import setting.txt

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 +78,122 @@ 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.
+}
+
+// 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};
+    const auto scratch = path.parent_path() / (".setting-init-" + std::to_string(
+        std::chrono::steady_clock::now().time_since_epoch().count()) + "-" + std::to_string(sequence++));
+    if (!std::filesystem::create_directory(scratch, ec)) {
+        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