Add: concept of a RandomAccessFile to replace the FIO slot functions

3 files changed, 216 insertions, 0 deletions

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index e0af79999..2d4fffc8c 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -309,6 +309,8 @@ add_files(
     rail_gui.h
     rail_map.h
     rail_type.h
+    random_access_file.cpp
+    random_access_file_type.h
     rev.h
     road.cpp
     road.h
diff --git a/src/random_access_file.cpp b/src/random_access_file.cpp
new file mode 100644
index 000000000..2fd6a64b6
--- /dev/null
+++ b/src/random_access_file.cpp
@@ -0,0 +1,156 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+ /** @file random_access_file.cpp Actual implementation of the RandomAccessFile class. */
+
+#include "stdafx.h"
+#include "random_access_file_type.h"
+
+#include "debug.h"
+#include "fileio_func.h"
+#include "string_func.h"
+
+#include "safeguards.h"
+
+/**
+ * Create the RandomAccesFile.
+ * @param filename Name of the file at the disk.
+ * @param subdir   The sub directory to search this file in.
+ */
+RandomAccessFile::RandomAccessFile(const std::string &filename, Subdirectory subdir) : filename(filename)
+{
+	this->file_handle = FioFOpenFile(filename, "rb", subdir);
+	if (this->file_handle == nullptr) usererror("Cannot open file '%s'", filename.c_str());
+
+	/* When files are in a tar-file, the begin of the file might not be at 0. */
+	long pos = ftell(this->file_handle);
+	if (pos < 0) usererror("Cannot read file '%s'", filename.c_str());
+
+	/* Store the filename without path and extension */
+	auto t = filename.rfind(PATHSEPCHAR);
+	std::string name_without_path = filename.substr(t != std::string::npos ? t + 1 : 0);
+	this->simplified_filename = name_without_path.substr(0, name_without_path.rfind('.'));
+	strtolower(this->simplified_filename);
+
+	this->SeekTo((size_t)pos, SEEK_SET);
+}
+
+/**
+ * Close the file's file handle.
+ */
+RandomAccessFile::~RandomAccessFile()
+{
+	fclose(this->file_handle);
+}
+
+/**
+ * Get the filename of the opened file with the path from the SubDirectory and the extension.
+ * @return Name of the file.
+ */
+const std::string& RandomAccessFile::GetFilename() const
+{
+	return this->filename;
+}
+
+/**
+ * Get the simplified filename of the opened file. The simplified filename is the name of the
+ * file without the SubDirectory or extension in lower case.
+ * @return Name of the file.
+ */
+const std::string& RandomAccessFile::GetSimplifiedFilename() const
+{
+	return this->simplified_filename;
+}
+
+/**
+ * Get position in the file.
+ * @return Position in the file.
+ */
+size_t RandomAccessFile::GetPos() const
+{
+	return this->pos + (this->buffer - this->buffer_end);
+}
+
+/**
+ * Seek in the current file.
+ * @param pos New position.
+ * @param mode Type of seek (\c SEEK_CUR means \a pos is relative to current position, \c SEEK_SET means \a pos is absolute).
+ */
+void RandomAccessFile::SeekTo(size_t pos, int mode)
+{
+	if (mode == SEEK_CUR) pos += this->GetPos();
+
+	this->pos = pos;
+	if (fseek(this->file_handle, this->pos, SEEK_SET) < 0) {
+		DEBUG(misc, 0, "Seeking in %s failed", this->filename.c_str());
+	}
+
+	/* Reset the buffer, so the next ReadByte will read bytes from the file. */
+	this->buffer = this->buffer_end = this->buffer_start;
+}
+
+/**
+ * Read a byte from the file.
+ * @return Read byte.
+ */
+byte RandomAccessFile::ReadByte()
+{
+	if (this->buffer == this->buffer_end) {
+		this->buffer = this->buffer_start;
+		size_t size = fread(this->buffer, 1, RandomAccessFile::BUFFER_SIZE, this->file_handle);
+		this->pos += size;
+		this->buffer_end = this->buffer_start + size;
+
+		if (size == 0) return 0;
+	}
+	return *this->buffer++;
+}
+
+/**
+ * Read a word (16 bits) from the file (in low endian format).
+ * @return Read word.
+ */
+uint16 RandomAccessFile::ReadWord()
+{
+	byte b = this->ReadByte();
+	return (this->ReadByte() << 8) | b;
+}
+
+/**
+ * Read a double word (32 bits) from the file (in low endian format).
+ * @return Read word.
+ */
+uint32 RandomAccessFile::ReadDword()
+{
+	uint b = this->ReadWord();
+	return (this->ReadWord() << 16) | b;
+}
+
+/**
+ * Read a block.
+ * @param ptr  Destination buffer.
+ * @param size Number of bytes to read.
+ */
+void RandomAccessFile::ReadBlock(void *ptr, size_t size)
+{
+	this->SeekTo(this->GetPos(), SEEK_SET);
+	this->pos += fread(ptr, 1, size, this->file_handle);
+}
+
+/**
+ * Skip \a n bytes ahead in the file.
+ * @param n Number of bytes to skip reading.
+ */
+void RandomAccessFile::SkipBytes(int n)
+{
+	int remaining = this->buffer_end - this->buffer;
+	if (n <= remaining) {
+		this->buffer += n;
+	} else {
+		this->SeekTo(n, SEEK_CUR);
+	}
+}
diff --git a/src/random_access_file_type.h b/src/random_access_file_type.h
new file mode 100644
index 000000000..ce0e9e358
--- /dev/null
+++ b/src/random_access_file_type.h
@@ -0,0 +1,58 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+ /** @file random_access_file_type.h Class related to random access to files. */
+
+#ifndef RANDOM_ACCESS_FILE_TYPE_H
+#define RANDOM_ACCESS_FILE_TYPE_H
+
+#include "fileio_type.h"
+#include <string>
+
+/**
+ * A file from which bytes, words and double words are read in (potentially) a random order.
+ *
+ * This is mostly intended to be used for things that can be read from GRFs when needed, so
+ * the graphics but also the sounds. This also ties into the spritecache as it uses these
+ * files to load the sprites from when needed.
+ */
+class RandomAccessFile {
+	/** The number of bytes to allocate for the buffer. */
+	static constexpr int BUFFER_SIZE = 512;
+
+	std::string filename;            ///< Full name of the file; relative path to subdir plus the extension of the file.
+	std::string simplified_filename; ///< Simplified lowecase name of the file; only the name, no path or extension.
+
+	FILE *file_handle;               ///< File handle of the open file.
+	size_t pos;                      ///< Position in the file of the end of the read buffer.
+
+	byte *buffer;                    ///< Current position within the local buffer.
+	byte *buffer_end;                ///< Last valid byte of buffer.
+	byte buffer_start[BUFFER_SIZE];  ///< Local buffer when read from file.
+
+public:
+	RandomAccessFile(const std::string &filename, Subdirectory subdir);
+	RandomAccessFile(const RandomAccessFile&) = delete;
+	void operator=(const RandomAccessFile&) = delete;
+
+	virtual ~RandomAccessFile();
+
+	const std::string &GetFilename() const;
+	const std::string &GetSimplifiedFilename() const;
+
+	size_t GetPos() const;
+	void SeekTo(size_t pos, int mode);
+
+	byte ReadByte();
+	uint16 ReadWord();
+	uint32 ReadDword();
+
+	void ReadBlock(void *ptr, size_t size);
+	void SkipBytes(int n);
+};
+
+#endif /* RANDOM_ACCESS_FILE_TYPE_H */