/*
Copyright (c) 2016, Nitin Gode
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
    * Redistributions of source code must retain the above copyright
      notice, this list of conditions and the following disclaimer.
    * Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in the
      documentation and/or other materials provided with the distribution.
    * Neither the name of the <organization> nor the
      names of its contributors may be used to endorse or promote products
      derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> BE LIABLE FOR ANY
DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

*/
package main

import (
    "fmt"
    "net"
    "syscall"
    "unsafe"
)

/*
#include <stdint.h>
#include <stdlib.h>

typedef struct __attribute__((packed))
{
    char dest[6];
    char sender[6];
    uint16_t protocolType;
} EthernetHeader;

typedef struct __attribute__((packed))
{
    uint16_t hwType;
    uint16_t protoType;
    char hwLen;
    char protocolLen;
    uint16_t oper;
    char SHA[6];
    char SPA[4];
    char THA[6];
    char TPA[4];
} ArpPacket;

typedef struct __attribute__((packed))
{
    EthernetHeader eth;
    ArpPacket arp;
} EthernetArpPacket;

char* FillRequestPacketFields(char* senderMac, char* senderIp)
{
    EthernetArpPacket * packet = malloc(sizeof(EthernetArpPacket));
    memset(packet, 0, sizeof(EthernetArpPacket));
    // Ethernet header
    // Dest = Broadcast (ff:ff:ff:ff:ff)
    packet->eth.dest[0] = 0xff;
    packet->eth.dest[1] = 0xff;
    packet->eth.dest[2] = 0xff;
    packet->eth.dest[3] = 0xff;
    packet->eth.dest[4] = 0xff;
    packet->eth.dest[5] = 0xff;

    packet->eth.sender[0] = strtol(senderMac, NULL, 16); senderMac += 3;
    packet->eth.sender[1] = strtol(senderMac, NULL, 16); senderMac += 3;
    packet->eth.sender[2] = strtol(senderMac, NULL, 16); senderMac += 3;
    packet->eth.sender[3] = strtol(senderMac, NULL, 16); senderMac += 3;
    packet->eth.sender[4] = strtol(senderMac, NULL, 16); senderMac += 3;
    packet->eth.sender[5] = strtol(senderMac, NULL, 16);

    packet->eth.protocolType = htons(0x0806); // ARP

    // ARP Packet fields
    packet->arp.hwType = htons(1); // Ethernet
    packet->arp.protoType = htons(0x800); //IP;
    packet->arp.hwLen = 6;
    packet->arp.protocolLen = 4;
    packet->arp.oper = htons(2); // response

    // Sender MAC (same as that in eth header)
    memcpy(packet->arp.SHA, packet->eth.sender, 6);

    // Sender IP
    packet->arp.SPA[0] = strtol(senderIp, NULL, 10); senderIp = strchr(senderIp, '.') + 1;
    packet->arp.SPA[1] = strtol(senderIp, NULL, 10); senderIp = strchr(senderIp, '.') + 1;
    packet->arp.SPA[2] = strtol(senderIp, NULL, 10); senderIp = strchr(senderIp, '.') + 1;
    packet->arp.SPA[3] = strtol(senderIp, NULL, 10);

    // Dest MAC: Same as SHA, as we use an ARP response
    memcpy(packet->arp.THA, packet->arp.SHA, 6);

    // Dest IP: Same as SPA
    memcpy(packet->arp.TPA, packet->arp.SPA, 4);

    return (char*) packet;
}
*/
import "C"

func main() {
    etherArp := new(C.EthernetArpPacket)
    size := uint(unsafe.Sizeof(*etherArp))
    fmt.Println("Size : ", size)

    fd, err := syscall.Socket(syscall.AF_PACKET, syscall.SOCK_RAW, syscall.ETH_P_ALL)
    if err != nil {
        fmt.Println("Error: " + err.Error())
        return
    }
    fmt.Println("Obtained fd ", fd)
    defer syscall.Close(fd)

    // Get Mac address of vboxnet1
    interf, err := net.InterfaceByName("vboxnet1")
    if err != nil {
        fmt.Println("Could not find vboxnet interface")
        return
    }

    fmt.Println("Interface hw address: ", interf.HardwareAddr)
    fmt.Println("Creating request for IP 10.10.10.2 from IP 10.10.10.1")

    iface_cstr := C.CString(interf.HardwareAddr.String())
    ip_cstr := C.CString("10.10.10.3")

    packet := C.GoBytes(unsafe.Pointer(C.FillRequestPacketFields(iface_cstr, ip_cstr)) , C.int(size))

    // Send the packet
    var addr syscall.SockaddrLinklayer
    addr.Protocol = syscall.ETH_P_ARP
    addr.Ifindex = interf.Index
    addr.Hatype = syscall.ARPHRD_ETHER

    err = syscall.Sendto(fd, packet, 0, &addr)

    if err != nil {
        fmt.Println("Error: ", err)
    } else {
        fmt.Println("Sent packet")
    }

}