C의 UDP 서버/클라이언트 - sendto 오류 : 프로토콜에 의해 지원되지 않는 주소 패밀리

Question

간단한 UDP 서버 클라이언트를 작성 중입니다. 서버는 클라이언트 입력에 따라 클라이언트의 네트워크 바이트 순서를 계산하여 클라이언트에 다시 전송해야합니다. 나는 하루 종일이 오류를 고치려고 노력했다. 어떤 도움이 필요합니다.

./udpserver.out 4545 
from.sin_family: 12079 
Little Endian 

ERROR UDP_SRV_004 - can not send message to client: Address family not supported by protocol 

클라이언트 시작 : 다음은 서버 시작과 출력은

./udpclient.out localhost 4545 

서버 코드 :

#include <stdio.h> 
#include <sys/types.h> 
#include <sys/socket.h> 
#include <stdlib.h> 
#include <strings.h> 
#include <string.h> 
#include <netinet/in.h> 
#define BUFFER_SIZE 80 

static void error(char *msg){ 
    perror(msg); 
    exit(1); 
} 


int main(int argc, char ** argv){ 

    int socketfd, portno, fromlen, n, length; 
    struct sockaddr_in server, from; 
    char buffer[BUFFER_SIZE]; 
    char response[BUFFER_SIZE]; 
    const char *le = "Little Endian\n"; 
    const char *be = "Big Endian\n"; 
    const char *unk = "Unknown \n"; 
    int cli_family; 

    if(argc!=2){ 
     fprintf(stderr,"Error starting the client, please start server as: %s port\n", argv[0]); 
     exit(0); 
    } 

    if((socketfd=socket(AF_INET,SOCK_DGRAM,0))<0) 
     error("ERROR UDP_SRV_001 - can not create socket"); 

    portno=atoi(argv[1]); 

    bzero(&server,sizeof(server)); 
    server.sin_family=AF_INET; 
    server.sin_addr.s_addr=INADDR_ANY; 
    server.sin_port=htons(portno); 

    if(bind(socketfd,(struct sockaddr *)&server,sizeof(server))<0) 
     error("ERROR UDP_SRV_002 - can not bind server address to a socket file descriptor"); 

    bzero(buffer, BUFFER_SIZE); 
    bzero(response,BUFFER_SIZE); 
    n=recvfrom(socketfd,buffer,BUFFER_SIZE-1,0,(struct sockaddr *)&from,&fromlen); 
    if (n<0) 
     error("ERROR UDP_SRV_003 - can not receive client's message"); 

    cli_family=from.sin_family; 
    printf("from.sin_family: %d\n", cli_family); 

    if (buffer[0] == 1 && buffer[1] == 2) 
     strcpy(response, be); 
    else if (buffer[0] == 2 && buffer[1] == 1) 
     strcpy(response, le); 
    else 
     strcpy(response, unk); 

    length=strlen(response); 
    printf("%s\n",response); 

    n=sendto(socketfd,response,length,0,(struct sockaddr *)&from,fromlen); 
    if(n<0) 
     error("ERROR UDP_SRV_004 - can not send message to client"); 


    return 0; 
} 

클라이언트 코드 : 서버에서

#include <stdio.h> 
#include <sys/types.h> 
#include <netdb.h> 
#include <sys/socket.h> 
#include <netinet/in.h> 
#include <stdlib.h> 
#include <strings.h> 
#include <string.h> 
#include <unistd.h> 
#define BUFFER_SIZE 80 

static void error(char *msg){ 
    perror(msg); 
    exit(1); 
} 

typedef union UNIT{ 
     short s; 
     char c[sizeof(short)]; 
    }unit; 

int main(int argc, char ** argv){ 

    int socketfd, portno, n, length; 
    struct sockaddr_in server, from; 
    struct hostent *host; 
    char buffer[BUFFER_SIZE]; 
    unit un; 
    un.s=0x0102; 

    if(argc!=3){ 
     fprintf(stderr,"Error starting the client, please start client as: %s hostname port\n", argv[0]); 
     exit(0); 
    } 

    if((host=gethostbyname(argv[1]))==NULL) 
     error("ERROR UDP_CLI_001 - no such host defined, please check your /etc/hosts file"); 

    portno=atoi(argv[2]); 

    if((socketfd=socket(AF_INET,SOCK_DGRAM,0))<0) 
     error("ERROR UDP_CLI_002 - can not create socket"); 

    bzero((char *)&server,sizeof(server)); 

    server.sin_family=AF_INET; 
    server.sin_port=htons(portno); 
    bcopy((char *)host->h_addr,(char *)&server.sin_addr,host->h_length); 
    length=sizeof(server); 

    if(sizeof(short)!=2){ 
     exit(0); 
    } 

    n=sendto(socketfd,un.c,strlen(un.c),0,(struct sockaddr *)&server,length); 
    if(n<0) 
     error("ERROR UDP_CLI_003 - can not send to server"); 
    bzero(buffer,BUFFER_SIZE); 
    n=recvfrom(socketfd,buffer,BUFFER_SIZE,0,(struct sockaddr *)&from, &length); 
    if(n<0) 
     error("ERROR UDP_CLI_004 - can receive from server"); 
    printf("%s",buffer); 


return 0; 
} 

Answer 1

, 당신 초기화 실패 fromlen에 전화하기 전에 sendto으로 전화하십시오. 따라서 from이 채워지지 않았습니다. man page에서

:

는

If src_addr is not NULL, and the underlying protocol provides the source address, this source address is filled in. When src_addr is NULL, nothing is filled in; in this case, addrlen is not used, and should also be NULL. The argument addrlen is a value-result argument, which the caller should initialize before the call to the size of the buffer associated with src_addr, and modified on return to indicate the actual size of the source address. The returned address is truncated if the buffer provided is too small; in this case, addrlen will return a value greater than was supplied to the call.

recvfrom 기능은 fromlen의 값을 읽으려고하지만, 초기화되지 않기 때문에 당신은 undefined behavior를 호출합니다.

fromlen을 초기화하면 문제가 해결됩니다.

fromlen = sizeof from; 
n=recvfrom(socketfd,buffer,BUFFER_SIZE-1,0,(struct sockaddr *)&from,&fromlen);