Merge branch 'graphql-resolvers-complexity' into 'master'

[CE] Compute resolver complexity based on items

See merge request gitlab-org/gitlab-ce!28017

app/graphql/resolvers/base_resolver.rb

@@ -9,5 +9,24 @@ module Resolvers
         end
       end
     end
+
+    def self.resolver_complexity(args)
+      complexity = 1
+      complexity += 1 if args[:sort]
+      complexity += 5 if args[:search]
+
+      complexity
+    end
+
+    def self.complexity_multiplier(args)
+      # When fetching many items, additional complexity is added to the field
+      # depending on how many items is fetched. For each item we add 1% of the
+      # original complexity - this means that loading 100 items (our default
+      # maxp_age_size limit) doubles the original complexity.
+      #
+      # Complexity is not increased when searching by specific ID(s), because
+      # complexity difference is minimal in this case.
+      [args[:iid], args[:iids]].any? ? 0 : 0.01
+    end
   end
 end

app/graphql/resolvers/concerns/resolves_pipelines.rb

@@ -19,6 +19,16 @@ module ResolvesPipelines
              description: "Filter pipelines by the sha of the commit they are run for"
   end
 
+  class_methods do
+    def resolver_complexity(args)
+      complexity = super
+      complexity += 2 if args[:sha]
+      complexity += 2 if args[:ref]
+
+      complexity
+    end
+  end
+
   def resolve_pipelines(project, params = {})
     PipelinesFinder.new(project, context[:current_user], params).execute
   end

app/graphql/resolvers/issues_resolver.rb

@@ -57,5 +57,12 @@ module Resolvers
 
       IssuesFinder.new(context[:current_user], args).execute
     end
+
+    def self.resolver_complexity(args)
+      complexity = super
+      complexity += 2 if args[:labelName]
+
+      complexity
+    end
   end
 end

app/graphql/resolvers/project_resolver.rb

@@ -9,5 +9,9 @@ module Resolvers
     def resolve(full_path:)
       model_by_full_path(Project, full_path)
     end
+
+    def self.complexity_multiplier(args)
+      0
+    end
   end
 end

app/graphql/types/base_field.rb

@@ -7,10 +7,40 @@ module Types
     DEFAULT_COMPLEXITY = 1
 
     def initialize(*args, **kwargs, &block)
-      # complexity is already defaulted to 1, but let's make it explicit
+      kwargs[:complexity] ||= field_complexity(kwargs[:resolver_class])
-      kwargs[:complexity] ||= DEFAULT_COMPLEXITY
 
       super(*args, **kwargs, &block)
     end
+
+    private
+
+    def field_complexity(resolver_class)
+      if resolver_class
+        field_resolver_complexity
+      else
+        DEFAULT_COMPLEXITY
+      end
+    end
+
+    def field_resolver_complexity
+      # Complexity can be either integer or proc. If proc is used then it's
+      # called when computing a query complexity and context and query
+      # arguments are available for computing complexity.  For resolvers we use
+      # proc because we set complexity depending on arguments and number of
+      # items which can be loaded.
+      proc do |ctx, args, child_complexity|
+        page_size = @max_page_size || ctx.schema.default_max_page_size
+        limit_value = [args[:first], args[:last], page_size].compact.min
+
+        # Resolvers may add extra complexity depending on used arguments
+        complexity = child_complexity + self.resolver&.try(:resolver_complexity, args).to_i
+
+        # Resolvers may add extra complexity depending on number of items being loaded.
+        multiplier = self.resolver&.try(:complexity_multiplier, args).to_f
+        complexity += complexity * limit_value * multiplier
+
+        complexity.to_i
+      end
+    end
   end
 end

app/graphql/types/issue_type.rb

@@ -19,9 +19,11 @@ module Types
           null: false,
           resolve: -> (obj, _args, _ctx) { Gitlab::Graphql::Loaders::BatchModelLoader.new(User, obj.author_id).find }
 
-    field :assignees, Types::UserType.connection_type, null: true
+    # Remove complexity when BatchLoader is used
+    field :assignees, Types::UserType.connection_type, null: true, complexity: 5
 
-    field :labels, Types::LabelType.connection_type, null: true
+    # Remove complexity when BatchLoader is used
+    field :labels, Types::LabelType.connection_type, null: true, complexity: 5
     field :milestone, Types::MilestoneType,
           null: true,
           resolve: -> (obj, _args, _ctx) { Gitlab::Graphql::Loaders::BatchModelLoader.new(Milestone, obj.milestone_id).find }

changelogs/unreleased/graphql-resolvers-complexity.yml

@@ -0,0 +1,6 @@
+---
+title: 'GraphQL: improve evaluation of query complexity based on arguments and query
+  limits.'
+merge_request: 28017
+author:
+type: added

