import setting.txt

runtime/CMakeLists.txt

@@ -278,6 +278,8 @@ target_compile_features(mkw_platform_paths_tests PRIVATE cxx_std_17)
 add_test(NAME mkw_platform_paths_tests COMMAND mkw_platform_paths_tests)
 
 add_executable(mkw_nand_settings_tests "${CMAKE_CURRENT_LIST_DIR}/tests/nand_settings_tests.cpp")
+find_package(Threads REQUIRED)
+target_link_libraries(mkw_nand_settings_tests PRIVATE Threads::Threads)
 target_include_directories(mkw_nand_settings_tests PRIVATE "${CMAKE_CURRENT_LIST_DIR}/include")
 target_compile_features(mkw_nand_settings_tests PRIVATE cxx_std_17)
 add_test(NAME mkw_nand_settings_tests COMMAND mkw_nand_settings_tests)

runtime/include/nand_path.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include "runtime_config.h"
+#include "nand_settings.h"
 #include "runtime_log.h"
 #include "system_bridge.h"
 
@@ -163,7 +164,7 @@ inline std::filesystem::path CreateManagedNandRoot() {
     return root;
 }
 
-inline std::filesystem::path DiscoverNandRootPath() {
+inline std::filesystem::path ResolveNandRootPath() {
     const std::string configPath = RuntimeConfigFile::NandRoot();
     if (!configPath.empty()) {
         const auto path = ResolveConfiguredPath(configPath);
@@ -179,4 +180,16 @@ inline std::filesystem::path DiscoverNandRootPath() {
     return CreateManagedNandRoot();
 }
 
+inline std::filesystem::path DiscoverNandRootPath() {
+    static const auto root = [] {
+        const auto resolved = ResolveNandRootPath();
+        std::string error;
+        if (!RuntimeNandSettings::Ensure(resolved, error)) {
+            FailNandRoot(error.c_str(), RuntimeNandSettings::FilePath(resolved));
+        }
+        return resolved;
+    }();
+    return root;
+}
+
 } // namespace RuntimeNandPath

runtime/include/nand_settings.h

@@ -1,6 +1,9 @@
 #pragma once
 
 #include <array>
+#include <atomic>
+#include <chrono>
+#include <ctime>
 #include <cstdint>
 #include <filesystem>
 #include <fstream>
@@ -9,14 +12,23 @@
 #include <string>
 #include <utility>
 
+#ifdef _WIN32
+#include <windows.h>
+#else
+#include <unistd.h>
+#endif
+
 namespace RuntimeNandSettings {
 
 using Settings = std::map<std::string, std::string>;
 
+inline std::filesystem::path FilePath(const std::filesystem::path& root) {
+    return root / "title/00000001/00000002/data/setting.txt";
+}
+
 // Wii setting.txt is a 256-byte buffer encrypted with a rotating XOR key.
 inline std::optional<Settings> Read(const std::filesystem::path& nandRoot) {
-    std::ifstream input(nandRoot / "title/00000001/00000002/data/setting.txt",
-                        std::ios::binary);
+    std::ifstream input(FilePath(nandRoot), std::ios::binary);
     std::array<uint8_t, 256> bytes{};
     if (!input.read(reinterpret_cast<char*>(bytes.data()), bytes.size())) {
         return std::nullopt;
@@ -66,4 +78,143 @@ inline bool HasIdentity(const Settings& settings) {
     return true;
 }
 
