Emulated local Wi-Fi multiplayer support

README.md

@@ -115,9 +115,9 @@ you can set its DNS address
 from within the emulated console's Wi-Fi settings menu.
 
 > [!NOTE]
-> Do not confuse this with local multiplayer.
-> melonDS DS does not support emulating local wireless
-> at this time.
+> Do not confuse this with local multiplayer,
+> which does not require access to the Internet
+> and is implemented using libretro's netplay API.
 
 ## Homebrew Save Data
 
@@ -191,11 +191,6 @@ These features have not yet been implemented in standalone [melonDS][melonds],
 or they haven't been integrated into melonDS DS.
 If you want to see them, ask how you can get involved!
 
-- **Local Wireless:**
-  Upstream melonDS supports emulating local wireless multiplayer
-  (e.g. Multi-Card Play, Download Play) with multiple instances of melonDS on the same computer
-  or on the same network.
-  This feature is not yet integrated into melonDS DS.
 - **Homebrew Savestates:**
   melonDS has limited support for taking savestates of homebrew games,
   as the virtual SD card is not included in savestate data.

src/libretro/CMakeLists.txt

@@ -60,6 +60,8 @@ add_library(melondsds_libretro ${LIBRARY_TYPE}
     net/pcap.hpp
     net/net.cpp
     net/net.hpp
+    net/mp.cpp
+    net/mp.hpp
     platform/file.cpp
     platform/lan.cpp
     platform/mp.cpp

src/libretro/core/core.cpp

@@ -21,7 +21,6 @@
 #include <GPU3D_OpenGL.h>
 #include <GPU3D_Soft.h>
 
-#include <libretro.h>
 #include <retro_assert.h>
 
 #include <NDS.h>

src/libretro/core/core.hpp

@@ -18,6 +18,7 @@
 #define MELONDSDS_CORE_HPP
 
 #include <cstddef>
+#include <libretro.h>
 #include <memory>
 #include <regex>
 
@@ -33,6 +34,7 @@
 #include "../PlatformOGLPrivate.h"
 #include "../sram.hpp"
 #include "net/net.hpp"
+#include "net/mp.hpp"
 #include "std/span.hpp"
 
 struct retro_game_info;
@@ -92,6 +94,14 @@ namespace MelonDsDs {
         int LanSendPacket(std::span<std::byte> data) noexcept;
         int LanRecvPacket(uint8_t* data) noexcept;
 
+        void MpStarted(retro_netpacket_send_t send, retro_netpacket_poll_receive_t poll_receive) noexcept;
+        void MpPacketReceived(const void *buf, size_t len) noexcept;
+        void MpStopped() noexcept;
+        bool MpSendPacket(const Packet &p) const noexcept;
+        std::optional<Packet> MpNextPacket() noexcept;
+        std::optional<Packet> MpNextPacketBlock() noexcept;
+        bool MpActive() const noexcept;
+
         void WriteNdsSave(std::span<const std::byte> savedata, uint32_t writeoffset, uint32_t writelen) noexcept;
         void WriteGbaSave(std::span<const std::byte> savedata, uint32_t writeoffset, uint32_t writelen) noexcept;
         void WriteFirmware(const melonDS::Firmware& firmware, uint32_t writeoffset, uint32_t writelen) noexcept;
@@ -142,6 +152,7 @@ namespace MelonDsDs {
         InputState _inputState {};
         MicrophoneState _micState {};
         RenderStateWrapper _renderState {};
+        MpState _mpState {};
         std::optional<retro::GameInfo> _ndsInfo = std::nullopt;
         std::optional<retro::GameInfo> _gbaInfo = std::nullopt;
         std::optional<retro::GameInfo> _gbaSaveInfo = std::nullopt;

src/libretro/environment.cpp

@@ -39,6 +39,7 @@
 #include "libretro.hpp"
 #include "config/config.hpp"
 #include "core/test.hpp"
+#include "net/mp.hpp"
 #include "tracy.hpp"
 #include "version.hpp"
 
@@ -737,6 +738,13 @@ PUBLIC_SYMBOL void retro_set_environment(retro_environment_t cb) {
     retro_core_options_update_display_callback update_display_cb {MelonDsDs::UpdateOptionVisibility};
     environment(RETRO_ENVIRONMENT_SET_CORE_OPTIONS_UPDATE_DISPLAY_CALLBACK, &update_display_cb);
 
