From 1e108ad7fba0a7a84ec24d436203eeccde8163c3 Mon Sep 17 00:00:00 2001
From: Arisotura <thetotalworm@gmail.com>
Date: Mon, 4 Mar 2019 20:52:29 +0100
Subject: [PATCH] start differenciating between direct and indirect LAN modes.

indirect mode will use regular sockets and not pcap.
---
 melonDS.cbp                             |   6 +-
 src/Wifi.cpp                            |   4 +-
 src/libui_sdl/{LAN.cpp => LAN_PCap.cpp} |   0
 src/libui_sdl/{LAN.h => LAN_PCap.h}     |   8 +-
 src/libui_sdl/LAN_Socket.cpp            | 977 ++++++++++++++++++++++++
 src/libui_sdl/LAN_Socket.h              |  38 +
 src/libui_sdl/main.cpp                  |  57 +-
 7 files changed, 1081 insertions(+), 9 deletions(-)
 rename src/libui_sdl/{LAN.cpp => LAN_PCap.cpp} (100%)
 rename src/libui_sdl/{LAN.h => LAN_PCap.h} (93%)
 create mode 100644 src/libui_sdl/LAN_Socket.cpp
 create mode 100644 src/libui_sdl/LAN_Socket.h

diff --git a/melonDS.cbp b/melonDS.cbp
index 204ceda9..d5ffc227 100644
--- a/melonDS.cbp
+++ b/melonDS.cbp
@@ -158,8 +158,10 @@
 		<Unit filename="src/libui_sdl/DlgInputConfig.h" />
 		<Unit filename="src/libui_sdl/DlgWifiSettings.cpp" />
 		<Unit filename="src/libui_sdl/DlgWifiSettings.h" />
-		<Unit filename="src/libui_sdl/LAN.cpp" />
-		<Unit filename="src/libui_sdl/LAN.h" />
+		<Unit filename="src/libui_sdl/LAN_PCap.cpp" />
+		<Unit filename="src/libui_sdl/LAN_PCap.h" />
+		<Unit filename="src/libui_sdl/LAN_Socket.cpp" />
+		<Unit filename="src/libui_sdl/LAN_Socket.h" />
 		<Unit filename="src/libui_sdl/Platform.cpp" />
 		<Unit filename="src/libui_sdl/libui/common/areaevents.c">
 			<Option compilerVar="CC" />
diff --git a/src/Wifi.cpp b/src/Wifi.cpp
index 0cab3c79..dbe836f7 100644
--- a/src/Wifi.cpp
+++ b/src/Wifi.cpp
@@ -28,8 +28,8 @@
 namespace Wifi
 {
 
-#define WIFI_LOG printf
-//#define WIFI_LOG(...) {}
+//#define WIFI_LOG printf
+#define WIFI_LOG(...) {}
 
 u8 RAM[0x2000];
 u16 IO[0x1000>>1];
diff --git a/src/libui_sdl/LAN.cpp b/src/libui_sdl/LAN_PCap.cpp
similarity index 100%
rename from src/libui_sdl/LAN.cpp
rename to src/libui_sdl/LAN_PCap.cpp
diff --git a/src/libui_sdl/LAN.h b/src/libui_sdl/LAN_PCap.h
similarity index 93%
rename from src/libui_sdl/LAN.h
rename to src/libui_sdl/LAN_PCap.h
index 016d2432..1af3cef5 100644
--- a/src/libui_sdl/LAN.h
+++ b/src/libui_sdl/LAN_PCap.h
@@ -16,12 +16,12 @@
     with melonDS. If not, see http://www.gnu.org/licenses/.
 */
 
-#ifndef LAN_H
-#define LAN_H
+#ifndef LAN_PCAP_H
+#define LAN_PCAP_H
 
 #include "../types.h"
 
-namespace LAN
+namespace LAN_PCap
 {
 
 typedef struct
@@ -55,4 +55,4 @@ int RecvPacket(u8* data);
 
 }
 
-#endif // LAN_H
+#endif // LAN_PCAP_H
diff --git a/src/libui_sdl/LAN_Socket.cpp b/src/libui_sdl/LAN_Socket.cpp
new file mode 100644
index 00000000..f621acf5
--- /dev/null
+++ b/src/libui_sdl/LAN_Socket.cpp
@@ -0,0 +1,977 @@
+/*
+    Copyright 2016-2019 Arisotura
+
+    This file is part of melonDS.
+
+    melonDS is free software: you can redistribute it and/or modify it under
+    the terms of the GNU General Public License as published by the Free
+    Software Foundation, either version 3 of the License, or (at your option)
+    any later version.
+
+    melonDS is distributed in the hope that it will be useful, but WITHOUT ANY
+    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+    FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License along
+    with melonDS. If not, see http://www.gnu.org/licenses/.
+*/
+
+// LAN interface. Currently powered by libpcap, may change.
