fs: Add path class

src/common/overflow.h

@@ -19,4 +19,21 @@ inline T WrappingAdd(T lhs, T rhs) {
     return BitCast<T>(lhs_u + rhs_u);
 }
 
+template <typename T>
+    requires(std::is_integral_v<T> && std::is_signed_v<T>)
+inline bool CanAddWithoutOverflow(T lhs, T rhs) {
+#ifdef _MSC_VER
+    if (lhs >= 0 && rhs >= 0) {
+        return WrappingAdd(lhs, rhs) >= std::max(lhs, rhs);
+    } else if (lhs < 0 && rhs < 0) {
+        return WrappingAdd(lhs, rhs) <= std::min(lhs, rhs);
+    } else {
+        return true;
+    }
+#else
+    T res;
+    return !__builtin_add_overflow(lhs, rhs, &res);
+#endif
+}
+
 } // namespace Common

src/core/CMakeLists.txt

@@ -58,7 +58,7 @@ add_library(core STATIC
     file_sys/fs_operate_range.h
     file_sys/fs_path.h
     file_sys/fs_path_utility.h
-    file_sys/fs_util_character_encoding.h
+    file_sys/fs_string_util.h
     file_sys/fsmitm_romfsbuild.cpp
     file_sys/fsmitm_romfsbuild.h
     file_sys/fssystem/fs_i_storage.h
@@ -104,25 +104,10 @@ add_library(core STATIC
     file_sys/fssystem/fssystem_switch_storage.h
     file_sys/fssystem/fssystem_utility.cpp
     file_sys/fssystem/fssystem_utility.h
-    file_sys/fssystem/fs_types.h
-    file_sys/bis_factory.cpp
-    file_sys/bis_factory.h
-    file_sys/card_image.cpp
-    file_sys/card_image.h
-    file_sys/common_funcs.h
-    file_sys/content_archive.cpp
-    file_sys/content_archive.h
-    file_sys/control_metadata.cpp
-    file_sys/control_metadata.h
-    file_sys/directory.h
-    file_sys/errors.h
-    file_sys/fsmitm_romfsbuild.cpp
-    file_sys/fsmitm_romfsbuild.h
     file_sys/ips_layer.cpp
     file_sys/ips_layer.h
     file_sys/kernel_executable.cpp
     file_sys/kernel_executable.h
-    file_sys/mode.h
     file_sys/nca_metadata.cpp
     file_sys/nca_metadata.h
     file_sys/partition_filesystem.cpp
@@ -215,7 +200,6 @@ add_library(core STATIC
     hle/kernel/board/nintendo/nx/secure_monitor.h
     hle/kernel/code_set.cpp
     hle/kernel/code_set.h
-    hle/kernel/svc_results.h
     hle/kernel/global_scheduler_context.cpp
     hle/kernel/global_scheduler_context.h
     hle/kernel/init/init_slab_setup.cpp
@@ -225,11 +209,11 @@ add_library(core STATIC
     hle/kernel/k_address_arbiter.h
     hle/kernel/k_address_space_info.cpp
     hle/kernel/k_address_space_info.h
+    hle/kernel/k_affinity_mask.h
     hle/kernel/k_auto_object.cpp
     hle/kernel/k_auto_object.h
     hle/kernel/k_auto_object_container.cpp
     hle/kernel/k_auto_object_container.h
-    hle/kernel/k_affinity_mask.h
     hle/kernel/k_capabilities.cpp
     hle/kernel/k_capabilities.h
     hle/kernel/k_class_token.cpp
@@ -253,9 +237,9 @@ add_library(core STATIC
     hle/kernel/k_event_info.h
     hle/kernel/k_handle_table.cpp
     hle/kernel/k_handle_table.h
-    hle/kernel/k_hardware_timer_base.h
     hle/kernel/k_hardware_timer.cpp
     hle/kernel/k_hardware_timer.h
+    hle/kernel/k_hardware_timer_base.h
     hle/kernel/k_interrupt_manager.cpp
     hle/kernel/k_interrupt_manager.h
     hle/kernel/k_light_client_session.cpp
@@ -282,10 +266,10 @@ add_library(core STATIC
     hle/kernel/k_page_bitmap.h
     hle/kernel/k_page_buffer.cpp
     hle/kernel/k_page_buffer.h
-    hle/kernel/k_page_heap.cpp
-    hle/kernel/k_page_heap.h
     hle/kernel/k_page_group.cpp
     hle/kernel/k_page_group.h
+    hle/kernel/k_page_heap.cpp
+    hle/kernel/k_page_heap.h
     hle/kernel/k_page_table.h
     hle/kernel/k_page_table_base.cpp
     hle/kernel/k_page_table_base.h
@@ -350,8 +334,6 @@ add_library(core STATIC
     hle/kernel/slab_helpers.h
     hle/kernel/svc.cpp
     hle/kernel/svc.h
-    hle/kernel/svc_common.h
-    hle/kernel/svc_types.h
     hle/kernel/svc/svc_activity.cpp
     hle/kernel/svc/svc_address_arbiter.cpp
     hle/kernel/svc/svc_address_translation.cpp
@@ -389,6 +371,9 @@ add_library(core STATIC
     hle/kernel/svc/svc_thread_profiler.cpp
     hle/kernel/svc/svc_tick.cpp
     hle/kernel/svc/svc_transfer_memory.cpp
+    hle/kernel/svc_common.h
+    hle/kernel/svc_results.h
+    hle/kernel/svc_types.h
     hle/result.h
     hle/service/acc/acc.cpp
     hle/service/acc/acc.h
@@ -519,17 +504,17 @@ add_library(core STATIC
     hle/service/filesystem/fsp/fs_i_filesystem.h
     hle/service/filesystem/fsp/fs_i_storage.cpp
     hle/service/filesystem/fsp/fs_i_storage.h
+    hle/service/filesystem/fsp/fsp_ldr.cpp
+    hle/service/filesystem/fsp/fsp_ldr.h
+    hle/service/filesystem/fsp/fsp_pr.cpp
+    hle/service/filesystem/fsp/fsp_pr.h
     hle/service/filesystem/fsp/fsp_srv.cpp
     hle/service/filesystem/fsp/fsp_srv.h
-    hle/service/filesystem/fsp_ldr.cpp
-    hle/service/filesystem/fsp_ldr.h
-    hle/service/filesystem/fsp_pr.cpp
-    hle/service/filesystem/fsp_pr.h
+    hle/service/filesystem/fsp/fsp_util.h
     hle/service/filesystem/romfs_controller.cpp
     hle/service/filesystem/romfs_controller.h
     hle/service/filesystem/save_data_controller.cpp
     hle/service/filesystem/save_data_controller.h
-    hle/service/filesystem/fsp_util.h
     hle/service/fgm/fgm.cpp
     hle/service/fgm/fgm.h
     hle/service/friend/friend.cpp

src/core/file_sys/errors.h

@@ -73,10 +73,21 @@ constexpr Result ResultUnexpectedInCompressedStorageA{ErrorModule::FS, 5324};
 constexpr Result ResultUnexpectedInCompressedStorageB{ErrorModule::FS, 5325};
 constexpr Result ResultUnexpectedInCompressedStorageC{ErrorModule::FS, 5326};
 constexpr Result ResultUnexpectedInCompressedStorageD{ErrorModule::FS, 5327};
+constexpr Result ResultUnexpectedInPathA{ErrorModule::FS, 5328};
 constexpr Result ResultInvalidArgument{ErrorModule::FS, 6001};
+constexpr Result ResultInvalidPath{ErrorModule::FS, 6002};
+constexpr Result ResultTooLongPath{ErrorModule::FS, 6003};
+constexpr Result ResultInvalidCharacter{ErrorModule::FS, 6004};
+constexpr Result ResultInvalidPathFormat{ErrorModule::FS, 6005};
+constexpr Result ResultDirectoryUnobtainable{ErrorModule::FS, 6006};
+constexpr Result ResultNotNormalized{ErrorModule::FS, 6007};
 constexpr Result ResultInvalidOffset{ErrorModule::FS, 6061};
 constexpr Result ResultInvalidSize{ErrorModule::FS, 6062};
 constexpr Result ResultNullptrArgument{ErrorModule::FS, 6063};
+constexpr Result ResultInvalidOpenMode{ErrorModule::FS, 6072};
+constexpr Result ResultFileExtensionWithoutOpenModeAllowAppend{ErrorModule::FS, 6201};
+constexpr Result ResultReadNotPermitted{ErrorModule::FS, 6202};
+constexpr Result ResultWriteNotPermitted{ErrorModule::FS, 6203};
 constexpr Result ResultUnsupportedSetSizeForIndirectStorage{ErrorModule::FS, 6325};
 constexpr Result ResultUnsupportedWriteForCompressedStorage{ErrorModule::FS, 6387};
 constexpr Result ResultUnsupportedOperateRangeForCompressedStorage{ErrorModule::FS, 6388};

src/core/file_sys/fs_file.h

@@ -0,0 +1,63 @@
+// SPDX-FileCopyrightText: Copyright 2023 yuzu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+namespace FileSys {
+
+struct ReadOption {
+    u32 _value;
+
+    static const ReadOption None;
+};
+
+enum ReadOptionFlag : u32 {
+    ReadOptionFlag_None = (0 << 0),
+};
+
+inline constexpr const ReadOption ReadOption::None = {ReadOptionFlag_None};
+
+inline constexpr bool operator==(const ReadOption& lhs, const ReadOption& rhs) {
+    return lhs._value == rhs._value;
+}
+
+inline constexpr bool operator!=(const ReadOption& lhs, const ReadOption& rhs) {
+    return !(lhs == rhs);
+}
+
+static_assert(sizeof(ReadOption) == sizeof(u32));
+
+enum WriteOptionFlag : u32 {
+    WriteOptionFlag_None = (0 << 0),
+    WriteOptionFlag_Flush = (1 << 0),
+};
+
+struct WriteOption {
+    u32 _value;
+
+    constexpr inline bool HasFlushFlag() const {
+        return _value & WriteOptionFlag_Flush;
+    }
+
+    static const WriteOption None;
+    static const WriteOption Flush;
+};
+
+inline constexpr const WriteOption WriteOption::None = {WriteOptionFlag_None};
+inline constexpr const WriteOption WriteOption::Flush = {WriteOptionFlag_Flush};
+
+inline constexpr bool operator==(const WriteOption& lhs, const WriteOption& rhs) {
+    return lhs._value == rhs._value;
+}
+
+inline constexpr bool operator!=(const WriteOption& lhs, const WriteOption& rhs) {
+    return !(lhs == rhs);
+}
+
+static_assert(sizeof(WriteOption) == sizeof(u32));
+
+struct FileHandle {
+    void* handle;
+};
+
+} // namespace FileSys