+    retro_netpacket_callback netpacket_callback {
+        .start = &MelonDsDs::MpStarted,
+        .receive = &MelonDsDs::MpReceived,
+        .stop = &MelonDsDs::MpStopped,
+    };
+    environment(RETRO_ENVIRONMENT_SET_NETPACKET_INTERFACE, &netpacket_callback);
+
     environment(RETRO_ENVIRONMENT_SET_CONTENT_INFO_OVERRIDE, (void*) MelonDsDs::content_overrides);
     environment(RETRO_ENVIRONMENT_SET_CONTROLLER_INFO, (void*) MelonDsDs::ports);
 
@@ -869,4 +877,4 @@ PUBLIC_SYMBOL void retro_set_input_poll(retro_input_poll_t input_poll) {
 
 PUBLIC_SYMBOL void retro_set_input_state(retro_input_state_t input_state) {
     retro::_input_state = input_state;
-}
+}

src/libretro/libretro.cpp

@@ -57,7 +57,6 @@ using std::unique_ptr;
 using std::make_unique;
 using retro::task::TaskSpec;
 
-
 namespace MelonDsDs {
     // Aligned with CoreState to prevent undefined behavior
     alignas(CoreState) static std::array<std::byte, sizeof(CoreState)> CoreStateBuffer;
@@ -325,4 +324,84 @@ void Platform::WriteFirmware(const Firmware& firmware, u32 writeoffset, u32 writ
     ZoneScopedN(TracyFunction);
 
     MelonDsDs::Core.WriteFirmware(firmware, writeoffset, writelen);
-}
+}
+
+extern "C" void MelonDsDs::MpStarted(uint16_t client_id, retro_netpacket_send_t send_fn, retro_netpacket_poll_receive_t poll_receive_fn) noexcept {
+    MelonDsDs::Core.MpStarted(send_fn, poll_receive_fn);
+}
+
+extern "C" void MelonDsDs::MpReceived(const void* buf, size_t len, uint16_t client_id) noexcept {
+    MelonDsDs::Core.MpPacketReceived(buf, len);
+}
+
+extern "C" void MelonDsDs::MpStopped() noexcept {
+    MelonDsDs::Core.MpStopped();
+}
+
+int DeconstructPacket(u8 *data, u64 *timestamp, const std::optional<MelonDsDs::Packet> &o_p) {
+    if (!o_p.has_value()) {
+        return 0;
+    }
+    memcpy(data, o_p->Data(), o_p->Length());
+    *timestamp = o_p->Timestamp();
+    return o_p->Length();
+}
+
+int Platform::MP_SendPacket(u8* data, int len, u64 timestamp, void*) {
+    return MelonDsDs::Core.MpSendPacket(MelonDsDs::Packet(data, len, timestamp, 0, false)) ? len : 0;
+}
+
+int Platform::MP_RecvPacket(u8* data, u64* timestamp, void*) {
+    std::optional<MelonDsDs::Packet> o_p = MelonDsDs::Core.MpNextPacket();
+    return DeconstructPacket(data, timestamp, o_p);
+}
+
+int Platform::MP_SendCmd(u8* data, int len, u64 timestamp, void*) {
+    return MelonDsDs::Core.MpSendPacket(MelonDsDs::Packet(data, len, timestamp, 0, false)) ? len : 0;
+}
+
+int Platform::MP_SendReply(u8 *data, int len, u64 timestamp, u16 aid, void*) {
+    // aid is always less than 16,
+    // otherwise sending a 16-bit wide aidmask in RecvReplies wouldn't make sense,
+    // and neither would this line[1] from melonDS itself.
+    // A blog post from melonDS[2] from 2017 also confirms that
+    // "each client is given an ID from 1 to 15"
+    // [1] https://github.com/melonDS-emu/melonDS/blob/817b409ec893fb0b2b745ee18feced08706419de/src/net/LAN.cpp#L1074
+    // [2] https://melonds.kuribo64.net/comments.php?id=25
+    retro_assert(aid < 16);
+    return MelonDsDs::Core.MpSendPacket(MelonDsDs::Packet(data, len, timestamp, aid, true)) ? len : 0;
+}
+
+int Platform::MP_SendAck(u8* data, int len, u64 timestamp, void*) {
+    return MelonDsDs::Core.MpSendPacket(MelonDsDs::Packet(data, len, timestamp, 0, false)) ? len : 0;
+}
+
+int Platform::MP_RecvHostPacket(u8* data, u64 * timestamp, void*) {
+    std::optional<MelonDsDs::Packet> o_p = MelonDsDs::Core.MpNextPacketBlock();
+    return DeconstructPacket(data, timestamp, o_p);
+}
+
+u16 Platform::MP_RecvReplies(u8* packets, u64 timestamp, u16 aidmask, void*) {
+    if(!MelonDsDs::Core.MpActive()) {
+        return 0;
+    }
+    u16 ret = 0;
+    int loops = 0;
+    while(ret != aidmask) {
+        std::optional<MelonDsDs::Packet> o_p = MelonDsDs::Core.MpNextPacketBlock();
+        if(!o_p.has_value()) {
+            return ret;
+        }
+        MelonDsDs::Packet p = std::move(o_p).value();
+        if(p.Timestamp() < (timestamp - 32)) {
+            continue;
+        }
+        if(!p.IsReply()) {
+            continue;
+        }
+        ret |= 1<<p.Aid();
+        memcpy(&packets[(p.Aid()-1)*1024], p.Data(), p.Length());
+        loops++;
+    }
+    return ret;
+}