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <SDL2/SDL.h>
+#include <pcap/pcap.h>
+#include "Wifi.h"
+#include "LAN.h"
+#include "../Config.h"
+
+#ifdef __WIN32__
+	#include <iphlpapi.h>
+#else
+	// Linux includes go here
+#endif
+
+
+// welp
+#ifndef PCAP_OPENFLAG_PROMISCUOUS
+#define PCAP_OPENFLAG_PROMISCUOUS 1
+#endif
+
+
+#define DECL_PCAP_FUNC(ret, name, args, args2) \
+    typedef ret (*type_##name) args; \
+    type_##name ptr_##name = NULL; \
+    ret name args { return ptr_##name args2; }
+
+DECL_PCAP_FUNC(int, pcap_findalldevs, (pcap_if_t** alldevs, char* errbuf), (alldevs,errbuf))
+DECL_PCAP_FUNC(void, pcap_freealldevs, (pcap_if_t* alldevs), (alldevs))
+DECL_PCAP_FUNC(pcap_t*, pcap_open_live, (const char* src, int snaplen, int flags, int readtimeout, char* errbuf), (src,snaplen,flags,readtimeout,errbuf))
+DECL_PCAP_FUNC(void, pcap_close, (pcap_t* dev), (dev))
+DECL_PCAP_FUNC(int, pcap_setnonblock, (pcap_t* dev, int nonblock, char* errbuf), (dev,nonblock,errbuf))
+DECL_PCAP_FUNC(int, pcap_sendpacket, (pcap_t* dev, const u_char* data, int len), (dev,data,len))
+DECL_PCAP_FUNC(int, pcap_dispatch, (pcap_t* dev, int num, pcap_handler callback, u_char* data), (dev,num,callback,data))
+DECL_PCAP_FUNC(const u_char*, pcap_next, (pcap_t* dev, struct pcap_pkthdr* hdr), (dev,hdr))
+
+
+namespace LAN
+{
+
+const char* PCapLibNames[] =
+{
+#ifdef __WIN32__
+    // TODO: name for npcap in non-WinPCap mode
+    "wpcap.dll",
+#else
+    // Linux lib names
+    "libpcap.so.1",
+    "libpcap.so",
+#endif
+    NULL
+};
+
+AdapterData* Adapters = NULL;
+int NumAdapters = 0;
+
+void* PCapLib = NULL;
+pcap_t* PCapAdapter = NULL;
+AdapterData* PCapAdapterData;
+
+u8 PCapPacketBuffer[2048];
+int PCapPacketLen;
+volatile int PCapRXNum;
+
+u16 IPv4ID;
+
+
+typedef struct
+{
+    u8 DestIP[4];
+    u16 DestPort;
+
+    // 0: unused
+    // 1: connected
+    u8 Status;
+
+} TCPSocket;
+
+TCPSocket TCPSocketList[64];
+
+
+#define LOAD_PCAP_FUNC(sym) \
+    ptr_##sym = (type_##sym)SDL_LoadFunction(lib, #sym); \
+    if (!ptr_##sym) return false;
+
+bool TryLoadPCap(void* lib)
+{
+    LOAD_PCAP_FUNC(pcap_findalldevs)
+    LOAD_PCAP_FUNC(pcap_freealldevs)
+    LOAD_PCAP_FUNC(pcap_open_live)
+    LOAD_PCAP_FUNC(pcap_close)
+    LOAD_PCAP_FUNC(pcap_setnonblock)
+    LOAD_PCAP_FUNC(pcap_sendpacket)
+    LOAD_PCAP_FUNC(pcap_dispatch)
+    LOAD_PCAP_FUNC(pcap_next)
+
+    return true;
+}
+
+bool Init()
+{
+    // TODO: how to deal with cases where an adapter is unplugged or changes config??
+    if (PCapLib) return true;
+
+    PCapLib = NULL;
+    PCapAdapter = NULL;
+    PCapPacketLen = 0;
+    PCapRXNum = 0;
+
+    IPv4ID = 1;
+
+    memset(TCPSocketList, 0, sizeof(TCPSocketList));
+
+    for (int i = 0; PCapLibNames[i]; i++)
+    {
+        void* lib = SDL_LoadObject(PCapLibNames[i]);
+        if (!lib) continue;
+
+        if (!TryLoadPCap(lib))
+        {
+            SDL_UnloadObject(lib);
+            continue;
+        }
+
+        printf("PCap: lib %s, init successful\n", PCapLibNames[i]);
+        PCapLib = lib;
+        break;
+    }
+
+    if (PCapLib == NULL)
+    {
+        printf("PCap: init failed\n");
+        return false;
+    }
+
+    char errbuf[PCAP_ERRBUF_SIZE];
+    int ret;
+
+    pcap_if_t* alldevs;
+    ret = pcap_findalldevs(&alldevs, errbuf);
+    if (ret < 0 || alldevs == NULL)
+    {
+        printf("PCap: no devices available\n");
+        return false;
+    }
+
+    pcap_if_t* dev = alldevs;
+    while (dev) { NumAdapters++; dev = dev->next; }
+
+    Adapters = new AdapterData[NumAdapters];
+    memset(Adapters, 0, sizeof(AdapterData)*NumAdapters);
+
+    AdapterData* adata = &Adapters[0];
+    dev = alldevs;
+    while (dev)
+    {
+        adata->Internal = dev;
+
+        // hax
+        int len = strlen(dev->name);
+        len -= 12; if (len > 127) len = 127;
+        strncpy(adata->DeviceName, &dev->name[12], len);
+        adata->DeviceName[len] = '\0';
+
+        dev = dev->next;
+        adata++;
+    }
+
+#ifdef __WIN32__
+
+    ULONG bufsize = 16384;
+    IP_ADAPTER_ADDRESSES* buf = (IP_ADAPTER_ADDRESSES*)HeapAlloc(GetProcessHeap(), 0, bufsize);
+    ULONG uret = GetAdaptersAddresses(AF_INET, 0, NULL, buf, &bufsize);
+    if (uret == ERROR_BUFFER_OVERFLOW)
+    {
+        HeapFree(GetProcessHeap(), 0, buf);
+        buf = (IP_ADAPTER_ADDRESSES*)HeapAlloc(GetProcessHeap(), 0, bufsize);
+        uret = GetAdaptersAddresses(AF_INET, 0, NULL, buf, &bufsize);
+    }
+    if (uret != ERROR_SUCCESS)
+    {
+        printf("GetAdaptersAddresses() shat itself: %08X\n", ret);
+        return false;
+    }
+
+    for (int i = 0; i < NumAdapters; i++)
+    {
+        adata = &Adapters[i];
+        IP_ADAPTER_ADDRESSES* addr = buf;
+        while (addr)
+        {
