c++ - 为什么我收到协议(protocol)不支持的地址族错误？

Question

我正在使用 UDP 协议(protocol)实现双向通信，最初我从客户端向服务器发送消息 HELO，该消息成功显示在服务器端，但是当我从服务器向客户端发送消息以回复 HELO 时，它给我错误:地址系列协议(protocol)不支持。

这是我的服务器代码:

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



using namespace std;
int main(void)
    {
    char write[100];
    int MAXBUFLEN=100;
    char* buf;
    char msg[100];
    char swp;
    int l,x,y;

    int conn_sock,n,err;
    struct sockaddr_in server_addr,client_addr;

    conn_sock=socket(AF_INET,SOCK_DGRAM,0);
    if(conn_sock == -1)
    {
    perror("\n\nError in making socket and error is");

    cout<<"Error No:\t\n"<<errno;
    exit(0);
    }

    server_addr.sin_family= AF_INET;
    server_addr.sin_port = 1234;
    server_addr.sin_addr.s_addr = inet_addr("127.0.0.1");

    err=bind(conn_sock,(struct sockaddr *)&server_addr,sizeof(server_addr)); // binding...

    if(err == -1)
    {

    perror("\n\nError in binding and error is:");
    cout<<"Error No:\t\n"<<errno;
    exit(0);
    }
    int s=sizeof(client_addr);

    n=recvfrom(conn_sock,msg,sizeof(msg),0,(struct sockaddr *)&client_addr,(socklen_t*)s); // reciving HELO from client..


    cout<<msg<<endl;

    cout<<"The messgae hasbeen recieved from client now enter a reply for HELO msg:"<<endl;
    cin>> write;

    // sending reply to client

    int m=sendto(conn_sock,write,strlen(write),0,(sockaddr *)&client_addr,s); // sending reply to client on reply of helo...
    if (m== -1){
     perror("talker: sendto");
    }
    // now recieve mail fromm...

    recvfrom(conn_sock,msg,sizeof(msg),0,(struct sockaddr *)&client_addr,(socklen_t*)s);

// sending rcpto client
    sendto(conn_sock,write,strlen(write),0,(sockaddr *)&client_addr,s);
    recvfrom(conn_sock,msg,sizeof(msg),0,(struct sockaddr *)&client_addr,(socklen_t*)s);
    cout<<"Recpt to: Nu.edu.pk"<<endl;  
    exit(0);

}

这是我的客户端代码:

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

#define SERVERPORT "4950"    // the port users will be connecting to
#define MAXBUFLEN 100
using namespace std;

int main(int argc, char*argv[])

{

    // declarations
    char msg3[]="DATA";
    int sockfd;
        struct addrinfo hints, *servinfo, *p;
        int rv;
        int numbytes;
        char buf[MAXBUFLEN];
        socklen_t addr_len;
        struct sockaddr_storage their_addr;
    char* bigarray;
    char msg[]="HELO";
    char msg2[]="Mail from: Mahnoorfatima@gmail.com";   
    int i=0;

    char * adress;
    char * subject;
    char * name;
    const char *delim="@";
    // getting commandline args into arrays.
    adress=argv[i+1];
    char* host=strtok(adress,delim );
    subject=argv[i+2];
    name=argv[i+3];


    // putting all in one array

    bigarray=adress;
    bigarray=subject;
    bigarray=name;




    if(argc>9){
    cout << "Just provide three arguments in commandline,please. " << endl;
        }

    // gets the name of the host:

    int a=gethostname(bigarray, 100);

    cout<<"The host of the client is:"<<a<<endl;


    int conn_sock,n,m,err;
    struct sockaddr_in server_addr;
    conn_sock=socket(AF_INET,SOCK_DGRAM,0);

    if(conn_sock ==-1)
    {
    perror("\n\nError in making socket and error is");

    cout<<"Error No:\t\n"<<errno;
    exit(0);
    }


    server_addr.sin_family= AF_INET;
    server_addr.sin_port = 1234;
    server_addr.sin_addr.s_addr = inet_addr("127.0.0.1");


    int pp=sizeof(server_addr);
    n=sendto(conn_sock,msg,strlen(msg),0,(sockaddr *)&server_addr,pp);//sending HELO to server...

    n=recvfrom(conn_sock,msg,sizeof(msg),0,(struct sockaddr *)&server_addr,(socklen_t*)pp);
    cout<<"Mail from: mahnoorfatima22@gmail.com"<<endl;
    n=sendto(conn_sock,msg2,strlen(msg2),0,(sockaddr *)&server_addr,pp);


        // sending file to server

    // reieving from server rcpto command

    recvfrom(conn_sock,msg,sizeof(msg),0,(struct sockaddr *)&server_addr,(socklen_t*)pp);   

    // sending data command to the server....

    n=sendto(conn_sock,msg3,strlen(msg3),0,(sockaddr *)&server_addr,pp);
        //Sending the filename to server...
        if ((n = sendto(sockfd,name,strlen(name), 0,p->ai_addr, p->ai_addrlen)) == -1) {
        //     perror("Error is sending");
                exit(1);
                                                }              
        //     Get the size of the file server sy 

    addr_len = sizeof their_addr;
        if ((n = recvfrom(sockfd, buf, MAXBUFLEN-1 , 0,(struct sockaddr *)&their_addr, &addr_len)) == -1) {
        //     perror("Error in recieving file");
         exit(1);
                                                        }


        cout<<"client: recieved file size: %s\nNumbytes:%d\n"<<buf<<numbytes;





    exit(0);

    }

Answer 1

问题很可能是 recvfrom 函数需要一个指向套接字地址结构大小的指针，而您按值提供了长度。这意味着编译器认为您设置的大小 (sizeof(client_addr)) 被解释为指针，并且无论结构大小是多少，它都不是有效指针或指向远程有效的东西。

这意味着 recvfrom 可能没有完全填充对等地址结构 (client_addr)，这会导致您的 sendto 失败。

尝试例如这代替:

n=recvfrom(conn_sock,msg,sizeof(msg),0,
          (struct sockaddr *)&client_addr,&s);
//                                        ^
//                                        |
//            Note address-of operator here