Make sure we send the extra zeros in chunks

util/dockerloadformat.py

@@ -1,4 +1,4 @@
-from util.gzipwrap import GzipWrap
+from util.gzipwrap import GzipWrap, GZIP_BUFFER_SIZE
 from util.streamlayerformat import StreamLayerMerger
 from app import app
 
@@ -75,7 +75,11 @@ def _import_format_generator(namespace, repository, tag, synthetic_image_id,
   # If the yielded size is less than the estimated size (which is likely), fill the rest with
   # zeros.
   if yielded_size < estimated_file_size:
-    yield '\0' * (estimated_file_size - yielded_size)
+    to_yield = estimated_file_size - yielded_size
+    while to_yield > 0:
+      yielded = min(to_yield, GZIP_BUFFER_SIZE)
+      yield '\0' * yielded
+      to_yield -= yielded
 
   # Yield any file padding to 512 bytes that is necessary.
   yield _tar_file_padding(estimated_file_size)

util/gzipwrap.py

@@ -1,5 +1,8 @@
 from gzip import GzipFile
 
+# 256K buffer to Gzip
+GZIP_BUFFER_SIZE = 1024 * 256
+
 class GzipWrap(object):
   def __init__(self, input, filename=None, compresslevel=1):
     self.input = iter(input)
@@ -21,7 +24,7 @@ class GzipWrap(object):
 
       input_size = 0
       input_buffer = ''
-      while input_size < 1024 * 256:  # 256K buffer to Gzip
+      while input_size < GZIP_BUFFER_SIZE:
         try:
           s = self.input.next()
           input_buffer += s