fix for chunk number calculation when unaligned - thanks to Daniel Lundin for the patch

doc/contributors.rst

@@ -18,3 +18,4 @@ The following is a list of people who have contributed to
 - Joshua Roesslein (joshthecoder)
 - Gregg Lind (gregglind)
 - Michael Schurter (schmichael)
+- Daniel Lundin

gridfs/grid_file.py

@@ -306,7 +306,7 @@ class GridFile(object):
             size = remainder
 
         bytes = self.__buffer
-        chunk_number = math.floor(self.__position / self.__chunk_size)
+        chunk_number = (len(bytes) + self.__position) / self.__chunk_size
 
         while len(bytes) < size:
             chunk = self.__collection.chunks.find_one({"files_id": self.__id, "n": chunk_number})

test/test_grid_file.py

@@ -406,5 +406,26 @@ class TestGridFile(unittest.TestCase):
         file = GridFile({"_id": "foobar", "filename": "foobar"}, self.db, "w")
         file.close()
 
+    def test_read_chunks_unaligned_buffer_size(self):
+        self.db.fs.files.remove({})
+        self.db.fs.chunks.remove({})
+
+        in_data = "This is a text that doesn't quite fit in a single 16-byte chunk."
+        f = GridFile({"filename":"test", "chunkSize":16}, self.db, "w")
+        f.write(in_data)
+        f.close()
+
+        f = GridFile({"filename":"test"}, self.db)
+        out_data = ''
+        while 1:
+            s = f.read(13)
+            if not s:
+                break
+            out_data += s
+        f.close()
+
+        self.assertEqual(in_data, out_data)
+
+
 if __name__ == "__main__":
     unittest.main()