Round timestamp and add uuid to payload.

Timestamp is now returned in UTC with second precision.
Payload hash is replaced by an uuid4. This allows us to distinguish
between duplicated payloads.
Removed a deprecated test related to the payload hash.
Renamded secondary index payload_hash -> payload_uuid

bigchaindb/db/utils.py

@@ -54,7 +54,7 @@ def init():
         .run(conn)
     # secondary index for payload hash
     r.db(dbname).table('bigchain')\
-        .index_create('payload_hash', r.row['block']['transactions']['transaction']['data']['hash'], multi=True)\
+        .index_create('payload_uuid', r.row['block']['transactions']['transaction']['data']['uuid'], multi=True)\
         .run(conn)
 
     # wait for rethinkdb to finish creating secondary indexes

bigchaindb/util.py

@@ -4,7 +4,7 @@ import contextlib
 import threading
 import queue
 import multiprocessing as mp
-from datetime import datetime
+import uuid
 
 import rapidjson
 
@@ -127,14 +127,13 @@ def deserialize(data):
 
 
 def timestamp():
-    """Calculate a UTC timestamp with microsecond precision.
+    """Calculate a UTC timestamp with second precision.
 
     Returns:
         str: UTC timestamp.
 
     """
-    dt = datetime.utcnow()
-    return "{0:.6f}".format(time.mktime(dt.timetuple()) + dt.microsecond / 1e6)
+    return str(round(time.time()))
 
 
 # TODO: Consider remove the operation (if there are no inputs CREATE else TRANSFER)
@@ -224,9 +223,8 @@ def create_tx(current_owners, new_owners, inputs, operation, payload=None):
     data = None
     if payload is not None:
         if isinstance(payload, dict):
-            hash_payload = crypto.hash_data(serialize(payload))
             data = {
-                'hash': hash_payload,
+                'uuid': str(uuid.uuid4()),
                 'payload': payload
             }
         else:

tests/db/test_bigchain_api.py

@@ -48,24 +48,6 @@ class TestBigchainApi(object):
         assert b.validate_fulfillments(tx) == False
         assert b.validate_fulfillments(tx_signed) == True
 
-    def test_transaction_hash(self, b, user_vk):
-        payload = {'cats': 'are awesome'}
-        tx = b.create_transaction(user_vk, user_vk, None, 'CREATE', payload)
-        tx_calculated = {
-            'conditions': [{'cid': 0,
-                            'condition': tx['transaction']['conditions'][0]['condition'],
-                            'new_owners': [user_vk]}],
-            'data': {'hash': crypto.hash_data(util.serialize(payload)),
-                     'payload': payload},
-            'fulfillments': [{'current_owners': [user_vk],
-                              'fid': 0,
-                              'fulfillment': None,
-                              'input': None}],
-            'operation': 'CREATE',
-            'timestamp': tx['transaction']['timestamp']
-        }
-        assert tx['transaction']['data'] == tx_calculated['data']
-        # assert tx_hash == tx_calculated_hash
 
     def test_transaction_signature(self, b, user_sk, user_vk):
         tx = b.create_transaction(user_vk, user_vk, None, 'CREATE')