// SPDX-License-Identifier: GPL-2.0
#include <string.h>

#include <linux/bpf.h>
#include <linux/in.h>
#include <linux/in6.h>
#include <sys/socket.h>

#include <bpf/bpf_helpers.h>
#include <bpf/bpf_endian.h>

#include <bpf_sockopt_helpers.h>

char _license[] SEC("license") = "GPL";

struct svc_addr {
        __be32 addr[4];
        __be16 port;
};

struct {
        __uint(type, BPF_MAP_TYPE_SK_STORAGE);
        __uint(map_flags, BPF_F_NO_PREALLOC);
        __type(key, int);
        __type(value, struct svc_addr);
} service_mapping SEC(".maps");

SEC("cgroup/connect6")
int connect6(struct bpf_sock_addr *ctx)
{
        struct sockaddr_in6 sa = {};
        struct svc_addr *orig;

        /* Force local address to [::1]:22223. */
        sa.sin6_family = AF_INET6;
        sa.sin6_port = bpf_htons(22223);
        sa.sin6_addr.s6_addr32[3] = bpf_htonl(1);

        if (bpf_bind(ctx, (struct sockaddr *)&sa, sizeof(sa)) != 0)
                return 0;

        /* Rewire service [fc00::1]:60000 to backend [::1]:60124. */
        if (ctx->user_port == bpf_htons(60000)) {
                orig = bpf_sk_storage_get(&service_mapping, ctx->sk, 0,
                                          BPF_SK_STORAGE_GET_F_CREATE);
                if (!orig)
                        return 0;

                orig->addr[0] = ctx->user_ip6[0];
                orig->addr[1] = ctx->user_ip6[1];
                orig->addr[2] = ctx->user_ip6[2];
                orig->addr[3] = ctx->user_ip6[3];
                orig->port = ctx->user_port;

                ctx->user_ip6[0] = 0;
                ctx->user_ip6[1] = 0;
                ctx->user_ip6[2] = 0;
                ctx->user_ip6[3] = bpf_htonl(1);
                ctx->user_port = bpf_htons(60124);
        }
        return 1;
}

SEC("cgroup/getsockname6")
int getsockname6(struct bpf_sock_addr *ctx)
{
        if (!get_set_sk_priority(ctx))
                return 1;

        /* Expose local server as [fc00::1]:60000 to client. */
        if (ctx->user_port == bpf_htons(60124)) {
                ctx->user_ip6[0] = bpf_htonl(0xfc000000);
                ctx->user_ip6[1] = 0;
                ctx->user_ip6[2] = 0;
                ctx->user_ip6[3] = bpf_htonl(1);
                ctx->user_port = bpf_htons(60000);
        }
        return 1;
}

SEC("cgroup/getpeername6")
int getpeername6(struct bpf_sock_addr *ctx)
{
        struct svc_addr *orig;

        if (!get_set_sk_priority(ctx))
                return 1;

        /* Expose service [fc00::1]:60000 as peer instead of backend. */
        if (ctx->user_port == bpf_htons(60124)) {
                orig = bpf_sk_storage_get(&service_mapping, ctx->sk, 0, 0);
                if (orig) {
                        ctx->user_ip6[0] = orig->addr[0];
                        ctx->user_ip6[1] = orig->addr[1];
                        ctx->user_ip6[2] = orig->addr[2];
                        ctx->user_ip6[3] = orig->addr[3];
                        ctx->user_port = orig->port;
                }
        }
        return 1;
}