+            if (strcmp(addr->AdapterName, adata->DeviceName))
+            {
+                addr = addr->Next;
+                continue;
+            }
+
+            WideCharToMultiByte(CP_UTF8, 0, addr->FriendlyName, 127, adata->FriendlyName, 127, NULL, NULL);
+            adata->FriendlyName[127] = '\0';
+
+            WideCharToMultiByte(CP_UTF8, 0, addr->Description, 127, adata->Description, 127, NULL, NULL);
+            adata->Description[127] = '\0';
+
+            if (addr->PhysicalAddressLength != 6)
+            {
+                printf("weird MAC addr length %d for %s\n", addr->PhysicalAddressLength, addr->AdapterName);
+            }
+            else
+                memcpy(adata->MAC, addr->PhysicalAddress, 6);
+
+            IP_ADAPTER_UNICAST_ADDRESS* ipaddr = addr->FirstUnicastAddress;
+            while (ipaddr)
+            {
+                SOCKADDR* sa = ipaddr->Address.lpSockaddr;
+                if (sa->sa_family == AF_INET)
+                {
+                    struct in_addr sa4 = ((sockaddr_in*)sa)->sin_addr;
+                    memcpy(adata->IP_v4, &sa4.S_un.S_addr, 4);
+                }
+
+                ipaddr = ipaddr->Next;
+            }
+
+            IP_ADAPTER_DNS_SERVER_ADDRESS* dnsaddr = addr->FirstDnsServerAddress;
+            int ndns = 0;
+            while (dnsaddr)
+            {
+                SOCKADDR* sa = dnsaddr->Address.lpSockaddr;
+                if (sa->sa_family == AF_INET)
+                {
+                    struct in_addr sa4 = ((sockaddr_in*)sa)->sin_addr;
+                    memcpy(adata->DNS[ndns++], &sa4.S_un.S_addr, 4);
+                }
+
+                if (ndns >= 8) break;
+                dnsaddr = dnsaddr->Next;
+            }
+
+            if (addr->Dhcpv4Enabled && addr->Dhcpv4Server.lpSockaddr)
+            {
+                SOCKADDR* sa = addr->Dhcpv4Server.lpSockaddr;
+                struct in_addr sa4 = ((sockaddr_in*)sa)->sin_addr;
+                memcpy(adata->DHCP_IP_v4, &sa4.S_un.S_addr, 4);
+            }
+            else
+                memset(adata->DHCP_IP_v4, 0, 4);
+
+            break;
+        }
+    }
+
+    HeapFree(GetProcessHeap(), 0, buf);
+
+#else
+
+    // TODO
+
+#endif // __WIN32__
+
+    // open pcap device
+    PCapAdapterData = &Adapters[0];
+    for (int i = 0; i < NumAdapters; i++)
+    {
+        if (!strncmp(Adapters[i].DeviceName, Config::LANDevice, 128))
+            PCapAdapterData = &Adapters[i];
+    }
+
+    dev = (pcap_if_t*)PCapAdapterData->Internal;
+    PCapAdapter = pcap_open_live(dev->name, 2048, PCAP_OPENFLAG_PROMISCUOUS, 1, errbuf);
+    if (!PCapAdapter)
+    {
+        printf("PCap: failed to open adapter\n");
+        return false;
+    }
+
+    pcap_freealldevs(alldevs);
+
+    for (int ntries = 0; ntries < 4; ntries++)
+    {
+        bool good = false;
+
+        // get router MAC
+        printf("DHCP: %d.%d.%d.%d\n",
+               PCapAdapterData->DHCP_IP_v4[0], PCapAdapterData->DHCP_IP_v4[1],
+               PCapAdapterData->DHCP_IP_v4[2], PCapAdapterData->DHCP_IP_v4[3]);
+
+        u8 arp[64];
+        u8* out = &arp[0];
+
+        *out++ = 0xFF; *out++ = 0xFF; *out++ = 0xFF;
+        *out++ = 0xFF; *out++ = 0xFF; *out++ = 0xFF;
+        memcpy(out, PCapAdapterData->MAC, 6); out += 6;
+        *(u16*)out = htons(0x0806); out += 2;
+
+        *(u16*)out = htons(0x0001); out += 2;
+        *(u16*)out = htons(0x0800); out += 2;
+        *out++ = 6;
+        *out++ = 4;
+
+        *(u16*)out = htons(0x0001); out += 2;
+        memcpy(out, PCapAdapterData->MAC, 6); out += 6;
+        memcpy(out, PCapAdapterData->IP_v4, 4); out += 4;
+        *out++ = 0; *out++ = 0; *out++ = 0;
+        *out++ = 0; *out++ = 0; *out++ = 0;
+        memcpy(out, PCapAdapterData->DHCP_IP_v4, 4); out += 4;
+
+        u32 len = (u32)(out - &arp[0]);
+        pcap_sendpacket(PCapAdapter, arp, len);
+
+        for (int t = 0; t < 16; t++)
+        {
+            struct pcap_pkthdr hdr;
+            const u8* rep = pcap_next(PCapAdapter, &hdr);
+            if (!rep) continue;
+            if (hdr.len < 0x2A) continue;
+
+            if (memcmp(&rep[0], PCapAdapterData->MAC, 6))
+                continue;
+            if (ntohs(*(u16*)&rep[12]) != 0x0806)
+                continue;
+            if (ntohs(*(u16*)&rep[14]) != 0x0001)
+                continue;
+            if (ntohs(*(u16*)&rep[16]) != 0x0800)
+                continue;
+            if (ntohs(*(u16*)&rep[18]) != 0x0604)
+                continue;
+            if (ntohs(*(u16*)&rep[20]) != 0x0002)
+                continue;
+            if (memcmp(&rep[28], PCapAdapterData->DHCP_IP_v4, 4))
+                continue;
+
+            printf("DHCP MAC: %02X:%02X:%02X:%02X:%02X:%02X\n",
