SQLite

** appended onto the end of some other file, such as an executable.
**
** A special record must appear at the end of the file that identifies the
** file as an appended database and provides an offset to page 1.  For
** best performance page 1 should be located at a disk page boundary, though
** that is not required.
**
** When opening a database using this VFS, the connection might treat
** the file as an ordinary SQLite database, or it might treat is as a
** database appended onto some other file.  Here are the rules:
**
**  (1)  When opening a new empty file, that file is treated as an ordinary
**       database.
**
**  (2)  When opening a file that begins with the standard SQLite prefix
**       string "SQLite format 3", that file is treated as an ordinary
**       database.
**
**  (3)  When opening a file that ends with the appendvfs trailer string
**       "Start-Of-SQLite3-NNNNNNNN" that file is treated as an appended
**       database.
**
**  (4)  If none of the above apply and the SQLITE_OPEN_CREATE flag is
**       set, then a new database is appended to the already existing file.
**
**  (5)  Otherwise, SQLITE_CANTOPEN is returned.
**
** To avoid unnecessary complications with the PENDING_BYTE, the size of
** the file containing the database is limited to 1GB.  This VFS will refuse
** to read or write past the 1GB mark.  This restriction might be lifted in
** future versions.  For now, if you need a large database, then keep the
** database in a separate file.
**
** If the file being opened is not an appended database, then this shim is
** a pass-through into the default underlying VFS.
**/
#include <sqlite3ext.h>
SQLITE_EXTENSION_INIT1
#include <string.h>

** The NNNNNNNN represents a 64-bit big-endian unsigned integer which is
** the offset to page 1.
*/
#define APND_MARK_PREFIX     "Start-Of-SQLite3-"
#define APND_MARK_PREFIX_SZ  17
#define APND_MARK_SIZE       25

/*
** Maximum size of the combined prefix + database + append-mark.  This
** must be less than 0x40000000 to avoid locking issues on Windows.
*/
#define APND_MAX_SIZE  (65536*15259)

/*
** Forward declaration of objects used by this utility
*/
typedef struct sqlite3_vfs ApndVfs;
typedef struct ApndFile ApndFile;

/* Access to a lower-level VFS that (might) implement dynamic loading,
** access to randomness, etc.
*/
#define ORIGVFS(p)  ((sqlite3_vfs*)((p)->pAppData))
#define ORIGFILE(p) ((sqlite3_file*)(((ApndFile*)(p))+1))

/* An open file */
struct ApndFile {
  sqlite3_file base;              /* IO methods */
  sqlite3_int64 iPgOne;           /* File offset to page 1 */
  sqlite3_int64 iMark;            /* Start of the append-mark */
};

/*
** Methods for ApndFile
*/
static int apndClose(sqlite3_file*);
static int apndRead(sqlite3_file*, void*, int iAmt, sqlite3_int64 iOfst);

  int iAmt, 
  sqlite_int64 iOfst
){
  ApndFile *p = (ApndFile *)pFile;
  pFile = ORIGFILE(pFile);
  return pFile->pMethods->xRead(pFile, zBuf, iAmt, iOfst+p->iPgOne);
}

/*
** Add the append-mark onto the end of the file.
*/
static int apndWriteMark(ApndFile *p, sqlite3_file *pFile){
  int i;
  unsigned char a[APND_MARK_SIZE];
  memcpy(a, APND_MARK_PREFIX, APND_MARK_PREFIX_SZ);
  for(i=0; i<8; i++){
    a[APND_MARK_PREFIX_SZ+i] = (p->iPgOne >> (56 - i*8)) & 0xff;
  }
  return pFile->pMethods->xWrite(pFile, a, APND_MARK_PREFIX_SZ, p->iMark);
}

/*
** Write data to an apnd-file.
*/
static int apndWrite(
  sqlite3_file *pFile,
  const void *zBuf,
  int iAmt,
  sqlite_int64 iOfst
){
  int rc;
  ApndFile *p = (ApndFile *)pFile;
  pFile = ORIGFILE(pFile);
  if( iOfst+iAmt>=APND_MAX_SIZE ) return SQLITE_FULL;
  rc = pFile->pMethods->xWrite(pFile, zBuf, iAmt, iOfst+p->iPgOne);
  if( rc==SQLITE_OK &&  iOfst + iAmt + p->iPgOne > p->iMark ){
    sqlite3_int64 sz = 0;
    rc = pFile->pMethods->xFileSize(pFile, &sz);
    if( rc==SQLITE_OK ){
      p->iMark = sz - APND_MARK_SIZE;
      if( iOfst + iAmt + p->iPgOne > p->iMark ){
        p->iMark = p->iPgOne + iOfst + iAmt;
        rc = apndWriteMark(p, pFile);
      }
    }
  }
  return rc;
}