src/core/file_sys/fs_memory_management.h

@@ -0,0 +1,48 @@
+// SPDX-FileCopyrightText: Copyright 2023 yuzu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <mutex>
+#include "common/alignment.h"
+
+namespace FileSys {
+
+std::mutex g_mutex;
+
+constexpr size_t RequiredAlignment = alignof(u64);
+
+void* AllocateUnsafe(size_t size) {
+    /* Allocate. */
+    void* const ptr = ::operator new(size, std::align_val_t{RequiredAlignment});
+
+    /* Check alignment. */
+    ASSERT(Common::IsAligned(reinterpret_cast<uintptr_t>(ptr), RequiredAlignment));
+
+    /* Return allocated pointer. */
+    return ptr;
+}
+
+void DeallocateUnsafe(void* ptr, size_t size) {
+    /* Deallocate the pointer. */
+    ::operator delete(ptr, std::align_val_t{RequiredAlignment});
+}
+
+void* Allocate(size_t size) {
+    /* Lock the allocator. */
+    std::scoped_lock lk(g_mutex);
+
+    return AllocateUnsafe(size);
+}
+
+void Deallocate(void* ptr, size_t size) {
+    /* If the pointer is non-null, deallocate it. */
+    if (ptr != nullptr) {
+        /* Lock the allocator. */
+        std::scoped_lock lk(g_mutex);
+
+        DeallocateUnsafe(ptr, size);
+    }
+}
+
+} // namespace FileSys

src/core/file_sys/fs_operate_range.h

@@ -0,0 +1,20 @@
+// SPDX-FileCopyrightText: Copyright 2023 yuzu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+namespace FileSys {
+
+enum class OperationId : s64 {
+    FillZero = 0,
+    DestroySignature = 1,
+    Invalidate = 2,
+    QueryRange = 3,
+    QueryUnpreparedRange = 4,
+    QueryLazyLoadCompletionRate = 5,
+    SetLazyLoadPriority = 6,
+
+    ReadLazyLoadFileForciblyForDebug = 10001,
+};
+
+} // namespace FileSys

