From 77ac2bd47dee84f41810e3f1986dceb66f73ca76 Mon Sep 17 00:00:00 2001
From: Ghabry <gabriel+github@mastergk.de>
Date: Tue, 4 Jun 2024 19:06:00 +0200
Subject: [PATCH] Add a custom buffered filebuf that uses a file descriptor

Implemented for the WiiU because IO through std::filebuf appears to be unbuffered.

But can maybe help on other platforms.

Can be toggled by setting USE_CUSTOM_FILE_READBUF to the prefered buffer size.
---
 src/filesystem_native.cpp | 20 ++++++++-
 src/filesystem_stream.cpp | 86 +++++++++++++++++++++++++++++++++++++++
 src/filesystem_stream.h   | 24 +++++++++++
 src/system.h              |  1 +
 4 files changed, 130 insertions(+), 1 deletion(-)

diff --git a/src/filesystem_native.cpp b/src/filesystem_native.cpp
index b3969f3b2c4..1ae415fcdfd 100644
--- a/src/filesystem_native.cpp
+++ b/src/filesystem_native.cpp
@@ -20,14 +20,21 @@
 #include <cstdlib>
 #include <cstring>
 #include <fstream>
+#include <ios>
 #include <string>
 #include <vector>
 #include <fmt/core.h>
 
+#include "filesystem_stream.h"
 #include "system.h"
 #include "output.h"
 #include "platform.h"
 
+#ifdef USE_CUSTOM_FILE_READBUF
+#  include <sys/stat.h>
+#  include <fcntl.h>
+#endif
+
 NativeFilesystem::NativeFilesystem(std::string base_path, FilesystemView parent_fs) : Filesystem(std::move(base_path), parent_fs) {
 }
 
@@ -48,7 +55,17 @@ int64_t NativeFilesystem::GetFilesize(StringView path) const {
 }
 
 std::streambuf* NativeFilesystem::CreateInputStreambuffer(StringView path, std::ios_base::openmode mode) const {
-	auto* buf = new std::filebuf();
+#ifdef USE_CUSTOM_FILE_READBUF
+	(void)mode;
+	int fd = open(ToString(path).c_str(), O_RDONLY);
+	if (fd < 0) {
+		return nullptr;
+	}
+
+	return new Filesystem_Stream::FdStreamBuf(fd);
+#else
+	auto buf = new std::filebuf();
+
 	buf->open(
 #ifdef _MSC_VER
 		Utils::ToWideString(path),
@@ -63,6 +80,7 @@ std::streambuf* NativeFilesystem::CreateInputStreambuffer(StringView path, std::
 	}
 
 	return buf;
+#endif
 }
 
 std::streambuf* NativeFilesystem::CreateOutputStreambuffer(StringView path, std::ios_base::openmode mode) const {
diff --git a/src/filesystem_stream.cpp b/src/filesystem_stream.cpp
index cadf97d4a4d..5d20a592497 100644
--- a/src/filesystem_stream.cpp
+++ b/src/filesystem_stream.cpp
@@ -19,6 +19,10 @@
 
 #include <utility>
 
+#ifdef USE_CUSTOM_FILE_READBUF
+#  include <unistd.h>
+#endif
+
 Filesystem_Stream::InputStream::InputStream(std::streambuf* sb, std::string name) :
 	std::istream(sb), name(std::move(name)) {}
 
@@ -122,3 +126,85 @@ Filesystem_Stream::InputMemoryStreamBuf::InputMemoryStreamBuf(std::vector<uint8_
 		: InputMemoryStreamBufView(buffer), buffer(std::move(buffer)) {
 
