GQL: Handle internal server error from missing variables

Author: JerrySentry

graphql_api/validation.py

@@ -1,10 +1,59 @@
-from typing import Any, Type
+from typing import Any, Dict, Type
 
 from graphql import GraphQLError, ValidationRule
-from graphql.language.ast import DocumentNode, FieldNode, OperationDefinitionNode
+from graphql.language.ast import (
+    DocumentNode,
+    FieldNode,
+    OperationDefinitionNode,
+    VariableDefinitionNode,
+)
 from graphql.validation import ValidationContext
 
 
+class MissingVariablesError(Exception):
+    """
+    Custom error class to represent errors where required variables defined in the query does
+    not have a matching definition in the variables part of the request. Normally when this
+    scenario occurs it would raise a GraphQLError type but that would cause a uncaught
+    exception for some reason. The aim of this is to surface the error in the response clearly
+    and to prevent internal server errors when it occurs.
+    """
+
+    pass
+
+
+def create_required_variables_rule(variables: Dict) -> Type[ValidationRule]:
+    class RequiredVariablesValidationRule(ValidationRule):
+        def __init__(self, context: ValidationContext) -> None:
+            super().__init__(context)
+            self.variables = variables
+
+        def enter_operation_definition(
+            self, node: OperationDefinitionNode, *_args: Any
+        ) -> None:
+            # Get variable definitions
+            variable_definitions = node.variable_definitions or []
+
+            # Extract variables marked as Non Null
+            required_variables = [
+                var_def.variable.name.value
+                for var_def in variable_definitions
+                if isinstance(var_def, VariableDefinitionNode)
+                and var_def.type.kind == "non_null_type"
+            ]
+
+            # Check if these required variables are provided
+            missing_variables = [
+                var for var in required_variables if var not in self.variables
+            ]
+            if missing_variables:
+                raise MissingVariablesError(
+                    f"Missing required variables: {', '.join(missing_variables)}",
+                )
+
+    return RequiredVariablesValidationRule
+
+
 def create_max_depth_rule(max_depth: int) -> Type[ValidationRule]:
     class MaxDepthRule(ValidationRule):
         def __init__(self, context: ValidationContext) -> None:

graphql_api/views.py

@@ -28,7 +28,12 @@
 from services.redis_configuration import get_redis_connection
 
 from .schema import schema
-from .validation import create_max_aliases_rule, create_max_depth_rule
+from .validation import (
+    MissingVariablesError,
+    create_max_aliases_rule,
+    create_max_depth_rule,
+    create_required_variables_rule,
+)
 
 log = logging.getLogger(__name__)
 
@@ -198,6 +203,7 @@ def get_validation_rules(
         data: dict,
     ) -> Optional[Collection]:
         return [
+            create_required_variables_rule(variables=data.get("variables")),
             create_max_aliases_rule(max_aliases=settings.GRAPHQL_MAX_ALIASES),
             create_max_depth_rule(max_depth=settings.GRAPHQL_MAX_DEPTH),
             cost_validator(
@@ -259,7 +265,16 @@ async def post(self, request, *args, **kwargs):
             )
 
         with RequestFinalizer(request):
-            response = await super().post(request, *args, **kwargs)
+            try:
+                response = await super().post(request, *args, **kwargs)
+            except MissingVariablesError as e:
+                return JsonResponse(
+                    data={
+                        "status": 400,
+                        "detail": str(e),
+                    },
+                    status=400,
+                )
 
             content = response.content.decode("utf-8")
             data = json.loads(content)