SQLite

/* Forward declaration of all object types */
typedef struct quotaGroup quotaGroup;
typedef struct quotaOpen quotaOpen;
typedef struct quotaFile quotaFile;

/*
** A "quota group" is a collection of files whose collective size we want

** to limit.  Each quota group is defined by a GLOB pattern.
**
** There is an instance of the following object for each defined quota
** group.  This object records the GLOB pattern that defines which files
** belong to the quota group.  The object also remembers the size limit
** for the group (the quota) and the callback to be invoked when the
** sum of the sizes of the files within the group goes over the limit.
**
** A quota group must be established (using sqlite3_quota_set(...))
** prior to opening any of the database connections that access files
** within the quota group.


*/
struct quotaGroup {
  const char *zPattern;          /* Filename pattern to be quotaed */
  sqlite3_int64 iLimit;          /* Upper bound on total file size */
  sqlite3_int64 iSize;           /* Current size of all files */
  void (*xCallback)(             /* Callback invoked when going over quota */
     const char *zFilename,         /* Name of file whose size increases */
     sqlite3_int64 *piLimit,        /* IN/OUT: The current limit */
     sqlite3_int64 iSize,           /* Total size of all files in the group */
     void *pArg                     /* Client data */
  );
  void *pArg;                    /* Third argument to the xCallback() */
  quotaGroup *pNext, **ppPrev;   /* Doubly linked list of all quota objects */
  quotaFile *pFile;              /* Files within this group */
};

/*
** An instance of this structure represents a single file that is part
** of a quota group.  A single file can be opened multiple times.  In
** order keep multiple openings of the same file from causing the size
** of the file to count against the quota multiple times, each file
** has a unique instance of this object and multiple open connections
** to the same file each point to a single instance of this object.
*/
struct quotaFile {
  char *zFilename;                /* Name of this file */
  quotaGroup *pGroup;             /* Upper bound on file size */
  sqlite3_int64 iSize;            /* Current size of this file */
  int nRef;                       /* Number of times this file is open */
  quotaFile *pNext, **ppPrev;     /* Linked list of files in the same group */
};

/*
** An instance of the following object represents each open connection
** to a file that participates in quota tracking.  This object is a 
** subclass of sqlite3_file.  The sqlite3_file object for the underlying
** VFS is appended to this structure.
*/
struct quotaOpen {
  sqlite3_file base;              /* Base class - must be first */
  quotaFile *pFile;               /* The underlying file */
  /* The underlying VFS sqlite3_file is appended to this object */
};

/************************* Global Variables **********************************/
/*
** All global variables used by this file are containing within the following
** gQuota structure.
*/
static struct {
  /* The pOrigVfs is the real, original underlying VFS implementation.
  ** Most operations pass-through to the real VFS.  This value is read-only
  ** during operation.  It is only modified at start-time and thus does not
  ** require a mutex.
  */
  sqlite3_vfs *pOrigVfs;

  /* The sThisVfs is the VFS structure used by this shim.  It is initialized

static quotaGroup *quotaGroupFind(const char *zFilename){
  quotaGroup *p;
  for(p=gQuota.pGroup; p && strglob(p->zPattern, zFilename)==0; p=p->pNext){}
  return p;
}

/* Translate an sqlite3_file* that is really a quotaOpen* into
** the sqlite3_file* for the underlying original VFS.
*/
static sqlite3_file *quotaSubOpen(sqlite3_file *pOpen){
  quotaOpen *p = (quotaOpen*)pOpen;
  return (sqlite3_file*)&p[1];
}

/************************* VFS Method Wrappers *****************************/
/*
** This is the xOpen method used for the "quota" VFS.
**
** Most of the work is done by the underlying original VFS.  This method
** simply links the new file into the appropriate quota group if it is a
** file that needs to be tracked.
*/
static int quotaxOpen(
  sqlite3_vfs *pVfs,          /* The quota VFS */
  const char *zName,          /* Name of file to be opened */
  sqlite3_file *pOpen,        /* Fill in this file descriptor */
  int flags,                  /* Flags to control the opening */
  int *pOutFlags              /* Flags showing results of opening */
){
  int rc;                                    /* Result code */         
  quotaOpen *pQuotaOpen;                     /* The new quota file descriptor */
  quotaFile *pFile;                          /* Corresponding quotaFile obj */
  quotaGroup *pGroup;                        /* The group file belongs to */
  sqlite3_file *pSubOpen;                    /* Real file descriptor */
  sqlite3_vfs *pOrigVfs = gQuota.pOrigVfs;   /* Real VFS */

  /* If the file is not a main database file or a WAL, then use the
  ** normal xOpen method.
  */
  if( (flags & (SQLITE_OPEN_MAIN_DB|SQLITE_OPEN_WAL))==0 ){
    return pOrigVfs->xOpen(pOrigVfs, zName, pOpen, flags, pOutFlags);
  }