TCP中 recv和sendf函数

recv和send函数：

#include<sys/socket.h>

ssize_t recv(int sockfd, void *buff, size_t nbytes, int flags);

ssize_t recv(int sockfd, const void *buff, size_t nbytes, int flags);

flags的值中 MSG_OOB和MSG_PEEK比较重要。

read和recv函数的区别在于：

read函数读取缓冲区的数据之后，会将缓冲区的数据删除，而recv不会删除缓冲区的数据。

因此，可以将falgs设置为MSG_PEEK，在此模式下，先查看发送过来的字符的个数，然后用read函数读取数据。

例子服务端代码如下：

#include<stdio.h>
#include<stdlib.h>
#include<errno.h>
#include<string.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<sys/un.h>
#include<sys/wait.h>      //*进程用的头文件*/
#include<netinet/in.h>
#include<arpa/inet.h>
#include<unistd.h>
#define MAXLINE  1024  //通信内容的最大长度


ssize_t readn(int fd, void *buf, size_t count)
{
    ssize_t nleft=count;
    ssize_t nread;
    char *charbuf=(char*) buf;

    while(nleft>0)
    {
        nread=read(fd,charbuf,nleft);
        if(nread<0)
          {
              if(errno==EINTR)
               continue;
                        return -1;
          }
        else if(nread==0)
                       return count-nleft;
                
        charbuf +=nread;
                nleft=count-nread;
    }
    return count;    
}

ssize_t writen(int fd, const void *buf, size_t count)
{
        ssize_t nleft=count;
        ssize_t nwrite;
        char *charbuf=(char*) buf;

        while(nleft>0)
        {
                nwrite=write(fd,charbuf,nleft);
                if(nwrite<0)
                  {
                        if(errno==EINTR)
                           continue;
                        return -1;
                  }
                else if(nwrite==0)
                       return count-nleft;
                charbuf +=nwrite;
                nleft=count-nwrite; 

        }
       return count;
}

 ssize_t recv_peek(int sockfd, void *buf, size_t len)
{
        int ret;
    while(1)
    {
            ret=recv(sockfd,buf,len,MSG_PEEK);
                if(ret==-1&& errno==EINTR)
                    continue;
                return ret;
    }
}

 ssize_t readline(int sockfd, void *buf, size_t len)
{
        ssize_t nleft=len,nread;
        int ret;
        char* bufchar=buf;
        while(1)
        {
                ret=recv_peek(sockfd,bufchar,len);
                if(ret<0||ret==0)
                        return ret;
                nread=ret;
                int i;
                for(i=0;i<nread;i++)
                {
                        if(bufchar[i]=='
')
                        {
                                ret=readn(sockfd,bufchar,i+1);
                                if(ret!=i+1)
                                        exit(EXIT_FAILURE);
                                return ret;
                        }
                }
                if(nread>nleft)
                        exit(EXIT_FAILURE);
                nleft-=nread;
                ret=readn(sockfd,bufchar,nread);
                if(ret!=nread)
                        exit(EXIT_FAILURE);
                bufchar+=nread;

        }
        return -1;

}


int main()
{
    int sock_fd,new_fd;//sock_fd用于监听，new_fd用于连接
    struct sockaddr_in srv_addr;//服务器的地址信息
    struct sockaddr_in client_addr;//客户机的地址信息
    int size; //地址结构数据的长度
    pid_t  pid;  //子进程id
    ssize_t n,ret;
    char buf[MAXLINE]; //用于存放通信的内容
     
        char sendbuf[1024],recvbuf[1024];
    memset(sendbuf,0,sizeof(sendbuf));
    memset(recvbuf,0,sizeof(recvbuf));

    /*创建套接字*/
    sock_fd=socket(AF_INET,SOCK_STREAM,0);//采用IPv4协议
    if(sock_fd==-1)
    {
        perror("creat socket failed");
        exit(1);
    }
    