/*
** Truncate an apnd-file.
*/
static int apndTruncate(sqlite3_file *pFile, sqlite_int64 size){
  int rc;
  ApndFile *p = (ApndFile *)pFile;
  pFile = ORIGFILE(pFile);
  rc = pFile->pMethods->xTruncate(pFile, size+p->iPgOne+APND_MARK_SIZE);
  if( rc==SQLITE_OK ){
    p->iMark = p->iPgOne+size;
    rc = apndWriteMark(p, pFile);
  }
  return rc;
}

/*
** Sync an apnd-file.
*/
static int apndSync(sqlite3_file *pFile, int flags){
  pFile = ORIGFILE(pFile);
  return pFile->pMethods->xSync(pFile, flags);
}

/*
** Return the current file-size of an apnd-file.
*/
static int apndFileSize(sqlite3_file *pFile, sqlite_int64 *pSize){
  ApndFile *p = (ApndFile *)pFile;
  int rc;
  pFile = ORIGFILE(p);
  rc = pFile->pMethods->xFileSize(pFile, pSize);
  if( rc==SQLITE_OK && p->iPgOne ){
    *pSize -= p->iPgOne + APND_MARK_SIZE;
  }
  return rc;
}

/*
** Lock an apnd-file.
*/
static int apndLock(sqlite3_file *pFile, int eLock){
  pFile = ORIGFILE(pFile);
  return pFile->pMethods->xLock(pFile, eLock);
}

/*
** Unlock an apnd-file.
*/
static int apndUnlock(sqlite3_file *pFile, int eLock){
  pFile = ORIGFILE(pFile);
  return pFile->pMethods->xUnlock(pFile, eLock);
}

/*
** Check if another file-handle holds a RESERVED lock on an apnd-file.
*/
static int apndCheckReservedLock(sqlite3_file *pFile, int *pResOut){
  pFile = ORIGFILE(pFile);
  return pFile->pMethods->xCheckReservedLock(pFile, pResOut);
}

/*
** File control method. For custom operations on an apnd-file.
*/
static int apndFileControl(sqlite3_file *pFile, int op, void *pArg){
  ApndFile *p = (ApndFile *)pFile;

static int apndShmMap(
  sqlite3_file *pFile,
  int iPg,
  int pgsz,
  int bExtend,
  void volatile **pp
){
  pFile = ORIGFILE(pFile);
  return pFile->pMethods->xShmMap(pFile,iPg,pgsz,bExtend,pp);
}

/* Perform locking on a shared-memory segment */
static int apndShmLock(sqlite3_file *pFile, int offset, int n, int flags){
  pFile = ORIGFILE(pFile);
  return pFile->pMethods->xShmLock(pFile,offset,n,flags);
}

/* Memory barrier operation on shared memory */
static void apndShmBarrier(sqlite3_file *pFile){
  pFile = ORIGFILE(pFile);
  pFile->pMethods->xShmBarrier(pFile);
}

/* Unmap a shared memory segment */
static int apndShmUnmap(sqlite3_file *pFile, int deleteFlag){
  pFile = ORIGFILE(pFile);
  return pFile->pMethods->xShmUnmap(pFile,deleteFlag);
}

/* Fetch a page of a memory-mapped file */
static int apndFetch(
  sqlite3_file *pFile,
  sqlite3_int64 iOfst,
  int iAmt,
  void **pp
){
  ApndFile *p = (ApndFile *)pFile;
  pFile = ORIGFILE(pFile);
  return pFile->pMethods->xFetch(pFile, iOfst+p->iPgOne, iAmt, pp);
}

/* Release a memory-mapped page */
static int apndUnfetch(sqlite3_file *pFile, sqlite3_int64 iOfst, void *pPage){
  ApndFile *p = (ApndFile *)pFile;
  pFile = ORIGFILE(pFile);
  return pFile->pMethods->xUnfetch(pFile, iOfst+p->iPgOne, pPage);
}

