Added better error handling for corrupt chunks

overviewer_core/cache.py

@@ -59,10 +59,10 @@ class LRUCache(object):
         """
         self.cache = {}
 
-        self.listhead = LRUCache._LinkNode()
-        self.listtail = LRUCache._LinkNode()
         # Two sentinel nodes at the ends of the linked list simplify boundary
         # conditions in the code below.
+        self.listhead = LRUCache._LinkNode()
+        self.listtail = LRUCache._LinkNode()
         self.listhead.right = self.listtail
         self.listtail.left = self.listhead
 
@@ -125,6 +125,18 @@ class LRUCache(object):
 
         cache[key] = link
 
+    def __delitem__(self, key):
+        # Used to flush the cache of this key
+        link = self.cache[key]
+        del cache[key]
+        link.left.right = link.right
+        link.right.left = link.left
+        
+        # Call the destructor
+        d = self.destructor
+        if d:
+            d(link.value)
+
 # memcached is an option, but unless your IO costs are really high, it just
 # ends up adding overhead and isn't worth it.
 try:

overviewer_core/nbt.py

@@ -180,11 +180,15 @@ class NBTFileReader(object):
         except (struct.error, ValueError), e:
             raise CorruptNBTError("could not parse nbt: %s" % (str(e),))
 
-class CorruptRegionError(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
 
 # For reference, the MCR format is outlined at
 # <http://www.minecraftwiki.net/wiki/Beta_Level_Format>
@@ -294,4 +298,7 @@ class MCRFileReader(object):
             raise CorruptRegionError("chunk length is invalid")
         data = StringIO.StringIO(data)
         
+        try:
             return NBTFileReader(data, is_gzip=is_gzip).read_all()
+        except Exception, e:
+            raise CorruptChunkError("Misc error parsing chunk: " + str(e))

overviewer_core/tileset.py

@@ -29,6 +29,7 @@ from itertools import product, izip
 from PIL import Image
 
 from .util import roundrobin
+from . import nbt
 from .files import FileReplacer
 from .optimizeimages import optimize_image
 import c_overviewer
@@ -934,9 +935,17 @@ class TileSet(object):
                 max_chunk_mtime = chunk_mtime
 
             # draw the chunk!
-            c_overviewer.render_loop(self.regionset, chunkx, chunky, chunkz,
+            try:
-                    tileimg, xpos, ypos, self.options['rendermode'],
+                c_overviewer.render_loop(self.regionset, chunkx, chunky,
-                    self.textures)
+                        chunkz, tileimg, xpos, ypos,
+                        self.options['rendermode'], self.textures)
+            except nbt.CorruptionError:
+                # A warning and traceback was already printed by world.py's
+                # get_chunk()
+                logging.debug("Skipping corrupt chunk at %s,%s", chunkx, chunkz)
+            except Exception, e:
+                logging.warning("Could not render chunk %s,%s for some reason. I'm going to ignore this and continue", chunkx, chunkz)
+                logging.debug("Full error was:", exc_info=1)
 
             ## Semi-handy routine for debugging the drawing routine
             ## Draw the outline of the top of the chunk

overviewer_core/world.py

@@ -279,6 +279,8 @@ class RegionSet(object):
             raise Exception("Woah, what kind of dimension is this?! %r" % self.regiondir)
 
     def _get_regionobj(self, regionfilename):
+        # Check the cache first. If it's not there, create the
+        # nbt.MCRFileReader object, cache it, and return it
         try:
             return self.regioncache[regionfilename]
         except KeyError:
@@ -317,8 +319,36 @@ 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
+        tries = 5
+        while True:
+            try:
                 region = self._get_regionobj(regionfile)
                 data = region.load_chunk(x, z)
+            except nbt.CorruptionError, e:
+                tries -= 1
+                if tries > 0:
+                    # Flush the region cache to possibly read a new region file
+                    # header
+                    logging.debug("Encountered a corrupt chunk at %s,%s. Flushing cache and retrying", x, z)
+                    logging.debug("Error was:", exc_info=1)
+                    del self.regioncache[regionfile]
+                    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.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
+                    # with the next chunk
+                    raise
+            else:
+                # no exception raised: break out of the loop
+                break
+
+
         if data is None:
             raise ChunkDoesntExist("Chunk %s,%s doesn't exist" % (x,z))
 
@@ -599,7 +629,10 @@ class CachedRegionSet(RegionSetWrapper):
             s += obj.__class__.__name__ + "."
             obj = obj._r
         # obj should now be the actual RegionSet object
+        try:
             s += obj.regiondir
+        except AttributeError:
+            s += repr(obj)
 
         logging.debug("Initializing a cache with key '%s'", s)