Sockets, client server communication using SOCK_DGRAM, epoll - c

Question

I'm trying to write a program with AF_INET, SOCK_DGRAM, where client connects to server sends it message "First message" and then the server responds to client with "Second message".
Q1: In my code server receives "First message", however client doesn't get server response "Second message", why?
Q2: In client I connect to server using msg_addr.sin_addr.s_addr =INADDR_ANY; I would like to change it for something like: msg_addr.sin_addr.s_addr =htonl(inet_addr("172.126.154.12")); where ip "172.126.154.12"is server ip;
server.c
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <pthread.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <arpa/inet.h>
#include <sys/epoll.h>
#include <errno.h>
#include <signal.h>
#include <string.h>
typedef struct{
int type;
int arg1;
int arg2;
int result;
char name[50];
}Msg;
#define WRITE(format, ...) { char buffer[255]; sprintf(buffer, format, ##__VA_ARGS__); write(1, buffer, strlen(buffer));}
#define FAILURE_EXIT(format, ...) { char buffer[255]; sprintf(buffer, format, ##__VA_ARGS__); write(1, buffer, strlen(buffer));exit(-1);}
int web_fd, epoll;
struct sockaddr_in server_addr;
Msg msg;
struct sockaddr msg_addr;
int main(int argc, char *argv[]){
if((web_fd = socket(AF_INET, SOCK_DGRAM,0)) == -1) FAILURE_EXIT("Failed to create communication endpoint web_fd\n");
int yes=1;
if (setsockopt(web_fd,SOL_SOCKET,SO_REUSEADDR,&yes,sizeof(yes)) == -1) FAILURE_EXIT("setsockopt web_fd\n");
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(9992);
server_addr.sin_addr.s_addr = INADDR_ANY;
if(bind(web_fd,(const struct sockaddr*) &server_addr,sizeof(struct sockaddr)) == -1) FAILURE_EXIT("Failed to assign server_addr to a web_fd: %s\n",strerror(errno));
epoll = epoll_create1(0);
if(epoll == -1) FAILURE_EXIT("Failed to create new epoll instance: %s\n",strerror(errno));
struct epoll_event event;
event.events = EPOLLIN;
event.data.fd = web_fd;
if(epoll_ctl(epoll,EPOLL_CTL_ADD,web_fd,&event)== -1) FAILURE_EXIT("Failed to register web_fd file descriptor on epoll instance: %s\n",strerror(errno));
printf("Server starts loop.\n");
while(1){
struct epoll_event event;
WRITE("Waiting for client message...\n");
int nfd = epoll_wait(epoll,&event,1,-1);
if(event.data.fd == web_fd){
recvfrom(event.data.fd,&msg,sizeof(Msg),0 ,&msg_addr,0);
WRITE("Received message from client %s\n",msg.name);
strcpy(msg.name,"Second message");
sendto(event.data.fd,&msg,sizeof(Msg),0 ,(struct sockaddr*)&msg_addr, (socklen_t) sizeof(msg_addr) );
}else{
WRITE("Unknown descriptor\n");
}
}
}
client.c
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <pthread.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <arpa/inet.h>
#include <sys/epoll.h>
#include <errno.h>
#include <signal.h>
#include <string.h>
typedef struct{
int type;
int arg1;
int arg2;
int result;
char name[50];
}Msg;
#define WRITE(format, ...) { char buffer[255]; sprintf(buffer, format, ##__VA_ARGS__); write(1, buffer, strlen(buffer));}
#define FAILURE_EXIT(format, ...) { char buffer[255]; sprintf(buffer, format, ##__VA_ARGS__); write(1, buffer, strlen(buffer));exit(-1);}
int socket_fd;
struct sockaddr_in msg_addr;
Msg msg;
int main(int argc, char *argv[]){
struct sockaddr_in msg_addr;
msg_addr.sin_family = AF_INET;
msg_addr.sin_addr.s_addr =INADDR_ANY;
msg_addr.sin_port = htons(9992);
socket_fd = socket(AF_INET, SOCK_DGRAM,0);
if(socket_fd == -1) FAILURE_EXIT("Failed to create client socket\n");
if(connect(socket_fd, (const struct sockaddr*) &msg_addr, sizeof(struct sockaddr)) == -1) FAILURE_EXIT("Failed to assign server_addr to a web_fd: %s\n",strerror(errno));
strcpy(msg.name,"First message ");
sendto(socket_fd,&msg,sizeof(Msg),0 ,(struct sockaddr*)&msg_addr,(socklen_t) sizeof(Msg));
WRITE("Waiting..\n");
recvfrom(socket_fd,&msg,sizeof(Msg),0 ,0,0);
WRITE("f %s\n",msg.name);
WRITE("I registered\n");
sleep(400);
}

Answer 1

In server code change recvfrom() call as this
socklen_t addrsize;
recvfrom(event.data.fd,&msg,sizeof(Msg),0 ,&msg_addr, &addrsize);
and change subsequent sendto() call as this
sendto(event.data.fd,&msg,sizeof(Msg),0 ,(struct sockaddr*)&msg_addr, addrsize);