Redirecting HTTP server

Makefile

CC=gcc
CFLAGS=-I. -Wall -Wextra
OBJ = redirect.o

redirect: $(OBJ)
	$(CC) -o $@ $^ $(CFLAGS)

clean:
	 rm -f redirect redirect.o

redirect.c

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

#define on_error(...) { fprintf(stderr, __VA_ARGS__);  fprintf(stderr, "%s\n", strerror(errno)); fflush(stderr); exit(1); }

int main (int argc, char *argv[]) {
	if (argc != 3) {
		fprintf(stderr, "Usage: %s [port] [url]\n", argv[0]);
		exit(2);
	}

	int port = atoi(argv[1]);
	char *url = argv[2];
	int server_fd, client_fd, err;

	char response[128];
	int response_len = snprintf(response, sizeof(response), "HTTP/1.0 302 Found\r\nLocation: %s\r\n", url);
	if (response_len == sizeof(response)) {
		fprintf(stderr, "URL too long\n");
		exit(2);
	}

	server_fd = socket(AF_INET, SOCK_STREAM, 0);
	if (server_fd < 0) on_error("Could not create socket\n");

	struct sockaddr_in server = {
		.sin_family      = AF_INET,
		.sin_port        = htons(port),
		.sin_addr.s_addr = htonl(INADDR_ANY),
	};

	int opt_val = 1;
	setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR, &opt_val, sizeof opt_val);

	err = bind(server_fd, (struct sockaddr *) &server, sizeof(server));
	if (err < 0) on_error("Could not bind socket\n");

	err = listen(server_fd, 128);
	if (err < 0) on_error("Could not listen on socket\n");

	printf("Server is listening on %d, redirecting to %s\n", port, url);

	while (1) {
		client_fd = accept(server_fd, NULL, NULL);

		if (client_fd < 0) {
			fprintf(stderr, "Client accept failed: %s\n", strerror(errno));
			continue;
		}

		err = send(client_fd, response, response_len, 0);
		if (err < 0) {
			fprintf(stderr, "Client write failed: %s\n", strerror(errno));
		}

		close(client_fd);
	}

	return 0;
}