Add support for contextual validation

By passing the Gin context to bindings, custom validators can take
advantage of the information in the context.

binding/binding.go

@@ -7,7 +7,10 @@
 
 package binding
 
-import "net/http"
+import (
+	"context"
+	"net/http"
+)
 
 // Content-Type MIME of the most common data formats.
 const (
@@ -32,20 +35,41 @@ type Binding interface {
 	Bind(*http.Request, interface{}) error
 }
 
-// BindingBody adds BindBody method to Binding. BindBody is similar with Bind,
+// ContextBinding enables contextual validation by adding BindContext to Binding.
+// Custom validators can take advantage of the information in the context.
+type ContextBinding interface {
+	Binding
+	BindContext(context.Context, *http.Request, interface{}) error
+}
+
+// BindingBody adds BindBody method to Binding. BindBody is similar to Bind,
 // but it reads the body from supplied bytes instead of req.Body.
 type BindingBody interface {
 	Binding
 	BindBody([]byte, interface{}) error
 }
 
-// BindingUri adds BindUri method to Binding. BindUri is similar with Bind,
-// but it read the Params.
+// ContextBindingBody enables contextual validation by adding BindBodyContext to BindingBody.
+// Custom validators can take advantage of the information in the context.
+type ContextBindingBody interface {
+	BindingBody
+	BindContext(context.Context, *http.Request, interface{}) error
+	BindBodyContext(context.Context, []byte, interface{}) error
+}
+
+// BindingUri is similar to Bind, but it read the Params.
 type BindingUri interface {
 	Name() string
 	BindUri(map[string][]string, interface{}) error
 }
 
+// ContextBindingUri enables contextual validation by adding BindUriContext to BindingUri.
+// Custom validators can take advantage of the information in the context.
+type ContextBindingUri interface {
+	BindingUri
+	BindUriContext(context.Context, map[string][]string, interface{}) error
+}
+
 // StructValidator is the minimal interface which needs to be implemented in
 // order for it to be used as the validator engine for ensuring the correctness
 // of the request. Gin provides a default implementation for this using
@@ -64,6 +88,14 @@ type StructValidator interface {
 	Engine() interface{}
 }
 
+// ContextStructValidator is an extension of StructValidator that requires implementing
+// context-aware validation.
+// Custom validators can take advantage of the information in the context.
+type ContextStructValidator interface {
+	StructValidator
+	ValidateStructContext(context.Context, interface{}) error
+}
+
 // Validator is the default validator which implements the StructValidator
 // interface. It uses https://github.com/go-playground/validator/tree/v10.6.1
 // under the hood.
@@ -110,9 +142,12 @@ func Default(method, contentType string) Binding {
 	}
 }
 
-func validate(obj interface{}) error {
+func validateContext(ctx context.Context, obj interface{}) error {
 	if Validator == nil {
 		return nil
 	}
+	if v, ok := Validator.(ContextStructValidator); ok {
+		return v.ValidateStructContext(ctx, obj)
+	}
 	return Validator.ValidateStruct(obj)
 }

binding/binding_msgpack_test.go

@@ -9,6 +9,7 @@ package binding
 
 import (
 	"bytes"
+	"context"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -35,7 +36,7 @@ func TestBindingMsgPack(t *testing.T) {
 		string(data), string(data[1:]))
 }
 
-func testMsgPackBodyBinding(t *testing.T, b Binding, name, path, badPath, body, badBody string) {
+func testMsgPackBodyBinding(t *testing.T, b ContextBinding, name, path, badPath, body, badBody string) {
 	assert.Equal(t, name, b.Name())
 
 	obj := FooStruct{}
@@ -48,7 +49,17 @@ func testMsgPackBodyBinding(t *testing.T, b Binding, name, path, badPath, body,
 	obj = FooStruct{}
 	req = requestWithBody("POST", badPath, badBody)
 	req.Header.Add("Content-Type", MIMEMSGPACK)
-	err = MsgPack.Bind(req, &obj)
+	err = b.Bind(req, &obj)
+	assert.Error(t, err)
+
+	obj2 := ConditionalFooStruct{}
+	req = requestWithBody("POST", path, body)
+	req.Header.Add("Content-Type", MIMEMSGPACK)
+	err = b.BindContext(context.Background(), req, &obj2)
+	assert.NoError(t, err)
+	assert.Equal(t, "bar", obj2.Foo)
+
+	err = b.BindContext(context.WithValue(context.Background(), "condition", true), req, &obj2) // nolint
 	assert.Error(t, err)
 }
 

