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, 102 insertions, 22 deletions

diff --git a/spec/requests/api/graphql/gitlab_schema_spec.rb b/spec/requests/api/graphql/gitlab_schema_spec.rb
index dd518274f82..a724c5c3f1c 100644
--- a/spec/requests/api/graphql/gitlab_schema_spec.rb
+++ b/spec/requests/api/graphql/gitlab_schema_spec.rb
@@ -3,41 +3,82 @@ require 'spec_helper'
 describe 'GitlabSchema configurations' do
   include GraphqlHelpers
 
-  let(:project) { create(:project, :repository) }
-  let(:query) { graphql_query_for('project', { 'fullPath' => project.full_path }, %w(id name description)) }
-  let(:current_user) { create(:user) }
+  let(:project) { create(:project) }
 
-  describe '#max_complexity' do
-    context 'when complexity is too high' do
-      it 'shows an error' do
-        allow(GitlabSchema).to receive(:max_query_complexity).and_return 1
+  shared_examples 'imposing query limits' do
+    describe '#max_complexity' do
+      context 'when complexity is too high' do
+        it 'shows an error' do
+          allow(GitlabSchema).to receive(:max_query_complexity).and_return 1
 
-        post_graphql(query, current_user: nil)
+          subject
 
-        expect(graphql_errors.first['message']).to include('which exceeds max complexity of 1')
+          expect(graphql_errors.flatten.first['message']).to include('which exceeds max complexity of 1')
+        end
       end
     end
-  end
 
-  describe '#max_depth' do
-    context 'when query depth is too high' do
-      it 'shows error' do
-        errors = [{ "message" => "Query has depth of 2, which exceeds max depth of 1" }]
-        allow(GitlabSchema).to receive(:max_query_depth).and_return 1
+    describe '#max_depth' do
+      context 'when query depth is too high' do
+        it 'shows error' do
+          errors = { "message" => "Query has depth of 2, which exceeds max depth of 1" }
+          allow(GitlabSchema).to receive(:max_query_depth).and_return 1
 
-        post_graphql(query)
+          subject
 
-        expect(graphql_errors).to eq(errors)
+          expect(graphql_errors.flatten).to include(errors)
+        end
       end
+
+      context 'when query depth is within range' do
+        it 'has no error' do
+          allow(GitlabSchema).to receive(:max_query_depth).and_return 5
+
+          subject
+
+          expect(Array.wrap(graphql_errors).compact).to be_empty
+        end
+      end
+    end
+  end
+
+  context 'regular queries' do
+    subject do
+      query = graphql_query_for('project', { 'fullPath' => project.full_path }, %w(id name description))
+      post_graphql(query)
     end
 
-    context 'when query depth is within range' do
-      it 'has no error' do
-        allow(GitlabSchema).to receive(:max_query_depth).and_return 5
+    it_behaves_like 'imposing query limits'
+  end
+
+  context 'multiplexed queries' do
+    subject do
+      queries = [
+        { query: graphql_query_for('project', { 'fullPath' => project.full_path }, %w(id name description)) },
+        { query: graphql_query_for('echo', { 'text' => "$test" }, []), variables: { "test" => "Hello world" } }
+      ]
+
+      post_multiplex(queries)
+    end
+
+    it_behaves_like 'imposing query limits' do
+      it "fails all queries when only one of the queries is too complex" do
+        # The `project` query above has a complexity of 5
+        allow(GitlabSchema).to receive(:max_query_complexity).and_return 4
+
+        subject
 
-        post_graphql(query)
+        # Expect a response for each query, even though it will be empty
+        expect(json_response.size).to eq(2)
+        json_response.each do |single_query_response|
+          expect(single_query_response).not_to have_key('data')
+        end
 
-        expect(graphql_errors).to be_nil
+        # Expect errors for each query
+        expect(graphql_errors.size).to eq(2)
+        graphql_errors.each do |single_query_errors|
+          expect(single_query_errors.first['message']).to include('which exceeds max complexity of 4')
+        end
       end
     end
   end
diff --git a/spec/requests/api/graphql/multiplexed_queries_spec.rb b/spec/requests/api/graphql/multiplexed_queries_spec.rb
new file mode 100644
index 00000000000..844fd979285
--- /dev/null
+++ b/spec/requests/api/graphql/multiplexed_queries_spec.rb
@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+require 'spec_helper'
+
+describe 'Multiplexed queries' do
+  include GraphqlHelpers
+
+  it 'returns responses for multiple queries' do
+    queries = [
+      { query: 'query($text: String) { echo(text: $text) }',
+        variables: { 'text' => 'Hello' } },
+      { query: 'query($text: String) { echo(text: $text) }',
+        variables: { 'text' => 'World' } }
+    ]
+
+    post_multiplex(queries)
+
+    first_response = json_response.first['data']['echo']
+    second_response = json_response.last['data']['echo']
+
+    expect(first_response).to eq('nil says: Hello')
+    expect(second_response).to eq('nil says: World')
+  end
+
+  it 'returns error and data combinations' do
+    queries = [
+      { query: 'query($text: String) { broken query }' },
+      { query: 'query working($text: String) { echo(text: $text) }',
+        variables: { 'text' => 'World' } }
+    ]
+
+    post_multiplex(queries)
+
+    first_response = json_response.first['errors']
+    second_response = json_response.last['data']['echo']
+
+    expect(first_response).not_to be_empty
+    expect(second_response).to eq('nil says: World')
+  end
+end