oldloader.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 "../debug.h"
#include "../strings_type.h"
#include "../string_func.h"
#include "../settings_type.h"
#include "../fileio_func.h"
 
#include "table/strings.h"
 
#include "saveload_internal.h"
#include "oldloader.h"
 
 
#include "../safeguards.h"
 
static const int TTO_HEADER_SIZE = 41;
static const int TTD_HEADER_SIZE = 49;
static const int HEADER_CHECKSUM_SIZE = 2;
 
uint32_t _bump_assert_value;
 
static inline OldChunkType GetOldChunkType(OldChunkType type)     {return (OldChunkType)GB(type, 0, 4);}
static inline OldChunkType GetOldChunkVarType(OldChunkType type)  {return (OldChunkType)(GB(type, 8, 8) << 8);}
static inline OldChunkType GetOldChunkFileType(OldChunkType type) {return (OldChunkType)(GB(type, 16, 8) << 16);}
 
static inline byte CalcOldVarLen(OldChunkType type)
{
  static const byte type_mem_size[] = {0, 1, 1, 2, 2, 4, 4, 8};
  byte length = GB(type, 8, 8);
  assert(length != 0 && length < lengthof(type_mem_size));
  return type_mem_size[length];
}
 
static byte ReadByteFromFile(LoadgameState *ls)
{
  /* To avoid slow reads, we read BUFFER_SIZE of bytes per time
  and just return a byte per time */
  if (ls->buffer_cur >= ls->buffer_count) {
 
    /* Read some new bytes from the file */
    int count = (int)fread(ls->buffer, 1, BUFFER_SIZE, ls->file);
 
    /* We tried to read, but there is nothing in the file anymore.. */
    if (count == 0) {
      Debug(oldloader, 0, "Read past end of file, loading failed");
      throw std::exception();
    }
 
    ls->buffer_count = count;
    ls->buffer_cur   = 0;
  }
 
  return ls->buffer[ls->buffer_cur++];
}
 
byte ReadByte(LoadgameState *ls)
{
  /* Old savegames have a nice compression algorithm (RLE)
  which means that we have a chunk, which starts with a length
  byte. If that byte is negative, we have to repeat the next byte
  that many times ( + 1). Else, we need to read that amount of bytes.
  Works pretty well if you have many zeros behind each other */
 
  if (ls->chunk_size == 0) {
    /* Read new chunk */
    int8_t new_byte = ReadByteFromFile(ls);
 
    if (new_byte < 0) {
      /* Repeat next char for new_byte times */
      ls->decoding    = true;
      ls->decode_char = ReadByteFromFile(ls);
      ls->chunk_size  = -new_byte + 1;
    } else {
      ls->decoding    = false;
      ls->chunk_size  = new_byte + 1;
    }
  }
 
  ls->total_read++;
  ls->chunk_size--;
 
  return ls->decoding ? ls->decode_char : ReadByteFromFile(ls);
}
 
bool LoadChunk(LoadgameState *ls, void *base, const OldChunks *chunks)
{
  for (const OldChunks *chunk = chunks; chunk->type != OC_END; chunk++) {
    if (((chunk->type & OC_TTD) && _savegame_type == SGT_TTO) ||
        ((chunk->type & OC_TTO) && _savegame_type != SGT_TTO)) {
      /* TTD(P)-only chunk, but TTO savegame || TTO-only chunk, but TTD/TTDP savegame */
      continue;
    }
 
    byte *ptr = (byte*)chunk->ptr;
    if (chunk->type & OC_DEREFERENCE_POINTER) ptr = *(byte**)ptr;
 
    for (uint i = 0; i < chunk->amount; i++) {
      /* Handle simple types */
      if (GetOldChunkType(chunk->type) != 0) {
        switch (GetOldChunkType(chunk->type)) {
          /* Just read the byte and forget about it */
          case OC_NULL: ReadByte(ls); break;
 
          case OC_CHUNK:
            /* Call function, with 'i' as parameter to tell which item we
             * are going to read */
            if (!chunk->proc(ls, i)) return false;
            break;
 
          case OC_ASSERT:
            Debug(oldloader, 4, "Assert point: 0x{:X} / 0x{:X}", ls->total_read, (uint)(size_t)chunk->ptr + _bump_assert_value);
            if (ls->total_read != (size_t)chunk->ptr + _bump_assert_value) throw std::exception();
          default: break;
        }
      } else {
        uint64_t res = 0;
 
        /* Reading from the file: bits 16 to 23 have the FILE type */
        switch (GetOldChunkFileType(chunk->type)) {
          case OC_FILE_I8:  res = (int8_t)ReadByte(ls); break;
          case OC_FILE_U8:  res = ReadByte(ls); break;
          case OC_FILE_I16: res = (int16_t)ReadUint16(ls); break;
          case OC_FILE_U16: res = ReadUint16(ls); break;
          case OC_FILE_I32: res = (int32_t)ReadUint32(ls); break;
          case OC_FILE_U32: res = ReadUint32(ls); break;
          default: NOT_REACHED();
        }
 
        /* When both pointers are nullptr, we are just skipping data */
        if (base == nullptr && chunk->ptr == nullptr) continue;
 
