Fix object copy with empty source

When s3 client make a copy request with empty copy source,
current swift3 will return a 500 error. This is caused from
a lack of header validation.

This fixes the behavior to make a 400 Bad Request (InvalidArgument).

Change-Id: I60c7e480582f5b9258433306bbf228b7291e6236

swift3/controllers/obj.py

@@ -58,14 +58,13 @@ class ObjectController(Controller):
         Handle PUT Object and PUT Object (Copy) request
         """
         if CONF.s3_acl:
-            if 'HTTP_X_AMZ_COPY_SOURCE' in req.environ:
-                src_path = req.environ['HTTP_X_AMZ_COPY_SOURCE']
-                src_path = src_path if src_path[0] == '/' else ('/' + src_path)
+            if 'X-Amz-Copy-Source' in req.headers:
+                src_path = req.headers['X-Amz-Copy-Source']
+                src_path = src_path if src_path.startswith('/') else \
+                    ('/' + src_path)
                 src_bucket, src_obj = split_path(src_path, 0, 2, True)
-
                 req.get_response(self.app, 'HEAD', src_bucket, src_obj,
                                  permission='READ')
-
             b_resp = req.get_response(self.app, 'HEAD', obj='')
             # To avoid overwriting the existing object by unauthorized user,
             # we send HEAD request first before writing the object to make
@@ -83,11 +82,11 @@ class ObjectController(Controller):
 
         resp = req.get_response(self.app)
 
-        if 'HTTP_X_COPY_FROM' in req.environ:
+        if 'X-Amz-Copy-Source' in req.headers:
             elem = Element('CopyObjectResult')
             SubElement(elem, 'ETag').text = '"%s"' % resp.etag
             body = tostring(elem, use_s3ns=False)
-            return HTTPOk(body=body)
+            return HTTPOk(body=body, headers=resp.headers)
 
         resp.status = HTTP_OK