+                   rep[22], rep[23], rep[24],
+                   rep[25], rep[26], rep[27]);
+
+            memcpy(PCapAdapterData->DHCP_MAC, &rep[22], 6);
+
+            good = true;
+            break;
+        }
+
+        if (good) break;
+    }
+
+    if (pcap_setnonblock(PCapAdapter, 1, errbuf) < 0)
+    {
+        printf("PCap: failed to set nonblocking mode\n");
+        pcap_close(PCapAdapter); PCapAdapter = NULL;
+        return false;
+    }
+
+    return true;
+}
+
+void DeInit()
+{
+    if (PCapLib)
+    {
+        if (PCapAdapter)
+        {
+            pcap_close(PCapAdapter);
+            PCapAdapter = NULL;
+        }
+
+        SDL_UnloadObject(PCapLib);
+        PCapLib = NULL;
+    }
+}
+
+bool HandleIncomingIPFrame(u8* data, int len)
+{
+    const u32 serverip = 0x0A404001;
+    const u32 clientip = 0x0A404010;
+
+    if (memcmp(&data[0x1E], PCapAdapterData->IP_v4, 4))
+        return false;
+
+    u8 protocol = data[0x17];
+
+    //memcpy(&data[6], &PCapAdapterData->DHCP_MAC[0], 6);
+    memcpy(&data[0], Wifi::GetMAC(), 6);
+    data[6] = 0x00; data[7] = 0xAB; data[8] = 0x33;
+    data[9] = 0x28; data[10] = 0x99; data[11] = 0x44;
+
+    *(u32*)&data[0x1E] = htonl(clientip);
+
+    u8* ipheader = &data[0xE];
+    u8* protoheader = &data[0x22];
+
+    // IP checksum
+    u32 tmp = 0;
+
+    *(u16*)&ipheader[10] = 0;
+    for (int i = 0; i < 20; i += 2)
+        tmp += ntohs(*(u16*)&ipheader[i]);
+    while (tmp >> 16)
+        tmp = (tmp & 0xFFFF) + (tmp >> 16);
+    tmp ^= 0xFFFF;
+    *(u16*)&ipheader[10] = htons(tmp);
+
+    if (protocol == 0x11)
+    {
+        u32 udplen = ntohs(*(u16*)&protoheader[4]);
+
+        // UDP checksum
+        tmp = 0;
+        *(u16*)&protoheader[6] = 0;
+        tmp += ntohs(*(u16*)&ipheader[12]);
+        tmp += ntohs(*(u16*)&ipheader[14]);
+        tmp += ntohs(*(u16*)&ipheader[16]);
+        tmp += ntohs(*(u16*)&ipheader[18]);
+        tmp += ntohs(0x1100);
+        tmp += udplen;
+        for (u8* i = protoheader; i < &protoheader[udplen-1]; i += 2)
+            tmp += ntohs(*(u16*)i);
+        if (udplen & 1) tmp += (protoheader[udplen-1] << 8);
+        while (tmp >> 16)
+            tmp = (tmp & 0xFFFF) + (tmp >> 16);
+        tmp ^= 0xFFFF;
+        if (tmp == 0) tmp = 0xFFFF;
+        *(u16*)&protoheader[6] = htons(tmp);
+    }
+    else if (protocol == 0x06)
+    {
+        u32 tcplen = ntohs(*(u16*)&ipheader[2]) - 0x14;
+
+        u16 srcport = ntohs(*(u16*)&protoheader[0]);
+        u16 dstport = ntohs(*(u16*)&protoheader[2]);
+        u16 flags = ntohs(*(u16*)&protoheader[12]);
+
+        // TODO: check if they send a FIN, I guess
+        int sockid = -1;
+        for (int i = 0; i < (sizeof(TCPSocketList)/sizeof(TCPSocket)); i++)
+        {
+            TCPSocket* sock = &TCPSocketList[i];
+            if (sock->Status == 1 && !memcmp(&sock->DestIP, &ipheader[12], 4) && sock->DestPort == srcport)
+            {
+                sockid = i;
+                break;
+            }
+        }
+
+        if (sockid == -1)
+        {
+            return true;
+        }
+
+        // TCP checksum
+        tmp = 0;
+        *(u16*)&protoheader[16] = 0;
+        tmp += ntohs(*(u16*)&ipheader[12]);
+        tmp += ntohs(*(u16*)&ipheader[14]);
+        tmp += ntohs(*(u16*)&ipheader[16]);
+        tmp += ntohs(*(u16*)&ipheader[18]);
+        tmp += ntohs(0x0600);
+        tmp += tcplen;
+        for (u8* i = protoheader; i < &protoheader[tcplen-1]; i += 2)
+            tmp += ntohs(*(u16*)i);
+        if (tcplen & 1) tmp += (protoheader[tcplen-1] << 8);
+        while (tmp >> 16)
+            tmp = (tmp & 0xFFFF) + (tmp >> 16);
+        tmp ^= 0xFFFF;
+        *(u16*)&protoheader[16] = htons(tmp);
+    }
+
+    return false;
+}
+
+void RXCallback(u_char* blarg, const struct pcap_pkthdr* header, const u_char* data)
+{
+    while (PCapRXNum > 0);
+
+    if (header->len > 2048-64) return;
+
+    PCapPacketLen = header->len;
+    memcpy(PCapPacketBuffer, data, PCapPacketLen);
+    PCapRXNum = 1;
+
+    if (!Config::DirectLAN)
+    {
+        u16 ethertype = ntohs(*(u16*)&data[0xC]);
+
+        if (ethertype == 0x0800) // IPv4
+        {
+            if (HandleIncomingIPFrame(PCapPacketBuffer, header->len))
+                PCapRXNum = 0;
+        }
+    }
+}
+u32 zarp=0;
+bool HandleDHCPFrame(u8* data, int len)
+{
+    const u32 serverip = 0x0A404001;
+    const u32 clientip = 0x0A404010;
+
+    u8 type = 0xFF;
+
+    u32 transid = *(u32*)&data[0x2E];
+zarp=transid;
+    u8* options = &data[0x11A];
+    for (;;)
+    {
+        if (options >= &data[len]) break;
+        u8 opt = *options++;
+        if (opt == 255) break;
+
+        u8 len = *options++;
+        switch (opt)
+        {
+        case 53: // frame type
