Merge pull request #74 from chenxiaolong/sparse

Produce sparse output files

avbroot/ota.py

@@ -659,7 +659,11 @@ class _TeeFileDescriptor:
             self.capture.write(data)
         else:
             for stream in self.streams:
-                stream.write(data)
+                # Naive hole punching to create sparse files
+                if stream is self.backing and util.is_zero(data):
+                    stream.seek(len(data), os.SEEK_CUR)
+                else:
+                    stream.write(data)
 
         return len(data)
 

avbroot/util.py

@@ -3,6 +3,9 @@ import os
 import tempfile
 
 
+_ZERO_BLOCK = memoryview(b'\0' * 16384)
+
+
 @contextlib.contextmanager
 def open_output_file(path):
     '''
@@ -145,3 +148,21 @@ def read_exact(f, size: int) -> bytes:
         return bytes(data)
     else:
         return data
+
+
+def is_zero(data):
+    '''
+    Check if all bytes in the bytes-like object are null bytes.
+    '''
+
+    view = memoryview(data)
+
+    while view:
+        n = min(len(view), len(_ZERO_BLOCK))
+
+        if view[:n] != _ZERO_BLOCK[:n]:
+            return False
+
+        view = view[n:]
+
+    return True