private int _loop; // num of hash slots searched under current key
/// <summary>
/// Open a constant database from the given file.
/// </summary>
/// <param name="filePath">Path to the CDB file.</param>
public CdbFile(string filePath)
{
_cdbFile = File.OpenRead(filePath);
_heads = new UInt32[256 * 2];
var bytes = new byte[2048];
CdbRead(bytes, bytes.Length);
for (int i = 0, offset = 0; i < 256; i++)
{
UInt32 pos = Cdb.UnpackInt32(bytes, offset);
offset += 4;
UInt32 len = Cdb.UnpackInt32(bytes, offset);
offset += 4;
_heads[i << 1] = pos;
_heads[(i << 1) + 1] = len;
}
_loop = 0;
}
/// <summary>
/// Find the next record stored under the given <paramref name="key"/>.
/// </summary>
/// <returns>The next record stored under the given key,
/// or <c>null</c> if no more records can be found.</returns>
public byte[] FindNext(byte[] key)
{
// We change object state in here, so nobody must intervene!
lock (_syncLock)
{
if (_cdbFile == null)
{
throw new ObjectDisposedException(GetType().Name);
}
// Initialize: locate hash table and entry in it:
if (_loop == 0)
{
UInt32 u = Cdb.Hash(key);
// Get hash table len&pos for this key:
UInt32 slot = u & 255;
_hslots = _heads[(slot << 1) + 1];
if (_hslots == 0)
{
return(null);
}
_hpos = _heads[slot << 1];
// Remember this key's hash:
_khash = u;
// Locate the slot in the table at _hpos:
u >>= 8;
u %= _hslots;
u <<= 3;
_kpos = _hpos + u;
}
// Search: iterate all hash slots for the given key:
var bytes = new byte[8];
while (_loop < _hslots)
{
// Read the entry for this key from the hash slot
CdbRead(bytes, 8, _kpos);
UInt32 h = Cdb.UnpackInt32(bytes, 0);
UInt32 pos = Cdb.UnpackInt32(bytes, 4);
if (pos == 0)
{
break;
}
// Advance loop counter and key position.
// Wrap key position if at end of hash table.
_loop += 1;
_kpos += 8;
if (_kpos == (_hpos + (_hslots << 3)))
{
_kpos = _hpos;
}
// Different hash? Probe next slot...
if (h != _khash)
{
continue;
}
// Jump to the record and see if key matches:
CdbRead(bytes, 8, pos);
UInt32 klen = Cdb.UnpackInt32(bytes, 0);
if (klen != key.Length)
{
continue;
}
if (!CdbMatch(key))
{
continue;
}
UInt32 dlen = Cdb.UnpackInt32(bytes, 4);
// Keys match: fetch the data
var data = new byte[dlen];
CdbRead(data, data.Length);
return(data);
}
return(null); // No such key
}
}