src/core/file_sys/fs_path.h

@@ -0,0 +1,570 @@
+// SPDX-FileCopyrightText: Copyright 2023 yuzu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include "common/alignment.h"
+#include "common/common_funcs.h"
+#include "core/file_sys/errors.h"
+#include "core/file_sys/fs_memory_management.h"
+#include "core/file_sys/fs_path_utility.h"
+#include "core/file_sys/fs_string_util.h"
+#include "core/hle/result.h"
+
+namespace FileSys {
+class DirectoryPathParser;
+
+class Path {
+    YUZU_NON_COPYABLE(Path);
+    YUZU_NON_MOVEABLE(Path);
+
+private:
+    static constexpr const char* EmptyPath = "";
+    static constexpr size_t WriteBufferAlignmentLength = 8;
+
+private:
+    friend class DirectoryPathParser;
+
+public:
+    class WriteBuffer {
+        YUZU_NON_COPYABLE(WriteBuffer);
+
+    private:
+        char* m_buffer;
+        size_t m_length_and_is_normalized;
+
+    public:
+        constexpr WriteBuffer() : m_buffer(nullptr), m_length_and_is_normalized(0) { /* ... */
+        }
+
+        constexpr ~WriteBuffer() {
+            if (m_buffer != nullptr) {
+                Deallocate(m_buffer, this->GetLength());
+                this->ResetBuffer();
+            }
+        }
+
+        constexpr WriteBuffer(WriteBuffer&& rhs)
+            : m_buffer(rhs.m_buffer), m_length_and_is_normalized(rhs.m_length_and_is_normalized) {
+            rhs.ResetBuffer();
+        }
+
+        constexpr WriteBuffer& operator=(WriteBuffer&& rhs) {
+            if (m_buffer != nullptr) {
+                Deallocate(m_buffer, this->GetLength());
+            }
+
+            m_buffer = rhs.m_buffer;
+            m_length_and_is_normalized = rhs.m_length_and_is_normalized;
+
+            rhs.ResetBuffer();
+
+            return *this;
+        }
+
+        constexpr void ResetBuffer() {
+            m_buffer = nullptr;
+            this->SetLength(0);
+        }
+
+        constexpr char* Get() const {
+            return m_buffer;
+        }
+
+        constexpr size_t GetLength() const {
+            return m_length_and_is_normalized >> 1;
+        }
+
+        constexpr bool IsNormalized() const {
+            return static_cast<bool>(m_length_and_is_normalized & 1);
+        }
+
+        constexpr void SetNormalized() {
+            m_length_and_is_normalized |= static_cast<size_t>(1);
+        }
+
+        constexpr void SetNotNormalized() {
+            m_length_and_is_normalized &= ~static_cast<size_t>(1);
+        }
+
+    private:
+        constexpr WriteBuffer(char* buffer, size_t length)
+            : m_buffer(buffer), m_length_and_is_normalized(0) {
+            this->SetLength(length);
+        }
+
+    public:
+        static WriteBuffer Make(size_t length) {
+            if (void* alloc = Allocate(length); alloc != nullptr) {
+                return WriteBuffer(static_cast<char*>(alloc), length);
+            } else {
+                return WriteBuffer();
+            }
+        }
+
+    private:
+        constexpr void SetLength(size_t size) {
+            m_length_and_is_normalized = (m_length_and_is_normalized & 1) | (size << 1);
+        }
+    };
+
+private:
+    const char* m_str;
+    WriteBuffer m_write_buffer;
+
+public:
+    constexpr Path() : m_str(EmptyPath), m_write_buffer() {
+        /* ... */
+    }
+
+    constexpr Path(const char* s) : m_str(s), m_write_buffer() {
+        m_write_buffer.SetNormalized();
+    }
+
+    constexpr ~Path() { /* ... */
+    }
+
+    constexpr Result SetShallowBuffer(const char* buffer) {
+        /* Check pre-conditions. */
+        ASSERT(m_write_buffer.GetLength() == 0);
+
+        /* Check the buffer is valid. */
+        R_UNLESS(buffer != nullptr, ResultNullptrArgument);
+
+        /* Set buffer. */
+        this->SetReadOnlyBuffer(buffer);
+
+        /* Note that we're normalized. */
+        this->SetNormalized();
+
+        R_SUCCEED();
+    }
+
+    constexpr const char* GetString() const {
+        /* Check pre-conditions. */
+        ASSERT(this->IsNormalized());
+
+        return m_str;
+    }
+
+    constexpr size_t GetLength() const {
+        if (std::is_constant_evaluated()) {
+            return Strlen(this->GetString());
+        } else {
+            return std::strlen(this->GetString());
+        }
+    }
+
+    constexpr bool IsEmpty() const {
+        return *m_str == '\x00';
+    }
+
+    constexpr bool IsMatchHead(const char* p, size_t len) const {
+        return Strncmp(this->GetString(), p, len) == 0;
+    }
+
+    Result Initialize(const Path& rhs) {
+        /* Check the other path is normalized. */
+        const bool normalized = rhs.IsNormalized();
+        R_UNLESS(normalized, ResultNotNormalized);
+
+        /* Allocate buffer for our path. */
+        const auto len = rhs.GetLength();
+        R_TRY(this->Preallocate(len + 1));
+
+        /* Copy the path. */
+        const size_t copied = Strlcpy<char>(m_write_buffer.Get(), rhs.GetString(), len + 1);
+        R_UNLESS(copied == len, ResultUnexpectedInPathA);
+
+        /* Set normalized. */
+        this->SetNormalized();
+        R_SUCCEED();
+    }
+
+    Result Initialize(const char* path, size_t len) {
+        /* Check the path is valid. */
+        R_UNLESS(path != nullptr, ResultNullptrArgument);
+
+        /* Initialize. */
+        R_TRY(this->InitializeImpl(path, len));
+
+        /* Set not normalized. */
+        this->SetNotNormalized();
+
+        R_SUCCEED();
+    }
+
+    Result Initialize(const char* path) {
+        /* Check the path is valid. */
+        R_UNLESS(path != nullptr, ResultNullptrArgument);
+
+        R_RETURN(this->Initialize(path, std::strlen(path)));
+    }
+
+    Result InitializeWithReplaceBackslash(const char* path) {
+        /* Check the path is valid. */
+        R_UNLESS(path != nullptr, ResultNullptrArgument);
+
+        /* Initialize. */
+        R_TRY(this->InitializeImpl(path, std::strlen(path)));
+
+        /* Replace slashes as desired. */
+        if (const auto write_buffer_length = m_write_buffer.GetLength(); write_buffer_length > 1) {
+            Replace(m_write_buffer.Get(), write_buffer_length - 1, '\\', '/');
+        }
+
+        /* Set not normalized. */
+        this->SetNotNormalized();
+
+        R_SUCCEED();
+    }
+
+    Result InitializeWithReplaceForwardSlashes(const char* path) {
+        /* Check the path is valid. */
+        R_UNLESS(path != nullptr, ResultNullptrArgument);
+
+        /* Initialize. */
+        R_TRY(this->InitializeImpl(path, std::strlen(path)));
+
+        /* Replace slashes as desired. */
+        if (m_write_buffer.GetLength() > 1) {
+            if (auto* p = m_write_buffer.Get(); p[0] == '/' && p[1] == '/') {
+                p[0] = '\\';
+                p[1] = '\\';
+            }
+        }
+
+        /* Set not normalized. */
+        this->SetNotNormalized();
+
+        R_SUCCEED();
+    }
+
+    Result InitializeWithNormalization(const char* path, size_t size) {
+        /* Check the path is valid. */
+        R_UNLESS(path != nullptr, ResultNullptrArgument);
+
+        /* Initialize. */
+        R_TRY(this->InitializeImpl(path, size));
+
+        /* Set not normalized. */
+        this->SetNotNormalized();
+
+        /* Perform normalization. */
+        PathFlags path_flags;
+        if (IsPathRelative(m_str)) {
+            path_flags.AllowRelativePath();
+        } else if (IsWindowsPath(m_str, true)) {
+            path_flags.AllowWindowsPath();
+        } else {
+            /* NOTE: In this case, Nintendo checks is normalized, then sets is normalized, then
+             * returns success. */
+            /* This seems like a bug. */
+            size_t dummy;
+            bool normalized;
+            R_TRY(PathFormatter::IsNormalized(std::addressof(normalized), std::addressof(dummy),
+                                              m_str));
+
+            this->SetNormalized();
+            R_SUCCEED();
+        }
+
+        /* Normalize. */
+        R_TRY(this->Normalize(path_flags));
+
+        this->SetNormalized();
+        R_SUCCEED();
+    }
+
+    Result InitializeWithNormalization(const char* path) {
+        /* Check the path is valid. */
+        R_UNLESS(path != nullptr, ResultNullptrArgument);
+
+        R_RETURN(this->InitializeWithNormalization(path, std::strlen(path)));
+    }
+
+    Result InitializeAsEmpty() {
+        /* Clear our buffer. */
+        this->ClearBuffer();
+
+        /* Set normalized. */
+        this->SetNormalized();
+
+        R_SUCCEED();
+    }
+
+    Result AppendChild(const char* child) {
+        /* Check the path is valid. */
+        R_UNLESS(child != nullptr, ResultNullptrArgument);
+
+        /* Basic checks. If we hvea a path and the child is empty, we have nothing to do. */
+        const char* c = child;
+        if (m_str[0]) {
+            /* Skip an early separator. */
+            if (*c == '/') {
+                ++c;
+            }
+
+            R_SUCCEED_IF(*c == '\x00');
+        }
+
+        /* If we don't have a string, we can just initialize. */
+        auto cur_len = std::strlen(m_str);
+        if (cur_len == 0) {
+            R_RETURN(this->Initialize(child));
+        }
+
+        /* Remove a trailing separator. */
+        if (m_str[cur_len - 1] == '/' || m_str[cur_len - 1] == '\\') {
+            --cur_len;
+        }
+
+        /* Get the child path's length. */
+        auto child_len = std::strlen(c);
+
+        /* Reset our write buffer. */
+        WriteBuffer old_write_buffer;
+        if (m_write_buffer.Get() != nullptr) {
+            old_write_buffer = std::move(m_write_buffer);
+            this->ClearBuffer();
+        }
+
+        /* Pre-allocate the new buffer. */
+        R_TRY(this->Preallocate(cur_len + 1 + child_len + 1));
+
+        /* Get our write buffer. */
+        auto* dst = m_write_buffer.Get();
+        if (old_write_buffer.Get() != nullptr && cur_len > 0) {
+            Strlcpy<char>(dst, old_write_buffer.Get(), cur_len + 1);
+        }
+
+        /* Add separator. */
+        dst[cur_len] = '/';
+
+        /* Copy the child path. */
+        const size_t copied = Strlcpy<char>(dst + cur_len + 1, c, child_len + 1);
+        R_UNLESS(copied == child_len, ResultUnexpectedInPathA);
+
+        R_SUCCEED();
+    }
+
+    Result AppendChild(const Path& rhs) {
+        R_RETURN(this->AppendChild(rhs.GetString()));
+    }
+
+    Result Combine(const Path& parent, const Path& child) {
+        /* Get the lengths. */
+        const auto p_len = parent.GetLength();
+        const auto c_len = child.GetLength();
+
+        /* Allocate our buffer. */
+        R_TRY(this->Preallocate(p_len + c_len + 1));
+
+        /* Initialize as parent. */
+        R_TRY(this->Initialize(parent));
+
+        /* If we're empty, we can just initialize as child. */
+        if (this->IsEmpty()) {
+            R_TRY(this->Initialize(child));
+        } else {
+            /* Otherwise, we should append the child. */
+            R_TRY(this->AppendChild(child));
+        }
+
+        R_SUCCEED();
+    }
+
+    Result RemoveChild() {
+        /* If we don't have a write-buffer, ensure that we have one. */
+        if (m_write_buffer.Get() == nullptr) {
+            if (const auto len = std::strlen(m_str); len > 0) {
+                R_TRY(this->Preallocate(len));
+                Strlcpy<char>(m_write_buffer.Get(), m_str, len + 1);
+            }
+        }
+
+        /* Check that it's possible for us to remove a child. */
+        auto* p = m_write_buffer.Get();
+        s32 len = std::strlen(p);
+        R_UNLESS(len != 1 || (p[0] != '/' && p[0] != '.'), ResultNotImplemented);
+
+        /* Handle a trailing separator. */
+        if (len > 0 && (p[len - 1] == '\\' || p[len - 1] == '/')) {
+            --len;
+        }
+
+        /* Remove the child path segment. */
+        while ((--len) >= 0 && p[len]) {
+            if (p[len] == '/' || p[len] == '\\') {
+                if (len > 0) {
+                    p[len] = 0;
+                } else {
+                    p[1] = 0;
+                    len = 1;
+                }
+                break;
+            }
+        }
+
+        /* Check that length remains > 0. */
+        R_UNLESS(len > 0, ResultNotImplemented);
+
+        R_SUCCEED();
+    }
+
+    Result Normalize(const PathFlags& flags) {
+        /* If we're already normalized, nothing to do. */
+        R_SUCCEED_IF(this->IsNormalized());
+
+        /* Check if we're normalized. */
+        bool normalized;
+        size_t dummy;
+        R_TRY(PathFormatter::IsNormalized(std::addressof(normalized), std::addressof(dummy), m_str,
+                                          flags));
+
+        /* If we're not normalized, normalize. */
+        if (!normalized) {
+            /* Determine necessary buffer length. */
+            auto len = m_write_buffer.GetLength();
+            if (flags.IsRelativePathAllowed() && IsPathRelative(m_str)) {
+                len += 2;
+            }
+            if (flags.IsWindowsPathAllowed() && IsWindowsPath(m_str, true)) {
+                len += 1;
+            }
+
+            /* Allocate a new buffer. */
+            const size_t size = Common::AlignUp(len, WriteBufferAlignmentLength);
+            auto buf = WriteBuffer::Make(size);
+            R_UNLESS(buf.Get() != nullptr, ResultAllocationMemoryFailedMakeUnique);
+
+            /* Normalize into it. */
+            R_TRY(PathFormatter::Normalize(buf.Get(), size, m_write_buffer.Get(),
+                                           m_write_buffer.GetLength(), flags));
+
+            /* Set the normalized buffer as our buffer. */
+            this->SetModifiableBuffer(std::move(buf));
+        }
+
+        /* Set normalized. */
+        this->SetNormalized();
+        R_SUCCEED();
+    }
+
+private:
+    void ClearBuffer() {
+        m_write_buffer.ResetBuffer();
+        m_str = EmptyPath;
+    }
+
+    void SetModifiableBuffer(WriteBuffer&& buffer) {
+        /* Check pre-conditions. */
+        ASSERT(buffer.Get() != nullptr);
+        ASSERT(buffer.GetLength() > 0);
+        ASSERT(Common::IsAligned(buffer.GetLength(), WriteBufferAlignmentLength));
+
+        /* Get whether we're normalized. */
+        if (m_write_buffer.IsNormalized()) {
+            buffer.SetNormalized();
+        } else {
+            buffer.SetNotNormalized();
+        }
+
+        /* Set write buffer. */
+        m_write_buffer = std::move(buffer);
+        m_str = m_write_buffer.Get();
+    }
+
+    constexpr void SetReadOnlyBuffer(const char* buffer) {
+        m_str = buffer;
+        m_write_buffer.ResetBuffer();
+    }
+
+    Result Preallocate(size_t length) {
+        /* Allocate additional space, if needed. */
+        if (length > m_write_buffer.GetLength()) {
+            /* Allocate buffer. */
+            const size_t size = Common::AlignUp(length, WriteBufferAlignmentLength);
+            auto buf = WriteBuffer::Make(size);
+            R_UNLESS(buf.Get() != nullptr, ResultAllocationMemoryFailedMakeUnique);
+
+            /* Set write buffer. */
+            this->SetModifiableBuffer(std::move(buf));
+        }
+
+        R_SUCCEED();
+    }
+
+    Result InitializeImpl(const char* path, size_t size) {
+        if (size > 0 && path[0]) {
+            /* Pre allocate a buffer for the path. */
+            R_TRY(this->Preallocate(size + 1));
+
+            /* Copy the path. */
+            const size_t copied = Strlcpy<char>(m_write_buffer.Get(), path, size + 1);
+            R_UNLESS(copied >= size, ResultUnexpectedInPathA);
+        } else {
+            /* We can just clear the buffer. */
+            this->ClearBuffer();
+        }
+
+        R_SUCCEED();
+    }
+
+    constexpr char* GetWriteBuffer() {
+        ASSERT(m_write_buffer.Get() != nullptr);
+        return m_write_buffer.Get();
+    }
+
+    constexpr size_t GetWriteBufferLength() const {
+        return m_write_buffer.GetLength();
+    }
+
+    constexpr bool IsNormalized() const {
+        return m_write_buffer.IsNormalized();
+    }
+
+    constexpr void SetNormalized() {
+        m_write_buffer.SetNormalized();
+    }
+
+    constexpr void SetNotNormalized() {
+        m_write_buffer.SetNotNormalized();
+    }
+
+public:
+    bool operator==(const FileSys::Path& rhs) const {
+        return std::strcmp(this->GetString(), rhs.GetString()) == 0;
+    }
+    bool operator!=(const FileSys::Path& rhs) const {
+        return !(*this == rhs);
+    }
+    bool operator==(const char* p) const {
+        return std::strcmp(this->GetString(), p) == 0;
+    }
+    bool operator!=(const char* p) const {
+        return !(*this == p);
+    }
+};
+
+inline Result SetUpFixedPath(FileSys::Path* out, const char* s) {
+    /* Verify the path is normalized. */
+    bool normalized;
+    size_t dummy;
+    R_TRY(PathNormalizer::IsNormalized(std::addressof(normalized), std::addressof(dummy), s));
+
+    R_UNLESS(normalized, ResultInvalidPathFormat);
+
+    /* Set the fixed path. */
+    R_RETURN(out->SetShallowBuffer(s));
+}
+
+constexpr inline bool IsWindowsDriveRootPath(const FileSys::Path& path) {
+    const char* const str = path.GetString();
+    return IsWindowsDrive(str) &&
+           (str[2] == StringTraits::DirectorySeparator ||
+            str[2] == StringTraits::AlternateDirectorySeparator) &&
+           str[3] == StringTraits::NullTerminator;
+}
+
+} // namespace FileSys

