Added ability to use your own directives usage

graphql.go

@@ -82,6 +82,7 @@ type Schema struct {
 	useStringDescriptions    bool
 	disableIntrospection     bool
 	subscribeResolverTimeout time.Duration
+	visitors                 map[string]types.DirectiveVisitor
 }
 
 func (s *Schema) ASTSchema() *types.Schema {
@@ -168,6 +169,14 @@ func SubscribeResolverTimeout(timeout time.Duration) SchemaOpt {
 	}
 }
 
+// DirectiveVisitors allows to pass custom directive visitors that will be able to handle
+// your GraphQL schema directives.
+func DirectiveVisitors(visitors map[string]types.DirectiveVisitor) SchemaOpt {
+	return func(s *Schema) {
+		s.visitors = visitors
+	}
+}
+
 // Response represents a typical response of a GraphQL server. It may be encoded to JSON directly or
 // it may be further processed to a custom response type, for example to include custom error data.
 // Errors are intentionally serialized first based on the advice in https://github.com/facebook/graphql/commit/7b40390d48680b15cb93e02d46ac5eb249689876#diff-757cea6edf0288677a9eea4cfc801d87R107
@@ -257,6 +266,7 @@ func (s *Schema) exec(ctx context.Context, queryString string, operationName str
 		Tracer:       s.tracer,
 		Logger:       s.logger,
 		PanicHandler: s.panicHandler,
+		Visitors:     s.visitors,
 	}
 	varTypes := make(map[string]*introspection.Type)
 	for _, v := range op.Vars {

graphql_test.go

@@ -14,6 +14,7 @@ import (
 	"github.com/graph-gophers/graphql-go/gqltesting"
 	"github.com/graph-gophers/graphql-go/introspection"
 	"github.com/graph-gophers/graphql-go/trace"
+	"github.com/graph-gophers/graphql-go/types"
 )
 
 type helloWorldResolver1 struct{}
@@ -48,6 +49,27 @@ func (r *helloSnakeResolver2) SayHello(ctx context.Context, args struct{ FullNam
 	return "Hello " + args.FullName + "!", nil
 }
 
+type customDirectiveVisitor struct {
+	beforeWasCalled bool
+}
+
+func (v *customDirectiveVisitor) Before(ctx context.Context, directive *types.Directive, input interface{}) error {
+	v.beforeWasCalled = true
+	return nil
+}
+
+func (v *customDirectiveVisitor) After(ctx context.Context, directive *types.Directive, output interface{}) (interface{}, error) {
+	if v.beforeWasCalled == false {
+		return nil, errors.New("Before directive visitor method wasn't called.")
+	}
+
+	if value, ok := directive.Arguments.Get("customAttribute"); ok {
+		return fmt.Sprintf("Directive '%s' (with arg '%s') modified result: %s", directive.Name.Name, value.String(), output.(string)), nil
+	} else {
+		return fmt.Sprintf("Directive '%s' modified result: %s", directive.Name.Name, output.(string)), nil
+	}
+}
+
 type theNumberResolver struct {
 	number int32
 }
@@ -191,7 +213,6 @@ func TestHelloWorld(t *testing.T) {
 				}
 			`,
 		},
-
 		{
 			Schema: graphql.MustParseSchema(`
 				schema {
@@ -216,6 +237,67 @@ func TestHelloWorld(t *testing.T) {
 	})
 }
 