+// Dolphin's normal (non-deterministic) first-boot algorithm. It is independent
+// of the ES device ID. Matching another NAND requires that NAND's saved serial.
+inline std::string GenerateSerial(std::time_t now) {
+    if (now < 0) {
+        return {};
+    }
+    const auto digits = std::to_string(now % 1000000000);
+    return std::string(9 - digits.size(), '0') + digits;
+}
+
+// This recompilation targets the European disc. These are Dolphin's PAL boot
+// defaults; an existing setting.txt always takes precedence, in every region.
+inline std::optional<std::array<uint8_t, 256>> EncodeNew(const std::string& serial) {
+    const Settings identity{{"SERNO", serial}, {"CODE", "LEH"}, {"AREA", "EUR"}, {"GAME", "EU"}};
+    if (!HasIdentity(identity)) {
+        return std::nullopt;
+    }
+    std::array<uint8_t, 256> bytes{};
+    size_t position = 0;
+    uint32_t key = 0x73B5DBFAu;
+    const auto writeByte = [&](char value) {
+        bytes[position++] = static_cast<uint8_t>(value) ^ static_cast<uint8_t>(key);
+        key = (key << 1) | (key >> 31);
+    };
+    for (const std::string& line : {std::string("AREA=EUR\r\n"), std::string("MODEL=RVL-001(EUR)\r\n"),
+             std::string("DVD=0\r\n"), std::string("MPCH=0x7FFE\r\n"), std::string("CODE=LEH\r\n"),
+             "SERNO=" + serial + "\r\n", std::string("VIDEO=PAL\r\n"), std::string("GAME=EU\r\n")}) {
+        for (;;) {
+            if (position + line.size() > bytes.size()) {
+                return std::nullopt;
+            }
+            const auto start = position;
+            const auto savedKey = key;
+            bool hasNull = false;
+            for (const char value : line) {
+                writeByte(value);
+                hasNull |= bytes[position - 1] == 0;
+            }
+            if (!hasNull) {
+                break;
+            }
+            // Nintendo stops at an encoded NUL. Dolphin inserts an extra LF
+            // before this line and retries with the shifted encryption key.
+            position = start;
+            key = savedKey;
+            writeByte('\n');
+        }
+    }
+    return bytes; // The unused tail stays raw zero, as in Dolphin.
+}
+
+// Atomically claim our own scratch directory. A collision belongs to another
+// launch (or a previous crashed launch); leave it untouched and try another name.
+inline std::optional<std::filesystem::path> CreateScratchDirectory(
+    const std::filesystem::path& parent, const std::string& token, std::error_code& ec) {
+    for (unsigned attempt = 0; attempt < 128; ++attempt) {
+        const auto candidate = parent / (".setting-init-" + token + "-" + std::to_string(attempt));
+        ec.clear();
+        if (std::filesystem::create_directory(candidate, ec)) return candidate;
+        if (ec && ec != std::errc::file_exists) return std::nullopt;
+    }
+    ec = std::make_error_code(std::errc::file_exists);
+    return std::nullopt;
+}
+
+// Never replace an existing file, including an unreadable or damaged one.
+// Publish a complete file atomically so simultaneous launches use one identity.
+inline bool Ensure(const std::filesystem::path& root, std::string& error,
+                   std::time_t now = std::time(nullptr)) {
+    const auto path = FilePath(root);
+    std::error_code ec;
+    const auto status = std::filesystem::symlink_status(path, ec);
+    if (ec && ec != std::errc::no_such_file_or_directory) {
+        error = "Cannot inspect NAND setting.txt: " + ec.message();
+        return false;
+    }
+    if (std::filesystem::exists(status)) {
+        const auto existing = Read(root);
+        if (existing && HasIdentity(*existing)) {
+            return true;
+        }
+        error = "Existing NAND setting.txt is unreadable or invalid; restore it from this console's backup";
+        return false;
+    }
+
+    const auto bytes = EncodeNew(GenerateSerial(now));
+    if (!bytes) {
+        error = "Cannot initialize NAND settings: invalid system clock";
+        return false;
+    }
+    ec.clear();
+    std::filesystem::create_directories(path.parent_path(), ec);
+    if (ec) {
+        error = "Cannot create NAND settings directory: " + ec.message();
+        return false;
+    }
+    static std::atomic<unsigned> sequence{0};
+#ifdef _WIN32
+    const auto processId = GetCurrentProcessId();
+#else
+    const auto processId = getpid();
+#endif
+    const auto scratch = CreateScratchDirectory(path.parent_path(),
+        std::to_string(processId) + "-" + std::to_string(
+            std::chrono::steady_clock::now().time_since_epoch().count()) + "-" +
+            std::to_string(sequence++), ec);
+    if (!scratch) {
+        error = "Cannot create temporary NAND settings directory: " + ec.message();
+        return false;
+    }
+    const auto temporary = *scratch / "setting.txt";
+    bool written = false;
+    {
+        std::ofstream output(temporary, std::ios::binary);
+        output.write(reinterpret_cast<const char*>(bytes->data()), bytes->size());
+        output.close();
+        written = static_cast<bool>(output);
+    }
+    bool published = false;
+    if (written) {
+#ifdef _WIN32
+        published = MoveFileExW(temporary.c_str(), path.c_str(), MOVEFILE_WRITE_THROUGH) != 0;
+#else
+        published = ::link(temporary.c_str(), path.c_str()) == 0;
+#endif
+    }
+    std::filesystem::remove(temporary, ec);
+    std::filesystem::remove(*scratch, ec);
+    // A competing launcher may have published its settings first. Always read
+    // the winner from NAND rather than using our unpersisted candidate serial.
+    const auto persisted = Read(root);
+    if (persisted && HasIdentity(*persisted)) {
+        return true;
+    }
+    error = published ? "Cannot read newly initialized NAND setting.txt" :
+                        "Cannot persist NAND setting.txt; check NAND directory permissions";
+    return false;
+}
+
 } // namespace RuntimeNandSettings

runtime/tests/nand_settings_tests.cpp

@@ -3,22 +3,78 @@
 #include <chrono>
 #include <iostream>
 #include <stdexcept>
+#include <thread>
+#include <vector>
 