 }
+
+
+#ifdef USE_CUSTOM_FILE_READBUF
+
+Filesystem_Stream::FdStreamBuf::FdStreamBuf(int fd) : fd(fd) {
+	clear_buffer();
+}
+
+Filesystem_Stream::FdStreamBuf::~FdStreamBuf() {
+	close(fd);
+}
+
+Filesystem_Stream::FdStreamBuf::int_type Filesystem_Stream::FdStreamBuf::underflow() {
+	assert(gptr() == egptr());
+
+	auto bytes_read = read(fd, buffer.begin(), buffer.size());
+	if (bytes_read <= 0) {
+		return traits_type::eof();
+	}
+	file_offset += bytes_read;
+
+	setg(buffer.begin(), buffer.begin(), buffer.begin() + bytes_read);
+
+	return traits_type::to_int_type(*gptr());
+}
+
+std::streambuf::pos_type Filesystem_Stream::FdStreamBuf::seekoff(std::streambuf::off_type offset, std::ios_base::seekdir dir, std::ios_base::openmode) {
+	if (dir == std::ios_base::beg) {
+		offset = offset - file_offset + bytes_remaining();
+		dir = std::ios_base::cur;
+	}
+
+	if (dir == std::ios_base::cur) {
+		if (offset < 0) {
+			auto dist = std::distance(gptr(), gptr() - offset);
+			if (gptr() + offset < eback()) {
+				// Not cached: Outside of the buffer: Reposition the stream
+				file_offset = lseek(fd, -dist - bytes_remaining(), SEEK_CUR);
+				clear_buffer();
+			} else {
+				setg(buffer.begin(), gptr() - dist, egptr());
+			}
+		} else if (offset > 0) {
+			auto dist = std::distance(gptr(), gptr() + offset);
+			if (gptr() + offset > egptr()) {
+				// Not cached: Outside of the buffer: Reposition the stream
+				file_offset = lseek(fd, dist - bytes_remaining(), SEEK_CUR);
+				clear_buffer();
+			} else {
+				setg(buffer.begin(), gptr() + dist, egptr());
+			}
+		}
+		return file_offset - bytes_remaining();
+	} else {
+		// Not cached: Seek to end
+		clear_buffer();
+		file_offset = lseek(fd, offset, SEEK_END);
+
+		if (file_offset < 0) {
+			file_offset = 0;
+			return -1;
+		}
+
+		return file_offset;
+	}
+
+	assert(false);
+}
+
+std::streambuf::pos_type Filesystem_Stream::FdStreamBuf::seekpos(std::streambuf::pos_type pos, std::ios_base::openmode mode) {
+	return seekoff(pos, std::ios_base::beg, mode);
+}
+
+void Filesystem_Stream::FdStreamBuf::clear_buffer() {
+	setg(buffer.begin(), buffer.end(), buffer.end());
+}
+
+ssize_t Filesystem_Stream::FdStreamBuf::bytes_remaining() const {
+	return egptr() - gptr();
+}
+
+#endif
diff --git a/src/filesystem_stream.h b/src/filesystem_stream.h
index 4a0d76bc7dc..2114f938172 100644
--- a/src/filesystem_stream.h
+++ b/src/filesystem_stream.h
@@ -24,6 +24,7 @@
 #include <ostream>
 #include "filesystem.h"
 #include "utils.h"
+#include "system.h"
 
 namespace Filesystem_Stream {
 	class InputStream final : public std::istream {
@@ -96,6 +97,29 @@ namespace Filesystem_Stream {
 		std::vector<uint8_t> buffer;
 	};
 
+#ifdef USE_CUSTOM_FILE_READBUF
+	class FdStreamBuf : public std::streambuf {
+	public:
+		FdStreamBuf(int fd);
+		FdStreamBuf(FdStreamBuf const& other) = delete;
+		FdStreamBuf const& operator=(FdStreamBuf const& other) = delete;
+		~FdStreamBuf();
+
+	protected:
+		int_type underflow();
+		std::streambuf::pos_type seekoff(std::streambuf::off_type offset, std::ios_base::seekdir dir, std::ios_base::openmode mode);
+		std::streambuf::pos_type seekpos(std::streambuf::pos_type pos, std::ios_base::openmode);
+
+	private:
+		void clear_buffer();
+		ssize_t bytes_remaining() const;
+
+		int fd;
+		off_t file_offset = 0;
+		std::array<char, USE_CUSTOM_FILE_READBUF> buffer;
+	};
+#endif
+
 	static constexpr std::ios_base::seekdir CSeekdirToCppSeekdir(int origin);
 
 	static constexpr int CppSeekdirToCSeekdir(std::ios_base::seekdir origin);
diff --git a/src/system.h b/src/system.h
index 74b8d0b12c0..74c2ba5c9ed 100644
--- a/src/system.h
+++ b/src/system.h
@@ -71,6 +71,7 @@
 #  define SUPPORT_JOYSTICK
 #  define SUPPORT_JOYSTICK_AXIS
 #  define SUPPORT_TOUCH
+#  define USE_CUSTOM_FILE_READBUF 16 * 1024
 #elif defined(_WIN32)
 #  define SUPPORT_ZOOM
 #  define SUPPORT_MOUSE