src/core/file_sys/fs_path_utility.h

@@ -0,0 +1,1240 @@
+// SPDX-FileCopyrightText: Copyright 2023 yuzu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include "common/assert.h"
+#include "common/common_types.h"
+#include "common/scope_exit.h"
+#include "core/file_sys/fs_directory.h"
+#include "core/file_sys/fs_memory_management.h"
+#include "core/file_sys/fs_string_util.h"
+#include "core/hle/result.h"
+
+namespace FileSys {
+
+constexpr inline size_t MountNameLengthMax = 15;
+using Result = ::Result;
+
+namespace StringTraits {
+
+constexpr inline char DirectorySeparator = '/';
+constexpr inline char DriveSeparator = ':';
+constexpr inline char Dot = '.';
+constexpr inline char NullTerminator = '\x00';
+
+constexpr inline char AlternateDirectorySeparator = '\\';
+
+constexpr inline const char InvalidCharacters[6] = {':', '*', '?', '<', '>', '|'};
+constexpr inline const char InvalidCharactersForHostName[6] = {':', '*', '<', '>', '|', '$'};
+constexpr inline const char InvalidCharactersForMountName[5] = {'*', '?', '<', '>', '|'};
+
+namespace impl {
+
+template <const char* InvalidCharacterSet, size_t NumInvalidCharacters>
+consteval u64 MakeInvalidCharacterMask(size_t n) {
+    u64 mask = 0;
+    for (size_t i = 0; i < NumInvalidCharacters; ++i) {
+        if ((static_cast<u64>(InvalidCharacterSet[i]) >> 6) == n) {
+            mask |= static_cast<u64>(1) << (static_cast<u64>(InvalidCharacterSet[i]) & 0x3F);
+        }
+    }
+    return mask;
+}
+
+template <const char* InvalidCharacterSet, size_t NumInvalidCharacters>
+constexpr bool IsInvalidCharacterImpl(char c) {
+    constexpr u64 Masks[4] = {
+        MakeInvalidCharacterMask<InvalidCharacterSet, NumInvalidCharacters>(0),
+        MakeInvalidCharacterMask<InvalidCharacterSet, NumInvalidCharacters>(1),
+        MakeInvalidCharacterMask<InvalidCharacterSet, NumInvalidCharacters>(2),
+        MakeInvalidCharacterMask<InvalidCharacterSet, NumInvalidCharacters>(3)};
+
+    return (Masks[static_cast<u64>(c) >> 6] &
+            (static_cast<u64>(1) << (static_cast<u64>(c) & 0x3F))) != 0;
+}
+
+} // namespace impl
+
+constexpr bool IsInvalidCharacter(char c) {
+    return impl::IsInvalidCharacterImpl<InvalidCharacters, size(InvalidCharacters)>(c);
+}
+constexpr bool IsInvalidCharacterForHostName(char c) {
+    return impl::IsInvalidCharacterImpl<InvalidCharactersForHostName,
+                                        size(InvalidCharactersForHostName)>(c);
+}
+constexpr bool IsInvalidCharacterForMountName(char c) {
+    return impl::IsInvalidCharacterImpl<InvalidCharactersForMountName,
+                                        size(InvalidCharactersForMountName)>(c);
+}
+
+} // namespace StringTraits
+
+constexpr inline size_t WindowsDriveLength = 2;
+constexpr inline size_t UncPathPrefixLength = 2;
+constexpr inline size_t DosDevicePathPrefixLength = 4;
+
+class PathFlags {
+private:
+    static constexpr u32 WindowsPathFlag = (1 << 0);
+    static constexpr u32 RelativePathFlag = (1 << 1);
+    static constexpr u32 EmptyPathFlag = (1 << 2);
+    static constexpr u32 MountNameFlag = (1 << 3);
+    static constexpr u32 BackslashFlag = (1 << 4);
+    static constexpr u32 AllCharactersFlag = (1 << 5);
+
+private:
+    u32 m_value;
+
+public:
+    constexpr PathFlags() : m_value(0) { /* ... */
+    }
+
+#define DECLARE_PATH_FLAG_HANDLER(__WHICH__)                                                       \
+    constexpr bool Is##__WHICH__##Allowed() const { return (m_value & __WHICH__##Flag) != 0; }     \
+    constexpr void Allow##__WHICH__() { m_value |= __WHICH__##Flag; }
+
+    DECLARE_PATH_FLAG_HANDLER(WindowsPath)
+    DECLARE_PATH_FLAG_HANDLER(RelativePath)
+    DECLARE_PATH_FLAG_HANDLER(EmptyPath)
+    DECLARE_PATH_FLAG_HANDLER(MountName)
+    DECLARE_PATH_FLAG_HANDLER(Backslash)
+    DECLARE_PATH_FLAG_HANDLER(AllCharacters)
+
+#undef DECLARE_PATH_FLAG_HANDLER
+};
+
+template <typename T>
+    requires(std::same_as<T, char> || std::same_as<T, wchar_t>)
+constexpr inline bool IsDosDevicePath(const T* path) {
+    ASSERT(path != nullptr);
+
+    using namespace StringTraits;
+
+    return path[0] == AlternateDirectorySeparator && path[1] == AlternateDirectorySeparator &&
+           (path[2] == Dot || path[2] == '?') &&
+           (path[3] == DirectorySeparator || path[3] == AlternateDirectorySeparator);
+}
+
+template <typename T>
+    requires(std::same_as<T, char> || std::same_as<T, wchar_t>)
+constexpr inline bool IsUncPath(const T* path, bool allow_forward_slash = true,
+                                bool allow_back_slash = true) {
+    ASSERT(path != nullptr);
+
+    using namespace StringTraits;
+
+    return (allow_forward_slash && path[0] == DirectorySeparator &&
+            path[1] == DirectorySeparator) ||
+           (allow_back_slash && path[0] == AlternateDirectorySeparator &&
+            path[1] == AlternateDirectorySeparator);
+}
+
+constexpr inline bool IsWindowsDrive(const char* path) {
+    ASSERT(path != nullptr);
+
+    return (('a' <= path[0] && path[0] <= 'z') || ('A' <= path[0] && path[0] <= 'Z')) &&
+           path[1] == StringTraits::DriveSeparator;
+}
+
+constexpr inline bool IsWindowsPath(const char* path, bool allow_forward_slash_unc) {
+    return IsWindowsDrive(path) || IsDosDevicePath(path) ||
+           IsUncPath(path, allow_forward_slash_unc, true);
+}
+
+constexpr inline int GetWindowsSkipLength(const char* path) {
+    if (IsDosDevicePath(path)) {
+        return DosDevicePathPrefixLength;
+    } else if (IsWindowsDrive(path)) {
+        return WindowsDriveLength;
+    } else if (IsUncPath(path)) {
+        return UncPathPrefixLength;
+    } else {
+        return 0;
+    }
+}
+
+constexpr inline bool IsPathAbsolute(const char* path) {
+    return IsWindowsPath(path, false) || path[0] == StringTraits::DirectorySeparator;
+}
+
+constexpr inline bool IsPathRelative(const char* path) {
+    return path[0] && !IsPathAbsolute(path);
+}
+
+constexpr inline bool IsCurrentDirectory(const char* path) {
+    return path[0] == StringTraits::Dot &&
+           (path[1] == StringTraits::NullTerminator || path[1] == StringTraits::DirectorySeparator);
+}
+
+constexpr inline bool IsParentDirectory(const char* path) {
+    return path[0] == StringTraits::Dot && path[1] == StringTraits::Dot &&
+           (path[2] == StringTraits::NullTerminator || path[2] == StringTraits::DirectorySeparator);
+}
+
+constexpr inline bool IsPathStartWithCurrentDirectory(const char* path) {
+    return IsCurrentDirectory(path) || IsParentDirectory(path);
+}
+
+constexpr inline bool IsSubPath(const char* lhs, const char* rhs) {
+    /* Check pre-conditions. */
+    ASSERT(lhs != nullptr);
+    ASSERT(rhs != nullptr);
+
+    /* Import StringTraits names for current scope. */
+    using namespace StringTraits;
+
+    /* Special case certain paths. */
+    if (IsUncPath(lhs) && !IsUncPath(rhs)) {
+        return false;
+    }
+    if (!IsUncPath(lhs) && IsUncPath(rhs)) {
+        return false;
+    }
+
+    if (lhs[0] == DirectorySeparator && lhs[1] == NullTerminator && rhs[0] == DirectorySeparator &&
+        rhs[1] != NullTerminator) {
+        return true;
+    }
+    if (rhs[0] == DirectorySeparator && rhs[1] == NullTerminator && lhs[0] == DirectorySeparator &&
+        lhs[1] != NullTerminator) {
+        return true;
+    }
+
+    /* Check subpath. */
+    for (size_t i = 0; /* ... */; ++i) {
+        if (lhs[i] == NullTerminator) {
+            return rhs[i] == DirectorySeparator;
+        } else if (rhs[i] == NullTerminator) {
+            return lhs[i] == DirectorySeparator;
+        } else if (lhs[i] != rhs[i]) {
+            return false;
+        }
+    }
+}
+
+/* Path utilities. */
+constexpr inline void Replace(char* dst, size_t dst_size, char old_char, char new_char) {
+    ASSERT(dst != nullptr);
+    for (char* cur = dst; cur < dst + dst_size && *cur; ++cur) {
+        if (*cur == old_char) {
+            *cur = new_char;
+        }
+    }
+}
+
+constexpr inline Result CheckUtf8(const char* s) {
+    /* Check pre-conditions. */
+    ASSERT(s != nullptr);
+
+    /* Iterate, checking for utf8-validity. */
+    while (*s) {
+        char utf8_buf[4] = {};
+
+        const auto pick_res = PickOutCharacterFromUtf8String(utf8_buf, std::addressof(s));
+        R_UNLESS(pick_res == CharacterEncodingResult_Success, ResultInvalidPathFormat);
+
+        u32 dummy;
+        const auto cvt_res = ConvertCharacterUtf8ToUtf32(std::addressof(dummy), utf8_buf);
+        R_UNLESS(cvt_res == CharacterEncodingResult_Success, ResultInvalidPathFormat);
+    }
+
+    R_SUCCEED();
+}
+
+/* Path formatting. */
+class PathNormalizer {
+private:
+    enum class PathState {
+        Start,
+        Normal,
+        FirstSeparator,
+        Separator,
+        CurrentDir,
+        ParentDir,
+    };
+
+private:
+    static constexpr void ReplaceParentDirectoryPath(char* dst, const char* src) {
+        /* Use StringTraits names for remainder of scope. */
+        using namespace StringTraits;
+
+        /* Start with a dir-separator. */
+        dst[0] = DirectorySeparator;
+
+        auto i = 1;
+        while (src[i] != NullTerminator) {
+            if ((src[i - 1] == DirectorySeparator || src[i - 1] == AlternateDirectorySeparator) &&
+                src[i + 0] == Dot && src[i + 1] == Dot &&
+                (src[i + 2] == DirectorySeparator || src[i + 2] == AlternateDirectorySeparator)) {
+                dst[i - 1] = DirectorySeparator;
+                dst[i + 0] = Dot;
+                dst[i + 1] = Dot;
+                dst[i + 2] = DirectorySeparator;
+                i += 3;
+            } else {
+                if (src[i - 1] == AlternateDirectorySeparator && src[i + 0] == Dot &&
+                    src[i + 1] == Dot && src[i + 2] == NullTerminator) {
+                    dst[i - 1] = DirectorySeparator;
+                    dst[i + 0] = Dot;
+                    dst[i + 1] = Dot;
+                    i += 2;
+                    break;
+                }
+
+                dst[i] = src[i];
+                ++i;
+            }
+        }
+
+        dst[i] = StringTraits::NullTerminator;
+    }
+
+public:
+    static constexpr bool IsParentDirectoryPathReplacementNeeded(const char* path) {
+        /* Use StringTraits names for remainder of scope. */
+        using namespace StringTraits;
+
+        if (path[0] != DirectorySeparator && path[0] != AlternateDirectorySeparator) {
+            return false;
+        }
+
+        /* Check to find a parent reference using alternate separators. */
+        if (path[0] != NullTerminator && path[1] != NullTerminator && path[2] != NullTerminator) {
+            size_t i;
+            for (i = 0; path[i + 3] != NullTerminator; ++path) {
+                if (path[i + 1] != Dot || path[i + 2] != Dot) {
+                    continue;
+                }
+
+                const char c0 = path[i + 0];
+                const char c3 = path[i + 3];
+
+                if (c0 == AlternateDirectorySeparator &&
+                    (c3 == DirectorySeparator || c3 == AlternateDirectorySeparator ||
+                     c3 == NullTerminator)) {
+                    return true;
+                }
+
+                if (c3 == AlternateDirectorySeparator &&
+                    (c0 == DirectorySeparator || c0 == AlternateDirectorySeparator)) {
+                    return true;
