// SPDX-License-Identifier: GPL-2.0
#include <string.h>
#include <stdbool.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;
        __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/connect4")
int connect4(struct bpf_sock_addr *ctx)
{
        struct sockaddr_in sa = {};
        struct svc_addr *orig;

        /* Force local address to 127.0.0.1:22222. */
        sa.sin_family = AF_INET;
        sa.sin_port = bpf_htons(22222);
        sa.sin_addr.s_addr = bpf_htonl(0x7f000001);

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

        /* Rewire service 1.2.3.4:60000 to backend 127.0.0.1:60123. */
        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 = ctx->user_ip4;
                orig->port = ctx->user_port;

                ctx->user_ip4 = bpf_htonl(0x7f000001);
                ctx->user_port = bpf_htons(60123);
        }
        return 1;
}

SEC("cgroup/getsockname4")
int getsockname4(struct bpf_sock_addr *ctx)
{
        if (!get_set_sk_priority(ctx))
                return 1;

        /* Expose local server as 1.2.3.4:60000 to client. */
        if (ctx->user_port == bpf_htons(60123)) {
                ctx->user_ip4 = bpf_htonl(0x01020304);
                ctx->user_port = bpf_htons(60000);
        }
        return 1;
}

SEC("cgroup/getpeername4")
int getpeername4(struct bpf_sock_addr *ctx)
{
        struct svc_addr *orig;

        if (!get_set_sk_priority(ctx))
                return 1;

        /* Expose service 1.2.3.4:60000 as peer instead of backend. */
        if (ctx->user_port == bpf_htons(60123)) {
                orig = bpf_sk_storage_get(&service_mapping, ctx->sk, 0, 0);
                if (orig) {
                        ctx->user_ip4 = orig->addr;
                        ctx->user_port = orig->port;
                }
        }
        return 1;
}