help!! why socket has no respone?

[wang rui]

Hi,james
thinks for your help.
but what's the CAP_NET_BIND_SERVICE capability and how to config it?
i am a freshman of it,please kind telling me the detail.thanks a lot.
best regard,wang

>
> > Hi,friends
> >
> > i have written a simple client-server app to test udp socket,but they
> > do not work correctly! For the server has
> >
> > no respone while request coming in.
> >
> > the program is below:
> >
> > Client.c:
> >
> > #include <stdio.h>
> > #include <sys/types.h>
> > #include <ctype.h>
> > #include <netinet/in.h>
> > #include <sys/socket.h>
> > #include <unistd.h>
> > #include <arpa/inet.h>
> >
> > int main(int argc,char* argv[]) {
> >   int sockfd;
> >   struct sockaddr_in their_addr;
> >   int addr_len;
> >   char sendbuf[8192]="\0";
> >
> >   if (argc<2) {   printf("Usage : client HOSTADDR\n");
> >
> >     exit(1);
> >   }
> >
> >   if ((sockfd=socket(AF_INET,SOCK_DGRAM,0))==-1) {
> >     printf("error in socket!\n");
> >     exit(1);
> >   }
> >
> >   their_addr.sin_family=AF_INET;
> >   their_addr.sin_port=htons(161);
> >   their_addr.sin_addr.s_addr=inet_addr(argv[1]);
> >   bzero(&(their_addr.sin_zero),8);
> >   addr_len=sizeof(their_addr);
> >   while (fgets(sendbuf,8192,stdin)!=NULL) {
> >     sendto(sockfd,sendbuf,strlen(sendbuf),0,(struct
> >     sockaddr*)&their_addr,addr_len);
> >
> >   }
> >
> >   close(sockfd);
> >   exit(1);
> > }
> > Server.c:
> >
> > #include <stdio.h>
> > #include <sys/types.h>
> > #include <ctype.h>
> > #include <netinet/in.h>
> > #include <sys/socket.h>
> > #include <unistd.h>
> > #include <arpa/inet.h>
> > #include <netdb.h>
> >
> > void pro_udp_service(int sockfd);
> >
> > int main(int argc,char* argv[]) {
> >   int sockfd;
> >   struct sockaddr_in my_addr;
> >   int addr_len;
> >   struct protoent *ppe;
> >   int htons_port;
> >   if ((ppe=getprotobyname("udp"))==0) {
> >     printf("error in getprotobyname!\n");
> >     exit(1);
> >   }
> >   if ((sockfd=socket(AF_INET,SOCK_DGRAM,ppe->p_proto))==-1) {
> >     printf("error in socket!\n");
> >     exit(1);
> >   }
> >
> >   my_addr.sin_family=AF_INET;  my_addr.sin_port=htons(161);
> >
> >   my_addr.sin_addr.s_addr=INADDR_ANY;
> >   if (bind(sockfd,(struct sockaddr*)&my_addr,sizeof(struct
> >   sockaddr))==-1) {
> >
> >     printf("error in binding!\n");
> >     exit(1);
> >   }
> >
> >   pro_udp_service(sockfd);
> >   close(sockfd);
> >   exit(1);
> > }
> >
> >
> > void pro_udp_service(int sockfd) {
> >   char recvbuf[8192];
> >   int n=0,len;
> >   struct sockaddr *addr;
>
>  This needs to be something like...
>
>    struct sockaddr_in addr;
>
>    len = sizeof(addr);
>
>...or you won't get the value of where the udp packet came from.
>
> >   while (1) {
> >
> >     len=sizeof(struct sockaddr_in);
> >     if ((n=recvfrom(sockfd,recvbuf,sizeof(recvbuf),0,addr,&len))==-1) {
> >       printf("error in recieving data!\n");
> >       exit(1);
> >     }
> >   }
> > }
> >
> > with "tcpdump" i can see that the udp packet is truely sent from
> > client to server,but the server doesn't work with the request.
> >
> >
> > 19:35:27.487859 z.32770 > w.snmp:  [len6<asnlen49] (DF)
> > 0x0000	 4500 0024 0000 4000 4011 a418 c0a8 0ab3	E..$..@.@.......
> > 0x0010	 c0a8 0aad 8002 00a1 0010 23dc 3131 3131	..........#.1111
> > 0x0020	 3131 310a 0000 0000 0000 0000 0000     	111...........
> >
> > But,on the other hand,if do such change,it works fine:
> > Client.c:
> > their_addr.sin_port=htons(161); ==> their_addr.sin_port=htons(6161);
> > /* portnum>1024 */
> >
> >
> > Server.c:
> > my_addr.sin_port=htons(161); ==> my_addr.sin_port=htons(6161);
> >
> > can you tell me why this happens?It puzzles me for a long time.
> > and how can i write my server deamon with port number below 1024?
> > thanks a lot for your help.
>
>  In unix all portnumbers <= 1024 are privileged, on Linux you cannot
>listen on them without having the CAP_NET_BIND_SERVICE capability.
>


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