, &len);
    }

    return ret;   
}

void UdpPoint_SetData(UdpPoint *point, void *data)
{
    Point *c = (Point*)point;

    if (c) {
        c->data = data;
    }
}

void *UdpPoint_GetData(UdpPoint *point)
{
    void *ret = NULL;
    Point *c = (Point*)point;

    if (c) {
        ret = c->data;
    }

    return ret;
}

int UdpPoint_SetOpt(UdpPoint *point, int levle, int optname, const void *optval, unsigned int optlen)
{
    int ret = -1;
    Point *c = (Point*)point;

    if (c) {
        ret = setsockopt(c->fd, levle, optname, optval, optlen);
    }

    return ret;
}

int UdpPoint_GetOpt(UdpPoint *point, int levle, int optname, void *optval, unsigned int *optlen)
{
    int ret = -1;
    Point *c = (Point*)point; 

    if (c) {
        ret = getsockopt(c->fd, levle, optname, optval, optlen);
    }

    return ret;  
}

输出：

p = 0x55bd81ba4260
ip: 192.168.2.24, port: 7777
msg: 0x55bd81ba46e0
msg->type = 1
msg->cmd = 2
msg->index = 3
msg->total = 4
03 02 01

---

tcp_client 添加属性相关操作

int TcpClient_SetOpt(TcpClient *client, int levle, int optname, const void *optval, unsigned int optlen);
int TcpClient_GetOpt(TcpClient *client, int levle, int optname, void *optval, unsigned int *optlen);

// ...

int TcpClient_SetOpt(TcpClient *client, int levle, int optname, const void *optval, unsigned int optlen)
{
    int ret = -1;
    Client *c = (Client*)client;

    if (c) {
        ret = setsockopt(c->fd, levle, optname, optval, optlen);
    }

    return ret;
}

int TcpClient_GetOpt(TcpClient *client, int levle, int optname, void *optval, unsigned int *optlen)
{
    int ret = -1;
    Client *c = (Client*)client; 

    if (c) {
        ret = getsockopt(c->fd, levle, optname, optval, optlen);
    }

    return ret; 
}

tcp_server 添加属性相关操作

int TcpClient_SetOpt(TcpServer *server, int levle, int optname, const void *optval, unsigned int optlen);
int TcpClient_GetOpt(TcpServer *server, int levle, int optname, void *optval, unsigned int *optlen);

// ...

int TcpServer_SetOpt(TcpServer *server, int levle, int optname, const void *optval, unsigned int optlen)
{
    int ret = -1;
    Server *s = (Server*)server;

    if (s) {
        ret = setsockopt(s->fd, levle, optname, optval, optlen);
    }

    return ret;
}

int TcpServer_GetOpt(TcpServer *server, int levle, int optname, void *optval, unsigned int *optlen)
{
    int ret = -1;
    Server *s = (Server*)server;

    if (s) {
        ret = getsockopt(s->fd, levle, optname, optval, optlen);
    }

    return ret;  
}