I took the UDP connection code from geeksforgeeks and made some changes as the code is problematic. I also took out some parts of it as I don't need my client to send an initial message. I just need the client to continuously receive 4 bytes of datagrams from the server.
The changes I made are mainly from:
Socket Programming Pointer Error
The problem I have now is that, as far as I know from my Python socket programming, a client would give an error if there is no port open to be connected, but my client seems to connect even though the server program is not running. However this is tcp that I am talking about. Is UDP supposed to act like this?
Second problem is that server sends a message even though there is no client and I assume this is the UDP process as there is no 3 way handshake and server assumes there is a client listening.
Basically it seems like server sends messages but client can't receive them even though both programs run without error.
The program can be in C or C++ as I am using cpp compiler and do not have a preference as long as it works.
server:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#define PORT 8080
#define MAXLINE 1024
// Driver code
int main() {
int sockfd;
char buffer[MAXLINE];
char *hello = "Hello from server";
struct sockaddr_in servaddr, cliaddr;
// Creating socket file descriptor
if ( (sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ) {
perror("socket creation failed");
exit(EXIT_FAILURE);
}
memset(&servaddr, 0, sizeof(servaddr));
memset(&cliaddr, 0, sizeof(cliaddr));
// Filling server information
servaddr.sin_family = AF_INET; // IPv4
servaddr.sin_addr.s_addr = INADDR_ANY;
servaddr.sin_port = htons(PORT);
// Bind the socket with the server address
if ( bind(sockfd, (const struct sockaddr *)&servaddr,
sizeof(servaddr)) < 0 )
{
perror("bind failed");
exit(EXIT_FAILURE);
}
int n;
socklen_t len;
len = sizeof(cliaddr); //len is value/resuslt
sendto(sockfd, (const char *)hello, strlen(hello),
0, (const struct sockaddr *) &cliaddr,
len);
printf("Hello message sent.\n");
return 0;
}
client:
// Client side implementation of UDP client-server model
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#define PORT 8080
#define MAXLINE 1024
// Driver code
int main() {
int sockfd;
char buffer[MAXLINE];
char *hello = "Hello from client";
struct sockaddr_in servaddr;
// Creating socket file descriptor
if ( (sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ) {
perror("socket creation failed");
exit(EXIT_FAILURE);
}
memset(&servaddr, 0, sizeof(servaddr));
// Filling server information
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(PORT);
servaddr.sin_addr.s_addr = INADDR_ANY;
int n;
socklen_t len;
n = recvfrom(sockfd, (char *)buffer, MAXLINE,
MSG_WAITALL, (struct sockaddr *) &servaddr,
&len);
buffer[n] = '\0';
printf("Server : %s\n", buffer);
close(sockfd);
return 0;
}