        /* Chunk refers to a struct member, get address in base. */
        if (chunk->ptr == nullptr) ptr = (byte *)chunk->offset(base);
 
        /* Write the data */
        switch (GetOldChunkVarType(chunk->type)) {
          case OC_VAR_I8: *(int8_t  *)ptr = GB(res, 0, 8); break;
          case OC_VAR_U8: *(uint8_t *)ptr = GB(res, 0, 8); break;
          case OC_VAR_I16:*(int16_t *)ptr = GB(res, 0, 16); break;
          case OC_VAR_U16:*(uint16_t*)ptr = GB(res, 0, 16); break;
          case OC_VAR_I32:*(int32_t *)ptr = res; break;
          case OC_VAR_U32:*(uint32_t*)ptr = res; break;
          case OC_VAR_I64:*(int64_t *)ptr = res; break;
          case OC_VAR_U64:*(uint64_t*)ptr = res; break;
          default: NOT_REACHED();
        }
 
        /* Increase pointer base for arrays when looping */
        if (chunk->amount > 1 && chunk->ptr != nullptr) ptr += CalcOldVarLen(chunk->type);
      }
    }
  }
 
  return true;
}
 
static void InitLoading(LoadgameState *ls)
{
  ls->chunk_size   = 0;
  ls->total_read   = 0;
 
  ls->decoding     = false;
  ls->decode_char  = 0;
 
  ls->buffer_cur   = 0;
  ls->buffer_count = 0;
  memset(ls->buffer, 0, BUFFER_SIZE);
 
  _bump_assert_value = 0;
 
  _settings_game.construction.freeform_edges = false; // disable so we can convert map array (SetTileType is still used)
}
 
static bool VerifyOldNameChecksum(char *title, uint len)
{
  uint16_t sum = 0;
  for (uint i = 0; i < len - HEADER_CHECKSUM_SIZE; i++) {
    sum += title[i];
    sum = std::rotl(sum, 1);
  }
 
  sum ^= 0xAAAA; // computed checksum
 
  uint16_t sum2 = title[len - HEADER_CHECKSUM_SIZE]; // checksum in file
  SB(sum2, 8, 8, title[len - HEADER_CHECKSUM_SIZE + 1]);
 
  return sum == sum2;
}
 
static std::tuple<SavegameType, std::string> DetermineOldSavegameTypeAndName(FILE *f)
{
  long pos = ftell(f);
  char buffer[std::max(TTO_HEADER_SIZE, TTD_HEADER_SIZE)];
  if (pos < 0 || fread(buffer, 1, lengthof(buffer), f) != lengthof(buffer)) {
    return { SGT_INVALID, "(broken) Unable to read file" };
  }
 
  if (VerifyOldNameChecksum(buffer, TTO_HEADER_SIZE) && fseek(f, pos + TTO_HEADER_SIZE, SEEK_SET) == 0) {
    return { SGT_TTO, "(TTO)" + StrMakeValid({buffer, TTO_HEADER_SIZE - HEADER_CHECKSUM_SIZE}) };
  }
 
  if (VerifyOldNameChecksum(buffer, TTD_HEADER_SIZE) && fseek(f, pos + TTD_HEADER_SIZE, SEEK_SET) == 0) {
    return { SGT_TTD, "(TTD)" + StrMakeValid({buffer, TTD_HEADER_SIZE - HEADER_CHECKSUM_SIZE}) };
  }
 
  return { SGT_INVALID, "(broken) Unknown" };
}
 
typedef bool LoadOldMainProc(LoadgameState *ls);
 
bool LoadOldSaveGame(const std::string &file)
{
  LoadgameState ls;
 
  Debug(oldloader, 3, "Trying to load a TTD(Patch) savegame");
 
  InitLoading(&ls);
 
  /* Open file */
  ls.file = FioFOpenFile(file, "rb", NO_DIRECTORY);
 
  if (ls.file == nullptr) {
    Debug(oldloader, 0, "Cannot open file '{}'", file);
    return false;
  }
 
  SavegameType type;
  std::tie(type, std::ignore) = DetermineOldSavegameTypeAndName(ls.file);
 
  LoadOldMainProc *proc = nullptr;
 
  switch (type) {
    case SGT_TTO: proc = &LoadTTOMain; break;
    case SGT_TTD: proc = &LoadTTDMain; break;
    default:
      Debug(oldloader, 0, "Unknown savegame type; cannot be loaded");
      break;
  }
 
  _savegame_type = type;
 
  bool game_loaded;
  try {
    game_loaded = proc != nullptr && proc(&ls);
  } catch (...) {
    game_loaded = false;
  }
 
  if (!game_loaded) {
    SetSaveLoadError(STR_GAME_SAVELOAD_ERROR_DATA_INTEGRITY_CHECK_FAILED);
    fclose(ls.file);
    return false;
  }
 
  _pause_mode = PM_PAUSED_SAVELOAD;
 
  return true;
}
 
std::string GetOldSaveGameName(const std::string &file)
{
  FILE *f = FioFOpenFile(file, "rb", NO_DIRECTORY);
  if (f == nullptr) return {};
 
  std::string name;
  std::tie(std::ignore, name) = DetermineOldSavegameTypeAndName(f);
  fclose(f);
  return name;
}