updated custom error func

graphql/error.go

@@ -32,5 +32,10 @@ func MarshalError(err *errors.QueryError) Marshaler {
 
 		errObj.Add("locations", locations)
 	}
+
+	if err.ExtraInfo != nil {
+		errObj.Add(`extraInfo`, MarshalJSON(err.ExtraInfo))
+	}
+
 	return errObj
 }

graphql/jsonw.go

@@ -1,6 +1,7 @@
 package graphql
 
 import (
+	"encoding/json"
 	"io"
 	"strconv"
 )
@@ -81,3 +82,10 @@ func lit(b []byte) Marshaler {
 		w.Write(b)
 	})
 }
+
+// MarshalJSON marshals an interface into JSON.
+func MarshalJSON(i interface{}) Marshaler {
+	return WriterFunc(func(w io.Writer) {
+		json.NewEncoder(w).Encode(i)
+	})
+}

handler/graphql.go

@@ -23,7 +23,7 @@ type params struct {
 type Config struct {
 	upgrader     websocket.Upgrader
 	recover      graphql.RecoverFunc
-	formatError  func(error) string
+	formatError  errors.ErrorMessageFunc
 	resolverHook graphql.ResolverMiddleware
 	requestHook  graphql.RequestMiddleware
 }
@@ -42,7 +42,7 @@ func RecoverFunc(recover graphql.RecoverFunc) Option {
 	}
 }
 
-func FormatErrorFunc(f func(error) string) Option {
+func FormatErrorFunc(f errors.ErrorMessageFunc) Option {
 	return func(cfg *Config) {
 		cfg.formatError = f
 	}

neelance/errors/errors.go

@@ -10,6 +10,7 @@ type QueryError struct {
 	Path          []interface{} `json:"path,omitempty"`
 	Rule          string        `json:"-"`
 	ResolverError error         `json:"-"`
+	ExtraInfo     interface{}   `json:"extraInfo,omitempty"`
 }
 
 type Location struct {
@@ -29,10 +30,11 @@ func Errorf(format string, a ...interface{}) *QueryError {
 
 // WithMessagef is the same as Errorf, except it will store the err inside
 // the ResolverError field.
-func WithMessagef(err error, format string, a ...interface{}) *QueryError {
+func WithMessagef(err error, extra interface{}, format string, a ...interface{}) *QueryError {
 	return &QueryError{
 		Message:       fmt.Sprintf(format, a...),
 		ResolverError: err,
+		ExtraInfo:     extra,
 	}
 }
 
@@ -49,25 +51,35 @@ func (err *QueryError) Error() string {
 
 var _ error = &QueryError{}
 
+// FormattedError a formatted error which includes the error message and extra information
+// which is JSON encoded and passed with the error.
+type FormattedError struct {
+	Message string
+	Extra   interface{}
+}
+
+// ErrorMessageFunc a func which given an error returns a formatted error.
+type ErrorMessageFunc func(err error) FormattedError
+
 type Builder struct {
 	Errors []*QueryError
 	// ErrorMessageFn will be used to generate the error
 	// message from errors given to Error().
 	//
 	// If ErrorMessageFn is nil, err.Error() will be used.
-	ErrorMessageFn func(error) string
+	ErrorMessageFn ErrorMessageFunc
 }
 
 func (c *Builder) Errorf(format string, args ...interface{}) {
 	c.Errors = append(c.Errors, Errorf(format, args...))
 }
 
 func (c *Builder) Error(err error) {
-	var gqlErrMessage string
+	fErr := FormattedError{Message: err.Error()}
+
 	if c.ErrorMessageFn != nil {
-		gqlErrMessage = c.ErrorMessageFn(err)
-	} else {
-		gqlErrMessage = err.Error()
+		fErr = c.ErrorMessageFn(err)
 	}
-	c.Errors = append(c.Errors, WithMessagef(err, gqlErrMessage))
+
+	c.Errors = append(c.Errors, WithMessagef(err, fErr.Extra, fErr.Message))
 }

neelance/errors/errors_test.go

@@ -55,9 +55,10 @@ func (err *publicErr) PublicError() string {
 	return err.public
 }
 
-func convertErr(err error) string {
+func convertErr(err error) FormattedError {
 	if errConv, ok := err.(*publicErr); ok {
-		return errConv.public
+		return FormattedError{Message: errConv.public}
 	}
-	return err.Error()
+
+	return FormattedError{Message: err.Error()}
 }

test/resolvers_test.go

@@ -18,6 +18,8 @@ import (
 	"github.com/vektah/gqlgen/test/models"
 )
 
+type fErr = gqlerrors.FormattedError
+
 func TestCompiles(t *testing.T) {}
 
 func TestErrorConverter(t *testing.T) {
@@ -28,11 +30,11 @@ func TestErrorConverter(t *testing.T) {
 	require.Nil(t, errs)
 
 	t.Run("with", func(t *testing.T) {
-		testConvErr := func(e error) string {
+		testConvErr := func(e error) fErr {
 			if _, ok := errors.Cause(e).(*specialErr); ok {
-				return "override special error message"
+				return fErr{Message: "override special error message"}
 			}
-			return e.Error()
+			return fErr{Message: e.Error()}
 		}
 		t.Run("special error", func(t *testing.T) {
 			resolvers.nestedOutputsErr = &specialErr{}
@@ -68,7 +70,7 @@ func TestErrorConverter(t *testing.T) {
 	})
 }
 
-func mkctx(doc *query.Document, errFn func(e error) string) context.Context {
+func mkctx(doc *query.Document, errFn gqlerrors.ErrorMessageFunc) context.Context {
 	return graphql.WithRequestContext(context.Background(), &graphql.RequestContext{
 		Doc: doc,
 		ResolverMiddleware: func(ctx context.Context, next graphql.Resolver) (res interface{}, err error) {