Test ephemeral port allocation for routed connections

socket-constant-rebind.cpp

#include <string>
#include <iostream>
#ifdef _WIN32
#include <WS2tcpip.h>
#define LAST_ERR WSAGetLastError()
#define SOCK_INVALID(s) s == INVALID_SOCKET
#else
#define LAST_ERR errno
#define SOCK_INVALID(s) s < 0
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <unistd.h>
#endif

const char data = 'A';

int main(int argc, char** argv){
	#ifdef _WIN32
	{
		WSADATA wsadata;
		WSAStartup(514, &wsadata);
	}
	#endif
	struct sockaddr_in dest = { 0 };
	dest.sin_family = AF_INET;
	dest.sin_addr.s_addr = htonl(3164981968);
	dest.sin_port = htons(7001);
	while(true){
		auto sock = socket(AF_INET, SOCK_DGRAM, 0);
		if (SOCK_INVALID(sock)){
			std::cerr << "failed to create socket with error: " << LAST_ERR << std::endl;
			continue;
		}
		auto res = sendto(sock, &data, 1, 0, (const struct sockaddr*)&dest, sizeof(dest));
		#ifdef _WIN32
		closesocket(sock);
		#else
		close(sock);
		#endif
	}
	#ifdef _WIN32
	WSACleanup();
	#endif
	return 0;
}

socket-port-test.cpp

#include <string>
#include <iostream>
#include <vector>
#include <stdexcept>
#ifdef _WIN32
#include <WS2tcpip.h>
#define LAST_ERR WSAGetLastError()
#define sock_t SOCKET
#define SOCK_INVALID(s) s == INVALID_SOCKET
#else
#define sock_t int
#define LAST_ERR errno
#define SOCK_INVALID(s) s < 0
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <unistd.h>
#endif

sock_t create_socket(int family, int type, int port);
void recv_print_address(sock_t socket);
struct sockaddr_in* recd = nullptr;

int main(int argc, char** argv){
	#ifdef _WIN32
	WSADATA data;
	WSAStartup(514, &data);
	#endif
	auto sock = create_socket(AF_INET, SOCK_DGRAM, 7001);
	while(true) recv_print_address(sock);
	#ifdef _WIN32
	closesocket(sock);
	WSACleanup();
	#else
	close(sock);
	#endif
	return 0;
}

sock_t create_socket(int family, int type, int port){
	auto sock = socket(family, type, 0);
	if (SOCK_INVALID(sock)){
		std::cerr << "failed to create socket with error: " << LAST_ERR << std::endl;
		exit(1);
	}
	struct sockaddr_in bind_addr = { 0 };
	bind_addr.sin_family = family;
	bind_addr.sin_addr.s_addr = INADDR_ANY;
	bind_addr.sin_port = htons(port);
	if (bind(sock, (struct sockaddr*)&bind_addr, sizeof(bind_addr)) < 0){
		std::cerr << "failed to bind socket with error: " << LAST_ERR << std::endl;
		exit(3);
	}
	return sock;
}

void recv_print_address(sock_t socket){
	recd = new struct sockaddr_in;
	std::vector<unsigned char> data;
	data.resize(1);
	auto addr_len = sizeof(recd);
	auto res = recvfrom(socket, (char*)data.data(), 1, 0, (struct sockaddr*)recd, (socklen_t*)&addr_len);
	if(res != 1){
		std::cerr << "udp socket threw error with code: " << LAST_ERR << std::endl;
		return;
	}
	std::cout << "Source port is: " << ntohs(recd->sin_port) << std::endl;
	delete recd;
}