spec/graphql/resolvers/base_resolver_spec.rb

@@ -28,4 +28,19 @@ describe Resolvers::BaseResolver do
       expect(result).to eq(test: 1)
     end
   end
+
+  it 'increases complexity based on arguments' do
+    field = Types::BaseField.new(name: 'test', type: GraphQL::STRING_TYPE, resolver_class: described_class, null: false, max_page_size: 1)
+
+    expect(field.to_graphql.complexity.call({}, { sort: 'foo' }, 1)).to eq 3
+    expect(field.to_graphql.complexity.call({}, { search: 'foo' }, 1)).to eq 7
+  end
+
+  it 'does not increase complexity when filtering by iids' do
+    field = Types::BaseField.new(name: 'test', type: GraphQL::STRING_TYPE, resolver_class: described_class, null: false, max_page_size: 100)
+
+    expect(field.to_graphql.complexity.call({}, { sort: 'foo' }, 1)).to eq 6
+    expect(field.to_graphql.complexity.call({}, { sort: 'foo', iid: 1 }, 1)).to eq 3
+    expect(field.to_graphql.complexity.call({}, { sort: 'foo', iids: [1, 2, 3] }, 1)).to eq 3
+  end
 end

spec/graphql/resolvers/concerns/resolves_pipelines_spec.rb

@@ -46,6 +46,14 @@ describe ResolvesPipelines do
     expect(resolve_pipelines({}, {})).to be_empty
   end
 
+  it 'increases field complexity based on arguments' do
+    field = Types::BaseField.new(name: 'test', type: GraphQL::STRING_TYPE, resolver_class: resolver, null: false, max_page_size: 1)
+
+    expect(field.to_graphql.complexity.call({}, {}, 1)).to eq 2
+    expect(field.to_graphql.complexity.call({}, { sha: 'foo' }, 1)).to eq 4
+    expect(field.to_graphql.complexity.call({}, { sha: 'ref' }, 1)).to eq 4
+  end
+
   def resolve_pipelines(args = {}, context = { current_user: current_user })
     resolve(resolver, obj: project, args: args, ctx: context)
   end

spec/graphql/resolvers/issues_resolver_spec.rb

@@ -120,6 +120,13 @@ describe Resolvers::IssuesResolver do
     end
   end
 
+  it 'increases field complexity based on arguments' do
+    field = Types::BaseField.new(name: 'test', type: GraphQL::STRING_TYPE, resolver_class: described_class, null: false, max_page_size: 100)
+
+    expect(field.to_graphql.complexity.call({}, {}, 1)).to eq 4
+    expect(field.to_graphql.complexity.call({}, { labelName: 'foo' }, 1)).to eq 8
+  end
+
   def resolve_issues(args = {}, context = { current_user: current_user })
     resolve(described_class, obj: project, args: args, ctx: context)
   end

spec/graphql/resolvers/project_resolver_spec.rb

@@ -26,6 +26,14 @@ describe Resolvers::ProjectResolver do
     end
   end
 
+  it 'does not increase complexity depending on number of load limits' do
+    field1 = Types::BaseField.new(name: 'test', type: GraphQL::STRING_TYPE, resolver_class: described_class, null: false, max_page_size: 100)
+    field2 = Types::BaseField.new(name: 'test', type: GraphQL::STRING_TYPE, resolver_class: described_class, null: false, max_page_size: 1)
+
+    expect(field1.to_graphql.complexity.call({}, {}, 1)).to eq 2
+    expect(field2.to_graphql.complexity.call({}, {}, 1)).to eq 2
+  end
+
   def resolve_project(full_path)
     resolve(described_class, args: { full_path: full_path })
   end

spec/graphql/types/base_field_spec.rb

@@ -4,6 +4,18 @@ require 'spec_helper'
 
 describe Types::BaseField do
   context 'when considering complexity' do
+    let(:resolver) do
+      Class.new(described_class) do
+        def self.resolver_complexity(args)
+          2 if args[:foo]
+        end
+
+        def self.complexity_multiplier(args)
+          0.01
+        end
+      end
+    end
+
     it 'defaults to 1' do
       field = described_class.new(name: 'test', type: GraphQL::STRING_TYPE, null: true)
 
@@ -15,5 +27,19 @@ describe Types::BaseField do
 
       expect(field.to_graphql.complexity).to eq 12
     end
+
+    it 'sets complexity depending on arguments for resolvers' do
+      field = described_class.new(name: 'test', type: GraphQL::STRING_TYPE, resolver_class: resolver, max_page_size: 100, null: true)
+
+      expect(field.to_graphql.complexity.call({}, {}, 2)).to eq 4
+      expect(field.to_graphql.complexity.call({}, { first: 50 }, 2)).to eq 3
+    end
+
+    it 'sets complexity depending on number load limits for resolvers' do
+      field = described_class.new(name: 'test', type: GraphQL::STRING_TYPE, resolver_class: resolver, max_page_size: 100, null: true)
+
+      expect(field.to_graphql.complexity.call({}, { first: 1 }, 2)).to eq 2
+      expect(field.to_graphql.complexity.call({}, { first: 1, foo: true }, 2)).to eq 4
+    end
   end
 end