#include <stdio.h>
#include <string.h>
#include <arpa/inet.h>
#include <assert.h>

#define PROXY2_SIG	"\x0D\x0A\x0D\x0A\x00\x0D\x0A\x51\x55\x49\x54\x0A"

uint16_t
port(const char *portspec)
{
	long int ptst = strtol(portspec, NULL, 10);
	if (ptst < 0 || ptst > 65535)
		assert(0);
	return htons(ptst);
}

void
dump_hex(const char *s, size_t len)
{
	const char *p;

	printf("\"");
	for (p = s; p != s + len; ++p) {
		printf("%02x ", *p);
	}
	printf("\"\n");
}

int
main(int argc, char **argv) {
	int af;
	long int ptst;

	struct {
		uint8_t		sig[12];
		uint8_t		ver_cmd;
		uint8_t		fam;
		uint16_t	len;
		union {
			struct {  /* for TCP/UDP over IPv4, len = 12 */
				uint32_t src_addr;
				uint32_t dst_addr;
				uint16_t src_port;
				uint16_t dst_port;
			} ip4;
			struct {  /* for TCP/UDP over IPv6, len = 36 */
				uint8_t  src_addr[16];
				uint8_t  dst_addr[16];
				uint16_t src_port;
				uint16_t dst_port;
			} ip6;
		} addr;
	} v2 = { 0 };

	if (argc != 6) {
		fprintf(stderr, "Usage: %s <proto> clientip serverip"
		    " clientport serverport\n", argv[0]);
		return (1);
	}

	if (strcmp("TCP4", argv[1]) == 0)
		af = AF_INET;
	else if (strcmp("TCP6", argv[1]) == 0)
		af = AF_INET6;
	else {
		fprintf(stderr, "proto must be one of 'TCP4' or 'TCP6'\n");
		return (1);
	}

	memcpy(&v2.sig, PROXY2_SIG, sizeof v2.sig);

	/* v2, PROXY */
	v2.ver_cmd = 0x21;

	if (af == AF_INET) {
		v2.len = htons(sizeof v2.addr.ip4);
		v2.fam = 0x11;
		v2.addr.ip4.src_port = port(argv[4]);
		v2.addr.ip4.dst_port = port(argv[5]);
		assert(inet_pton(af, argv[2], &v2.addr.ip4.src_addr) == 1);
		assert(inet_pton(af, argv[3], &v2.addr.ip4.dst_addr) == 1);

	} else if (af == AF_INET6) {
		v2.len = htons(sizeof v2.addr.ip6);
		v2.fam = 0x21;
		v2.addr.ip6.src_port = port(argv[4]);
		v2.addr.ip6.dst_port = port(argv[5]);
		assert(inet_pton(af, argv[2], &v2.addr.ip6.src_addr) == 1);
		assert(inet_pton(af, argv[3], &v2.addr.ip6.dst_addr) == 1);
	}

	dump_hex((const char *) &v2, ntohs(v2.len) + 16);

	return (0);
}