+            type = options[0];
+            break;
+        }
+
+        options += len;
+    }
+
+    if (type == 0xFF)
+    {
+        printf("DHCP: bad frame\n");
+        return false;
+    }
+
+    printf("DHCP: frame type %d, transid %08X\n", type, transid);
+
+    if (type == 1 || // discover
+        type == 3)   // request
+    {
+        u8 resp[512];
+        u8* out = &resp[0];
+
+        // ethernet
+        memcpy(out, &data[6], 6); out += 6;
+        *out++ = 0x00; *out++ = 0xAB; *out++ = 0x33;
+        *out++ = 0x28; *out++ = 0x99; *out++ = 0x44;
+        *(u16*)out = htons(0x0800); out += 2;
+
+        // IP
+        u8* ipheader = out;
+        *out++ = 0x45;
+        *out++ = 0x00;
+        *(u16*)out = 0; out += 2; // total length
+        *(u16*)out = htons(IPv4ID); out += 2; IPv4ID++;
+        *out++ = 0x00;
+        *out++ = 0x00;
+        *out++ = 0x80; // TTL
+        *out++ = 0x11; // protocol (UDP)
+        *(u16*)out = 0; out += 2; // checksum
+        *(u32*)out = htonl(serverip); out += 4; // source IP
+        if (type == 1)
+        {
+            *(u32*)out = htonl(0xFFFFFFFF); out += 4; // destination IP
+        }
+        else if (type == 3)
+        {
+            *(u32*)out = htonl(clientip); out += 4; // destination IP
+        }
+
+        // UDP
+        u8* udpheader = out;
+        *(u16*)out = htons(67); out += 2; // source port
+        *(u16*)out = htons(68); out += 2; // destination port
+        *(u16*)out = 0; out += 2; // length
+        *(u16*)out = 0; out += 2; // checksum
+
+        // DHCP
+        u8* body = out;
+        *out++ = 0x02;
+        *out++ = 0x01;
+        *out++ = 0x06;
+        *out++ = 0x00;
+        *(u32*)out = transid; out += 4;
+        *(u16*)out = 0; out += 2; // seconds elapsed
+        *(u16*)out = 0; out += 2;
+        *(u32*)out = htonl(0x00000000); out += 4; // client IP
+        *(u32*)out = htonl(clientip); out += 4; // your IP
+        *(u32*)out = htonl(serverip); out += 4; // server IP
+        *(u32*)out = htonl(0x00000000); out += 4; // gateway IP
+        memcpy(out, &data[6], 6); out += 6;
+        memset(out, 0, 10); out += 10;
+        memset(out, 0, 192); out += 192;
+        *(u32*)out = 0x63538263; out += 4; // DHCP magic
+
+        // DHCP options
+        *out++ = 53; *out++ = 1;
+        *out++ = (type==1) ? 2 : 5; // DHCP type: offer/ack
+        *out++ = 1; *out++ = 4;
+        *(u32*)out = htonl(0xFFFFFF00); out += 4; // subnet mask
+        *out++ = 3; *out++ = 4;
+        *(u32*)out = htonl(serverip); out += 4; // router
+        *out++ = 51; *out++ = 4;
+        *(u32*)out = htonl(442030); out += 4; // lease time
+        *out++ = 54; *out++ = 4;
+        *(u32*)out = htonl(serverip); out += 4; // DHCP server
+
+        u8 numdns = 0;
+        for (int i = 0; i < 8; i++)
+        {
+            if (*(u32*)&PCapAdapterData->DNS[i][0] != 0)
+                numdns++;
+        }
+        *out++ = 6; *out++ = 4*numdns;
+        for (int i = 0; i < 8; i++)
+        {
+            u32 dnsip = *(u32*)&PCapAdapterData->DNS[i][0];
+            if (dnsip != 0)
+            {
+                *(u32*)out = dnsip; out += 4;
+            }
+        }
+
+        *out++ = 0xFF;
+        memset(out, 0, 20); out += 20;
+
+        // lengths
+        u32 framelen = (u32)(out - &resp[0]);
+        if (framelen & 1) { *out++ = 0; framelen++; }
+        *(u16*)&ipheader[2] = htons(framelen - 0xE);
+        *(u16*)&udpheader[4] = htons(framelen - (0xE + 0x14));
+
+        // IP checksum
+        u32 tmp = 0;
+
+        for (int i = 0; i < 20; i += 2)
+            tmp += ntohs(*(u16*)&ipheader[i]);
+        while (tmp >> 16)
+            tmp = (tmp & 0xFFFF) + (tmp >> 16);
+        tmp ^= 0xFFFF;
+        *(u16*)&ipheader[10] = htons(tmp);
+
+        // UDP checksum
+        // (note: normally not mandatory, but some older sgIP versions require it)
+        tmp = 0;
+        tmp += ntohs(*(u16*)&ipheader[12]);
+        tmp += ntohs(*(u16*)&ipheader[14]);
+        tmp += ntohs(*(u16*)&ipheader[16]);
+        tmp += ntohs(*(u16*)&ipheader[18]);
+        tmp += ntohs(0x1100);
+        tmp += (u32)(out - udpheader);
+        for (u8* i = udpheader; i < out; i += 2)
+            tmp += ntohs(*(u16*)i);
+        while (tmp >> 16)
+            tmp = (tmp & 0xFFFF) + (tmp >> 16);
+        tmp ^= 0xFFFF;
+        if (tmp == 0) tmp = 0xFFFF;
+        *(u16*)&udpheader[6] = htons(tmp);
+
+        // TODO: if there is already a packet queued, this will overwrite it
+        // that being said, this will only happen during DHCP setup, so probably
+        // not a big deal
+
+        PCapPacketLen = framelen;
+        memcpy(PCapPacketBuffer, resp, PCapPacketLen);
+        PCapRXNum = 1;
+
+        // DEBUG!!