    /*服务器地址参数*/
    srv_addr.sin_family=AF_INET;  
    srv_addr.sin_port=htons(3490);
    srv_addr.sin_addr.s_addr=htonl(INADDR_ANY);
    bzero(&srv_addr.sin_zero,sizeof(struct sockaddr_in));//bzero位清零函数，将sin_zero清零，sin_zero为填充字段，必须全部为零
    
    int on=1; //表示开启reuseaddr
    if(setsockopt(sock_fd,SOL_SOCKET,SO_REUSEADDR,&on,sizeof(on))<0)  //打开地址、端口重用
        perror("setsockopt");
    
    /*绑定地址和端口*/
    if(bind(sock_fd,(struct sockaddr*)&srv_addr,sizeof(struct sockaddr))==-1)
    {
        perror("bind failed");
        exit(1);
    }
    
    /*连接到服务器
    if(connect(sock_fd,(struct sockaddr*)&srv_addr,sizeof(sock_fd))==-1)
    {
        perror("bind failed");
        exit(1);
    }*/
    
    /*设置监听模式，等待客户机的监听*/
    if((listen(sock_fd,5))==-1)
    {
        perror("listen failed");
        exit(1);
    }
    
    /*接受连接,采用非阻塞是的模式调用accep*/
    //while(1)
    //{
        size=sizeof(struct sockaddr_in);
        new_fd=accept(sock_fd,(struct sockaddr*)&client_addr,&size);
        if(new_fd==-1)
        {
            perror("accept failed");
            //continue;//restart accept when EINTR
        }
        
        printf("server:got connection from IP= %s prot= %d 
",inet_ntoa(client_addr.sin_addr),ntohs(client_addr.sin_port));//连接成功，打印客户机IP地址和端口号
        /*char *inet_nota(struct sockaddr_in in);
        头文件：
        arpa/inet.h
        Winsock2.h
        参数：
        一个网络上的IP地址
        返回值：
          如果正确，返回一个字符指针，指向一块存储着点分格式IP地址的静态缓冲区（同一线程内共享此内存）；错误，返回NULL。
        uint31_t ntohs(uint32_t net32bitvalue);
        头文件：
        #include<netinet/in.h>
        把net32bitvalue有网络字节序转换为主机字节序。
        */
        if(send(new_fd,"Hello client,I am 192.168.229.125!
",50,0)==-1)  //192.168.229.125为子进程IP，可更改
            perror("send failed");

        pid=fork();  //父进程建立套接字的连接之后，创建子进程用于通信
        if(pid<0)
               perror("fork error
");
        if(!pid)//创建新的子进程,用于发送数据
        {  
         //  close(sock_fd);//子进程不需要监听，所以子进程关闭监
            while(fgets(sendbuf,sizeof(sendbuf),stdin)!=NULL)
            {
                writen(new_fd,sendbuf,strlen(sendbuf));
                memset(sendbuf,0,sizeof(sendbuf));   //清空，以免和下一次混淆
           // exit(EXIT_SUCCESS);
                    }
            exit(EXIT_SUCCESS);
        }
        //close(new_fd);//父进程不需要连接，所以关闭连接套接字     
           else
        {
            while(1)
                {
                memset(recvbuf,0,sizeof(recvbuf)); 
                ret=readline(new_fd,recvbuf,1024);
                                if(ret<0)
                                        perror("read from client error");
                                else if(ret==0)
                                {
                                        printf("peer closed
");
                                        break;
                                }
                               fputs(recvbuf,stdout);
            }
             exit(EXIT_SUCCESS);
        }
        //while(waitpid(-1,NULL,WNOHANG)>0);//等待子进程结束，进行新的连接
    //}
    return 0;
}

客户端代码

#include<stdio.h>
#include<stdlib.h>
#include<errno.h>
#include<string.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<sys/un.h>
#include<sys/wait.h>      //*进程用的头文件*/
#include<netinet/in.h>
#include<arpa/inet.h>