/*
** Check to see if the file is an ordinary SQLite database file.
*/
static int apndIsOrdinaryDatabaseFile(sqlite3_int64 sz, sqlite3_file *pFile){
  int rc;
  char zHdr[16];
  static const char aSqliteHdr[] = "SQLite format 3";
  if( sz<512 ) return 0;
  rc = pFile->pMethods->xRead(pFile, zHdr, sizeof(zHdr), 0);
  if( rc ) return 0;
  return memcmp(zHdr, aSqliteHdr, sizeof(zHdr))==0;
}

/*
** Try to read the append-mark off the end of a file.  Return the
** start of the appended database if the append-mark is present.  If
** there is no append-mark, return -1;
*/
static sqlite3_int64 apndReadMark(sqlite3_int64 sz, sqlite3_file *pFile){
  int rc, i;
  sqlite3_int64 iMark;
  unsigned char a[APND_MARK_SIZE];

  if( sz<=APND_MARK_SIZE ) return -1;
  rc = pFile->pMethods->xRead(pFile, a, APND_MARK_SIZE, sz-APND_MARK_SIZE);
  if( rc ) return -1;
  if( memcmp(a, APND_MARK_PREFIX, APND_MARK_PREFIX_SZ)!=0 ) return -1;
  iMark = ((sqlite3_int64)(a[APND_MARK_PREFIX_SZ]&0x7f))<<56;
  for(i=1; i<8; i++){    
    iMark += (sqlite3_int64)a[APND_MARK_PREFIX_SZ+i]<<(56-8*i);
  }
  return iMark;
}

/*
** Open an apnd file handle.
*/
static int apndOpen(
  sqlite3_vfs *pVfs,
  const char *zName,
  sqlite3_file *pFile,
  int flags,
  int *pOutFlags
){
  ApndFile *p;
  sqlite3_file *pSubFile;
  sqlite3_vfs *pSubVfs;
  int rc;
  sqlite3_int64 sz;
  pSubVfs = ORIGVFS(pVfs);
  if( (flags & SQLITE_OPEN_MAIN_DB)==0 ){
    return pSubVfs->xOpen(pSubVfs, zName, pFile, flags, pOutFlags);
  }
  p = (ApndFile*)pFile;
  memset(p, 0, sizeof(*p));
  p->base.pMethods = &apnd_io_methods;
  pSubFile = ORIGFILE(pFile);


  rc = pSubVfs->xOpen(pSubVfs, zName, pSubFile, flags, pOutFlags);
  if( rc ) return rc;
  rc = pSubFile->pMethods->xFileSize(pSubFile, &sz);
  if( rc ){

    pSubFile->pMethods->xClose(pSubFile);
    return rc;
  }
  if( apndIsOrdinaryDatabaseFile(sz, pSubFile) ){
    memmove(pFile, pSubFile, pSubVfs->szOsFile);
    return SQLITE_OK;


  }
  p->iMark = 0;
  p->iPgOne = apndReadMark(sz, pFile);

  if( p->iPgOne>0 ){
    return SQLITE_OK;





  }
  if( (flags & SQLITE_OPEN_CREATE)==0 ){
    pSubFile->pMethods->xClose(pSubFile);
    return SQLITE_CANTOPEN;
  }
  p->iPgOne = (sz+0xfff) & ~(sqlite3_int64)0xfff;
  return SQLITE_OK;
}

/*
** All other VFS methods are pass-thrus.
*/
static int apndDelete(sqlite3_vfs *pVfs, const char *zPath, int dirSync){

  int rc = SQLITE_OK;
  sqlite3_vfs *pOrig;
  SQLITE_EXTENSION_INIT2(pApi);
  pOrig = sqlite3_vfs_find(0);
  apnd_vfs.iVersion = pOrig->iVersion;
  apnd_vfs.pAppData = pOrig;
  apnd_vfs.szOsFile = sizeof(ApndFile);
  rc = sqlite3_vfs_register(&apnd_vfs, 0);
#ifdef APPENDVFS_TEST
  if( rc==SQLITE_OK ){
    rc = sqlite3_auto_extension((void(*)(void))apndvfsRegister);
  }
#endif
  if( rc==SQLITE_OK ) rc = SQLITE_OK_LOAD_PERMANENTLY;
  return rc;
}