getpeername() and getsockname() example server in C

peername-sockname.c

#include <stdio.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>

void handle_client(int);

#define BACKLOG 10
#define PORT 5678

int main() {
	// ! socket
	int server_fd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
	if (server_fd == -1) {
		perror("socket()");
		exit(EXIT_FAILURE);
	}

	// ! bind
	struct sockaddr_in sa;
	memset(&sa, 0, sizeof sa);
	sa.sin_family = AF_INET;
	sa.sin_port = htons(PORT);
	sa.sin_addr.s_addr = htonl(INADDR_ANY);

	int retval = bind(server_fd, (struct sockaddr *) &sa, sizeof sa);
	if (retval == -1) {
		perror("bind()");
		close(server_fd);
		exit(EXIT_FAILURE);
	}

	// ! listen
	retval = listen(server_fd, BACKLOG);
	if (retval == -1) {
		perror("listen()");
		close(server_fd);
		exit(EXIT_FAILURE);
	}

	for (;;) {
		// ! accept
		int client_fd = accept(server_fd, NULL, NULL);
		if (client_fd == -1) {
			perror("accept()");
			close(server_fd);
			exit(EXIT_FAILURE);
		}

		// * getpeername
		struct sockaddr_in peeraddr;
		socklen_t peeraddrlen;

		retval = getpeername(client_fd, (struct sockaddr *) &peeraddr, &peeraddrlen);
		if (retval == -1) {
			perror("getpeername()");
			close(server_fd);
			close(client_fd);
			exit(EXIT_FAILURE);
		}

		char *peeraddrpresn = inet_ntoa(peeraddr.sin_addr);

		printf("Peer information:\n");
		printf("Peer Address Family: %d\n", peeraddr.sin_family);
		printf("Peer Port: %d\n", ntohs(peeraddr.sin_port));
		printf("Peer IP Address: %s\n\n", peeraddrpresn);

		// * getsockname
		struct sockaddr_in localaddr;
		socklen_t localaddrlen;

		retval = getpeername(client_fd, (struct sockaddr *) &localaddr, &localaddrlen);
		if (retval == -1) {
			perror("getsockname()");
			close(server_fd);
			close(client_fd);
			exit(EXIT_FAILURE);
		}

		char *localaddrpresn = inet_ntoa(localaddr.sin_addr);

		printf("Socket information:\n");
		printf("Local Address Family: %d\n", localaddr.sin_family);
		printf("Local Port: %d\n", ntohs(localaddr.sin_port));
		printf("Local IP Address: %s\n\n", localaddrpresn);


		handle_client(client_fd);
		close(client_fd);
	}
}

void handle_client(int client_fd) {
	int size = 100;
	char buffer[size];

	// ! read
	int readlen = read(client_fd, buffer, size);
	if (readlen == -1) {
		perror("read()");
		close(client_fd);
		exit(EXIT_FAILURE);
	}
	printf("%d bytes read from client: %s\n", readlen, buffer);

	// ! write
	int writelen = write(client_fd, buffer, readlen);
	if (writelen == -1) {
		perror("write()");
		close(client_fd);
		exit(EXIT_FAILURE);
	}
	printf("%d bytes written to client: %s\n", writelen, buffer);
}