#define MAXBYTEMUN   1024


ssize_t readn(int fd, void *buf, size_t count)   
{
        ssize_t nleft=count;
        ssize_t nread;
        char *charbuf=(char*) buf;

        while(nleft>0)
        {
                nread=read(fd,charbuf,nleft);
                if(nread<0)
                  {
                        if(errno==EINTR)
                           continue;
                        return -1;
                  }
                else if(nread==0)
                       return count-nleft;

                charbuf +=nread;
                nleft=count-nread;
        }

        return count;
}

ssize_t writen(int fd, const void *buf, size_t count)
{
        ssize_t nleft=count;
        ssize_t nwrite;
        char *charbuf=(char*) buf;

        while(nleft>0)
        {
                nwrite=write(fd,charbuf,nleft);
                if(nwrite<0)
                  {
                        if(errno==EINTR)
                           continue;
                        return -1;
                  }
                else if(nwrite==0)
                       return count-nleft;

         charbuf +=nwrite;
                nleft=count-nwrite;
    }
    return count;
}
 
 ssize_t recv_peek(int sockfd, void *buf, size_t len)
{
    int ret;
    while(1)
    {
        ret=recv(sockfd,buf,len,MSG_PEEK);
        if(ret==-1&& errno==EINTR)
            continue;
        return ret;
    }
}

 ssize_t readline(int sockfd, void *buf, size_t len)
{ 
    ssize_t nleft=len,nread;
    int ret;
    char* bufchar=buf;
    while(1)
    {
         ret=recv_peek(sockfd,bufchar,len);
        if(ret<0||ret==0)
            return ret;
        nread=ret;
        int i;
        for(i=0;i<nread;i++)
        {
            if(bufchar[i]=='
')
            {
                ret=readn(sockfd,bufchar,i+1);
                if(ret!=i+1)
                    exit(EXIT_FAILURE);
                return ret;
            }
        }
        if(nread>nleft)
            exit(EXIT_FAILURE);
        nleft-=nread;
        ret=readn(sockfd,bufchar,nread);
        if(ret!=nread)
            exit(EXIT_FAILURE);
        bufchar+=nread;
        
    }
    return -1;

}


int main(int argc,char *argv[])
{
    int sock_fd,numbytes;
    char buf[MAXBYTEMUN];
    struct hostent *he;
    struct sockaddr_in client_addr;//客户机的地址信息
    ssize_t n,ret;
    char recvbuf[1024]={'0'},sendbuf[1024]={'0'};
    
    if(argc!=2)
    {
        fprintf(stderr,"usage: client IPAddress
");   //执行客户端程序时，输入客户端程序名称和其IP地址
        exit(1);    
    }
    
    /*创建套接字*/
    sock_fd=socket(AF_INET,SOCK_STREAM,0);//采用IPv4协议
    if(sock_fd==-1)
    {
        perror("creat socket failed");
        exit(1);
    }
    
    /*服务器地址参数*/
    client_addr.sin_family=AF_INET;  
    client_addr.sin_port=htons(3490);
    client_addr.sin_addr.s_addr=inet_addr(argv[1]);
    bzero(&client_addr.sin_zero,sizeof(struct sockaddr_in));//bzero位清零函数，将sin_zero清零，sin_zero为填充字段，必须全部为零
    
    
    /*连接到服务器*/
    if(connect(sock_fd,(struct sockaddr*)&client_addr,sizeof(struct sockaddr))==-1)
    {
        perror("connect failed");
        exit(1);
    }
    if((numbytes=recv(sock_fd,buf,MAXBYTEMUN,0))==-1)
        {       
            perror("receive failed");
             exit(1);
        }
    buf[numbytes]='';//在字符串末尾加上，否则字符串无法输出
    printf("Received: %s
",buf);
    
    pid_t pid;
    pid=fork();
    if(!pid)//创建新的子进程,用于接收数据
        {
            while(1)
            {
                memset(recvbuf,0,sizeof(recvbuf));
                ret=readline(sock_fd,recvbuf,1024);
                if(ret<0)
                                        perror("read from server error");
                else if(ret==0)
                {
                    printf("peer closed
");
                    break;
                }
                fputs(recvbuf,stdout);
            }
            close(sock_fd);
        }
        else   //f=父进程用于发送数据
        {
            //close(sock_fd);//父进程不需要连接，所以关闭连接套接字
            while(fgets(sendbuf,sizeof(sendbuf),stdin)!=NULL)
            {
                writen(sock_fd,sendbuf,strlen(sendbuf));
                memset(sendbuf,0,sizeof(sendbuf));    //清空，以免和下一次混淆
            }
             close(sock_fd);
        }
    return 0;
}