+        //pcap_sendpacket(PCapAdapter, data, len);
+        //pcap_sendpacket(PCapAdapter, resp, framelen);
+
+        return true;
+    }
+
+    return false;
+}
+
+bool HandleIPFrame(u8* data, int len)
+{
+    const u32 serverip = 0x0A404001;
+    const u32 clientip = 0x0A404010;
+
+    // debug
+    //pcap_sendpacket(PCapAdapter, data, len);
+
+    u8 protocol = data[0x17];
+
+    // any kind of IPv4 frame that isn't DHCP
+    // we do NAT and forward it to the network
+
+    // like:
+    // melonRouter -> host
+    // destination MAC set to host MAC
+    // source MAC set to melonRouter MAC
+
+    memcpy(&data[0], &PCapAdapterData->DHCP_MAC[0], 6);
+    memcpy(&data[6], &PCapAdapterData->MAC[0], 6);
+
+    *(u32*)&data[0x1A] = *(u32*)&PCapAdapterData->IP_v4[0];
+
+    u8* ipheader = &data[0xE];
+    u8* protoheader = &data[0x22];
+
+    // IP checksum
+    u32 tmp = 0;
+
+    *(u16*)&ipheader[10] = 0;
+    for (int i = 0; i < 20; i += 2)
+        tmp += ntohs(*(u16*)&ipheader[i]);
+    while (tmp >> 16)
+        tmp = (tmp & 0xFFFF) + (tmp >> 16);
+    tmp ^= 0xFFFF;
+    *(u16*)&ipheader[10] = htons(tmp);
+
+    if (protocol == 0x11)
+    {
+        u32 udplen = ntohs(*(u16*)&protoheader[4]);
+
+        // UDP checksum
+        tmp = 0;
+        *(u16*)&protoheader[6] = 0;
+        tmp += ntohs(*(u16*)&ipheader[12]);
+        tmp += ntohs(*(u16*)&ipheader[14]);
+        tmp += ntohs(*(u16*)&ipheader[16]);
+        tmp += ntohs(*(u16*)&ipheader[18]);
+        tmp += ntohs(0x1100);
+        tmp += udplen;
+        for (u8* i = protoheader; i < &protoheader[udplen]; i += 2)
+            tmp += ntohs(*(u16*)i);
+        while (tmp >> 16)
+            tmp = (tmp & 0xFFFF) + (tmp >> 16);
+        tmp ^= 0xFFFF;
+        if (tmp == 0) tmp = 0xFFFF;
+        *(u16*)&protoheader[6] = htons(tmp);
+    }
+    else if (protocol == 0x06)
+    {
+        u32 tcplen = ntohs(*(u16*)&ipheader[2]) - 0x14;
+
+        u16 srcport = ntohs(*(u16*)&protoheader[0]);
+        u16 dstport = ntohs(*(u16*)&protoheader[2]);
+        u16 flags = ntohs(*(u16*)&protoheader[12]);
+
+        if (flags & 0x002) // SYN
+        {
+            int sockid = -1;
+            for (int i = 0; i < (sizeof(TCPSocketList)/sizeof(TCPSocket)); i++)
+            {
+                TCPSocket* sock = &TCPSocketList[i];
+                if (sock->Status == 1 && !memcmp(&sock->DestIP, &ipheader[16], 4) && sock->DestPort == dstport)
+                {
+                    printf("LANMAGIC: duplicate TCP socket\n");
+                    sockid = i;
+                    break;
+                }
+            }
+
+            if (sockid == -1)
+            {
+                for (int i = 0; i < (sizeof(TCPSocketList)/sizeof(TCPSocket)); i++)
+                {
+                    TCPSocket* sock = &TCPSocketList[i];
+                    if (sock->Status == 0)
+                    {
+                        sockid = i;
+                        break;
+                    }
+                }
+            }
+
+            if (sockid == -1)
+            {
+                printf("LANMAGIC: !! TCP SOCKET LIST FULL\n");
+                return true;
+            }
+
+            printf("LANMAGIC: opening TCP socket #%d to %d.%d.%d.%d:%d\n",
+                   sockid,
+                   ipheader[16], ipheader[17], ipheader[18], ipheader[19],
+                   dstport);
+
+            // keep track of it
+            // (TODO: also keep track of source port?)
+
+            TCPSocket* sock = &TCPSocketList[sockid];
+            sock->Status = 1;
+            memcpy(sock->DestIP, &ipheader[16], 4);
+            sock->DestPort = dstport;
+        }
+        else
+        {
+            int sockid = -1;
+            for (int i = 0; i < (sizeof(TCPSocketList)/sizeof(TCPSocket)); i++)
+            {
+                TCPSocket* sock = &TCPSocketList[i];
+                if (sock->Status == 1 && !memcmp(&sock->DestIP, &ipheader[16], 4) && sock->DestPort == dstport)
+                {
+                    sockid = i;
+                    break;
+                }
+            }
+
+            if (sockid == -1)
+            {
+                printf("LANMAGIC: bad TCP packet\n");
+                return true;
+            }
+
+            if (flags & 0x001) // FIN
+            {
+                // TODO: cleverer termination?