+func TestCustomDirective(t *testing.T) {
+	t.Parallel()
+
+	gqltesting.RunTests(t, []*gqltesting.Test{
+		{
+			Schema: graphql.MustParseSchema(`
+				directive @customDirective on FIELD_DEFINITION
+
+				schema {
+					query: Query
+				}
+
+				type Query {
+					hello_html: String! @customDirective
+				}
+			`, &helloSnakeResolver1{},
+				graphql.DirectiveVisitors(map[string]types.DirectiveVisitor{
+					"customDirective": &customDirectiveVisitor{},
+				})),
+			Query: `
+				{
+					hello_html
+				}
+			`,
+			ExpectedResult: `
+				{
+					"hello_html": "Directive 'customDirective' modified result: Hello snake!"
+				}
+			`,
+		},
+		{
+			Schema: graphql.MustParseSchema(`
+				directive @customDirective(
+					customAttribute: String!
+			    ) on FIELD_DEFINITION
+
+				schema {
+					query: Query
+				}
+
+				type Query {
+					say_hello(full_name: String!): String! @customDirective(customAttribute: hi)
+				}
+			`, &helloSnakeResolver1{},
+				graphql.DirectiveVisitors(map[string]types.DirectiveVisitor{
+					"customDirective": &customDirectiveVisitor{},
+				})),
+			Query: `
+				{
+					say_hello(full_name: "Johnny")
+				}
+			`,
+			ExpectedResult: `
+				{
+					"say_hello": "Directive 'customDirective' (with arg 'hi') modified result: Hello Johnny!"
+				}
+			`,
+		},
+	})
+}
+
 func TestHelloSnake(t *testing.T) {
 	t.Parallel()
 

internal/exec/exec.go

@@ -25,6 +25,7 @@ type Request struct {
 	Logger                   log.Logger
 	PanicHandler             errors.PanicHandler
 	SubscribeResolverTimeout time.Duration
+	Visitors                 map[string]types.DirectiveVisitor
 }
 
 func (r *Request) handlePanic(ctx context.Context) {
@@ -208,8 +209,47 @@ func execFieldSelection(ctx context.Context, r *Request, s *resolvable.Schema, f
 			if f.field.ArgsPacker != nil {
 				in = append(in, f.field.PackedArgs)
 			}
+
+			// Before hook directive visitor
+			if len(f.field.Directives) > 0 {
+				for _, directive := range f.field.Directives {
+					if visitor, ok := r.Visitors[directive.Name.Name]; ok {
+						var values = make([]interface{}, 0)
+						for _, inValue := range in {
+							values = append(values, inValue.Interface())
+						}
+
+						if visitorErr := visitor.Before(ctx, directive, values); err != nil {
+							err := errors.Errorf("%s", visitorErr)
+							err.Path = path.toSlice()
+							err.ResolverError = visitorErr
+							return err
+						}
+					}
+				}
+			}
+
+			// Call method
 			callOut := res.Method(f.field.MethodIndex).Call(in)
 			result = callOut[0]
+
+			// After hook directive visitor (when no error is returned from resolver)
+			if !f.field.HasError && len(f.field.Directives) > 0 {
+				for _, directive := range f.field.Directives {
+					if visitor, ok := r.Visitors[directive.Name.Name]; ok {
+						returned, visitorErr := visitor.After(ctx, directive, result.Interface())
+						if err != nil {
+							err := errors.Errorf("%s", visitorErr)
+							err.Path = path.toSlice()
+							err.ResolverError = visitorErr
+							return err
+						} else {
+							result = reflect.ValueOf(returned)
+						}
+					}
+				}
+			}
+
 			if f.field.HasError && !callOut[1].IsNil() {
 				resolverErr := callOut[1].Interface().(error)
 				err := errors.Errorf("%s", resolverErr)

types/directive.go

@@ -1,6 +1,10 @@
 package types
 
-import "github.com/graph-gophers/graphql-go/errors"
+import (
+	"context"
+
+	"github.com/graph-gophers/graphql-go/errors"
+)
 
 // Directive is a representation of the GraphQL Directive.
 //
@@ -23,6 +27,11 @@ type DirectiveDefinition struct {
 
 type DirectiveList []*Directive
 
+type DirectiveVisitor interface {
+	Before(ctx context.Context, directive *Directive, input interface{}) error
+	After(ctx context.Context, directive *Directive, output interface{}) (interface{}, error)
+}
+
 // Returns the Directive in the DirectiveList by name or nil if not found.
 func (l DirectiveList) Get(name string) *Directive {
 	for _, d := range l {