// SPDX-License-Identifier: GPL-2.0#include <stdio.h>#include <assert.h>#include <unistd.h>#include <bpf/bpf.h>#include <bpf/libbpf.h>#include <sys/socket.h>#include <netinet/in.h>#include <arpa/inet.h> int main(int ac, char **argv){	struct sockaddr_in *serv_addr_in, *mapped_addr_in, *tmp_addr_in;	struct sockaddr serv_addr, mapped_addr, tmp_addr;	int serverfd, serverconnfd, clientfd, map_fd;	struct bpf_link *link = NULL;	struct bpf_program *prog;	struct bpf_object *obj;	socklen_t sockaddr_len;	char filename[256];	char *ip; 	serv_addr_in = (struct sockaddr_in *)&serv_addr;	mapped_addr_in = (struct sockaddr_in *)&mapped_addr;	tmp_addr_in = (struct sockaddr_in *)&tmp_addr; 	snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);	obj = bpf_object__open_file(filename, NULL);	if (libbpf_get_error(obj)) {		fprintf(stderr, "ERROR: opening BPF object file failed\n");		return 0;	} 	prog = bpf_object__find_program_by_name(obj, "bpf_prog1");	if (libbpf_get_error(prog)) {		fprintf(stderr, "ERROR: finding a prog in obj file failed\n");		goto cleanup;	} 	/* load BPF program */	if (bpf_object__load(obj)) {		fprintf(stderr, "ERROR: loading BPF object file failed\n");		goto cleanup;	} 	map_fd = bpf_object__find_map_fd_by_name(obj, "dnat_map");	if (map_fd < 0) {		fprintf(stderr, "ERROR: finding a map in obj file failed\n");		goto cleanup;	} 	link = bpf_program__attach(prog);	if (libbpf_get_error(link)) {		fprintf(stderr, "ERROR: bpf_program__attach failed\n");		link = NULL;		goto cleanup;	} 	assert((serverfd = socket(AF_INET, SOCK_STREAM, 0)) > 0);	assert((clientfd = socket(AF_INET, SOCK_STREAM, 0)) > 0); 	/* Bind server to ephemeral port on lo */	memset(&serv_addr, 0, sizeof(serv_addr));	serv_addr_in->sin_family = AF_INET;	serv_addr_in->sin_port = 0;	serv_addr_in->sin_addr.s_addr = htonl(INADDR_LOOPBACK); 	assert(bind(serverfd, &serv_addr, sizeof(serv_addr)) == 0); 	sockaddr_len = sizeof(serv_addr);	assert(getsockname(serverfd, &serv_addr, &sockaddr_len) == 0);	ip = inet_ntoa(serv_addr_in->sin_addr);	printf("Server bound to: %s:%d\n", ip, ntohs(serv_addr_in->sin_port)); 	memset(&mapped_addr, 0, sizeof(mapped_addr));	mapped_addr_in->sin_family = AF_INET;	mapped_addr_in->sin_port = htons(5555);	mapped_addr_in->sin_addr.s_addr = inet_addr("255.255.255.255"); 	assert(!bpf_map_update_elem(map_fd, &mapped_addr, &serv_addr, BPF_ANY)); 	assert(listen(serverfd, 5) == 0); 	ip = inet_ntoa(mapped_addr_in->sin_addr);	printf("Client connecting to: %s:%d\n",	       ip, ntohs(mapped_addr_in->sin_port));	assert(connect(clientfd, &mapped_addr, sizeof(mapped_addr)) == 0); 	sockaddr_len = sizeof(tmp_addr);	ip = inet_ntoa(tmp_addr_in->sin_addr);	assert((serverconnfd = accept(serverfd, &tmp_addr, &sockaddr_len)) > 0);	printf("Server received connection from: %s:%d\n",	       ip, ntohs(tmp_addr_in->sin_port)); 	sockaddr_len = sizeof(tmp_addr);	assert(getpeername(clientfd, &tmp_addr, &sockaddr_len) == 0);	ip = inet_ntoa(tmp_addr_in->sin_addr);	printf("Client's peer address: %s:%d\n",	       ip, ntohs(tmp_addr_in->sin_port)); 	/* Is the server's getsockname = the socket getpeername */	assert(memcmp(&serv_addr, &tmp_addr, sizeof(struct sockaddr_in)) == 0); cleanup:	bpf_link__destroy(link);	bpf_object__close(obj);	return 0;}