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#include <netinet/ip.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
int main()
{
int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if (sockfd < 0) {
fprintf(stderr, "socket error: %s\n", strerror(errno));
return EXIT_FAILURE;
}
struct sockaddr_in server_address;
bzero (&server_address, sizeof(server_address));
server_address.sin_family = AF_INET;
server_address.sin_port = htons(54321);
server_address.sin_addr.s_addr = htonl(INADDR_ANY);
if (bind (sockfd, (struct sockaddr*)&server_address, sizeof(server_address)) < 0) {
fprintf(stderr, "bind error: %s\n", strerror(errno));
return EXIT_FAILURE;
}
for (;;) {
struct sockaddr_in sender;
socklen_t sender_len = sizeof(sender);
u_int8_t buffer[IP_MAXPACKET+1];
ssize_t datagram_len = recvfrom (sockfd, buffer, IP_MAXPACKET, 0, (struct sockaddr*)&sender, &sender_len);
if (datagram_len < 0) {
fprintf(stderr, "recvfrom error: %s\n", strerror(errno));
return EXIT_FAILURE;
}
char sender_ip_str[20];
inet_ntop(AF_INET, &(sender.sin_addr), sender_ip_str, sizeof(sender_ip_str));
printf ("Received UDP packet from IP address: %s, port: %d\n", sender_ip_str, ntohs(sender.sin_port));
buffer[datagram_len] = 0;
printf ("%ld-byte message: +%s+\n", datagram_len, buffer);
char* reply = "Thank you!";
ssize_t reply_len = strlen(reply);
if (sendto(sockfd, reply, reply_len, 0, (struct sockaddr*)&sender, sender_len) != reply_len) {
fprintf(stderr, "sendto error: %s\n", strerror(errno));
return EXIT_FAILURE;
}
fflush(stdout);
}
close (sockfd);
return EXIT_SUCCESS;
}
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