From ff0f4fe46ef02ada1d83e846ed38b3cdace5b110 Mon Sep 17 00:00:00 2001
From: Andrew Brown <brownan@gmail.com>
Date: Sun, 18 Mar 2012 13:52:59 -0400
Subject: [PATCH] fixed error handling code. Now more robust against corrupt
 chunks!

---
 overviewer_core/cache.py |  3 ++-
 overviewer_core/nbt.py   | 28 +++++++++++++++-------------
 overviewer_core/world.py | 10 +++++-----
 3 files changed, 22 insertions(+), 19 deletions(-)

diff --git a/overviewer_core/cache.py b/overviewer_core/cache.py
index 6c5a5a2..d21dbc5 100644
--- a/overviewer_core/cache.py
+++ b/overviewer_core/cache.py
@@ -127,7 +127,8 @@ class LRUCache(object):
 
     def __delitem__(self, key):
         # Used to flush the cache of this key
-        link = self.cache[key]
+        cache = self.cache
+        link = cache[key]
         del cache[key]
         link.left.right = link.right
         link.right.left = link.left
diff --git a/overviewer_core/nbt.py b/overviewer_core/nbt.py
index faf94bf..3d69f8b 100644
--- a/overviewer_core/nbt.py
+++ b/overviewer_core/nbt.py
@@ -42,7 +42,17 @@ def load_region(fileobj):
     for accessing the chunks inside."""
     return MCRFileReader(fileobj)
 
-class CorruptNBTError(Exception):
+
+class CorruptionError(Exception):
+    pass
+class CorruptRegionError(CorruptionError):
+    """An exception raised when the MCRFileReader class encounters an
+    error during region file parsing.
+    """
+    pass
+class CorruptChunkError(CorruptionError):
+    pass
+class CorruptNBTError(CorruptionError):
     """An exception raised when the NBTFileReader class encounters
     something unexpected in an NBT file."""
     pass
@@ -180,16 +190,6 @@ class NBTFileReader(object):
         except (struct.error, ValueError), e:
             raise CorruptNBTError("could not parse nbt: %s" % (str(e),))
 
-class CorruptionError(Exception):
-    pass
-class CorruptRegionError(CorruptionError):
-    """An exception raised when the MCRFileReader class encounters an
-    error during region file parsing.
-    """
-    pass
-class CorruptChunkError(CorruptionError):
-    pass
-
 # For reference, the MCR format is outlined at
 # <http://www.minecraftwiki.net/wiki/Beta_Level_Format>
 class MCRFileReader(object):
@@ -215,7 +215,7 @@ class MCRFileReader(object):
         timestamp_data = self._file.read(4096)
         if not len(timestamp_data) == 4096:
             raise CorruptRegionError("invalid timestamp table")
-        
+
         # turn this data into a useful list
         self._locations = self._table_format.unpack(location_data)
         self._timestamps = self._table_format.unpack(timestamp_data)
@@ -289,7 +289,7 @@ class MCRFileReader(object):
             is_gzip = False
         else:
             # unsupported!
-            raise CorruptRegionError("unsupported chunk compression type: %i" % (compression))
+            raise CorruptRegionError("unsupported chunk compression type: %i (should be 1 or 2)" % (compression,))
         
         # turn the rest of the data into a StringIO object
         # (using data_length - 1, as we already read 1 byte for compression)
@@ -300,5 +300,7 @@ class MCRFileReader(object):
         
         try:
             return NBTFileReader(data, is_gzip=is_gzip).read_all()
+        except CorruptionError:
+            raise
         except Exception, e:
             raise CorruptChunkError("Misc error parsing chunk: " + str(e))
diff --git a/overviewer_core/world.py b/overviewer_core/world.py
index f8cbc57..8511a2c 100644
--- a/overviewer_core/world.py
+++ b/overviewer_core/world.py
@@ -246,7 +246,7 @@ class RegionSet(object):
         # This is populated below. It is a mapping from (x,y) region coords to filename
         self.regionfiles = {}
 
-        # This holds up to 16 open regionfile objects
+        # This holds a cache of open regionfile objects
         self.regioncache = cache.LRUCache(size=16, destructor=lambda regionobj: regionobj.close())
         
         for x, y, regionfile in self._iterate_regionfiles():
@@ -319,8 +319,8 @@ class RegionSet(object):
         if regionfile is None:
             raise ChunkDoesntExist("Chunk %s,%s doesn't exist (and neither does its region)" % (x,z))
 
-        # Try 3 times to load and parse this chunk before giving up and raising
-        # an error
+        # Try a few times to load and parse this chunk before giving up and
+        # raising an error
         tries = 5
         while True:
             try:
@@ -337,8 +337,8 @@ class RegionSet(object):
                     time.sleep(0.5)
                     continue
                 else:
-                    logging.warning("Tried %d times to read chunk %d,%d but I got error %s",
-                            tries, x, z, e)
+                    logging.warning("Tried several times to read chunk %d,%d. Giving up.",
+                            x, z, e)
                     logging.debug("Full traceback:", exc_info=1)
                     # Let this exception propagate out through the C code into
                     # tileset.py, where it is caught and gracefully continues