Added validate_transaction function in web API and client.

bigchaindb/client.py

@@ -90,6 +90,24 @@ class Client:
             tx, private_key=self.private_key)
         return self._push(signed_tx)
 
+    def validate(self, tx):
+        """Validate a transaction object.
+
+        If tx is a `CREATE` transaction, this method will return (True, '') even
+        without the federation signature as long as the transaction is otherwise
+        valid.
+
+        Args:
+            tx (dict): the transaction object to be validated
+
+        Return:
+            (bool, str): (True, '') if the tx is valid, else (False, errormsg)
+        """
+
+        res = requests.post(self.api_endpoint + '/transactions/validate/',
+                            json=tx)
+        return (res.json()['valid'], res.json()['error'])
+
     def _push(self, tx):
         """Submit a transaction to the Federation.
 

bigchaindb/web/views.py

@@ -7,7 +7,7 @@ For more information please refer to the documentation in Apiary:
 import flask
 from flask import current_app, request, Blueprint
 
-from bigchaindb import util
+from bigchaindb import util, exceptions
 
 
 basic_views = Blueprint('basic_views', __name__)
@@ -68,3 +68,30 @@ def create_transaction():
 
     return flask.jsonify(**tx)
 
+@basic_views.route('/transactions/validate/', methods=['POST'])
+def validate_transaction():
+    """API endpoint to validate transactions without pushing them to the
+    Federation. No federation node signature is required for `CREATE`
+    transactions.
+
+    Return:
+        A JSON object with the `valid` field populated with a boolean value
+        and the `error` field populated with an error message or an empty str
+    """
+    bigchain = current_app.config['bigchain']
+
+    tx = request.get_json(force=True)
+
+    if tx['transaction']['operation'] == 'CREATE':
+        tx = util.transform_create(tx)
+
+    try:
+        bigchain.validate_transaction(tx)
+    except exceptions.InvalidSignature as e:
+        # We skipped signing CREATEs with the node's private key, so expect this
+        if tx['transaction']['operation'] != 'CREATE':
+            return flask.jsonify({'valid': False, 'error': repr(e)})
+    except Exception as e:
+        return flask.jsonify({'valid': False, 'error': repr(e)})
+
+    return flask.jsonify({'valid': True, 'error': ''})