binding/binding_nomsgpack.go

@@ -7,7 +7,10 @@
 
 package binding
 
-import "net/http"
+import (
+	"context"
+	"net/http"
+)
 
 // Content-Type MIME of the most common data formats.
 const (
@@ -30,20 +33,41 @@ type Binding interface {
 	Bind(*http.Request, interface{}) error
 }
 
-// BindingBody adds BindBody method to Binding. BindBody is similar with Bind,
+// ContextBinding enables contextual validation by adding BindContext to Binding.
+// Custom validators can take advantage of the information in the context.
+type ContextBinding interface {
+	Binding
+	BindContext(context.Context, *http.Request, interface{}) error
+}
+
+// BindingBody adds BindBody method to Binding. BindBody is similar to Bind,
 // but it reads the body from supplied bytes instead of req.Body.
 type BindingBody interface {
 	Binding
 	BindBody([]byte, interface{}) error
 }
 
-// BindingUri adds BindUri method to Binding. BindUri is similar with Bind,
-// but it read the Params.
+// ContextBindingBody enables contextual validation by adding BindBodyContext to BindingBody.
+// Custom validators can take advantage of the information in the context.
+type ContextBindingBody interface {
+	BindingBody
+	BindContext(context.Context, *http.Request, interface{}) error
+	BindBodyContext(context.Context, []byte, interface{}) error
+}
+
+// BindingUri is similar to Bind, but it read the Params.
 type BindingUri interface {
 	Name() string
 	BindUri(map[string][]string, interface{}) error
 }
 
+// ContextBindingUri enables contextual validation by adding BindUriContext to BindingUri.
+// Custom validators can take advantage of the information in the context.
+type ContextBindingUri interface {
+	BindingUri
+	BindUriContext(context.Context, map[string][]string, interface{}) error
+}
+
 // StructValidator is the minimal interface which needs to be implemented in
 // order for it to be used as the validator engine for ensuring the correctness
 // of the request. Gin provides a default implementation for this using
@@ -62,6 +86,14 @@ type StructValidator interface {
 	Engine() interface{}
 }
 
+// ContextStructValidator is an extension of StructValidator that requires implementing
+// context-aware validation.
+// Custom validators can take advantage of the information in the context.
+type ContextStructValidator interface {
+	StructValidator
+	ValidateStructContext(context.Context, interface{}) error
+}
+
 // Validator is the default validator which implements the StructValidator
 // interface. It uses https://github.com/go-playground/validator/tree/v10.6.1
 // under the hood.
@@ -85,7 +117,7 @@ var (
 // Default returns the appropriate Binding instance based on the HTTP method
 // and the content type.
 func Default(method, contentType string) Binding {
-	if method == "GET" {
+	if method == http.MethodGet {
 		return Form
 	}
 
@@ -105,9 +137,12 @@ func Default(method, contentType string) Binding {
 	}
 }
 
-func validate(obj interface{}) error {
+func validateContext(ctx context.Context, obj interface{}) error {
 	if Validator == nil {
 		return nil
 	}
+	if v, ok := Validator.(ContextStructValidator); ok {
+		return v.ValidateStructContext(ctx, obj)
+	}
 	return Validator.ValidateStruct(obj)
 }

binding/binding_test.go

@@ -6,6 +6,7 @@ package binding
 
 import (
 	"bytes"
+	"context"
 	"encoding/json"
 	"errors"
 	"io"
@@ -20,6 +21,7 @@ import (
 	"time"
 
