feature: implement request auto binder utility

auto_binder.go

@@ -0,0 +1,100 @@
+package gin
+
+import (
+	"errors"
+	"fmt"
+	"reflect"
+)
+
+type binderType func(obj any) error
+
+func isFunc(obj any) bool {
+	return reflect.TypeOf(obj).Kind() == reflect.Func
+}
+
+func isGinContext(rt reflect.Type) bool {
+	return rt == reflect.TypeOf((*Context)(nil))
+}
+
+func isPtr(rt reflect.Type) bool {
+	return rt.Kind() == reflect.Pointer
+}
+
+func isStruct(rt reflect.Type) bool {
+	return rt.Kind() == reflect.Struct
+}
+
+func constructStruct(prt reflect.Type, binder binderType) (reflect.Value, error) {
+	var pInstancePtr any
+
+	if isPtr(prt) {
+		pInstancePtr = reflect.New(prt.Elem()).Interface()
+	} else {
+		pInstancePtr = reflect.New(prt).Interface()
+	}
+
+	if err := binder(pInstancePtr); err != nil {
+		return reflect.Value{}, err
+	}
+
+	if prt.Kind() == reflect.Pointer {
+		return reflect.ValueOf(pInstancePtr), nil
+	}
+
+	return reflect.ValueOf(pInstancePtr).Elem(), nil
+}
+
+func callHandler(rt reflect.Type, rv reflect.Value, ctx *Context, binder binderType) error {
+	numberOfParams := rt.NumIn()
+
+	var args []reflect.Value
+
+	for i := 0; i < numberOfParams; i++ {
+		prt := rt.In(i)
+
+		if isGinContext(prt) {
+			args = append(args, reflect.ValueOf(ctx))
+			continue
+		}
+
+		if isStruct(prt) || isStruct(prt.Elem()) {
+			if prv, err := constructStruct(prt, binder); err != nil {
+				return err
+			} else {
+				args = append(args, prv)
+			}
+		}
+	}
+
+	rv.Call(args)
+
+	return nil
+}
+
+// AutoBinder is a handler wrapper that binds the actual handler's request.
+//
+// Example: func MyGetHandler(ctx *gin.Context, request *MyRequest) {}
+//
+// engine.GET("/endpoint", gin.AutoBinder(MyGetHandler))
+func AutoBinder(handler any) HandlerFunc {
+	rt := reflect.TypeOf(handler)
+
+	if rt.Kind() != reflect.Func {
+		panic(errors.New("invalid handler type"))
+	}
+
+	if rt.NumIn() == 0 {
+		panic(fmt.Errorf("handler should have at least one parameter, handler: %v", rt.Name()))
+	}
+
+	return func(ctx *Context) {
+		rt := reflect.TypeOf(handler)
+		rv := reflect.ValueOf(handler)
+
+		if err := callHandler(rt, rv, ctx, func(obj any) error {
+			return ctx.ShouldBind(obj)
+		}); err != nil {
+			ctx.Error(err)
+		}
+	}
+}

auto_binder_test.go

@@ -0,0 +1,144 @@
+package gin
+
+import (
+	"encoding/json"
+	"reflect"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+type myRequest struct {
+	Field1 string `json:"field_1"`
+}
+
+func TestAutoBinder_isFunc(t *testing.T) {
+	tests := []struct {
+		name  string
+		input any
+		want  bool
+	}{
+		{
+			"valid function",
+			func(string, int) error { return nil },
+			true,
+		},
+		{
+			"valid zero-param function",
+			func() error { return nil },
+			true,
+		},
+		{
+			"invalid function",
+			func() string { return "" }(),
+			false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			actual := isFunc(tt.input)
+			assert.Equal(t, tt.want, actual)
+		})
+	}
+}
+
+func TestAutoBinder_isGinContext(t *testing.T) {
+	assert.True(t, isGinContext(reflect.TypeOf(&Context{})))
+	assert.False(t, isGinContext(reflect.TypeOf(Context{})))
+	assert.False(t, isGinContext(reflect.TypeOf([]string{})))
+}
+
+func TestAutoBinder_constructStruct_pointer(t *testing.T) {
+	type myType struct {
+		Field int `json:"field"`
+	}
+
+	rv, err := constructStruct(reflect.TypeOf(&myType{}), func(obj any) error {
+		assert.True(t, isPtr(reflect.TypeOf(obj)))
+
+		return json.Unmarshal(
+			[]byte(`{"field": 10}`),
+			obj,
+		)
+	})
+
+	assert.NoError(t, err)
+
+	instance, ok := rv.Interface().(*myType)
+
+	assert.True(t, ok)
+
+	assert.Equal(t, 10, instance.Field)
+}
+
+func TestAutoBinder_constructStruct_nonPointer(t *testing.T) {
+	type myType struct {
+		Field int `json:"field"`
+	}
+
+	rv, err := constructStruct(reflect.TypeOf(myType{}), func(obj any) error {
+		assert.True(t, isPtr(reflect.TypeOf(obj)))
+
+		return json.Unmarshal(
+			[]byte(`{"field": 10}`),
+			obj,
+		)
+	})
+
+	assert.NoError(t, err)
+
+	instance, ok := rv.Interface().(myType)
+
+	assert.True(t, ok)
+
+	assert.Equal(t, 10, instance.Field)
+}
+
+func TestAutoBinder_constructStruct_nonStruct(t *testing.T) {
+	_, err := constructStruct(reflect.TypeOf("string test"), func(obj any) error {
+		assert.True(t, isPtr(reflect.TypeOf(obj)))
+
+		return json.Unmarshal(
+			[]byte(`{"field": 10}`),
+			obj,
+		)
+	})
+
+	assert.Error(t, err)
+}
+
+func TestAutoBinder_callHandler(t *testing.T) {
+	called := false
+
+	handler := func(ctx *Context, req *myRequest) {
+		if ctx == nil {
+			t.Errorf("ctx should not passed as nil")
+			return
+		}
+
+		if req.Field1 != "value1" {
+			t.Errorf("expected %v, actual %v", "value1", req.Field1)
+		}
+
+		called = true
+	}
+
+	rt := reflect.TypeOf(handler)
+	rv := reflect.ValueOf(handler)
+
+	ctx := &Context{}
+
+	err := callHandler(rt, rv, ctx, func(obj any) error {
+		return json.Unmarshal([]byte(`{"field_1": "value1"}`), obj)
+	})
+
+	if err != nil {
+		panic(err)
+	}
+
+	if !called {
+		t.Error("handler should be called")
+	}
+
+}