+                }
+            }
+
+            if (path[i + 0] == AlternateDirectorySeparator && path[i + 1] == Dot &&
+                path[i + 2] == Dot /* && path[i + 3] == NullTerminator */) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    static constexpr Result IsNormalized(bool* out, size_t* out_len, const char* path,
+                                         bool allow_all_characters = false) {
+        /* Use StringTraits names for remainder of scope. */
+        using namespace StringTraits;
+
+        /* Parse the path. */
+        auto state = PathState::Start;
+        size_t len = 0;
+        while (path[len] != NullTerminator) {
+            /* Get the current character. */
+            const char c = path[len++];
+
+            /* Check the current character is valid. */
+            if (!allow_all_characters && state != PathState::Start) {
+                R_UNLESS(!IsInvalidCharacter(c), ResultInvalidCharacter);
+            }
+
+            /* Process depending on current state. */
+            switch (state) {
+                /* Import the PathState enums for convenience. */
+                using enum PathState;
+
+            case Start:
+                R_UNLESS(c == DirectorySeparator, ResultInvalidPathFormat);
+                state = FirstSeparator;
+                break;
+            case Normal:
+                if (c == DirectorySeparator) {
+                    state = Separator;
+                }
+                break;
+            case FirstSeparator:
+            case Separator:
+                if (c == DirectorySeparator) {
+                    *out = false;
+                    R_SUCCEED();
+                }
+
+                if (c == Dot) {
+                    state = CurrentDir;
+                } else {
+                    state = Normal;
+                }
+                break;
+            case CurrentDir:
+                if (c == DirectorySeparator) {
+                    *out = false;
+                    R_SUCCEED();
+                }
+
+                if (c == Dot) {
+                    state = ParentDir;
+                } else {
+                    state = Normal;
+                }
+                break;
+            case ParentDir:
+                if (c == DirectorySeparator) {
+                    *out = false;
+                    R_SUCCEED();
+                }
+
+                state = Normal;
+                break;
+            default:
+                UNREACHABLE();
+                break;
+            }
+        }
+
+        /* Check the final state. */
+        switch (state) {
+            /* Import the PathState enums for convenience. */
+            using enum PathState;
+        case Start:
+            R_THROW(ResultInvalidPathFormat);
+        case Normal:
+        case FirstSeparator:
+            *out = true;
+            break;
+        case Separator:
+        case CurrentDir:
+        case ParentDir:
+            *out = false;
+            break;
+        default:
+            UNREACHABLE();
+            break;
+        }
+
+        /* Set the output length. */
+        *out_len = len;
+        R_SUCCEED();
+    }
+
+    static Result Normalize(char* dst, size_t* out_len, const char* path, size_t max_out_size,
+                            bool is_windows_path, bool is_drive_relative_path,
+                            bool allow_all_characters = false) {
+        /* Use StringTraits names for remainder of scope. */
+        using namespace StringTraits;
+
+        /* Prepare to iterate. */
+        const char* cur_path = path;
+        size_t total_len = 0;
+
+        /* If path begins with a separator, check that we're not drive relative. */
+        if (cur_path[0] != DirectorySeparator) {
+            R_UNLESS(is_drive_relative_path, ResultInvalidPathFormat);
+
+            dst[total_len++] = DirectorySeparator;
+        }
+
+        /* We're going to need to do path replacement, potentially. */
+        char* replacement_path = nullptr;
+        size_t replacement_path_size = 0;
+
+        SCOPE_EXIT({
+            if (replacement_path != nullptr) {
+                if (std::is_constant_evaluated()) {
+                    delete[] replacement_path;
+                } else {
+                    Deallocate(replacement_path, replacement_path_size);
+                }
+            }
+        });
+
+        /* Perform path replacement, if necessary. */
+        if (IsParentDirectoryPathReplacementNeeded(cur_path)) {
+            if (std::is_constant_evaluated()) {
+                replacement_path_size = EntryNameLengthMax + 1;
+                replacement_path = new char[replacement_path_size];
+            } else {
+                replacement_path_size = EntryNameLengthMax + 1;
+                replacement_path = static_cast<char*>(Allocate(replacement_path_size));
+            }
+
+            ReplaceParentDirectoryPath(replacement_path, cur_path);
+
+            cur_path = replacement_path;
+        }
+
+        /* Iterate, normalizing path components. */
+        bool skip_next_sep = false;
+        size_t i = 0;
+
+        while (cur_path[i] != NullTerminator) {
+            /* Process a directory separator, if we run into one. */
+            if (cur_path[i] == DirectorySeparator) {
+                /* Swallow separators. */
+                do {
+                    ++i;
+                } while (cur_path[i] == DirectorySeparator);
+
+                /* Check if we hit end of string. */
+                if (cur_path[i] == NullTerminator) {
+                    break;
+                }
+
+                /* If we aren't skipping the separator, write it, checking that we remain in bounds.
+                 */
+                if (!skip_next_sep) {
+                    if (total_len + 1 == max_out_size) {
+                        dst[total_len] = NullTerminator;
+                        *out_len = total_len;
+                        R_THROW(ResultTooLongPath);
+                    }
+
+                    dst[total_len++] = DirectorySeparator;
+                }
+
+                /* Don't skip the next separator. */
+                skip_next_sep = false;
+            }
+
+            /* Get the length of the current directory component. */
+            size_t dir_len = 0;
+            while (cur_path[i + dir_len] != DirectorySeparator &&
+                   cur_path[i + dir_len] != NullTerminator) {
+                /* Check for validity. */
+                if (!allow_all_characters) {
+                    R_UNLESS(!IsInvalidCharacter(cur_path[i + dir_len]), ResultInvalidCharacter);
+                }
+
+                ++dir_len;
+            }
+
+            /* Handle the current dir component. */
+            if (IsCurrentDirectory(cur_path + i)) {
+                skip_next_sep = true;
+            } else if (IsParentDirectory(cur_path + i)) {
+                /* We should have just written a separator. */
+                ASSERT(dst[total_len - 1] == DirectorySeparator);
+
+                /* We should have started with a separator, for non-windows paths. */
+                if (!is_windows_path) {
+                    ASSERT(dst[0] == DirectorySeparator);
+                }
+
+                /* Remove the previous component. */
+                if (total_len == 1) {
+                    R_UNLESS(is_windows_path, ResultDirectoryUnobtainable);
+
+                    --total_len;
+                } else {
+                    total_len -= 2;
+
+                    do {
+                        if (dst[total_len] == DirectorySeparator) {
+                            break;
+                        }
+                    } while ((--total_len) != 0);
+                }
+
+                /* We should be pointing to a directory separator, for non-windows paths. */
+                if (!is_windows_path) {
+                    ASSERT(dst[total_len] == DirectorySeparator);
+                }
+
+                /* We should remain in bounds. */
+                ASSERT(total_len < max_out_size);
+            } else {
+                /* Copy, possibly truncating. */
+                if (total_len + dir_len + 1 > max_out_size) {
+                    const size_t copy_len = max_out_size - (total_len + 1);
+
+                    for (size_t j = 0; j < copy_len; ++j) {
+                        dst[total_len++] = cur_path[i + j];
+                    }
+
+                    dst[total_len] = NullTerminator;
+                    *out_len = total_len;
+                    R_THROW(ResultTooLongPath);
+                }
+
+                for (size_t j = 0; j < dir_len; ++j) {
+                    dst[total_len++] = cur_path[i + j];
+                }
+            }
+
+            /* Advance past the current directory component. */
+            i += dir_len;
+        }
+
+        if (skip_next_sep) {
+            --total_len;
+        }
+
+        if (total_len == 0 && max_out_size != 0) {
+            total_len = 1;
+            dst[0] = DirectorySeparator;
+        }
+
+        /* NOTE: Probable nintendo bug, as max_out_size must be at least total_len + 1 for the null
+         * terminator. */
+        R_UNLESS(max_out_size >= total_len - 1, ResultTooLongPath);
+
+        dst[total_len] = NullTerminator;
+
+        /* Check that the result path is normalized. */
+        bool is_normalized;
+        size_t dummy;
+        R_TRY(IsNormalized(std::addressof(is_normalized), std::addressof(dummy), dst,
+                           allow_all_characters));
+
+        /* Assert that the result path is normalized. */
+        ASSERT(is_normalized);
+
+        /* Set the output length. */
+        *out_len = total_len;
+        R_SUCCEED();
+    }
+};
+
+class PathFormatter {
+private:
+    static constexpr Result CheckSharedName(const char* name, size_t len) {
+        /* Use StringTraits names for remainder of scope. */
+        using namespace StringTraits;
+
+        if (len == 1) {
+            R_UNLESS(name[0] != Dot, ResultInvalidPathFormat);
+        } else if (len == 2) {
+            R_UNLESS(name[0] != Dot || name[1] != Dot, ResultInvalidPathFormat);
+        }
+
+        for (size_t i = 0; i < len; ++i) {
+            R_UNLESS(!IsInvalidCharacter(name[i]), ResultInvalidCharacter);
+        }
+
+        R_SUCCEED();
+    }
+
+    static constexpr Result CheckHostName(const char* name, size_t len) {
+        /* Use StringTraits names for remainder of scope. */
+        using namespace StringTraits;
+
+        if (len == 2) {
+            R_UNLESS(name[0] != Dot || name[1] != Dot, ResultInvalidPathFormat);
+        }
+
+        for (size_t i = 0; i < len; ++i) {
+            R_UNLESS(!IsInvalidCharacterForHostName(name[i]), ResultInvalidCharacter);
+        }
+
+        R_SUCCEED();
+    }
+
+    static constexpr Result CheckInvalidBackslash(bool* out_contains_backslash, const char* path,
+                                                  bool allow_backslash) {
+        /* Use StringTraits names for remainder of scope. */
+        using namespace StringTraits;
+
+        /* Default to no backslashes, so we can just write if we see one. */
+        *out_contains_backslash = false;
+
+        while (*path != NullTerminator) {
+            if (*(path++) == AlternateDirectorySeparator) {
+                *out_contains_backslash = true;
+
