如何确定哪个客户端在UDP套接字编程中发送了消息

Question

I'm creating a two way chat program using C This is the code for the server

#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<errno.h>
#include<string.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<netdb.h>
#include<signal.h>
// the port users will be connecting to
#define RCVPORT "4950"
#define MAXBUFLEN 100

// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa){
    if (sa->sa_family == AF_INET) {
        return &(((struct sockaddr_in*)sa)->sin_addr);
    }
    return &(((struct sockaddr_in6*)sa)->sin6_addr);
}

int main(void){
int sockfd;
struct addrinfo hints,*servinfo,*p1;
int rv;
int numbytes;
int yes = 1;
struct sockaddr_storage client1_addr,client2_addr;
char buf[MAXBUFLEN];
char buf2[MAXBUFLEN];
char auth[6],auth2[6];
socklen_t client1_addrlen,client2_addrlen;
char s[INET6_ADDRSTRLEN];
pid_t pid1,pid2;    
char exiter[20];
memset(&hints, 0, sizeof hints);

hints.ai_family = AF_UNSPEC; // set to AF_INET to force IPv4
hints.ai_socktype = SOCK_DGRAM;
hints.ai_flags = AI_PASSIVE; // use my IP


if ((rv = getaddrinfo(NULL, RCVPORT, &hints, &servinfo)) != 0) {
    fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
    return 1;
}
// loop through all the results and bind to the first we can
for(p1 = servinfo; p1 != NULL; p1 = p1->ai_next) {
    if ((sockfd = socket(p1->ai_family, p1->ai_socktype,p1->ai_protocol)) == -1) {
        perror("listener: socket");
        continue;
    }
    if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &yes,sizeof(int)) == -1) {
        perror("setsockopt");
        exit(1);
    }
    if (bind(sockfd, p1->ai_addr, p1->ai_addrlen) == -1) {
        close(sockfd);
        perror("listener: bind");
        continue;
    }
    break;
}
if (p1 == NULL) {
    fprintf(stderr, "listener: failed to bind socket\n");
    return 2;
}
freeaddrinfo(servinfo);

client1_addrlen = sizeof(client1_addr);
client2_addrlen = sizeof(client2_addr); 
//WAIT for CLIENT 1 
printf("listener: waiting for clients...\n");
if ((numbytes = recvfrom(sockfd,auth, MAXBUFLEN-1 , 0,(struct sockaddr *)&client1_addr, &client1_addrlen)) == -1) {
    perror("recvfrom");
    exit(1);
}
if(strcmp(auth,"AUTH")!=0){
    printf("CLIENT AUTHENTICATION FAILED");     
    exit(0);    
}
printf("GOT CLIENT 1!!\n");
//WAIT for CLIENT 2 
if ((numbytes = recvfrom(sockfd,auth2, MAXBUFLEN-1 , 0,(struct sockaddr *)&client2_addr, &client2_addrlen)) == -1) {
        perror("recvfrom");
        exit(1);
}
if(strcmp(auth2,"AUTH")!=0){
    printf("CLIENT AUTHENTICATION FAILED");     
    exit(0);    
}
if ((numbytes=sendto(sockfd,"ok",3,0,(struct sockaddr *)&client1_addr, client1_addrlen)) == -1) {
    perror("talker: sendto");
    exit(1);
}
if ((numbytes=sendto(sockfd,"ok",3,0,(struct sockaddr *)&client2_addr, client2_addrlen)) == -1) {
    perror("talker: sendto");
    exit(1);
}
printf("GOT CLIENT 2!!!\n");
printf("Server Ready!!!\n");
//for CLIENT 1
if(fork()==0){
    while(1){
        if ((numbytes = recvfrom(sockfd, buf, MAXBUFLEN-1 , 0,NULL,NULL)) == -1) {
            perror("recvfrom");
            exit(1);
        }

        if(numbytes!=0){
            printf("listener: packet contains %s \n", buf);
            if ((numbytes=sendto(sockfd, buf, strlen(buf)+1,0,(struct sockaddr *)&client2_addr, client2_addrlen)) == -1) {
                perror("talker: sendto");
                exit(1);
            }
        }
        else{
            printf("CLIENT 1 has disconnected\n");
            break;          
        }

