linux下socket数据传输错误

Question

我想在linux下用openssl做一个socket传输的加密demo，但是原来没接触过，有些问题。下面这个是我发送和接收的代码，里面发送和接收了rsa公钥的数据和长度，但是不是每次发送都能成功，比如第一次成功接收，之后再次运行这两个程序，就接收不到了，求帮助解决。

//send.cpp
int sendKey(unsigned char *pk,int pk_len,int serv_sock){
    int32_t conv=htonl(pk_len);
    char *data = (char*)&conv;
    int len = sizeof(conv);
    char *key=(char*)pk;
    struct sockaddr_in clnt_addr;
    socklen_t clnt_addr_size = sizeof(clnt_addr);
    int clnt_sock = accept(serv_sock, (struct sockaddr*)&clnt_addr, &clnt_addr_size);
    int rc1=write(clnt_sock, data, len);
    if(rc1<0){
        printf("errno is %d\n",errno);
    }
    int rc2=write(clnt_sock, key, pk_len);
    if(rc2<0){
        printf("errno is %d\n",errno);
    }    
    close(clnt_sock);
}

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
int main(){
    int sock = socket(AF_INET, SOCK_STREAM, 0);
    struct sockaddr_in serv_addr;
    memset(&serv_addr, 0, sizeof(serv_addr));  
    serv_addr.sin_family = AF_INET;  
    serv_addr.sin_addr.s_addr = inet_addr("192.168.0.100");  
    serv_addr.sin_port = htons(8000);  
    connect(sock, (struct sockaddr*)&serv_addr, sizeof(serv_addr));

    unsigned char buffer[100000];
    int32_t pk_len=0;
    char *data=(char*)&pk_len;
    read(sock, data, sizeof(pk_len));
    read(sock, buffer, ntohl(pk_len));
    for (int i=0; i<ntohl(pk_len); i++)
    {
        printf("0x%02x, ", *(buffer+i));
    }
    printf("pklen from server:%d\n",ntohl(pk_len));


    close(sock);
    return 0;
}

Answer 1

因为你握手的时候调用了 close(clnt_sock); ，之后客户端发送，还需要重新调用 accept 才行。

看下下面的例子：

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <stdio.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
/************************************************************************************************************************
1、int socket(int family,int type,int protocol)
family:
    指定使用的协议簇:AF_INET（IPv4） AF_INET6（IPv6） AF_LOCAL（UNIX协议） AF_ROUTE（路由套接字） AF_KEY（秘钥套接字）
type:
    指定使用的套接字的类型:SOCK_STREAM（字节流套接字） SOCK_DGRAM
protocol:
    如果套接字类型不是原始套接字，那么这个参数就为0
2、int bind(int sockfd, struct sockaddr *myaddr, int addrlen)
sockfd:
    socket函数返回的套接字描述符
myaddr:
    是指向本地IP地址的结构体指针
myaddrlen:
    结构长度
struct sockaddr{
    unsigned short sa_family; //通信协议类型族AF_xx
    char sa_data[14];  //14字节协议地址，包含该socket的IP地址和端口号
};
struct sockaddr_in{
    short int sin_family; //通信协议类型族
    unsigned short int sin_port; //端口号
    struct in_addr sin_addr; //IP地址
    unsigned char si_zero[8];  //填充0以保持与sockaddr结构的长度相同
};
3、int connect(int sockfd,const struct sockaddr *serv_addr,socklen_t addrlen)
sockfd:
    socket函数返回套接字描述符
serv_addr:
    服务器IP地址结构指针
addrlen:
    结构体指针的长度
4、int listen(int sockfd, int backlog)
sockfd:
    socket函数绑定bind后套接字描述符
backlog:
    设置可连接客户端的最大连接个数，当有多个客户端向服务器请求时，收到此值的影响。默认值20
5、int accept(int sockfd,struct sockaddr *cliaddr,socklen_t *addrlen)
sockfd:
    socket函数经过listen后套接字描述符
cliaddr:
    客户端套接字接口地址结构
addrlen:
    客户端地址结构长度
6、int send(int sockfd, const void *msg,int len,int flags)
7、int recv(int sockfd, void *buf,int len,unsigned int flags)
sockfd:
    socket函数的套接字描述符
msg:
    发送数据的指针
buf:
    存放接收数据的缓冲区
len:
    数据的长度，把flags设置为0
*************************************************************************************************************************/
int main(int argc, char *argv[])
{
    int fd, new_fd, struct_len, numbytes,i;
    struct sockaddr_in server_addr;
    struct sockaddr_in client_addr;
    char buff[BUFSIZ];

    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(8000);
    server_addr.sin_addr.s_addr = INADDR_ANY;
    bzero(&(server_addr.sin_zero), 8);
    struct_len = sizeof(struct sockaddr_in);

    fd = socket(AF_INET, SOCK_STREAM, 0);
    while(bind(fd, (struct sockaddr *)&server_addr, struct_len) == -1);
    printf("Bind Success!\n");
    while(listen(fd, 10) == -1);
    printf("Listening....\n");
    printf("Ready for Accept,Waitting...\n");
    new_fd = accept(fd, (struct sockaddr *)&client_addr, &struct_len);
    printf("Get the Client.\n");
    numbytes = send(new_fd,"Welcome to my server\n",21,0); 
    while((numbytes = recv(new_fd, buff, BUFSIZ, 0)) > 0)
    {
        buff[numbytes] = '\0';
        printf("%s\n",buff);
            if(send(new_fd,buff,numbytes,0)<0)  
            {  
                perror("write");  
                return 1;  
            }  
    }
    close(new_fd);
    close(fd);
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <arpa/inet.h>

int main(int argc,char *argv[])
{
    int sockfd,numbytes;
    char buf[BUFSIZ];
    struct sockaddr_in their_addr;
    printf("break!");
    while((sockfd = socket(AF_INET,SOCK_STREAM,0)) == -1);
    printf("We get the sockfd~\n");
    their_addr.sin_family = AF_INET;
    their_addr.sin_port = htons(8000);
    their_addr.sin_addr.s_addr=inet_addr("127.0.0.1");
    bzero(&(their_addr.sin_zero), 8);

    while(connect(sockfd,(struct sockaddr*)&their_addr,sizeof(struct sockaddr)) == -1);
    printf("Get the Server~Cheers!\n");
    numbytes = recv(sockfd, buf, BUFSIZ,0);//接收服务器端信息  
    buf[numbytes]='\0';  
    printf("%s",buf);
    while(1)
    {
        printf("Entersome thing:");
        scanf("%s",buf);
        numbytes = send(sockfd, buf, strlen(buf), 0);
            numbytes=recv(sockfd,buf,BUFSIZ,0);  
        buf[numbytes]='\0'; 
        printf("received:%s\n",buf);  
    }
    close(sockfd);
    return 0;
}

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