 	"github.com/gin-gonic/gin/testdata/protoexample"
+	"github.com/go-playground/validator/v10"
 	"github.com/stretchr/testify/assert"
 	"google.golang.org/protobuf/proto"
 )
@@ -38,6 +40,10 @@ type FooStruct struct {
 	Foo string `msgpack:"foo" json:"foo" form:"foo" xml:"foo" binding:"required,max=32"`
 }
 
+type ConditionalFooStruct struct {
+	Foo string `msgpack:"foo" json:"foo" form:"foo" xml:"foo" binding:"required_if_condition,max=32"`
+}
+
 type FooBarStruct struct {
 	FooStruct
 	Bar string `msgpack:"bar" json:"bar" form:"bar" xml:"bar" binding:"required"`
@@ -144,6 +150,16 @@ type FooStructForMapPtrType struct {
 	PtrBar *map[string]interface{} `form:"ptr_bar"`
 }
 
+func init() {
+	_ = Validator.Engine().(*validator.Validate).RegisterValidationCtx(
+		"required_if_condition", func(ctx context.Context, fl validator.FieldLevel) bool {
+			if ctx.Value("condition") == true {
+				return !fl.Field().IsZero()
+			}
+			return true
+		})
+}
+
 func TestBindingDefault(t *testing.T) {
 	assert.Equal(t, Form, Default("GET", ""))
 	assert.Equal(t, Form, Default("GET", MIMEJSON))
@@ -796,6 +812,38 @@ func TestUriBinding(t *testing.T) {
 	assert.Equal(t, map[string]interface{}(nil), not.Name)
 }
 
+func TestUriBindingWithContext(t *testing.T) {
+	b := Uri
+
+	type Tag struct {
+		Name string `uri:"name" binding:"required_if_condition"`
+	}
+
+	empty := make(map[string][]string)
+	assert.NoError(t, b.BindUriContext(context.Background(), empty, new(Tag)))
+	assert.Error(t, b.BindUriContext(context.WithValue(context.Background(), "condition", true), empty, new(Tag))) // nolint
+}
+
+func TestUriBindingWithNotContextValidator(t *testing.T) {
+	prev := Validator
+	defer func() {
+		Validator = prev
+	}()
+	Validator = &notContextValidator{}
+
+	TestUriBinding(t)
+}
+
+type notContextValidator defaultValidator
+
+func (v *notContextValidator) ValidateStruct(obj interface{}) error {
+	return (*defaultValidator)(v).ValidateStruct(obj)
+}
+
+func (v *notContextValidator) Engine() interface{} {
+	return (*defaultValidator)(v).Engine()
+}
+
 func TestUriInnerBinding(t *testing.T) {
 	type Tag struct {
 		Name string `uri:"name"`
@@ -1179,7 +1227,7 @@ func testQueryBindingBoolFail(t *testing.T, method, path, badPath, body, badBody
 	assert.Error(t, err)
 }
 
-func testBodyBinding(t *testing.T, b Binding, name, path, badPath, body, badBody string) {
+func testBodyBinding(t *testing.T, b ContextBinding, name, path, badPath, body, badBody string) {
 	assert.Equal(t, name, b.Name())
 
 	obj := FooStruct{}
@@ -1190,7 +1238,16 @@ func testBodyBinding(t *testing.T, b Binding, name, path, badPath, body, badBody
 
 	obj = FooStruct{}
 	req = requestWithBody("POST", badPath, badBody)
-	err = JSON.Bind(req, &obj)
+	err = b.Bind(req, &obj)
+	assert.Error(t, err)
+
+	obj2 := ConditionalFooStruct{}
+	req = requestWithBody("POST", path, body)
+	err = b.BindContext(context.Background(), req, &obj2)
+	assert.NoError(t, err)
+	assert.Equal(t, "bar", obj2.Foo)
+
+	err = b.BindContext(context.WithValue(context.Background(), "condition", true), req, &obj2) // nolint
 	assert.Error(t, err)
 }
 
@@ -1204,7 +1261,7 @@ func testBodyBindingSlice(t *testing.T, b Binding, name, path, badPath, body, ba
 
 	var obj2 []FooStruct
 	req = requestWithBody("POST", badPath, badBody)
-	err = JSON.Bind(req, &obj2)
+	err = b.Bind(req, &obj2)
 	assert.Error(t, err)
 }
 