+                R_UNLESS(allow_backslash, ResultInvalidCharacter);
+            }
+        }
+
+        R_SUCCEED();
+    }
+
+public:
+    static constexpr Result CheckPathFormat(const char* path, const PathFlags& flags) {
+        bool normalized;
+        size_t len;
+        R_RETURN(IsNormalized(std::addressof(normalized), std::addressof(len), path, flags));
+    }
+
+    static constexpr Result SkipMountName(const char** out, size_t* out_len, const char* path) {
+        R_RETURN(ParseMountName(out, out_len, nullptr, 0, path));
+    }
+
+    static constexpr Result ParseMountName(const char** out, size_t* out_len, char* out_mount_name,
+                                           size_t out_mount_name_buffer_size, const char* path) {
+        /* Check pre-conditions. */
+        ASSERT(path != nullptr);
+        ASSERT(out_len != nullptr);
+        ASSERT(out != nullptr);
+        ASSERT((out_mount_name == nullptr) == (out_mount_name_buffer_size == 0));
+
+        /* Use StringTraits names for remainder of scope. */
+        using namespace StringTraits;
+
+        /* Determine max mount length. */
+        const auto max_mount_len =
+            out_mount_name_buffer_size == 0
+                ? MountNameLengthMax + 1
+                : std::min(MountNameLengthMax + 1, out_mount_name_buffer_size);
+
+        /* Parse the path until we see a drive separator. */
+        size_t mount_len = 0;
+        for (/* ... */; mount_len < max_mount_len && path[mount_len]; ++mount_len) {
+            const char c = path[mount_len];
+
+            /* If we see a drive separator, advance, then we're done with the pre-drive separator
+             * part of the mount. */
+            if (c == DriveSeparator) {
+                ++mount_len;
+                break;
+            }
+
+            /* If we see a directory separator, we're not in a mount name. */
+            if (c == DirectorySeparator || c == AlternateDirectorySeparator) {
+                *out = path;
+                *out_len = 0;
+                R_SUCCEED();
+            }
+        }
+
+        /* Check to be sure we're actually looking at a mount name. */
+        if (mount_len <= 2 || path[mount_len - 1] != DriveSeparator) {
+            *out = path;
+            *out_len = 0;
+            R_SUCCEED();
+        }
+
+        /* Check that all characters in the mount name are allowable. */
+        for (size_t i = 0; i < mount_len; ++i) {
+            R_UNLESS(!IsInvalidCharacterForMountName(path[i]), ResultInvalidCharacter);
+        }
+
+        /* Copy out the mount name. */
+        if (out_mount_name_buffer_size > 0) {
+            R_UNLESS(mount_len < out_mount_name_buffer_size, ResultTooLongPath);
+
+            for (size_t i = 0; i < mount_len; ++i) {
+                out_mount_name[i] = path[i];
+            }
+            out_mount_name[mount_len] = NullTerminator;
+        }
+
+        /* Set the output. */
+        *out = path + mount_len;
+        *out_len = mount_len;
+        R_SUCCEED();
+    }
+
+    static constexpr Result SkipRelativeDotPath(const char** out, size_t* out_len,
+                                                const char* path) {
+        R_RETURN(ParseRelativeDotPath(out, out_len, nullptr, 0, path));
+    }
+
+    static constexpr Result ParseRelativeDotPath(const char** out, size_t* out_len,
+                                                 char* out_relative,
+                                                 size_t out_relative_buffer_size,
+                                                 const char* path) {
+        /* Check pre-conditions. */
+        ASSERT(path != nullptr);
+        ASSERT(out_len != nullptr);
+        ASSERT(out != nullptr);
+        ASSERT((out_relative == nullptr) == (out_relative_buffer_size == 0));
+
+        /* Use StringTraits names for remainder of scope. */
+        using namespace StringTraits;
+
+        /* Initialize the output buffer, if we have one. */
+        if (out_relative_buffer_size > 0) {
+            out_relative[0] = NullTerminator;
+        }
+
+        /* Check if the path is relative. */
+        if (path[0] == Dot && (path[1] == NullTerminator || path[1] == DirectorySeparator ||
+                               path[1] == AlternateDirectorySeparator)) {
+            if (out_relative_buffer_size > 0) {
+                R_UNLESS(out_relative_buffer_size >= 2, ResultTooLongPath);
+
+                out_relative[0] = Dot;
+                out_relative[1] = NullTerminator;
+            }
+
+            *out = path + 1;
+            *out_len = 1;
+            R_SUCCEED();
+        }
+
+        /* Ensure the path isn't a parent directory. */
+        R_UNLESS(!(path[0] == Dot && path[1] == Dot), ResultDirectoryUnobtainable);
+
+        /* There was no relative dot path. */
+        *out = path;
+        *out_len = 0;
+        R_SUCCEED();
+    }
+
+    static constexpr Result SkipWindowsPath(const char** out, size_t* out_len, bool* out_normalized,
+                                            const char* path, bool has_mount_name) {
+        /* We're normalized if and only if the parsing doesn't throw ResultNotNormalized(). */
+        *out_normalized = true;
+
+        R_TRY_CATCH(ParseWindowsPath(out, out_len, nullptr, 0, path, has_mount_name)) {
+            R_CATCH(ResultNotNormalized) {
+                *out_normalized = false;
+            }
+        }
+        R_END_TRY_CATCH;
+        ON_RESULT_INCLUDED(ResultNotNormalized) {
+            *out_normalized = false;
+        };
+
+        R_SUCCEED();
+    }
+
+    static constexpr Result ParseWindowsPath(const char** out, size_t* out_len, char* out_win,
+                                             size_t out_win_buffer_size, const char* path,
+                                             bool has_mount_name) {
+        /* Check pre-conditions. */
+        ASSERT(path != nullptr);
+        ASSERT(out_len != nullptr);
+        ASSERT(out != nullptr);
+        ASSERT((out_win == nullptr) == (out_win_buffer_size == 0));
+
+        /* Use StringTraits names for remainder of scope. */
+        using namespace StringTraits;
+
+        /* Initialize the output buffer, if we have one. */
+        if (out_win_buffer_size > 0) {
+            out_win[0] = NullTerminator;
+        }
+
+        /* Handle path start. */
+        const char* cur_path = path;
+        if (has_mount_name && path[0] == DirectorySeparator) {
+            if (path[1] == AlternateDirectorySeparator && path[2] == AlternateDirectorySeparator) {
+                R_UNLESS(out_win_buffer_size > 0, ResultNotNormalized);
+
+                ++cur_path;
+            } else if (IsWindowsDrive(path + 1)) {
+                R_UNLESS(out_win_buffer_size > 0, ResultNotNormalized);
+
+                ++cur_path;
+            }
+        }
+
+        /* Handle windows drive. */
+        if (IsWindowsDrive(cur_path)) {
+            /* Parse up to separator. */
+            size_t win_path_len = WindowsDriveLength;
+            for (/* ... */; cur_path[win_path_len] != NullTerminator; ++win_path_len) {
+                R_UNLESS(!IsInvalidCharacter(cur_path[win_path_len]), ResultInvalidCharacter);
+
+                if (cur_path[win_path_len] == DirectorySeparator ||
+                    cur_path[win_path_len] == AlternateDirectorySeparator) {
+                    break;
+                }
+            }
+
+            /* Ensure that we're normalized, if we're required to be. */
+            if (out_win_buffer_size == 0) {
+                for (size_t i = 0; i < win_path_len; ++i) {
+                    R_UNLESS(cur_path[i] != AlternateDirectorySeparator, ResultNotNormalized);
+                }
+            } else {
+                /* Ensure we can copy into the normalized buffer. */
+                R_UNLESS(win_path_len < out_win_buffer_size, ResultTooLongPath);
+
+                for (size_t i = 0; i < win_path_len; ++i) {
+                    out_win[i] = cur_path[i];
+                }
+                out_win[win_path_len] = NullTerminator;
+
+                Replace(out_win, win_path_len, AlternateDirectorySeparator, DirectorySeparator);
+            }
+
+            *out = cur_path + win_path_len;
+            *out_len = win_path_len;
+            R_SUCCEED();
+        }
+
+        /* Handle DOS device. */
+        if (IsDosDevicePath(cur_path)) {
+            size_t dos_prefix_len = DosDevicePathPrefixLength;
+
+            if (IsWindowsDrive(cur_path + dos_prefix_len)) {
+                dos_prefix_len += WindowsDriveLength;
+            } else {
+                --dos_prefix_len;
+            }
+
+            if (out_win_buffer_size > 0) {
+                /* Ensure we can copy into the normalized buffer. */
+                R_UNLESS(dos_prefix_len < out_win_buffer_size, ResultTooLongPath);
+
+                for (size_t i = 0; i < dos_prefix_len; ++i) {
+                    out_win[i] = cur_path[i];
+                }
+                out_win[dos_prefix_len] = NullTerminator;
+
+                Replace(out_win, dos_prefix_len, DirectorySeparator, AlternateDirectorySeparator);
+            }
+
+            *out = cur_path + dos_prefix_len;
+            *out_len = dos_prefix_len;
+            R_SUCCEED();
+        }
+
+        /* Handle UNC path. */
+        if (IsUncPath(cur_path, false, true)) {
+            const char* final_path = cur_path;
+
+            R_UNLESS(cur_path[UncPathPrefixLength] != DirectorySeparator, ResultInvalidPathFormat);
+            R_UNLESS(cur_path[UncPathPrefixLength] != AlternateDirectorySeparator,
+                     ResultInvalidPathFormat);
+
+            size_t cur_component_offset = 0;
+            size_t pos = UncPathPrefixLength;
+            for (/* ... */; cur_path[pos] != NullTerminator; ++pos) {
+                if (cur_path[pos] == DirectorySeparator ||
+                    cur_path[pos] == AlternateDirectorySeparator) {
+                    if (cur_component_offset != 0) {
+                        R_TRY(CheckSharedName(cur_path + cur_component_offset,
+                                              pos - cur_component_offset));
+
+                        final_path = cur_path + pos;
+                        break;
+                    }
+
+                    R_UNLESS(cur_path[pos + 1] != DirectorySeparator, ResultInvalidPathFormat);
+                    R_UNLESS(cur_path[pos + 1] != AlternateDirectorySeparator,
+                             ResultInvalidPathFormat);
+
+                    R_TRY(CheckHostName(cur_path + 2, pos - 2));
+
+                    cur_component_offset = pos + 1;
+                }
+            }
+
+            R_UNLESS(cur_component_offset != pos, ResultInvalidPathFormat);
+
+            if (cur_component_offset != 0 && final_path == cur_path) {
+                R_TRY(CheckSharedName(cur_path + cur_component_offset, pos - cur_component_offset));
+
+                final_path = cur_path + pos;
+            }
+
+            size_t unc_prefix_len = final_path - cur_path;
+
+            /* Ensure that we're normalized, if we're required to be. */
+            if (out_win_buffer_size == 0) {
+                for (size_t i = 0; i < unc_prefix_len; ++i) {
+                    R_UNLESS(cur_path[i] != DirectorySeparator, ResultNotNormalized);
+                }
+            } else {
+                /* Ensure we can copy into the normalized buffer. */