+                // also timeout etc
+                TCPSocketList[sockid].Status = 0;
+            }
+        }
+
+        // TCP checksum
+        tmp = 0;
+        *(u16*)&protoheader[16] = 0;
+        tmp += ntohs(*(u16*)&ipheader[12]);
+        tmp += ntohs(*(u16*)&ipheader[14]);
+        tmp += ntohs(*(u16*)&ipheader[16]);
+        tmp += ntohs(*(u16*)&ipheader[18]);
+        tmp += ntohs(0x0600);
+        tmp += tcplen;
+        for (u8* i = protoheader; i < &protoheader[tcplen]; i += 2)
+            tmp += ntohs(*(u16*)i);
+        while (tmp >> 16)
+            tmp = (tmp & 0xFFFF) + (tmp >> 16);
+        tmp ^= 0xFFFF;
+        if (tmp == 0) tmp = 0xFFFF;
+        *(u16*)&protoheader[16] = htons(tmp);
+    }
+
+    return false;
+}
+
+bool HandleARPFrame(u8* data, int len)
+{
+    const u32 serverip = 0x0A404001;
+    const u32 clientip = 0x0A404010;
+
+    u16 protocol = ntohs(*(u16*)&data[0x10]);
+    if (protocol != 0x0800) return false;
+
+    u16 op = ntohs(*(u16*)&data[0x14]);
+    u32 targetip = ntohl(*(u32*)&data[0x26]);
+
+    // TODO: handle ARP to the client
+    // this only handles ARP to the DHCP/router
+
+    if (op == 1 && targetip == serverip)
+    {
+        // opcode 1=req 2=reply
+        // sender MAC
+        // sender IP
+        // target MAC
+        // target IP
+
+        u8 resp[64];
+        u8* out = &resp[0];
+
+        // ethernet
+        memcpy(out, &data[6], 6); out += 6;
+        *out++ = 0x00; *out++ = 0xAB; *out++ = 0x33;
+        *out++ = 0x28; *out++ = 0x99; *out++ = 0x44;
+        *(u16*)out = htons(0x0806); out += 2;
+
+        // ARP
+        *(u16*)out = htons(0x0001); out += 2; // hardware type
+        *(u16*)out = htons(0x0800); out += 2; // protocol
+        *out++ = 6; // MAC address size
+        *out++ = 4; // IP address size
+        *(u16*)out = htons(0x0002); out += 2; // opcode
+        *out++ = 0x00; *out++ = 0xAB; *out++ = 0x33;
+        *out++ = 0x28; *out++ = 0x99; *out++ = 0x44;
+        *(u32*)out = htonl(targetip); out += 4;
+        memcpy(out, &data[0x16], 6+4); out += 6+4;
+
+        u32 framelen = (u32)(out - &resp[0]);
+
+        // TODO: if there is already a packet queued, this will overwrite it
+        // that being said, this will only happen during DHCP setup, so probably
+        // not a big deal
+
+        PCapPacketLen = framelen;
+        memcpy(PCapPacketBuffer, resp, PCapPacketLen);
+        PCapRXNum = 1;
+
+        // also broadcast them to the network
+        pcap_sendpacket(PCapAdapter, data, len);
+        pcap_sendpacket(PCapAdapter, resp, framelen);
+
+        return true;
+    }
+
+    return false;
+}
+
+bool HandlePacket(u8* data, int len)
+{
+    u16 ethertype = ntohs(*(u16*)&data[0xC]);
+
+    if (ethertype == 0x0800) // IPv4
+    {
+        u8 protocol = data[0x17];
+        if (protocol == 0x11) // UDP
+        {
+            u16 srcport = ntohs(*(u16*)&data[0x22]);
+            u16 dstport = ntohs(*(u16*)&data[0x24]);
+            if (srcport == 68 && dstport == 67) // DHCP
+            {
+                printf("LANMAGIC: DHCP packet\n");
+                return HandleDHCPFrame(data, len);
+            }
+        }
+
+        printf("LANMAGIC: IP frame, doing NAT\n");
+        return HandleIPFrame(data, len);
+    }
+    else if (ethertype == 0x0806) // ARP
+    {
+        printf("LANMAGIC: ARP\n");
+        return HandleARPFrame(data, len);
+    }
+
+    return false;
+}
+
+int SendPacket(u8* data, int len)
+{
+    if (PCapAdapter == NULL)
+        return 0;
+
+    if (len > 2048)
+    {
+        printf("LAN_SendPacket: error: packet too long (%d)\n", len);
+        return 0;
+    }
+
+    if (!Config::DirectLAN)
+    {
+        if (HandlePacket(data, len))
+            return len;
+    }
+
+    pcap_sendpacket(PCapAdapter, data, len);
+    // TODO: check success
+    return len;
+}
+
+int RecvPacket(u8* data)
+{
+    if (PCapAdapter == NULL)
+        return 0;
+
+    int ret = 0;
+    if (PCapRXNum > 0)
+    {
+        memcpy(data, PCapPacketBuffer, PCapPacketLen);
+        ret = PCapPacketLen;
+        PCapRXNum = 0;
+    }
+
+    pcap_dispatch(PCapAdapter, 1, RXCallback, NULL);
+    return ret;
+}
+
+}
diff --git a/src/libui_sdl/LAN_Socket.h b/src/libui_sdl/LAN_Socket.h
new file mode 100644
index 00000000..a0abe45e
--- /dev/null
+++ b/src/libui_sdl/LAN_Socket.h
@@ -0,0 +1,38 @@
+/*
+    Copyright 2016-2019 Arisotura
+
+    This file is part of melonDS.
