Enables GraphQL batch requests

Enabling GraphQL batch requests allows for multiple queries
to be sent in 1 request reducing the amount of requests
we send to the server.

Responses come come back in the same order as the queries were
provided.

2 files changed, 52 insertions, 9 deletions

diff --git a/app/controllers/graphql_controller.rb b/app/controllers/graphql_controller.rb
index 7b5dc22815c..e8f38899647 100644
--- a/app/controllers/graphql_controller.rb
+++ b/app/controllers/graphql_controller.rb
@@ -16,13 +16,8 @@ class GraphqlController < ApplicationController
   before_action(only: [:execute]) { authenticate_sessionless_user!(:api) }
 
   def execute
-    variables = Gitlab::Graphql::Variables.new(params[:variables]).to_h
-    query = params[:query]
-    operation_name = params[:operationName]
-    context = {
-      current_user: current_user
-    }
-    result = GitlabSchema.execute(query, variables: variables, context: context, operation_name: operation_name)
+    result = multiplex? ? execute_multiplex : execute_query
+
     render json: result
   end
 
@@ -38,6 +33,43 @@ class GraphqlController < ApplicationController
 
   private
 
+  def execute_multiplex
+    GitlabSchema.multiplex(multiplex_queries, context: context)
+  end
+
+  def execute_query
+    variables = build_variables(params[:variables])
+    operation_name = params[:operationName]
+
+    GitlabSchema.execute(query, variables: variables, context: context, operation_name: operation_name)
+  end
+
+  def query
+    params[:query]
+  end
+
+  def multiplex_queries
+    params[:_json].map do |single_query_info|
+      {
+        query: single_query_info[:query],
+        variables: build_variables(single_query_info[:variables]),
+        operation_name: single_query_info[:operationName]
+      }
+    end
+  end
+
+  def context
+    @context ||= { current_user: current_user }
+  end
+
+  def build_variables(variable_info)
+    Gitlab::Graphql::Variables.new(variable_info).to_h
+  end
+
+  def multiplex?
+    params[:_json].present?
+  end
+
   def authorize_access_api!
     access_denied!("API not accessible for user.") unless can?(current_user, :access_api)
   end
diff --git a/app/graphql/gitlab_schema.rb b/app/graphql/gitlab_schema.rb
index 897e12c1b56..a63f45f231c 100644
--- a/app/graphql/gitlab_schema.rb
+++ b/app/graphql/gitlab_schema.rb
@@ -7,7 +7,7 @@ class GitlabSchema < GraphQL::Schema
   AUTHENTICATED_COMPLEXITY = 250
   ADMIN_COMPLEXITY         = 300
 
-  ANONYMOUS_MAX_DEPTH = 10
+  DEFAULT_MAX_DEPTH = 10
   AUTHENTICATED_MAX_DEPTH = 15
 
   use BatchLoader::GraphQL
@@ -23,10 +23,21 @@ class GitlabSchema < GraphQL::Schema
   default_max_page_size 100
 
   max_complexity DEFAULT_MAX_COMPLEXITY
+  max_depth DEFAULT_MAX_DEPTH
 
   mutation(Types::MutationType)
 
   class << self
+    def multiplex(queries, **kwargs)
+      kwargs[:max_complexity] ||= max_query_complexity(kwargs[:context])
+
+      queries.each do |query|
+        query[:max_depth] = max_query_depth(kwargs[:context])
+      end
+
+      super(queries, **kwargs)
+    end
+
     def execute(query_str = nil, **kwargs)
       kwargs[:max_complexity] ||= max_query_complexity(kwargs[:context])
       kwargs[:max_depth] ||= max_query_depth(kwargs[:context])
@@ -54,7 +65,7 @@ class GitlabSchema < GraphQL::Schema
       if current_user
         AUTHENTICATED_MAX_DEPTH
       else
-        ANONYMOUS_MAX_DEPTH
+        DEFAULT_MAX_DEPTH
       end
     end
   end