    }
    exit(0);

}
//for CLIENT 2
if(fork()==0){
    while(1){
        if ((numbytes = recvfrom(sockfd, buf2, MAXBUFLEN-1 , 0,NULL,NULL)) == -1) {
            perror("recvfrom");
            exit(1);
        }

        printf("listener: packet contains %s \n", buf2);

        if(numbytes!=0){            
            if ((numbytes=sendto(sockfd, buf2, strlen(buf2)+1,0,(struct sockaddr *)&client1_addr, client1_addrlen)) == -1) {
                perror("talker: sendto");
                exit(1);
            }
        }
        else{
            printf("CLIENT 2 has disconnected\n");
            break;      
        }       
    }
    exit(0);

}
wait(NULL);
//fgets(exiter,sizeof(exiter),stdin);
close(sockfd);

return 0;}

Then this is the code for the client

#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<errno.h>
#include<string.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<netdb.h>
#include<signal.h>
#define SERVERPORT "4950"
#define MAXBUFLEN 100
// the port users will be connecting to
int main(int argc, char *argv[]){
    int sockfd;
    char ok[3];
    struct addrinfo hints, *servinfo, *p;
    struct sockaddr_storage server_addr;
    socklen_t server_addrlen = sizeof(server_addr);
    int rv;
    int numbytes;
    char sendbuffer[256];
    char rcvbuffer[256];
    pid_t pid;

    if (argc != 2) {
        fprintf(stderr,"usage: talker hostname\n");
        exit(1);
    }
    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_DGRAM;

    if ((rv = getaddrinfo(argv[1], SERVERPORT, &hints, &servinfo)) != 0) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
        return 1;
    }

    // loop through all the results and make a socket
    for(p = servinfo; p != NULL; p = p->ai_next) {
        if ((sockfd = socket(p->ai_family, p->ai_socktype,p->ai_protocol)) == -1) {
            perror("talker: socket");
            continue;
        }
        break;
    }

    if (p == NULL) {
        fprintf(stderr, "talker: failed to bind socket\n");
        return 2;
    }
    //SEND an authentication to server
    if ((numbytes = sendto(sockfd,"AUTH",5,0,p->ai_addr, p->ai_addrlen)) == -1) {
        perror("talker: sendto");
        exit(1);
    }
    if(numbytes == 0){
        printf("CLIENT FAILED TO AUTHENTICATE TO SERVER\n");
        exit(0);    

    }
    // WAIT for go signal from server
    printf("Waiting for Server Response\n");    
    if ((numbytes = recvfrom(sockfd,ok, MAXBUFLEN-1 , 0,(struct sockaddr *)&server_addr, &server_addrlen)) == -1) {
            perror("recvfrom");
            exit(1);
    }
    if(strcmp(ok,"ok")!=0){
        printf("NO SERVER RESPONSE\n");     
        exit(0);    
    }
    pid = fork();   
    if(pid>0){                      

        do {    
            printf("Enter message to send >>> ");   
            fgets(sendbuffer,sizeof(sendbuffer),stdin);
            printf("\n");
            if ((numbytes = sendto(sockfd, sendbuffer, strlen(sendbuffer)+1,0,p->ai_addr, p->ai_addrlen)) == -1) {
                perror("talker: sendto");
                exit(1);
            }

        } while(strcmp(".exit\n",sendbuffer) != 0);

    }
    else if(pid==0){
        while(1){
            if ((numbytes = recvfrom(sockfd,rcvbuffer,MAXBUFLEN-1 ,0,NULL,NULL)) == -1) {
                perror("recvfrom");
                exit(1);
            }
            printf("\nMessage Received >>>%s",rcvbuffer);
        }
    }

    freeaddrinfo(servinfo);
    close(sockfd);
    kill(pid,SIGUSR1);
    return 0;
}

I'd like to know how to determine if client 1 sent the message so I can relay it to client2 or vice versa. Thanks!

Answer 1

The 5th and 6th arguments to recvfrom get filled in with the address of the socket that sent the packet. So after you get a packet, compare that address with the addresses of your clients. That will tell you which client sent that message.

Answer 2

您可以创建可以存储活动连接的链表，一旦收到来自任何客户端的消息，就可以中继到所有活动客户端...