utun2/!/utun_test_hooks.h

#ifndef UTUN_TEST_HOOKS_H
#define UTUN_TEST_HOOKS_H

#include <sys/types.h>
#include <sys/socket.h>
#include <stdint.h>
#include <stddef.h>
#include <unistd.h>

// Forward declarations
struct UTUN_INSTANCE;
struct ETCP_SOCKET;

// UDP packet interception callbacks
typedef ssize_t (*utun_sendto_hook_t)(int sockfd, const void *buf, size_t len, int flags,
                                      const struct sockaddr *dest_addr, socklen_t addrlen, 
                                      void* context);
typedef ssize_t (*utun_recvfrom_hook_t)(int sockfd, void *buf, size_t len, int flags,
                                        struct sockaddr *src_addr, socklen_t *addrlen, 
                                        void* context);

// TUN virtual interface callbacks  
typedef int (*tun_create_hook_t)(void* priv_data);
typedef ssize_t (*tun_read_hook_t)(int fd, void *buf, size_t count, void* priv_data);
typedef ssize_t (*tun_write_hook_t)(int fd, const void *buf, size_t count, void* priv_data);

// Socket creation callback
typedef int (*socket_create_hook_t)(int domain, int type, int protocol, void* context);

// Test packet capture callback
typedef void (*packet_capture_hook_t)(struct UTUN_INSTANCE* instance, 
                                     const uint8_t* packet, size_t len,
                                     const char* direction, // "tun_in", "tun_out", "udp_in", "udp_out"
                                     void* context);

struct utun_test_hooks {
    // UDP socket hooks
    utun_sendto_hook_t sendto_override;
    utun_recvfrom_hook_t recvfrom_override;
    
    // TUN hooks  
    tun_create_hook_t tun_create_override;
    tun_read_hook_t tun_read_override;
    tun_write_hook_t tun_write_override;
    
    // Socket creation hook
    socket_create_hook_t socket_create_override;
    
    // Packet capture
    packet_capture_hook_t packet_captured;
    
    // Context for callbacks
    void* test_context;
};

// Global test hooks - NULL in production, set only by test code
extern struct utun_test_hooks* g_utun_test_hooks;

// Test-aware wrapper functions - inline for zero overhead when NULL
static inline ssize_t utun_sendto_hook(int sockfd, const void *buf, size_t len, int flags,
                                       const struct sockaddr *dest_addr, socklen_t addrlen) {
    if (g_utun_test_hooks && g_utun_test_hooks->sendto_override) {
        return g_utun_test_hooks->sendto_override(sockfd, buf, len, flags, dest_addr, addrlen, 
                                                 g_utun_test_hooks->test_context);
    }
    return sendto(sockfd, buf, len, flags, dest_addr, addrlen);
}

static inline ssize_t utun_recvfrom_hook(int sockfd, void *buf, size_t len, int flags,
                                         struct sockaddr *src_addr, socklen_t *addrlen) {
    if (g_utun_test_hooks && g_utun_test_hooks->recvfrom_override) {
        return g_utun_test_hooks->recvfrom_override(sockfd, buf, len, flags, src_addr, addrlen,
                                                   g_utun_test_hooks->test_context);
    }
    return recvfrom(sockfd, buf, len, flags, src_addr, addrlen);
}

static inline int tun_create_hook(void* priv_data) {
    if (g_utun_test_hooks && g_utun_test_hooks->tun_create_override) {
        return g_utun_test_hooks->tun_create_override(priv_data);
    }
    return -1; // Default: no TUN available in test mode
}

static inline ssize_t tun_read_hook(int fd, void *buf, size_t count, void* priv_data) {
    if (g_utun_test_hooks && g_utun_test_hooks->tun_read_override) {
        return g_utun_test_hooks->tun_read_override(fd, buf, count, priv_data);
    }
    return read(fd, buf, count);
}

static inline ssize_t tun_write_hook(int fd, const void *buf, size_t count, void* priv_data) {
    if (g_utun_test_hooks && g_utun_test_hooks->tun_write_override) {
        return g_utun_test_hooks->tun_write_override(fd, buf, count, priv_data);
    }
    return write(fd, buf, count);
}

static inline int socket_create_hook(int domain, int type, int protocol) {
    if (g_utun_test_hooks && g_utun_test_hooks->socket_create_override) {
        return g_utun_test_hooks->socket_create_override(domain, type, protocol, 
                                                        g_utun_test_hooks->test_context);
    }
    return socket(domain, type, protocol);
}

static inline void packet_capture_hook(struct UTUN_INSTANCE* instance, 
                                      const uint8_t* packet, size_t len,
                                      const char* direction) {
    if (g_utun_test_hooks && g_utun_test_hooks->packet_captured) {
        g_utun_test_hooks->packet_captured(instance, packet, len, direction,
                                          g_utun_test_hooks->test_context);
    }
}

// Functions to set/clear test hooks (only available in test builds)
#ifdef TEST_BUILD
void utun_test_hooks_set(struct utun_test_hooks* hooks);
void utun_test_hooks_clear(void);
#else
// In production builds, these are no-ops for safety
static inline void utun_test_hooks_set(struct utun_test_hooks* hooks) { (void)hooks; }
static inline void utun_test_hooks_clear(void) {}
#endif

#endif // UTUN_TEST_HOOKS_H