random_access_file.cpp

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/*
 * 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/>.
 */
 
#include "stdafx.h"
#include "random_access_file_type.h"
 
#include "debug.h"
#include "error_func.h"
#include "fileio_func.h"
#include "string_func.h"
 
#include "safeguards.h"
 
RandomAccessFile::RandomAccessFile(const std::string &filename, Subdirectory subdir) : filename(filename)
{
  size_t file_size;
  this->file_handle = FioFOpenFile(filename, "rb", subdir, &file_size);
  if (!this->file_handle.has_value()) UserError("Cannot open file '{}'", filename);
 
  /* 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 '{}'", filename);
 
  /* Make a note of start and end position for readers who check bounds. */
  this->start_pos = pos;
  this->end_pos = this->start_pos + file_size;
 
  /* 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(static_cast<size_t>(pos), SEEK_SET);
}
 
const std::string &RandomAccessFile::GetFilename() const
{
  return this->filename;
}
 
const std::string &RandomAccessFile::GetSimplifiedFilename() const
{
  return this->simplified_filename;
}
 
size_t RandomAccessFile::GetPos() const
{
  return this->pos + (this->buffer - this->buffer_end);
}
 
bool RandomAccessFile::AtEndOfFile() const
{
  return this->GetPos() >= this->GetEndPos();
}
 
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 {} failed", this->filename);
  }
 
  /* Reset the buffer, so the next ReadByte will read bytes from the file. */
  this->buffer = this->buffer_end = this->buffer_start;
}
 
uint8_t 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++;
}
 
uint16_t RandomAccessFile::ReadWord()
{
  uint8_t b = this->ReadByte();
  return (this->ReadByte() << 8) | b;
}
 
uint32_t RandomAccessFile::ReadDword()
{
  uint b = this->ReadWord();
  return (this->ReadWord() << 16) | b;
}
 
void RandomAccessFile::ReadBlock(void *ptr, size_t size)
{
  if (this->buffer != this->buffer_end) {
    size_t to_copy = std::min<size_t>(size, this->buffer_end - this->buffer);
    memcpy(ptr, this->buffer, to_copy);
    this->buffer += to_copy;
    size -= to_copy;
    if (size == 0) return;
    ptr = static_cast<char *>(ptr) + to_copy;
  }
 
  this->pos += fread(ptr, 1, size, *this->file_handle);
}
 
void RandomAccessFile::SkipBytes(size_t n)
{
  assert(this->buffer_end >= this->buffer);
  size_t remaining = this->buffer_end - this->buffer;
  if (n <= remaining) {
    this->buffer += n;
  } else {
    this->SeekTo(n, SEEK_CUR);
  }
}