+
+    melonDS is free software: you can redistribute it and/or modify it under
+    the terms of the GNU General Public License as published by the Free
+    Software Foundation, either version 3 of the License, or (at your option)
+    any later version.
+
+    melonDS is distributed in the hope that it will be useful, but WITHOUT ANY
+    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+    FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License along
+    with melonDS. If not, see http://www.gnu.org/licenses/.
+*/
+
+#ifndef LAN_SOCKET_H
+#define LAN_SOCKET_H
+
+#include "../types.h"
+
+namespace LAN_Socket
+{
+
+//
+
+
+bool Init();
+void DeInit();
+
+int SendPacket(u8* data, int len);
+int RecvPacket(u8* data);
+
+}
+
+#endif // LAN_SOCKET_H
diff --git a/src/libui_sdl/main.cpp b/src/libui_sdl/main.cpp
index fcc0dd3d..f65b9d19 100644
--- a/src/libui_sdl/main.cpp
+++ b/src/libui_sdl/main.cpp
@@ -1683,7 +1683,7 @@ void ApplyNewSettings(int type)
     EmuRunning = prevstatus;
 }
 
-
+u16 zogg(u16 val) { return (val>>8)|(val<<8);}
 int main(int argc, char** argv)
 {
     srand(time(NULL));
@@ -1691,6 +1691,61 @@ int main(int argc, char** argv)
     printf("melonDS " MELONDS_VERSION "\n");
     printf(MELONDS_URL "\n");
 
+    {
+        /*u8 shit[] =
+        {
+            0x84, 0x7A, 0x88, 0x1E, 0x8D, 0x1E, 0x34, 0x02, 0x86, 0xC5, 0x45, 0x2C, 0x08, 0x00, 0x45, 0x00,
+            0x00, 0x28, 0x12, 0x00, 0x00, 0x00, 0x80, 0x06, 0x37, 0x8D, 0xC0, 0xA8, 0x06, 0x5E, 0xA3, 0xAC,
+            0x86, 0x90, 0x9D, 0xC5, 0x14, 0x46, 0xF9, 0xE0, 0x5B, 0x65, 0x00, 0x00, 0x00, 0x00, 0x50, 0x02,
+            0x05, 0x78, 0x00, 0x00, 0x00, 0x00, 0x03, 0x69, 0x72, 0x63, 0x07, 0x67, 0x62, 0x61, 0x74, 0x65,
+            0x6D, 0x70, 0x03, 0x6E
+        };*/
+        u8 shit[] =
+        {
+            0x00, 0xAB, 0x33, 0x28, 0x99, 0x44, 0x00, 0x09, 0xBF, 0x53, 0xC4, 0x49, 0x08, 0x00, 0x45, 0x00,
+            0x00, 0x28, 0x7E, 0x00, 0x00, 0x00, 0x80, 0x06, 0x48, 0x43, 0x0A, 0x40, 0x40, 0x10, 0xA3, 0xAC,
+            0x86, 0x90, 0x9C, 0x99, 0x14, 0x46, 0x31, 0x2F, 0x08, 0x59, 0x00, 0x00, 0x00, 0x00, 0x50, 0x02,
+            0x05, 0x78, 0x00, 0x00, 0x00, 0x00, 0x03, 0x69, 0x72, 0x63, 0x07, 0x67, 0x62, 0x61, 0x74, 0x65,
+            0x6D, 0x70, 0x03, 0x6E
+        };
+        // 4B76 (B489)
+        u32 len=0x44;
+        u8* ipheader = &shit[0xE];
+        u8* protoheader = &shit[0x22];
+        u32 tcplen = 0x14;//len-0x22;
+
+        // TCP checksum
+        u32 tmp = 0;
+        *(u16*)&protoheader[16] = 0;
+        tmp += zogg(*(u16*)&ipheader[12]);
+        printf("%04X  %04X\n", zogg(*(u16*)&ipheader[12]), tmp);
+        tmp += zogg(*(u16*)&ipheader[14]);
+        printf("%04X  %04X\n", zogg(*(u16*)&ipheader[14]), tmp);
+        tmp += zogg(*(u16*)&ipheader[16]);
+        printf("%04X  %04X\n", zogg(*(u16*)&ipheader[16]), tmp);
+        tmp += zogg(*(u16*)&ipheader[18]);
+        printf("%04X  %04X\n", zogg(*(u16*)&ipheader[18]), tmp);
+        tmp += zogg(0x0600);
+        printf("%04X  %04X\n", zogg(0x600), tmp);
+        tmp += tcplen;
+        printf("%04X  %04X\n", tcplen, tmp);
+        for (u8* i = protoheader; i < &protoheader[tcplen-1]; i += 2)
+        {
+            tmp += zogg(*(u16*)i);
+            printf("plarff: %d (%d) -> %04X  %04X\n",
+                   (u32)(i-protoheader), (u32)(i-&shit[0]),
+                   zogg(*(u16*)i), tmp);
+        }
+        if (tcplen & 1) tmp += (protoheader[tcplen-1] << 8);
+        printf("tmp1=%04X\n", tmp);
+        while (tmp >> 16)
+            tmp = (tmp & 0xFFFF) + (tmp >> 16);
+        printf("tmp2=%04X\n", tmp);
+        tmp ^= 0xFFFF;
+        printf("chk = %04X\n", (tmp));
+        printf("expected = B1D5, bad = 2E8C\n");
+    }
+
     if (argc > 0 && strlen(argv[0]) > 0)
     {
         int len = strlen(argv[0]);