+                R_UNLESS(unc_prefix_len < out_win_buffer_size, ResultTooLongPath);
+
+                for (size_t i = 0; i < unc_prefix_len; ++i) {
+                    out_win[i] = cur_path[i];
+                }
+                out_win[unc_prefix_len] = NullTerminator;
+
+                Replace(out_win, unc_prefix_len, DirectorySeparator, AlternateDirectorySeparator);
+            }
+
+            *out = cur_path + unc_prefix_len;
+            *out_len = unc_prefix_len;
+            R_SUCCEED();
+        }
+
+        /* There's no windows path to parse. */
+        *out = path;
+        *out_len = 0;
+        R_SUCCEED();
+    }
+
+    static constexpr Result IsNormalized(bool* out, size_t* out_len, const char* path,
+                                         const PathFlags& flags = {}) {
+        /* Ensure nothing is null. */
+        R_UNLESS(out != nullptr, ResultNullptrArgument);
+        R_UNLESS(out_len != nullptr, ResultNullptrArgument);
+        R_UNLESS(path != nullptr, ResultNullptrArgument);
+
+        /* Verify that the path is valid utf-8. */
+        R_TRY(CheckUtf8(path));
+
+        /* Use StringTraits names for remainder of scope. */
+        using namespace StringTraits;
+
+        /* Handle the case where the path is empty. */
+        if (path[0] == NullTerminator) {
+            R_UNLESS(flags.IsEmptyPathAllowed(), ResultInvalidPathFormat);
+
+            *out = true;
+            *out_len = 0;
+            R_SUCCEED();
+        }
+
+        /* All normalized paths start with a directory separator...unless they're windows paths,
+         * relative paths, or have mount names. */
+        if (path[0] != DirectorySeparator) {
+            R_UNLESS(flags.IsWindowsPathAllowed() || flags.IsRelativePathAllowed() ||
+                         flags.IsMountNameAllowed(),
+                     ResultInvalidPathFormat);
+        }
+
+        /* Check that the path is allowed to be a windows path, if it is. */
+        if (IsWindowsPath(path, false)) {
+            R_UNLESS(flags.IsWindowsPathAllowed(), ResultInvalidPathFormat);
+        }
+
+        /* Skip past the mount name, if one is present. */
+        size_t total_len = 0;
+        size_t mount_name_len = 0;
+        R_TRY(SkipMountName(std::addressof(path), std::addressof(mount_name_len), path));
+
+        /* If we had a mount name, check that that was allowed. */
+        if (mount_name_len > 0) {
+            R_UNLESS(flags.IsMountNameAllowed(), ResultInvalidPathFormat);
+
+            total_len += mount_name_len;
+        }
+
+        /* Check that the path starts as a normalized path should. */
+        if (path[0] != DirectorySeparator && !IsPathStartWithCurrentDirectory(path) &&
+            !IsWindowsPath(path, false)) {
+            R_UNLESS(flags.IsRelativePathAllowed(), ResultInvalidPathFormat);
+            R_UNLESS(!IsInvalidCharacter(path[0]), ResultInvalidPathFormat);
+
+            *out = false;
+            R_SUCCEED();
+        }
+
+        /* Process relative path. */
+        size_t relative_len = 0;
+        R_TRY(SkipRelativeDotPath(std::addressof(path), std::addressof(relative_len), path));
+
+        /* If we have a relative path, check that was allowed. */
+        if (relative_len > 0) {
+            R_UNLESS(flags.IsRelativePathAllowed(), ResultInvalidPathFormat);
+
+            total_len += relative_len;
+
+            if (path[0] == NullTerminator) {
+                *out = true;
+                *out_len = total_len;
+                R_SUCCEED();
+            }
+        }
+
+        /* Process windows path. */
+        size_t windows_len = 0;
+        bool normalized_win = false;
+        R_TRY(SkipWindowsPath(std::addressof(path), std::addressof(windows_len),
+                              std::addressof(normalized_win), path, mount_name_len > 0));
+
+        /* If the windows path wasn't normalized, we're not normalized. */
+        if (!normalized_win) {
+            R_UNLESS(flags.IsWindowsPathAllowed(), ResultInvalidPathFormat);
+
+            *out = false;
+            R_SUCCEED();
+        }
+
+        /* If we had a windows path, check that was allowed. */
+        if (windows_len > 0) {
+            R_UNLESS(flags.IsWindowsPathAllowed(), ResultInvalidPathFormat);
+
+            total_len += windows_len;
+
+            /* We can't have both a relative path and a windows path. */
+            R_UNLESS(relative_len == 0, ResultInvalidPathFormat);
+
+            /* A path ending in a windows path isn't normalized. */
+            if (path[0] == NullTerminator) {
+                *out = false;
+                R_SUCCEED();
+            }
+
+            /* Check that there are no windows directory separators in the path. */
+            for (size_t i = 0; path[i] != NullTerminator; ++i) {
+                if (path[i] == AlternateDirectorySeparator) {
+                    *out = false;
+                    R_SUCCEED();
+                }
+            }
+        }
+
+        /* Check that parent directory replacement is not needed if backslashes are allowed. */
+        if (flags.IsBackslashAllowed() &&
+            PathNormalizer::IsParentDirectoryPathReplacementNeeded(path)) {
+            *out = false;
+            R_SUCCEED();
+        }
+
+        /* Check that the backslash state is valid. */
+        bool is_backslash_contained = false;
+        R_TRY(CheckInvalidBackslash(std::addressof(is_backslash_contained), path,
+                                    flags.IsWindowsPathAllowed() || flags.IsBackslashAllowed()));
+
+        /* Check that backslashes are contained only if allowed. */
+        if (is_backslash_contained && !flags.IsBackslashAllowed()) {
+            *out = false;
+            R_SUCCEED();
+        }
+
+        /* Check that the final result path is normalized. */
+        size_t normal_len = 0;
+        R_TRY(PathNormalizer::IsNormalized(out, std::addressof(normal_len), path,
+                                           flags.IsAllCharactersAllowed()));
+
+        /* Add the normal length. */
+        total_len += normal_len;
+
+        /* Set the output length. */
+        *out_len = total_len;
+        R_SUCCEED();
+    }
+
+    static Result Normalize(char* dst, size_t dst_size, const char* path, size_t path_len,
+                            const PathFlags& flags) {
+        /* Use StringTraits names for remainder of scope. */
+        using namespace StringTraits;
+
+        /* Prepare to iterate. */
+        const char* src = path;
+        size_t cur_pos = 0;
+        bool is_windows_path = false;
+
+        /* Check if the path is empty. */
+        if (src[0] == NullTerminator) {
+            if (dst_size != 0) {
+                dst[0] = NullTerminator;
+            }
+
+            R_UNLESS(flags.IsEmptyPathAllowed(), ResultInvalidPathFormat);
+
+            R_SUCCEED();
+        }
+
+        /* Handle a mount name. */
+        size_t mount_name_len = 0;
+        if (flags.IsMountNameAllowed()) {
+            R_TRY(ParseMountName(std::addressof(src), std::addressof(mount_name_len), dst + cur_pos,
+                                 dst_size - cur_pos, src));
+
+            cur_pos += mount_name_len;
+        }
+
+        /* Handle a drive-relative prefix. */
+        bool is_drive_relative = false;
+        if (src[0] != DirectorySeparator && !IsPathStartWithCurrentDirectory(src) &&
+            !IsWindowsPath(src, false)) {
+            R_UNLESS(flags.IsRelativePathAllowed(), ResultInvalidPathFormat);
+            R_UNLESS(!IsInvalidCharacter(src[0]), ResultInvalidPathFormat);
+
+            dst[cur_pos++] = Dot;
+            is_drive_relative = true;
+        }
+
+        size_t relative_len = 0;
+        if (flags.IsRelativePathAllowed()) {
+            R_UNLESS(cur_pos < dst_size, ResultTooLongPath);
+
+            R_TRY(ParseRelativeDotPath(std::addressof(src), std::addressof(relative_len),
+                                       dst + cur_pos, dst_size - cur_pos, src));
+
+            cur_pos += relative_len;
+
+            if (src[0] == NullTerminator) {
+                R_UNLESS(cur_pos < dst_size, ResultTooLongPath);
+
+                dst[cur_pos] = NullTerminator;
+                R_SUCCEED();
+            }
+        }
+
+        /* Handle a windows path. */
+        if (flags.IsWindowsPathAllowed()) {
+            const char* const orig = src;
+
+            R_UNLESS(cur_pos < dst_size, ResultTooLongPath);
+
+            size_t windows_len = 0;
+            R_TRY(ParseWindowsPath(std::addressof(src), std::addressof(windows_len), dst + cur_pos,
+                                   dst_size - cur_pos, src, mount_name_len != 0));
+
+            cur_pos += windows_len;
+
+            if (src[0] == NullTerminator) {
+                /* NOTE: Bug in original code here repeated, should be checking cur_pos + 2. */
+                R_UNLESS(cur_pos + 1 < dst_size, ResultTooLongPath);
+
+                dst[cur_pos + 0] = DirectorySeparator;
+                dst[cur_pos + 1] = NullTerminator;
+                R_SUCCEED();
+            }
+
+            if ((src - orig) > 0) {
+                is_windows_path = true;
+            }
+        }
+
+        /* Check for invalid backslash. */
+        bool backslash_contained = false;
+        R_TRY(CheckInvalidBackslash(std::addressof(backslash_contained), src,
+                                    flags.IsWindowsPathAllowed() || flags.IsBackslashAllowed()));
+
+        /* Handle backslash replacement as necessary. */
+        if (backslash_contained && flags.IsWindowsPathAllowed()) {
+            /* Create a temporary buffer holding a slash-replaced version of the path. */
+            /* NOTE: Nintendo unnecessarily allocates and replaces here a fully copy of the path,
+             * despite having skipped some of it already. */
+            const size_t replaced_src_len = path_len - (src - path);
+
+            char* replaced_src = nullptr;
+            SCOPE_EXIT({
+                if (replaced_src != nullptr) {
+                    if (std::is_constant_evaluated()) {
+                        delete[] replaced_src;
+                    } else {
+                        Deallocate(replaced_src, replaced_src_len);
+                    }
+                }
+            });
+
+            if (std::is_constant_evaluated()) {
+                replaced_src = new char[replaced_src_len];
+            } else {
+                replaced_src = static_cast<char*>(Allocate(replaced_src_len));
+            }
+
+            Strlcpy<char>(replaced_src, src, replaced_src_len);
+
+            Replace(replaced_src, replaced_src_len, AlternateDirectorySeparator,
+                    DirectorySeparator);
+
+            size_t dummy;
+            R_TRY(PathNormalizer::Normalize(dst + cur_pos, std::addressof(dummy), replaced_src,
+                                            dst_size - cur_pos, is_windows_path, is_drive_relative,
+                                            flags.IsAllCharactersAllowed()));
+        } else {
+            /* We can just do normalization. */
+            size_t dummy;
+            R_TRY(PathNormalizer::Normalize(dst + cur_pos, std::addressof(dummy), src,
+                                            dst_size - cur_pos, is_windows_path, is_drive_relative,
+                                            flags.IsAllCharactersAllowed()));
+        }
+
+        R_SUCCEED();
+    }
+};
+
+} // namespace FileSys