src/libretro/libretro.hpp

@@ -40,6 +40,9 @@ namespace MelonDsDs {
     extern "C" void HardwareContextReset() noexcept;
     extern "C" void HardwareContextDestroyed() noexcept;
     extern "C" bool UpdateOptionVisibility() noexcept;
+    extern "C" void MpStarted(uint16_t client_id, retro_netpacket_send_t send_fn, retro_netpacket_poll_receive_t poll_receive_fn) noexcept;
+    extern "C" void MpReceived(const void* buf, size_t len, uint16_t client_id) noexcept;
+    extern "C" void MpStopped() noexcept;
 }
 
 #endif //MELONDS_DS_LIBRETRO_HPP

src/libretro/net/mp.cpp

@@ -0,0 +1,100 @@
+#include "mp.hpp"
+#include "environment.hpp"
+#include <ctime>
+#include <libretro.h>
+#include <retro_assert.h>
+#include <retro_endianness.h>
+using namespace MelonDsDs;
+
+constexpr long RECV_TIMEOUT_MS = 25;
+
+uint64_t swapToNetwork(uint64_t n) {
+    return swap_if_little64(n);
+}
+
+Packet Packet::parsePk(const void *buf, uint64_t len) {
+    // Necessary because arithmetic on void* is forbidden
+    const char *indexableBuf = (const char *)buf;
+    const char *data = indexableBuf + HeaderSize;
+    retro_assert(len > HeaderSize);
+    size_t dataLen = len - HeaderSize;
+    uint64_t timestamp = swapToNetwork(*(const uint64_t*)(indexableBuf));
+    uint8_t aid = *(const uint8_t*)(indexableBuf + 8);
+    uint8_t isReply = *(const uint8_t*)(indexableBuf + 9);
+    retro_assert(isReply == 1 || isReply == 0);
+    return Packet(data, dataLen, timestamp, aid, isReply == 1);
+}
+
+Packet::Packet(const void *data, uint64_t len, uint64_t timestamp, uint8_t aid, bool isReply) :
+    _data((unsigned char*)data, (unsigned char*)data + len),
+    _timestamp(timestamp),
+    _aid(aid),
+    _isReply(isReply){
+}
+
+std::vector<uint8_t> Packet::ToBuf() const {
+    std::vector<uint8_t> ret;
+    ret.reserve(HeaderSize + Length());
+    uint64_t netTimestamp = swapToNetwork(_timestamp);
+    ret.insert(ret.end(), (const char *)&netTimestamp, ((const char *)&netTimestamp) + sizeof(uint64_t));
+    ret.push_back(_aid);
+    ret.push_back(_isReply);
+    ret.insert(ret.end(), _data.begin(), _data.end());
+    return ret;
+}
+
+bool MpState::IsReady() const noexcept {
+    return _sendFn != nullptr && _pollFn != nullptr;
+}
+
+void MpState::SetSendFn(retro_netpacket_send_t sendFn) noexcept {
+    _sendFn = sendFn;
+}
+
+void MpState::SetPollFn(retro_netpacket_poll_receive_t pollFn) noexcept {
+    _pollFn = pollFn;
+}
+
+void MpState::PacketReceived(const void *buf, size_t len) noexcept {
+    retro_assert(IsReady());
+    receivedPackets.push(Packet::parsePk(buf, len));
+}
+
+std::optional<Packet> MpState::NextPacket() noexcept {
+    retro_assert(IsReady());
+    if(receivedPackets.empty()) {
+        _sendFn(RETRO_NETPACKET_FLUSH_HINT, NULL, 0, RETRO_NETPACKET_BROADCAST);
