I'm trying to do socket programming. I made some example, which is getting ip and port from sockets.
I tried to get IP and port in server and client both.
server has two sockets, listening socket and socket for data transfer with client(I named it "Client socket"). and client has one socket. I wanted these socket's local ip&port and peer's ip&port.so I used getsockname() and getpeername().
code is below.
** server **
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
void error_handling(char *message);
int main(int argc, char *argv[])
{
int serv_sock;
int clnt_sock;
struct sockaddr_in serv_addr;
struct sockaddr_in clnt_addr;
socklen_t clnt_addr_size;
char message[]="Hello World!";
if(argc!=2){
printf("Usage : %s <port>\n", argv[0]);
exit(1);
}
serv_sock=socket(PF_INET, SOCK_STREAM, 0);
if(serv_sock == -1)
error_handling("socket() error");
memset(&serv_addr, 0, sizeof(serv_addr));
serv_addr.sin_family=AF_INET;
serv_addr.sin_addr.s_addr=htonl(INADDR_ANY);
serv_addr.sin_port=htons(atoi(argv[1]));
if(bind(serv_sock, (struct sockaddr*) &serv_addr, sizeof(serv_addr))==-1 )
error_handling("bind() error");
if(listen(serv_sock, 5)==-1)
error_handling("listen() error");
clnt_addr_size=sizeof(clnt_addr);
clnt_sock=accept(serv_sock, (struct sockaddr*)&clnt_addr,&clnt_addr_size);
if(clnt_sock==-1)
error_handling("accept() error");
write(clnt_sock, message, sizeof(message));
struct sockaddr_in addr1;
struct sockaddr_in addr2;
struct sockaddr_in addr3;
struct sockaddr_in addr4;
socklen_t serv_len = sizeof(serv_addr);
int serv_peer_err = getpeername(serv_sock, (struct sockaddr *)&addr1, &serv_len);
int clnt_peer_err = getpeername(clnt_sock, (struct sockaddr *)&addr2, &clnt_addr_size);
int serv_sock_err = getsockname(serv_sock, (struct sockaddr *)&addr3, &serv_len);
int clnt_sock_err = getsockname(clnt_sock, (struct sockaddr *)&addr4, &clnt_addr_size);
printf("Server socket's ip : %s\n", inet_ntoa(addr3.sin_addr));
printf("Server socket's port : %d\n", ntohs(addr3.sin_port));
printf("Server socket's peer ip : %s\n", inet_ntoa(addr1.sin_addr));
printf("Server socket's peer port : %d\n\n\n\n\n\n", ntohs(addr1.sin_port));
printf("Client socket's ip : %s\n", inet_ntoa(addr4.sin_addr));
printf("Client socket's port : %d\n", ntohs(addr4.sin_port));
printf("Client socket's peer ip : %s\n", inet_ntoa(addr2.sin_addr));
printf("client socket's peer port %d\n", ntohs(addr2.sin_port));
printf("%d %d %d %d\n", serv_peer_err, clnt_peer_err, serv_sock_err, clnt_sock_err);
close(clnt_sock);
close(serv_sock);
return 0;
}
void error_handling(char *message)
{
fputs(message, stderr);
fputc('\n', stderr);
exit(1);
}
** client **
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
void error_handling(char *message);
int main(int argc, char* argv[])
{
int sock;
struct sockaddr_in serv_addr;
char message[30];
int str_len;
if(argc!=3){
printf("Usage : %s <IP> <port>\n", argv[0]);
exit(1);
}
sock=socket(PF_INET, SOCK_STREAM, 0);
if(sock == -1)
error_handling("socket() error");
memset(&serv_addr, 0, sizeof(serv_addr));
serv_addr.sin_family=AF_INET;
serv_addr.sin_addr.s_addr=inet_addr(argv[1]);
serv_addr.sin_port=htons(atoi(argv[2]));
if(connect(sock, (struct sockaddr*)&serv_addr, sizeof(serv_addr))==-1)
error_handling("connect() error!");
str_len=read(sock, message, sizeof(message)-1);
if(str_len==-1)
error_handling("read() error!");
struct sockaddr_in addr1;
struct sockaddr_in addr2;
int clnt_sock_err, clnt_peer_err;
socklen_t serv_len = sizeof(serv_addr);
clnt_peer_err = getpeername(sock, (struct sockaddr *)&addr1, &serv_len);
clnt_sock_err = getsockname(sock, (struct sockaddr *)&addr2, &serv_len);
printf("Client socket's ip : %s\n", inet_ntoa(addr2.sin_addr));
printf("client socket's port %d\n", ntohs(addr2.sin_port));
printf("Client socket's peer ip : %s\n", inet_ntoa(addr1.sin_addr));
printf("Client socket's peer port : %d\n", ntohs(addr1.sin_port));
printf("%d %d\n", clnt_sock_err, clnt_peer_err);
printf("Message from server: %s \n", message);
close(sock);
return 0;
}
void error_handling(char *message)
{
fputs(message, stderr);
fputc('\n', stderr);
exit(1);
}
and I run it, ip is loopback(127.0.0.1) and port is 7755.
the result is :
server
Server socket's ip : 0.0.0.0
Server socket's port : 7755
Server socket's peer ip : 1.0.0.0
Server socket's peer port : 4992
Client socket's ip : 127.0.0.1
Client socket's port : 7755
Client socket's peer ip : 127.0.0.1
client socket's peer port 6311
-1 0 0 0
client
Client socket's ip : 127.0.0.1
client socket's port 6311
Client socket's peer ip : 127.0.0.1
Client socket's peer port : 7755
0 0
Message from server: Hello World!
I noticed getpeername() failed with server socket's peer, then returned -1. but it showed IP and port : 1.0.0.0 and 4992. I don't know what these mean. and I think another results make sense. I know listening(server) socket only deal with connection, not data transfer, server create another socket for data transfer by accept().
my question is ㅡ if listening(server) socket only deal with client's connection, then its peer should not be exist? what's that wrong IP and Port? just garbage value?
