optimize block size without overflows fix #5755

libtransmission/metainfo.c

@@ -7,7 +7,7 @@
  * This exemption does not extend to derived works not owned by
  * the Transmission project.
  *
- * $Id: metainfo.c 14234 2014-02-08 15:25:18Z cfpp2p $
+ * $Id: metainfo.c 14305 2014-07-21 12:27:38Z cfpp2p $
  */
 
 #include <assert.h>
@@ -564,7 +564,7 @@ tr_metainfoParseImpl( const tr_session  * session,
 
     /* piece length */
     if( !isMagnet ) {
-        if( !tr_bencDictFindInt( infoDict, "piece length", &i ) || ( i < 1 ) || ( i >= 4294967296 ) )
+        if( !tr_bencDictFindInt( infoDict, "piece length", &i ) || ( i < 1 ) || ( i >= 536870912 ) )
             return "piece length";
         inf->pieceSize = i;
     }

libtransmission/torrent.c

@@ -705,12 +705,30 @@ static void torrentStart( tr_torrent * tor, bool bypass_queue );
 uint32_t
 tr_getBlockSize( uint32_t pieceSize )
 {
-    uint32_t b = pieceSize;
-
-    while( b > MAX_BLOCK_SIZE )
-        b /= 2u;
-
-    if( !b || ( pieceSize % b ) ) /* not cleanly divisible */
+    uint32_t b = MAX_BLOCK_SIZE;
+
+//  this was established in the previos revision logic
+//  do we really want to allow ANY piece sizes less than MAX_BLOCK_SIZE?	
+  if( pieceSize <= MAX_BLOCK_SIZE ) return pieceSize;
+
+  /**
+  * ticket 4005
+  * use a MIN_BLOCK_SIZE of 8193 - same as previous revision 
+  * lesser block sizes create an undo number of requests
+  * note - allowing a block size of 1 would guarantee any piece size
+  * but smaller requests result in higher overhead
+  * due to tracking a greater number of requests
+  * there should be some constraints on this
+  * we cant have everything
+  */
+
+// try for the LARGEST block size we can find
+// not just any one thats greater than 8192 as per previous revision
+// this way we are more efficient and less overhead
+    while( (b > 8193) && (pieceSize % b) )
+        b--;
+
+    if( pieceSize % b ) /* not cleanly divisible */
         return 0;
     return b;
 }