+        _pollFn();
+    }
+    if(receivedPackets.empty()) {
+        return std::nullopt;
+    } else {
+        Packet p = receivedPackets.front();
+        receivedPackets.pop();
+        return p;
+    }
+}
+
+std::optional<Packet> MpState::NextPacketBlock() noexcept {
+    retro_assert(IsReady());
+    if (receivedPackets.empty()) {
+        for(std::clock_t start = std::clock(); std::clock() < (start + (RECV_TIMEOUT_MS * CLOCKS_PER_SEC / 1000));) {
+            _sendFn(RETRO_NETPACKET_FLUSH_HINT, NULL, 0, RETRO_NETPACKET_BROADCAST);
+            _pollFn();
+            if(!receivedPackets.empty()) {
+                return NextPacket();
+            }
+        }
+    } else {
+        return NextPacket();
+    }
+    retro::debug("Timeout while waiting for packet");
+    return std::nullopt;
+}
+
+void MpState::SendPacket(const Packet &p) const noexcept {
+    retro_assert(IsReady());
+    _sendFn(RETRO_NETPACKET_UNSEQUENCED | RETRO_NETPACKET_UNRELIABLE | RETRO_NETPACKET_FLUSH_HINT, p.ToBuf().data(), p.Length() + HeaderSize, RETRO_NETPACKET_BROADCAST);
+}
+
+

src/libretro/net/mp.hpp

@@ -0,0 +1,55 @@
+#pragma once
+#include <cstdint>
+#include <queue>
+#include <optional>
+#include <vector>
+#include <libretro.h>
+
+namespace MelonDsDs {
+// timestamp, aid, and isReply, respectively.
+constexpr size_t HeaderSize = sizeof(uint64_t) + sizeof(uint8_t) + sizeof(uint8_t);
+
+class Packet {
+public:
+    static Packet parsePk(const void *buf, uint64_t len);
+    explicit Packet(const void *data, uint64_t len, uint64_t timestamp, uint8_t aid, bool isReply);
+
+    [[nodiscard]] uint64_t Timestamp() const noexcept {
+        return _timestamp;
+    };
+    [[nodiscard]] uint8_t Aid() const noexcept {
+        return _aid;
+    };
+    [[nodiscard]] bool IsReply() const noexcept {
+        return _isReply;
+    };
+    [[nodiscard]] const void *Data() const noexcept {
+        return _data.data();
+    };
+    [[nodiscard]] uint64_t Length() const noexcept {
+        return _data.size();
+    };
+
+    std::vector<uint8_t> ToBuf() const;
+private:
+    uint64_t _timestamp;
+    uint8_t _aid;
+    bool _isReply;
+    std::vector<uint8_t> _data;
+};
+
+class MpState {
+public:
+    void PacketReceived(const void *buf, size_t len) noexcept;
+    void SetSendFn(retro_netpacket_send_t sendFn) noexcept;
+    void SetPollFn(retro_netpacket_poll_receive_t pollFn) noexcept;
+    bool IsReady() const noexcept;
+    void SendPacket(const Packet &p) const noexcept;
+    std::optional<Packet> NextPacket() noexcept;
+    std::optional<Packet> NextPacketBlock() noexcept;
+private:
+    retro_netpacket_send_t _sendFn;
+    retro_netpacket_poll_receive_t _pollFn;
+    std::queue<Packet> receivedPackets;
+};
+}