-static void Require(bool condition) {
+static void Require(bool condition, const char* message = "NAND settings check failed") {
     if (!condition) {
-        throw std::runtime_error("NAND settings check failed");
+        throw std::runtime_error(message);
     }
 }
 
+static std::string ReadBytes(const std::filesystem::path& path) {
+    std::ifstream input(path, std::ios::binary);
+    return {std::istreambuf_iterator<char>(input), std::istreambuf_iterator<char>()};
+}
+
 int main() {
     const auto root = std::filesystem::temp_directory_path() /
         ("wiicomp-nand-settings-" + std::to_string(
             std::chrono::steady_clock::now().time_since_epoch().count()));
     const auto path = root / "title/00000001/00000002/data/setting.txt";
     try {
+        using namespace RuntimeNandSettings;
+        Require(GenerateSerial(1800000123) == "800000123", "Dolphin timestamp modulo");
+        Require(GenerateSerial(1000000001) == "000000001", "Dolphin leading zero padding");
+        Require(GenerateSerial(-1).empty(), "Invalid clock must not supply an identity");
+        // Golden bytes generated by Dolphin's unmodified SettingsHandler.cpp
+        // (upstream 2026-09-06), PAL boot fields and synthetic serial 000000001.
+        // Everything after this prefix is raw zero padding to 256 bytes.
+        const std::string goldenHex =
+            "bba6ac929a0bc96b7eed83d27f33a1e7e73d9b836d8b47c59ee23df6b275baab"
+            "bec9d9dead03cc7a3bdafee50c30ab9fb86194e119fe4ba19eff62d5ec3aacb3"
+            "b5c9d9e3977eac0943d7ff903120a49ef024eafe1cf77be79cf6229a823aabf0f0";
+        std::array<uint8_t, 256> golden{};
+        for (size_t i = 0; i < goldenHex.size() / 2; ++i) {
+            golden[i] = static_cast<uint8_t>(std::stoul(goldenHex.substr(i * 2, 2), nullptr, 16));
+        }
+        Require(EncodeNew("000000001") == golden, "Exact Dolphin writer golden fixture");
+        std::string error;
         Require(!RuntimeNandSettings::Read(root));
         Require(!std::filesystem::exists(root));
         std::filesystem::create_directories(path.parent_path());
+        const auto scratchParent = root / "scratch-collisions";
+        std::filesystem::create_directories(scratchParent / ".setting-init-fixed-0");
+        const auto sentinel = scratchParent / ".setting-init-fixed-0" / "setting.txt";
+        { std::ofstream output(sentinel); output << "another launch owns this"; }
+        const auto occupiedFile = scratchParent / ".setting-init-fixed-1";
+        { std::ofstream output(occupiedFile); output << "leave this file alone"; }
+        std::error_code scratchError;
+        const auto claimed = CreateScratchDirectory(scratchParent, "fixed", scratchError);
+        Require(claimed && *claimed == scratchParent / ".setting-init-fixed-2" && !scratchError,
+                "Retry collisions with both existing directories and files");
+        Require(ReadBytes(sentinel) == "another launch owns this" &&
+                ReadBytes(occupiedFile) == "leave this file alone", "Never modify another launch's scratch data");
+        Require(!CreateScratchDirectory(occupiedFile / "not-a-directory", "fixed", scratchError) && scratchError,
+                "Real filesystem errors must fail rather than retry indefinitely");
+
+        // Force all claimants to use the same token; this deterministically
+        // exercises the collision path even when host clock precision is high.
+        std::array<std::optional<std::filesystem::path>, 16> claims;
+        std::vector<std::thread> claimants;
+        for (size_t i = 0; i < claims.size(); ++i) {
+            claimants.emplace_back([&, i] {
+                std::error_code ec;
+                claims[i] = CreateScratchDirectory(scratchParent, "shared", ec);
+            });
+        }
+        for (auto& claimant : claimants) claimant.join();
+        for (size_t i = 0; i < claims.size(); ++i) {
+            Require(claims[i].has_value(), "Every concurrent claimant must acquire a scratch directory");
+            for (size_t j = 0; j < i; ++j) {
+                Require(claims[i] != claims[j], "Concurrent claimants must own different scratch directories");
+            }
+        }
         const std::string plain = "AREA=USA\r\n\nCODE=LU\r\nSERNO=987654321\r\nGAME=US\r\n";
         std::array<uint8_t, 256> fixture{};
         for (size_t i = 0; i < fixture.size(); ++i) {
@@ -35,6 +91,7 @@ int main() {
         Require(settings && RuntimeNandSettings::HasIdentity(*settings));
