stellar-stellar/include/stellar/tunnel.h

#ifndef _TUNNEL_H
#define _TUNNEL_H

#ifdef __cplusplus
extern "C"
{
#endif

#include "layer.h"

enum tunnel_type
{
    TUNNEL_IPV4 = 1, // contain layers: IPv4, (next inner layer must be IPv4 / IPv6)
    TUNNEL_IPV6 = 2, // contain layers: IPv6, (next inner layer must be IPv4 / IPv6)

    TUNNEL_GRE = 3, // contain layers: IPv4 + GRE
                    // contain layers: IPv6 + GRE

    TUNNEL_GTP = 4, // contain layers: IPv4 + UDP + GTP
                    // contain layers: IPv6 + UDP + GTP

    TUNNEL_VXLAN = 5, // contain layers: IPv4 + UDP + VXLAN
                      // contain layers: IPv6 + UDP + VXLAN

    TUNNEL_L2TP = 6, // contain layers: IPv4 + UDP + L2TP
                     // contain layers: IPv6 + UDP + L2TP

    TUNNEL_TEREDO = 7, // contain layers: IPv4 + UDP, (next inner layer must be IPv6)
};

#define MAX_LAYERS_PER_TUNNEL 3
struct tunnel
{
    enum tunnel_type type;

    int layer_count;
    struct layer layers[MAX_LAYERS_PER_TUNNEL];
};

int packet_get_tunnel_count(const struct packet *pkt);
// return  0: success 
// return -1: failed
int packet_get_tunnel_by_idx(const struct packet *pkt, int idx, struct tunnel *out);

#define PACKET_FOREACH_TUNNEL_INORDER(pkt, tunnel) \
    for (int i = 0; i < packet_get_tunnel_count(pkt) && packet_get_tunnel_by_idx(pkt, i, &tunnel) == 0; i++)

#define PACKET_FOREACH_TUNNEL_REVERSE(pkt, tunnel) \
    for (int i = packet_get_tunnel_count(pkt) - 1; i >= 0 && packet_get_tunnel_by_idx(pkt, i, &tunnel) == 0; i--)

#define PACKET_GETALL_TUNNELS(pkt, tunnels)                                                  \
    {                                                                                        \
        int num = MIN(packet_get_tunnel_count(pkt), (sizeof(tunnels) / sizeof(tunnels[0]))); \
        for (int i = 0; i < num && packet_get_tunnel_by_idx(pkt, i, &tunnels[i]) == 0; i++)  \
            /* void */;                                                                      \
        return num;                                                                          \
    }

#ifdef __cplusplus
}
#endif

#endif