From 956592d6154d101bbf0d4090bafbfbd7f6540e4f Mon Sep 17 00:00:00 2001
From: Bert Blommers <info@bertblommers.nl>
Date: Thu, 22 Aug 2019 16:12:48 +0100
Subject: [PATCH] 2380 - Validate parameter-list for duplicates in
 dynamodb.batch_get_item

---
 moto/dynamodb2/responses.py           | 12 +++++++
 tests/test_dynamodb2/test_dynamodb.py | 52 +++++++++++++++++++++++++++
 2 files changed, 64 insertions(+)

diff --git a/moto/dynamodb2/responses.py b/moto/dynamodb2/responses.py
index 86ca9a362..3e9fbb553 100644
--- a/moto/dynamodb2/responses.py
+++ b/moto/dynamodb2/responses.py
@@ -318,6 +318,9 @@ class DynamoHandler(BaseResponse):
 
         for table_name, table_request in table_batches.items():
             keys = table_request['Keys']
+            if self._contains_duplicates(keys):
+                er = 'com.amazon.coral.validate#ValidationException'
+                return self.error(er, 'Provided list of item keys contains duplicates')
             attributes_to_get = table_request.get('AttributesToGet')
             results["Responses"][table_name] = []
             for key in keys:
@@ -333,6 +336,15 @@ class DynamoHandler(BaseResponse):
             })
         return dynamo_json_dump(results)
 
+    def _contains_duplicates(self, keys):
+        unique_keys = []
+        for k in keys:
+            if k in unique_keys:
+                return True
+            else:
+                unique_keys.append(k)
+        return False
+
     def query(self):
         name = self.body['TableName']
         # {u'KeyConditionExpression': u'#n0 = :v0', u'ExpressionAttributeValues': {u':v0': {u'S': u'johndoe'}}, u'ExpressionAttributeNames': {u'#n0': u'username'}}
diff --git a/tests/test_dynamodb2/test_dynamodb.py b/tests/test_dynamodb2/test_dynamodb.py
index a8f73bee6..fb6c0e17d 100644
--- a/tests/test_dynamodb2/test_dynamodb.py
+++ b/tests/test_dynamodb2/test_dynamodb.py
@@ -2141,3 +2141,55 @@ def test_scan_by_non_exists_index():
     ex.exception.response['Error']['Message'].should.equal(
         'The table does not have the specified index: non_exists_index'
     )
+
+
+@mock_dynamodb2
+def test_batch_items_returns_all():
+    dynamodb = _create_user_table()
+    returned_items = dynamodb.batch_get_item(RequestItems={
+        'users': {
+            'Keys': [{
+                'username': {'S': 'user0'}
+            }, {
+                'username': {'S': 'user1'}
+            }, {
+                'username': {'S': 'user2'}
+            }, {
+                'username': {'S': 'user3'}
+            }],
+            'ConsistentRead': True
+        }
+    })['Responses']['users']
+    assert len(returned_items) == 3
+    assert [item['username']['S'] for item in returned_items] == ['user1', 'user2', 'user3']
+
+
+@mock_dynamodb2
+def test_batch_items_should_throw_exception_for_duplicate_request():
+    client = _create_user_table()
+    with assert_raises(ClientError) as ex:
+        client.batch_get_item(RequestItems={
+            'users': {
+                'Keys': [{
+                    'username': {'S': 'user0'}
+                }, {
+                    'username': {'S': 'user0'}
+                }],
+                'ConsistentRead': True
+            }})
+    ex.exception.response['Error']['Code'].should.equal('ValidationException')
+    ex.exception.response['Error']['Message'].should.equal('Provided list of item keys contains duplicates')
+
+
+def _create_user_table():
+    client = boto3.client('dynamodb', region_name='us-east-1')
+    client.create_table(
+        TableName='users',
+        KeySchema=[{'AttributeName': 'username', 'KeyType': 'HASH'}],
+        AttributeDefinitions=[{'AttributeName': 'username', 'AttributeType': 'S'}],
+        ProvisionedThroughput={'ReadCapacityUnits': 5, 'WriteCapacityUnits': 5}
+    )
+    client.put_item(TableName='users', Item={'username': {'S': 'user1'}, 'foo': {'S': 'bar'}})
+    client.put_item(TableName='users', Item={'username': {'S': 'user2'}, 'foo': {'S': 'bar'}})
+    client.put_item(TableName='users', Item={'username': {'S': 'user3'}, 'foo': {'S': 'bar'}})
+    return client