Spec of bp support-md5-of-body support

Now, Zaqar will add a non-URL-encoded message body MD5 validation function.
This is essential for the security of the message body, it can prevent the
message from being tampered.

Change-Id: Ic01e37be1ab59a42d10c53ffadfb6569ffccce2b
blueprint: support-md5-of-body

specs/queens/support-md5-of-body.rst

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+..
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+
+================================
+Support Checksum Of Message Body
+================================
+
+https://blueprints.launchpad.net/zaqar/+spec/support-md5-of-body
+
+Now, Zaqar will add a non-URL-encoded message body checksum function.
+This is essential for the security of the message body, it can prevent the
+message from being tampered.
+
+Problem description
+===================
+
+Currently, Zaqar has no checksum of the non-URL-encoded message body. It is
+a good feature for the security of the message body.
+
+AWS SQS service has supported the function, that would be a good reference for
+Zaqar[1].
+
+Proposed change
+===============
+
+When user claim or get the messages, the checksum will be returned with message
+body together, So user can use it to verify that the message body is correct.
+Currently zaqar only support the checksum of the non-URL-encoded message body based
+on MD5 digests. We may support other algorithms in future versions, including SHA1,
+sha256, sha512, and so on. So, It is necessary to change the following:
+
+1. Add new property named ``checksum`` for message. This property is a string type.
+
+   When you send a message to queue, Zaqar will use the default checksum algorithm
+   MD5 to calculate the ``checksum`` value of the non-URL-encoded message body.
+   Finally Zaqar will store the value on the backend. Now the backend Mongodb,
+   Redis and Swift can be supported.
+
+2. Return the property ``checksum`` for message when user claims or gets the message.
+
+   When user gets or claims the message, The API will return the k-v pair of ``checksum``
+   in the body of the message. The user can then use this value to verify that the
+   body of the newly retrieved message is correct or not.
+
+3. This feature is backward compatible.
+
+   For old messages that do not have the checksum attribute, the checksum will return
+   ``None`` for both ``claim`` and ``get`` operation. This feature will also transit
+   smoothly as the old messages gradually expire.
+
+4. Add new data model for message body and queue on different backend.
+
+   MESSAGE::
+
+        +----------------------+---------+
+        |  Name                |  Field  |
+        +======================+=========+
+        |  checksum            |   cs   |
+        +----------------------+---------+
+        |  body                |   b     |
+        +----------------------+---------+
+        |  ...                 |   ...   |
+        +----------------------+---------+
+
+Drawbacks
+---------
+
+None
+
+Alternatives
+------------
+
+None
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee:
+  cdyangzhenyu <cdyangzhenyu@gmail.com>
+
+Milestones
+----------
+
+Target Milestone for completion:
+  Queens RC1
+
+Work Items
+----------
+
+#. Add message body checksum support for Mongodb, Redis and Swift.
+#. Add release note for this feature.
+#. Update API reference.
+#. Add user/developer document for this feature.
+#. Change unit, functional and tempest tests accordingly.
+
+Dependencies
+============
+
+None
+
+References
+==========
+
+[1]:https://docs.aws.amazon.com/AWSSimpleQueueService/latest/APIReference/API_Message.html