ECFragGetter: assume policy.fragment_size is non-zero

Simplify ECFragGetter by removing code that guards against the policy
fragment_size being None or zero.

Policy fragment_size must be > 0: the fragment_size is based on the
ec_segment_size, which is verified as > 0 when constructing an EC
policy. This is asserted by test_parse_storage_policies in
test.unit.common.test_storage_policy.TestStoragePolicies.

Also, rename client_chunk_size to fragment_size for clarity.

Change-Id: Ie1efaab3bd0510275d534b5c023cb73c98bec90d

swift/proxy/controllers/obj.py

@@ -2497,7 +2497,7 @@ class ECFragGetter(object):
         self.backend_headers = backend_headers
         self.header_provider = header_provider
         self.req_query_string = req.query_string
-        self.client_chunk_size = policy.fragment_size
+        self.fragment_size = policy.fragment_size
         self.skip_bytes = 0
         self.bytes_used_from_backend = 0
         self.source = self.node = None
@@ -2578,8 +2578,8 @@ class ECFragGetter(object):
 
     def learn_size_from_content_range(self, start, end, length):
         """
-        If client_chunk_size is set, makes sure we yield things starting on
+        Make sure we yield things starting on fragment boundaries based on the
-        chunk boundaries based on the Content-Range header in the response.
+        Content-Range header in the response.
 
         Sets our Range header's first byterange to the value learned from
         the Content-Range header in the response; if we were given a
@@ -2593,8 +2593,7 @@ class ECFragGetter(object):
         if length == 0:
             return
 
-        if self.client_chunk_size:
+        self.skip_bytes = bytes_to_skip(self.fragment_size, start)
-            self.skip_bytes = bytes_to_skip(self.client_chunk_size, start)
 
         if 'Range' in self.backend_headers:
             try:
@@ -2725,10 +2724,9 @@ class ECFragGetter(object):
                         self.bytes_used_from_backend += len(buf)
                         buf = b''
 
-                client_chunk_size = self.client_chunk_size or len(buf)
+                while buf and (len(buf) >= self.fragment_size or not chunk):
-                while buf and (len(buf) >= client_chunk_size or not chunk):
+                    client_chunk = buf[:self.fragment_size]
-                    client_chunk = buf[:client_chunk_size]
+                    buf = buf[self.fragment_size:]
-                    buf = buf[client_chunk_size:]
                     with WatchdogTimeout(self.app.watchdog,
                                          self.app.client_timeout,
                                          ChunkWriteTimeout):

test/unit/proxy/controllers/test_obj.py

@@ -6715,27 +6715,12 @@ class TestECFragGetter(BaseObjectControllerMixin, unittest.TestCase):
                     b''.join(it)
         self.assertEqual('9 seconds', str(cm.exception))
 
-    def test_iter_bytes_from_response_part_null_chunk_size(self):
+    def test_iter_bytes_from_response_part_small_fragment_size(self):
-        # we don't expect a policy to have fragment_size None or zero but
+        self.getter.fragment_size = 4
-        # verify that the getter is defensive
-        self.getter.client_chunk_size = None
-        part = FileLikeIter([b'some', b'thing', b''])
-        it = self.getter.iter_bytes_from_response_part(part, nbytes=None)
-        self.assertEqual(b'something', b''.join(it))
-
-        self.getter.client_chunk_size = 0
-        part = FileLikeIter([b'some', b'thing', b''])
-        it = self.getter.iter_bytes_from_response_part(part, nbytes=None)
-        self.assertEqual(b'something', b''.join(it))
-
-    def test_iter_bytes_from_response_part_small_chunk_size(self):
-        # we don't expect a policy to have fragment_size None or zero but
-        # verify that the getter is defensive
-        self.getter.client_chunk_size = 4
         part = FileLikeIter([b'some', b'thing', b''])
         it = self.getter.iter_bytes_from_response_part(part, nbytes=None)
         self.assertEqual([b'some', b'thin', b'g'], [ch for ch in it])
-        self.getter.client_chunk_size = 1
+        self.getter.fragment_size = 1
         part = FileLikeIter([b'some', b'thing', b''])
         it = self.getter.iter_bytes_from_response_part(part, nbytes=None)
         self.assertEqual([c.encode() for c in 'something'], [ch for ch in it])