storage/ReadOnlyNoLockVFS.cpp

   1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
   2  * vim: sw=2 ts=2 et lcs=trail\:.,tab\:>~ :
   3  * This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /**
   8  * This VFS is built on top of the (unix|win32)-none, but it additionally
   9  * sets any opened file as immutable, that allows to also open in read-only
  10  * mode databases using WAL, or other journals that need auxiliary files, when
  11  * such files cannot be created.
  12  * This is useful when trying to read from third-party databases, avoiding any
  13  * risk of creating auxiliary files (e.g. journals).
  14  * It can only be used on read-only connections, because being a no-lock VFS
  15  * it would be trivial to corrupt the data.
  16  */
  17
  18 #include "nsDebug.h"
  19 #include "sqlite3.h"
  20
  21 #define ORIGVFS(p) ((sqlite3_vfs*)((p)->pAppData))
  22
  23 #if defined(XP_WIN)
  24 #  define BASE_VFS "win32-none"
  25 #else
  26 #  define BASE_VFS "unix-none"
  27 #endif
  28
  29 #define VFS_NAME "readonly-immutable-nolock"
  30
  31 namespace {
  32
  33 static int vfsOpen(sqlite3_vfs* vfs, const char* zName, sqlite3_file* pFile,
  34                    int flags, int* pOutFlags) {
  35   if ((flags & SQLITE_OPEN_READONLY) == 0) {
  36     // This is not done to be used in readwrite connections.
  37     return SQLITE_CANTOPEN;
  38   }
  39
  40   sqlite3_vfs* pOrigVfs = ORIGVFS(vfs);
  41   int rc = pOrigVfs->xOpen(pOrigVfs, zName, pFile, flags, pOutFlags);
  42   if (rc != SQLITE_OK) {
  43     return rc;
  44   }
  45
  46   const sqlite3_io_methods* pOrigMethods = pFile->pMethods;
  47
  48   // If the IO version is higher than the last known one, you should update
  49   // this IO adding appropriate methods for any methods added in the version
  50   // change.
  51   MOZ_ASSERT(pOrigMethods->iVersion <= 3);
  52
  53   static const sqlite3_io_methods vfs_io_methods = {
  54       pOrigMethods->iVersion,           /* iVersion */
  55       pOrigMethods->xClose,             /* xClose */
  56       pOrigMethods->xRead,              /* xRead */
  57       pOrigMethods->xWrite,             /* xWrite */
  58       pOrigMethods->xTruncate,          /* xTruncate */
  59       pOrigMethods->xSync,              /* xSync */
  60       pOrigMethods->xFileSize,          /* xFileSize */
  61       pOrigMethods->xLock,              /* xLock */
  62       pOrigMethods->xUnlock,            /* xUnlock */
  63       pOrigMethods->xCheckReservedLock, /* xCheckReservedLock */
  64       pOrigMethods->xFileControl,       /* xFileControl */
  65       pOrigMethods->xSectorSize,        /* xSectorSize */
  66       [](sqlite3_file*) {
  67         return SQLITE_IOCAP_IMMUTABLE;
  68       },                         /* xDeviceCharacteristics */
  69       pOrigMethods->xShmMap,     /* xShmMap */
  70       pOrigMethods->xShmLock,    /* xShmLock */
  71       pOrigMethods->xShmBarrier, /* xShmBarrier */
  72       pOrigMethods->xShmUnmap,   /* xShmUnmap */
  73       pOrigMethods->xFetch,      /* xFetch */
  74       pOrigMethods->xUnfetch     /* xUnfetch */
  75   };
  76   pFile->pMethods = &vfs_io_methods;
  77   if (pOutFlags) {
  78     *pOutFlags = flags;
  79   }
  80
  81   return SQLITE_OK;
  82 }
  83
  84 }  // namespace
  85
  86 namespace mozilla::storage {
  87
  88 UniquePtr<sqlite3_vfs> ConstructReadOnlyNoLockVFS() {
  89   if (sqlite3_vfs_find(VFS_NAME) != nullptr) {
  90     return nullptr;
  91   }
  92   sqlite3_vfs* pOrigVfs = sqlite3_vfs_find(BASE_VFS);
  93   if (!pOrigVfs) {
  94     return nullptr;
  95   }
  96
  97   // If the VFS version is higher than the last known one, you should update
  98   // this VFS adding appropriate methods for any methods added in the version
  99   // change.
 100   MOZ_ASSERT(pOrigVfs->iVersion <= 3);
 101
 102   static const sqlite3_vfs vfs = {
 103       pOrigVfs->iVersion,          /* iVersion  */
 104       pOrigVfs->szOsFile,          /* szOsFile */
 105       pOrigVfs->mxPathname,        /* mxPathname */
 106       nullptr,                     /* pNext */
 107       VFS_NAME,                    /* zName */
 108       pOrigVfs,                    /* pAppData */
 109       vfsOpen,                     /* xOpen */
 110       pOrigVfs->xDelete,           /* xDelete */
 111       pOrigVfs->xAccess,           /* xAccess */
 112       pOrigVfs->xFullPathname,     /* xFullPathname */
 113       pOrigVfs->xDlOpen,           /* xDlOpen */
 114       pOrigVfs->xDlError,          /* xDlError */
 115       pOrigVfs->xDlSym,            /* xDlSym */
 116       pOrigVfs->xDlClose,          /* xDlClose */
 117       pOrigVfs->xRandomness,       /* xRandomness */
 118       pOrigVfs->xSleep,            /* xSleep */
 119       pOrigVfs->xCurrentTime,      /* xCurrentTime */
 120       pOrigVfs->xGetLastError,     /* xGetLastError */
 121       pOrigVfs->xCurrentTimeInt64, /* xCurrentTimeInt64 */
 122       pOrigVfs->xSetSystemCall,    /* xSetSystemCall */
 123       pOrigVfs->xGetSystemCall,    /* xGetSystemCall */
 124       pOrigVfs->xNextSystemCall    /* xNextSystemCall */
 125   };
 126
 127   return MakeUnique<sqlite3_vfs>(vfs);
 128 }
 129
 130 }  // namespace mozilla::storage