src/random_access_file.cpp

   1 /*
   2  * This file is part of OpenTTD.
   3  * 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.
   4  * 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.
   5  * 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/>.
   6  */
   7
   8  /** @file random_access_file.cpp Actual implementation of the RandomAccessFile class. */
   9
  10 #include "stdafx.h"
  11 #include "random_access_file_type.h"
  12
  13 #include "debug.h"
  14 #include "error_func.h"
  15 #include "fileio_func.h"
  16 #include "string_func.h"
  17
  18 #include "safeguards.h"
  19
  20 /**
  21  * Create the RandomAccesFile.
  22  * @param filename Name of the file at the disk.
  23  * @param subdir   The sub directory to search this file in.
  24  */
  25 RandomAccessFile::RandomAccessFile(const std::string &filename, Subdirectory subdir) : filename(filename)
  26 {
  27         size_t file_size;
  28         this->file_handle = FioFOpenFile(filename, "rb", subdir, &file_size);
  29         if (!this->file_handle.has_value()) UserError("Cannot open file '{}'", filename);
  30
  31         /* When files are in a tar-file, the begin of the file might not be at 0. */
  32         long pos = ftell(*this->file_handle);
  33         if (pos < 0) UserError("Cannot read file '{}'", filename);
  34
  35         /* Make a note of start and end position for readers who check bounds. */
  36         this->start_pos = pos;
  37         this->end_pos = this->start_pos + file_size;
  38
  39         /* Store the filename without path and extension */
  40         auto t = filename.rfind(PATHSEPCHAR);
  41         std::string name_without_path = filename.substr(t != std::string::npos ? t + 1 : 0);
  42         this->simplified_filename = name_without_path.substr(0, name_without_path.rfind('.'));
  43         strtolower(this->simplified_filename);
  44
  45         this->SeekTo(static_cast<size_t>(pos), SEEK_SET);
  46 }
  47
  48 /**
  49  * Get the filename of the opened file with the path from the SubDirectory and the extension.
  50  * @return Name of the file.
  51  */
  52 const std::string &RandomAccessFile::GetFilename() const
  53 {
  54         return this->filename;
  55 }
  56
  57 /**
  58  * Get the simplified filename of the opened file. The simplified filename is the name of the
  59  * file without the SubDirectory or extension in lower case.
  60  * @return Name of the file.
  61  */
  62 const std::string &RandomAccessFile::GetSimplifiedFilename() const
  63 {
  64         return this->simplified_filename;
  65 }
  66
  67 /**
  68  * Get position in the file.
  69  * @return Position in the file.
  70  */
  71 size_t RandomAccessFile::GetPos() const
  72 {
  73         return this->pos + (this->buffer - this->buffer_end);
  74 }
  75
  76 /**
  77  * Test if we have reached the end of the file.
  78  * @return True iff the current position as at or after the end of the file.
  79  */
  80 bool RandomAccessFile::AtEndOfFile() const
  81 {
  82         return this->GetPos() >= this->GetEndPos();
  83 }
  84
  85 /**
  86  * Seek in the current file.
  87  * @param pos New position.
  88  * @param mode Type of seek (\c SEEK_CUR means \a pos is relative to current position, \c SEEK_SET means \a pos is absolute).
  89  */
  90 void RandomAccessFile::SeekTo(size_t pos, int mode)
  91 {
  92         if (mode == SEEK_CUR) pos += this->GetPos();
  93
  94         this->pos = pos;
  95         if (fseek(*this->file_handle, this->pos, SEEK_SET) < 0) {
  96                 Debug(misc, 0, "Seeking in {} failed", this->filename);
  97         }
  98
  99         /* Reset the buffer, so the next ReadByte will read bytes from the file. */
 100         this->buffer = this->buffer_end = this->buffer_start;
 101 }
 102
 103 /**
 104  * Read a byte from the file.
 105  * @return Read byte.
 106  */
 107 uint8_t RandomAccessFile::ReadByte()
 108 {
 109         if (this->buffer == this->buffer_end) {
 110                 this->buffer = this->buffer_start;
 111                 size_t size = fread(this->buffer, 1, RandomAccessFile::BUFFER_SIZE, *this->file_handle);
 112                 this->pos += size;
 113                 this->buffer_end = this->buffer_start + size;
 114
 115                 if (size == 0) return 0;
 116         }
 117         return *this->buffer++;
 118 }
 119
 120 /**
 121  * Read a word (16 bits) from the file (in low endian format).
 122  * @return Read word.
 123  */
 124 uint16_t RandomAccessFile::ReadWord()
 125 {
 126         uint8_t b = this->ReadByte();
 127         return (this->ReadByte() << 8) | b;
 128 }
 129
 130 /**
 131  * Read a double word (32 bits) from the file (in low endian format).
 132  * @return Read word.
 133  */
 134 uint32_t RandomAccessFile::ReadDword()
 135 {
 136         uint b = this->ReadWord();
 137         return (this->ReadWord() << 16) | b;
 138 }
 139
 140 /**
 141  * Read a block.
 142  * @param ptr  Destination buffer.
 143  * @param size Number of bytes to read.
 144  */
 145 void RandomAccessFile::ReadBlock(void *ptr, size_t size)
 146 {
 147         this->SeekTo(this->GetPos(), SEEK_SET);
 148         this->pos += fread(ptr, 1, size, *this->file_handle);
 149 }
 150
 151 /**
 152  * Skip \a n bytes ahead in the file.
 153  * @param n Number of bytes to skip reading.
 154  */
 155 void RandomAccessFile::SkipBytes(size_t n)
 156 {
 157         assert(this->buffer_end >= this->buffer);
 158         size_t remaining = this->buffer_end - this->buffer;
 159         if (n <= remaining) {
 160                 this->buffer += n;
 161         } else {
 162                 this->SeekTo(n, SEEK_CUR);
 163         }
 164 }