src/core/file_sys/fs_string_util.h

@@ -0,0 +1,241 @@
+// SPDX-FileCopyrightText: Copyright 2023 yuzu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include "common/assert.h"
+
+namespace FileSys {
+
+template <typename T>
+constexpr int Strlen(const T* str) {
+    ASSERT(str != nullptr);
+
+    int length = 0;
+    while (*str++) {
+        ++length;
+    }
+
+    return length;
+}
+
+template <typename T>
+constexpr int Strnlen(const T* str, int count) {
+    ASSERT(str != nullptr);
+    ASSERT(count >= 0);
+
+    int length = 0;
+    while (count-- && *str++) {
+        ++length;
+    }
+
+    return length;
+}
+
+template <typename T>
+constexpr int Strncmp(const T* lhs, const T* rhs, int count) {
+    ASSERT(lhs != nullptr);
+    ASSERT(rhs != nullptr);
+    ASSERT(count >= 0);
+
+    if (count == 0) {
+        return 0;
+    }
+
+    T l, r;
+    do {
+        l = *(lhs++);
+        r = *(rhs++);
+    } while (l && (l == r) && (--count));
+
+    return l - r;
+}
+
+template <typename T>
+static constexpr int Strlcpy(T* dst, const T* src, int count) {
+    ASSERT(dst != nullptr);
+    ASSERT(src != nullptr);
+
+    const T* cur = src;
+    if (count > 0) {
+        while ((--count) && *cur) {
+            *(dst++) = *(cur++);
+        }
+        *dst = 0;
+    }
+
+    while (*cur) {
+        cur++;
+    }
+
+    return static_cast<int>(cur - src);
+}
+
+/* std::size() does not support zero-size C arrays. We're fixing that. */
+template <class C>
+constexpr auto size(const C& c) -> decltype(c.size()) {
+    return std::size(c);
+}
+
+template <class C>
+constexpr std::size_t size(const C& c) {
+    if constexpr (sizeof(C) == 0) {
+        return 0;
+    } else {
+        return std::size(c);
+    }
+}
+
+enum CharacterEncodingResult {
+    CharacterEncodingResult_Success = 0,
+    CharacterEncodingResult_InsufficientLength = 1,
+    CharacterEncodingResult_InvalidFormat = 2,
+};
+
+namespace impl {
+
+class CharacterEncodingHelper {
+public:
+    static constexpr int8_t Utf8NBytesInnerTable[0x100 + 1] = {
+        -1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+        1,  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+        1,  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+        1,  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+        1,  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
+        2,  2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3,
+        3,  3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 6, 6, 7, 8,
+    };
+
+    static constexpr char GetUtf8NBytes(size_t i) {
+        return static_cast<char>(Utf8NBytesInnerTable[1 + i]);
+    }
+};
+
+} // namespace impl
+
+constexpr inline CharacterEncodingResult ConvertCharacterUtf8ToUtf32(u32* dst, const char* src) {
+    /* Check pre-conditions. */
+    ASSERT(dst != nullptr);
+    ASSERT(src != nullptr);
+
+    /* Perform the conversion. */
+    const auto* p = src;
+    switch (impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[0]))) {
+    case 1:
+        *dst = static_cast<u32>(p[0]);
+        return CharacterEncodingResult_Success;
+    case 2:
+        if ((static_cast<u32>(p[0]) & 0x1E) != 0) {
+            if (impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[1])) ==
+                0) {
+                *dst = (static_cast<u32>(p[0] & 0x1F) << 6) | (static_cast<u32>(p[1] & 0x3F) << 0);
+                return CharacterEncodingResult_Success;
+            }
+        }
+        break;
+    case 3:
+        if (impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[1])) == 0 &&
+            impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[2])) == 0) {
+            const u32 c = (static_cast<u32>(p[0] & 0xF) << 12) |
+                          (static_cast<u32>(p[1] & 0x3F) << 6) |
+                          (static_cast<u32>(p[2] & 0x3F) << 0);
+            if ((c & 0xF800) != 0 && (c & 0xF800) != 0xD800) {
+                *dst = c;
+                return CharacterEncodingResult_Success;
+            }
+        }
+        return CharacterEncodingResult_InvalidFormat;
+    case 4:
+        if (impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[1])) == 0 &&
+            impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[2])) == 0 &&
+            impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[3])) == 0) {
+            const u32 c =
+                (static_cast<u32>(p[0] & 0x7) << 18) | (static_cast<u32>(p[1] & 0x3F) << 12) |
+                (static_cast<u32>(p[2] & 0x3F) << 6) | (static_cast<u32>(p[3] & 0x3F) << 0);
+            if (c >= 0x10000 && c < 0x110000) {
+                *dst = c;
+                return CharacterEncodingResult_Success;
+            }
+        }
+        return CharacterEncodingResult_InvalidFormat;
+    default:
+        break;
+    }
+
+    /* We failed to convert. */
+    return CharacterEncodingResult_InvalidFormat;
+}
+
+constexpr inline CharacterEncodingResult PickOutCharacterFromUtf8String(char* dst,
+                                                                        const char** str) {
+    /* Check pre-conditions. */
+    ASSERT(dst != nullptr);
+    ASSERT(str != nullptr);
+    ASSERT(*str != nullptr);
+
+    /* Clear the output. */
+    dst[0] = 0;
+    dst[1] = 0;
+    dst[2] = 0;
+    dst[3] = 0;
+
+    /* Perform the conversion. */
+    const auto* p = *str;
+    u32 c = static_cast<u32>(*p);
+    switch (impl::CharacterEncodingHelper::GetUtf8NBytes(c)) {
+    case 1:
+        dst[0] = (*str)[0];
+        ++(*str);
+        break;
+    case 2:
+        if ((p[0] & 0x1E) != 0) {
+            if (impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[1])) ==
+                0) {
+                c = (static_cast<u32>(p[0] & 0x1F) << 6) | (static_cast<u32>(p[1] & 0x3F) << 0);
+                dst[0] = (*str)[0];
+                dst[1] = (*str)[1];
+                (*str) += 2;
+                break;
+            }
+        }
+        return CharacterEncodingResult_InvalidFormat;
+    case 3:
+        if (impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[1])) == 0 &&
+            impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[2])) == 0) {
+            c = (static_cast<u32>(p[0] & 0xF) << 12) | (static_cast<u32>(p[1] & 0x3F) << 6) |
+                (static_cast<u32>(p[2] & 0x3F) << 0);
+            if ((c & 0xF800) != 0 && (c & 0xF800) != 0xD800) {
+                dst[0] = (*str)[0];
+                dst[1] = (*str)[1];
+                dst[2] = (*str)[2];
+                (*str) += 3;
+                break;
+            }
+        }
+        return CharacterEncodingResult_InvalidFormat;
+    case 4:
+        if (impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[1])) == 0 &&
+            impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[2])) == 0 &&
+            impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[3])) == 0) {
+            c = (static_cast<u32>(p[0] & 0x7) << 18) | (static_cast<u32>(p[1] & 0x3F) << 12) |
+                (static_cast<u32>(p[2] & 0x3F) << 6) | (static_cast<u32>(p[3] & 0x3F) << 0);
+            if (c >= 0x10000 && c < 0x110000) {
+                dst[0] = (*str)[0];
+                dst[1] = (*str)[1];
+                dst[2] = (*str)[2];
+                dst[3] = (*str)[3];
+                (*str) += 4;
+                break;
+            }
+        }
+        return CharacterEncodingResult_InvalidFormat;
+    default:
+        return CharacterEncodingResult_InvalidFormat;
+    }
+
+    return CharacterEncodingResult_Success;
+}
+
+} // namespace FileSys

src/core/hle/service/filesystem/fsp/fs_i_directory.cpp

@@ -1,6 +1,7 @@
 // SPDX-FileCopyrightText: Copyright 2023 yuzu Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
+#include "core/file_sys/fs_filesystem.h"
 #include "core/file_sys/savedata_factory.h"
 #include "core/hle/service/filesystem/fsp/fs_i_directory.h"
 #include "core/hle/service/ipc_helpers.h"

src/core/hle/service/filesystem/fsp/fs_i_directory.h

@@ -3,12 +3,14 @@
 
 #pragma once
 
-#include "core/file_sys/fs_filesystem.h"
 #include "core/file_sys/vfs/vfs.h"
 #include "core/hle/service/filesystem/filesystem.h"
-#include "core/hle/service/filesystem/fsp/fsp_util.h"
 #include "core/hle/service/service.h"
 
+namespace FileSys {
+struct DirectoryEntry;
+}
+
 namespace Service::FileSystem {
 
 class IDirectory final : public ServiceFramework<IDirectory> {