         Require(settings->at("SERNO") == "987654321" && settings->at("CODE") == "LU");
         Require(settings->at("AREA") == "USA" && settings->at("GAME") == "US");
+        Require(Ensure(root, error, 1800000123), "Existing imported NAND must work");
         std::array<uint8_t, 256> after{};
         {
             std::ifstream input(path, std::ios::binary);
@@ -54,6 +111,67 @@ int main() {
         Require(!RuntimeNandSettings::HasIdentity(*settings));
         std::filesystem::resize_file(path, 128);
         Require(!RuntimeNandSettings::Read(root));
+        const auto damaged = ReadBytes(path);
+        Require(!Ensure(root, error, 1800000123), "Do not replace a truncated identity");
+        Require(ReadBytes(path) == damaged, "Damaged file must remain untouched");
+
+        const auto fresh = root / "fresh";
+        Require(Ensure(fresh, error, 1800000123), "Missing setting.txt must initialize");
+        const auto generated = Read(fresh);
+        Require(generated && HasIdentity(*generated), "Generated file must be readable");
+        Require(generated->at("SERNO") == "800000123", "Persist Dolphin-generated serial");
+        Require(generated->at("CODE") == "LEH" && generated->at("AREA") == "EUR" &&
+                generated->at("GAME") == "EU", "PAL first-boot fields");
+        Require(generated->at("MODEL") == "RVL-001(EUR)" && generated->at("VIDEO") == "PAL" &&
+                generated->at("DVD") == "0" && generated->at("MPCH") == "0x7FFE",
+                "Complete Dolphin boot settings");
+        const auto firstBoot = ReadBytes(FilePath(fresh));
+        Require(firstBoot.size() == 256 && firstBoot.back() == 0, "Dolphin buffer size and raw zero padding");
+        Require(Ensure(fresh, error, 1900000999), "Second boot");
+        Require(ReadBytes(FilePath(fresh)) == firstBoot, "Second boot must not change any bytes");
+
+        const auto blocked = root / "blocked";
+        { std::ofstream output(blocked); output << "file obstructing NAND directory"; }
+        Require(!Ensure(blocked, error, 1800000123), "Write failure must not return an ephemeral identity");
+        Require(!Ensure(root / "bad-clock", error, -1), "Clock failure must not initialize");
+
+        const auto concurrent = root / "concurrent";
+        std::array<bool, 16> results{};
+        std::vector<std::thread> workers;
+        for (size_t i = 0; i < results.size(); ++i) {
+            workers.emplace_back([&, i] {
+                std::string detail;
+                results[i] = Ensure(concurrent, detail, 1800000001 + i);
+            });
+        }
+        for (auto& worker : workers) worker.join();
+        for (const bool result : results) Require(result, "Concurrent boot must read the persisted winner");
+        const auto winner = ReadBytes(FilePath(concurrent));
+        Require(Read(concurrent) && HasIdentity(*Read(concurrent)), "Concurrent boot must persist valid settings");
+        Require(Ensure(concurrent, error, 1900000999), "Boot after concurrent initialization");
+        Require(ReadBytes(FilePath(concurrent)) == winner, "Concurrent winner must remain stable");
+
+        // Independently decode as Nintendo does: stop at the first encoded NUL.
+        // Exercise serials that force Dolphin's extra-LF escaping, not only
+        // values that happen to work with a plain rotating-XOR encoder.
+        bool sawExtraLf = false;
+        for (int serial = 1; serial <= 10000; ++serial) {
+            const auto number = GenerateSerial(1000000000 + serial);
+            const auto encoded = EncodeNew(number);
+            Require(encoded.has_value(), "Serial encoding must fit");
+            std::string decoded;
+            for (size_t i = 0; i < encoded->size() && (*encoded)[i] != 0; ++i) {
+                const unsigned shift = i % 32;
+                const uint32_t key = shift == 0 ? 0x73B5DBFAu :
+                    (0x73B5DBFAu << shift) | (0x73B5DBFAu >> (32 - shift));
+                decoded += static_cast<char>((*encoded)[i] ^ static_cast<uint8_t>(key));
+            }
+            Require(decoded.find("SERNO=" + number + "\r\n") != std::string::npos &&
+                    decoded.find("GAME=EU\r\n") != std::string::npos,
+                    "Encoded NUL must not truncate settings");
+            sawExtraLf |= decoded.find("\r\n\n") != std::string::npos;
+        }
+        Require(sawExtraLf, "Exercise Dolphin LF escape path");
         std::filesystem::remove_all(root);
         std::cout << "NAND settings checks passed\n";
         return 0;