rgw: add a new multipart test

test for the following ceph issue:
http://tracker.ceph.com/issues/15886

Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>

s3tests/functional/test_s3.py

@@ -5760,6 +5760,68 @@ def test_atomic_multipart_upload_write():
     got = key.get_contents_as_string()
     eq(got, 'bar')
 
+class Counter:
+    def __init__(self, default_val):
+        self.val = default_val
+
+    def inc(self):
+        self.val = self.val + 1
+
+class ActionOnCount:
+    def __init__(self, trigger_count, action):
+        self.count = 0
+        self.trigger_count = trigger_count
+        self.action = action
+
+    def trigger(self):
+        self.count = self.count + 1
+
+        if self.count == self.trigger_count:
+            self.action()
+
+@attr(resource='object')
+@attr(method='put')
+@attr(operation='multipart check for two writes of the same part, first write finishes last')
+@attr(assertion='object contains correct content')
+def test_multipart_resend_first_finishes_last():
+    bucket = get_new_bucket()
+    key_name = "mymultipart"
+    mp = bucket.initiate_multipart_upload(key_name)
+
+    file_size = 8 * 1024 * 1024
+
+    counter = Counter(0)
+
+    # mp.upload_part_from_file might read multiple times from the object
+    # first time when it calculates md5, second time when it writes data
+    # out. We want to interject only on the last time, but we can't be
+    # sure how many times it's going to read, so let's have a test run
+    # and count the number of reads
+    fp_dryrun = FakeWriteFile(file_size, 'C',
+        lambda: counter.inc()
+        )
+    mp.upload_part_from_file(fp_dryrun, 1)
+    mp.complete_upload
+
+    bucket.delete_key(key_name)
+
+    # ok, now for the actual test
+
+    fp_b = FakeWriteFile(file_size, 'B')
+
+    action = ActionOnCount(counter.val, lambda: mp.upload_part_from_file(fp_b, 1))
+
+    fp_a = FakeWriteFile(file_size, 'A',
+        lambda: action.trigger()
+        )
+
+    mp = bucket.initiate_multipart_upload(key_name)
+    mp.upload_part_from_file(fp_a, 1)
+    mp.complete_upload()
+
+    key = bucket.get_key(key_name)
+    _verify_atomic_key_data(key, file_size, 'A')
+
 @attr(resource='object')
 @attr(method='get')
 @attr(operation='range')