Add reference counting so we can delete unused chunks

1 files changed, 19 insertions, 7 deletions

diff --git a/FuseArchive/Chunk.py b/FuseArchive/Chunk.py
index 9bb05bd..082df68 100644
--- a/FuseArchive/Chunk.py
+++ b/FuseArchive/Chunk.py
@@ -8,11 +8,11 @@ import struct, zlib, logging
 hformat = 'HLBL48x'
 compress_level = 6
 
-header_length = 64
+_header_length = 64
 
-assert struct.calcsize( hformat ) == header_length, \
-    "Header struct must be 64 bytes not %d bytes" % \
-    struct.calcsize( hformat )
+assert struct.calcsize( hformat ) == _header_length, \
+    "Header struct must be %d bytes not %d bytes" % \
+    ( _header_length, struct.calcsize( hformat ) )
 
 # This handles serialization and deserialization of compressed chunks with
 # some header data
@@ -59,15 +59,15 @@ class Chunk:
     @staticmethod
     def deserialize(data):
         logging.debug( "Deserializing data of length %d" % len( data ) )
-        hd = Chunk.parse_header( data[ :header_length ] )
+        hd = Chunk.parse_header( data[ :_header_length ] )
         obj = Chunk()
         obj.count = hd[ 'count' ]
 
         compression = hd[ 'compression' ]
         if compression == 0:
-            obj.chunk = data[ header_length: ]
+            obj.chunk = data[ _header_length: ]
         elif compression == 1:
-            obj.chunk = zlib.decompress( data[ header_length: ] )
+            obj.chunk = zlib.decompress( data[ _header_length: ] )
         else:
             raise ValueError( "Invalid compression type: %d" % compression )
 
@@ -87,3 +87,15 @@ class Chunk:
             'count': fields[ 3 ]
         }
 
+    # This is for updating header info, returns a tuple with the new count
+    # + the data
+    @staticmethod
+    def inc_header_ref(data, count):
+        logging.debug( "Incrementing ref count by %d" % count )
+        fields = list( struct.unpack( hformat, data ) )
+        fields[ 3 ] += count
+        return( fields[ 3 ], struct.pack( hformat, *fields ) )
+
+    @staticmethod
+    def header_length():
+        return( _header_length )