// Project Calico BPF dataplane programs.
// Copyright (c) 2020-2026 Tigera, Inc. All rights reserved.
// SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later

#ifndef __CALI_NAT6_H__
#define __CALI_NAT6_H__

#include <stddef.h>

#include <linux/if_ether.h>
#include <linux/udp.h>

#include "bpf.h"
#include "skb.h"
#include "routes.h"
#include "nat_types.h"

/* Number of bytes we add to a packet when we do encap. */
#define VXLAN_ENCAP_SIZE	(sizeof(struct ethhdr) + sizeof(struct iphdr) + \
				sizeof(struct udphdr) + sizeof(struct vxlanhdr))

static CALI_BPF_INLINE int vxlan_encap(struct cali_tc_ctx *ctx, ipv6_addr_t *ip_src, ipv6_addr_t *ip_dst, __u16 src_port)
{
	__u32 new_hdrsz = sizeof(struct ethhdr) + sizeof(struct ipv6hdr) +
			sizeof(struct udphdr) + sizeof(struct vxlanhdr);

	if (bpf_skb_adjust_room(ctx->skb, new_hdrsz, BPF_ADJ_ROOM_MAC,
						  BPF_F_ADJ_ROOM_ENCAP_L4_UDP |
						  BPF_F_ADJ_ROOM_ENCAP_L3_IPV6 |
						  BPF_F_ADJ_ROOM_ENCAP_L2(sizeof(struct ethhdr)))) {
		return -1;
	}

	if (skb_refresh_validate_ptrs(ctx, new_hdrsz)) {
		deny_reason(ctx, CALI_REASON_SHORT);
		CALI_DEBUG("Too short VXLAN encap");
		return -1;
	}

	// Note: assuming L2 packet here so this code can't be used on an L3 device.
	struct udphdr *udp = (struct udphdr*) ((void *)ip_hdr(ctx) + IP_SIZE);
	struct vxlanhdr *vxlan = (void *)(udp + 1);
	struct ethhdr *eth_inner = (void *)(vxlan+1);
	struct ipv6hdr *ip_inner = (void*)(eth_inner+1);

	/* Copy the original IP header. Since it is already DNATed, the dest IP is
	 * already set. All we need to do is to change the source IP
	 */
	*ip_hdr(ctx) = *ip_inner;

	/* decrement TTL for the inner IP header. TTL must be > 1 to get here */
	ip_inner->hop_limit--;

	ipv6_addr_t_to_ipv6hdr_ip(&ip_hdr(ctx)->saddr, ip_src);
	ipv6_addr_t_to_ipv6hdr_ip(&ip_hdr(ctx)->daddr, ip_dst);
	ip_hdr(ctx)->payload_len = bpf_htons(bpf_ntohs(ip_hdr(ctx)->payload_len) + new_hdrsz);
	ip_hdr(ctx)->nexthdr = IPPROTO_UDP;

	udp->source = bpf_htons(src_port);
	udp->dest = bpf_htons(VXLAN_PORT);
	udp->len = bpf_htons(bpf_ntohs(ip_hdr(ctx)->payload_len) - sizeof(struct iphdr));
	/* XXX we leave udp->check == 0 which is not legal in IPv6, but we are
	 * the only ones parsing that packet!
	 */

	*((__u8*)&vxlan->flags) = 1 << 3; /* set the I flag to make the VNI valid */
	vxlan->vni = bpf_htonl(CALI_VXLAN_VNI) >> 8; /* it is actually 24-bit, last 8 reserved */

	/* keep eth_inner MACs zeroed, it is useless after decap */
	eth_inner->h_proto = eth_hdr(ctx)->h_proto;

	CALI_DEBUG("vxlan encap %x : %x",
		bpf_ntohl(ip_hdr(ctx)->saddr.in6_u.u6_addr32[3]), bpf_ntohl(ip_hdr(ctx)->daddr.in6_u.u6_addr32[3]));

	return 0;
}

static CALI_BPF_INLINE int vxlan_decap(struct __sk_buff *skb)
{
	__u32 extra_hdrsz;
	int ret = -1;

	extra_hdrsz = sizeof(struct ethhdr) + sizeof(struct ipv6hdr) +
		sizeof(struct udphdr) + sizeof(struct vxlanhdr);

	ret = bpf_skb_adjust_room(skb, -extra_hdrsz, BPF_ADJ_ROOM_MAC, BPF_F_ADJ_ROOM_FIXED_GSO);

	return ret;
}

static CALI_BPF_INLINE bool vxlan_size_ok(struct cali_tc_ctx *ctx)
{
	return !skb_refresh_validate_ptrs(ctx, UDP_SIZE + sizeof(struct vxlanhdr));
}

static CALI_BPF_INLINE __u32 vxlan_vni(struct cali_tc_ctx *ctx)
{
	struct vxlanhdr *vxlan;

	vxlan = skb_ptr_after(skb, udp_hdr(ctx));

	return bpf_ntohl(vxlan->vni << 8); /* 24-bit field, last 8 reserved */
}

static CALI_BPF_INLINE bool vxlan_vni_is_valid(struct cali_tc_ctx *ctx)
{
	struct vxlanhdr *vxlan;

	vxlan = skb_ptr_after(ctx->skb, udp_hdr(ctx));

	return *((__u8*)&vxlan->flags) & (1 << 3);
}

#endif /* __CALI_NAT6_H__ */
