Retry file uploads via SwiftService

When we introduced LengthWrapper, we neglected to make it resettable. As
a result, upload failures result in errors like:

    put_object(...) failure and no ability to reset contents for reupload.

Now, LengthWrappers will be resettable if their _readable has seek/tell.

Related-Change: I6c8bc1366dfb591a26d934a30cd21c9e6b9a04ce
Change-Id: I21f43f06e8c78b24d1fc081efedf2687942e042f

1 files changed, 28 insertions, 4 deletions

diff --git a/swiftclient/utils.py b/swiftclient/utils.py
index 9d94b6b..ef65bbb 100644
--- a/swiftclient/utils.py
+++ b/swiftclient/utils.py
@@ -202,27 +202,36 @@ class LengthWrapper(object):
     def __init__(self, readable, length, md5=False):
         """
         :param readable: The filelike object to read from.
-        :param length: The maximum amount of content to that can be read from
+        :param length: The maximum amount of content that can be read from
                        the filelike object before it is simulated to be
                        empty.
         :param md5: Flag to enable calculating the MD5 of the content
                     as it is read.
         """
-        self.md5sum = hashlib.md5() if md5 else NoopMD5()
+        self._md5 = md5
+        self._reset_md5()
         self._length = self._remaining = length
         self._readable = readable
+        self._can_reset = all(hasattr(readable, attr)
+                              for attr in ('seek', 'tell'))
+        if self._can_reset:
+            self._start = readable.tell()
 
     def __len__(self):
         return self._length
 
+    def _reset_md5(self):
+        self.md5sum = hashlib.md5() if self._md5 else NoopMD5()
+
     def get_md5sum(self):
         return self.md5sum.hexdigest()
 
-    def read(self, *args, **kwargs):
+    def read(self, size=-1):
         if self._remaining <= 0:
             return ''
 
-        chunk = self._readable.read(*args, **kwargs)[:self._remaining]
+        to_read = self._remaining if size < 0 else min(size, self._remaining)
+        chunk = self._readable.read(to_read)
         self._remaining -= len(chunk)
 
         try:
@@ -232,6 +241,21 @@ class LengthWrapper(object):
 
         return chunk
 
+    @property
+    def reset(self):
+        if self._can_reset:
+            return self._reset
+        raise AttributeError("%r object has no attribute 'reset'" %
+                             type(self).__name__)
+
+    def _reset(self, *args, **kwargs):
+        if not self._can_reset:
+            raise TypeError('%r object cannot be reset; needs both seek and '
+                            'tell methods' % type(self._readable).__name__)
+        self._readable.seek(self._start)
+        self._reset_md5()
+        self._remaining = self._length
+
 
 def iter_wrapper(iterable):
     for chunk in iterable: