嵌入式学习

tcp粘包解决方案

tcp是可靠的，面向字节流的协议，传输过程中可能就会

完整的服务器端代码:

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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <unistd.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/types.h>         /* See NOTES */
#include <sys/socket.h>

#define BACKLOG 10

//./a.out ip port
int main(int argc,char *argv[])
{
    int sfd,cfd,ret;
    struct sockaddr_in svr_addr,cli_addr;
    char buffer[1024] = {0};
    ssize_t sbytes = 0,rbytes = 0;
    int length;
    int total_received;
    socklen_t len = sizeof(struct sockaddr_in);
    if (argc != 3){
        fprintf(stderr,"Usage : %s < ip > < port >.\n",argv[0]) ;
        exit(EXIT_FAILURE);
    }

    //1.创建套接字
    sfd = socket(AF_INET,SOCK_STREAM,0);
    if (sfd == -1){
        perror("[ERROR] Failed to socket.");
        exit(EXIT_FAILURE);
    }

    bzero(&svr_addr,sizeof(struct sockaddr_in));
    svr_addr.sin_family = AF_INET;
    svr_addr.sin_port = htons(atoi(argv[2]));
    svr_addr.sin_addr.s_addr = inet_addr(argv[1]);
    
    //2.绑定ip地址与端口号
    ret = bind(sfd,(const struct sockaddr *)&svr_addr,sizeof(struct sockaddr));
    if (ret == -1){
        perror("[ERROR] Failed to bind.");
        exit(EXIT_FAILURE);
    }
    //3.设置监听套接字为监听状态<span class="bd-box"><h-char class="bd bd-beg"><h-inner>，</h-inner></h-char></span>建立监听队列
    ret = listen(sfd,BACKLOG);
    if (ret == -1){
        perror("[ERROR] Failed to listen.");
        exit(EXIT_FAILURE);
    }

    //4.与客户端进行三次握手<span class="bd-box"><h-char class="bd bd-beg"><h-inner>，</h-inner></h-char></span>并建立连接,默认是阻塞
    cfd = accept(sfd,(struct sockaddr *)&cli_addr,&len);
    if (ret == -1){
        perror("[ERROR] Failed to accpet.");
        exit(EXIT_FAILURE);
    }

    printf("ip : %s port :%d\n",inet_ntoa(cli_addr.sin_addr),ntohs(cli_addr.sin_port));
    for(;;){
        length = 0;
        total_received = 0;
        //接收数据的长度
        rbytes = recv(cfd,&length,4,0);
        if (rbytes == -1){
            perror("[ERROR] Failed to recv.");
            exit(EXIT_FAILURE);
        }
        for(;;){

            rbytes = recv(cfd,buffer + total_received,length - total_received,0);
            if (rbytes == -1){
                perror("[ERROR] Failed to recv.");
                exit(EXIT_FAILURE);
            }else if (rbytes == 0){
                printf("The client has been shutdown.\n");
            }else if (rbytes > 0){
                total_received += rbytes;
                if (total_received == length)
                    break;
            }
        }
            printf("buffer : %s\n",buffer);
        sleep(1);
    }

    close(sfd);
<span class="bd-box"><h-char class="bd bd-beg"><h-inner>。</h-inner></h-char></span>
    return 0;
}

中特别要注意rbytes = recv(cfd,buffer + total_received,length - total_received,0);
这段代码的意思就是，从cfd中读取数据到buffer+已经接收的数据地址段，为什么要length+total_received，因为一段数据可能会被拆分发送，也就是说，如果只填length的话，第一次的recv可能只会接收前半段的拆分数据，那么后面的数据就接受不到。如果像上面正确设置，即使第一次没有接受完，因为total_received的值和length不等，就会在下个循环继续接收，接受的字节数就等于length-已经接受的字节数。