Add utils and validation modules to support subscriptions

Author: hballard

graphql_subscriptions/utils.py

@@ -0,0 +1,18 @@
+import re
+
+
+# From this response in Stackoverflow
+# http://stackoverflow.com/a/19053800/1072990
+def to_camel_case(snake_str):
+    components = snake_str.split('_')
+    # We capitalize the first letter of each component except the first one
+    # with the 'title' method and join them together.
+    return components[0] + "".join(x.title() if x else '_'
+                                   for x in components[1:])
+
+
+# From this response in Stackoverflow
+# http://stackoverflow.com/a/1176023/1072990
+def to_snake_case(name):
+    s1 = re.sub('(.)([A-Z][a-z]+)', r'\1_\2', name)
+    return re.sub('([a-z0-9])([A-Z])', r'\1_\2', s1).lower()

graphql_subscriptions/validation.py

@@ -0,0 +1,42 @@
+from graphql import GraphQLError
+from graphql.validation.rules.base import ValidationRule
+
+FIELD = 'Field'
+
+# XXX from Apollo pacakge: Temporarily use this validation
+# rule to make our life a bit easier.
+
+
+class SubscriptionHasSingleRootField(ValidationRule):
+    __slots__ = 'field',
+
+    def __init__(self, context):
+        self.field = FIELD
+        super(SubscriptionHasSingleRootField, self).__init__(context)
+
+    def enter_OperationDefinition(self, node, key, parent, path, ancestors):
+        schema = self.context.get_schema()
+        schema.get_subscription_type()
+        operation_name = node.name.value if node.name else ''
+        num_fields = 0
+        for selection in node.selection_set.selections:
+            # TODO: Fix this string assertion of "Field"...Apollo did this
+            # in their package and since I was porting, just followed the same
+            if type(selection).__name__ == self.field:
+                num_fields += 1
+            else:
+                self.context.report_error(
+                    GraphQLError(
+                        'Apollo subscriptions do not support fragments on\
+ the root field', [node]))
+        if num_fields > 1:
+            self.context.report_error(
+                GraphQLError(
+                    self.too_many_subscription_fields_error(operation_name),
+                    [node]))
+        return False
+
+    @staticmethod
+    def too_many_subscription_fields_error(subscription_name):
+        return 'Subscription "{0}" must have only one\
+ field.'.format(subscription_name)