@@ -1249,7 +1306,7 @@ func testBodyBindingUseNumber(t *testing.T, b Binding, name, path, badPath, body
 
 	obj = FooStructUseNumber{}
 	req = requestWithBody("POST", badPath, badBody)
-	err = JSON.Bind(req, &obj)
+	err = b.Bind(req, &obj)
 	assert.Error(t, err)
 }
 
@@ -1267,7 +1324,7 @@ func testBodyBindingUseNumber2(t *testing.T, b Binding, name, path, badPath, bod
 
 	obj = FooStructUseNumber{}
 	req = requestWithBody("POST", badPath, badBody)
-	err = JSON.Bind(req, &obj)
+	err = b.Bind(req, &obj)
 	assert.Error(t, err)
 }
 
@@ -1285,7 +1342,7 @@ func testBodyBindingDisallowUnknownFields(t *testing.T, b Binding, path, badPath
 
 	obj = FooStructDisallowUnknownFields{}
 	req = requestWithBody("POST", badPath, badBody)
-	err = JSON.Bind(req, &obj)
+	err = b.Bind(req, &obj)
 	assert.Error(t, err)
 	assert.Contains(t, err.Error(), "what")
 }
@@ -1301,7 +1358,7 @@ func testBodyBindingFail(t *testing.T, b Binding, name, path, badPath, body, bad
 
 	obj = FooStruct{}
 	req = requestWithBody("POST", badPath, badBody)
-	err = JSON.Bind(req, &obj)
+	err = b.Bind(req, &obj)
 	assert.Error(t, err)
 }
 
@@ -1318,7 +1375,7 @@ func testProtoBodyBinding(t *testing.T, b Binding, name, path, badPath, body, ba
 	obj = protoexample.Test{}
 	req = requestWithBody("POST", badPath, badBody)
 	req.Header.Add("Content-Type", MIMEPROTOBUF)
-	err = ProtoBuf.Bind(req, &obj)
+	err = b.Bind(req, &obj)
 	assert.Error(t, err)
 }
 
@@ -1349,7 +1406,7 @@ func testProtoBodyBindingFail(t *testing.T, b Binding, name, path, badPath, body
 	obj = protoexample.Test{}
 	req = requestWithBody("POST", badPath, badBody)
 	req.Header.Add("Content-Type", MIMEPROTOBUF)
-	err = ProtoBuf.Bind(req, &obj)
+	err = b.Bind(req, &obj)
 	assert.Error(t, err)
 }
 

binding/default_validator.go

@@ -5,6 +5,7 @@
 package binding
 
 import (
+	"context"
 	"fmt"
 	"reflect"
 	"sync"
@@ -92,10 +93,14 @@ func (fe mapFieldError) Unwrap() error {
 	return fe.FieldError
 }
 
-var _ StructValidator = &defaultValidator{}
+var _ ContextStructValidator = &defaultValidator{}
 
 // ValidateStruct receives any kind of type, but validates only structs, pointers, slices, arrays, and maps.
 func (v *defaultValidator) ValidateStruct(obj interface{}) error {
+	return v.ValidateStructContext(context.Background(), obj)
+}
+
+func (v *defaultValidator) ValidateStructContext(ctx context.Context, obj interface{}) error {
 	if obj == nil {
 		return nil
 	}
@@ -103,21 +108,21 @@ func (v *defaultValidator) ValidateStruct(obj interface{}) error {
 	value := reflect.ValueOf(obj)
 	switch value.Kind() {
 	case reflect.Ptr:
-		return v.ValidateStruct(value.Elem().Interface())
+		return v.ValidateStructContext(ctx, value.Elem().Interface())
 	case reflect.Struct:
-		return v.validateStruct(obj)
+		return v.validateStruct(ctx, obj)
 	case reflect.Slice, reflect.Array:
 		var errs validator.ValidationErrors
 
 		if tag, ok := validatorTags[value.Type()]; ok {
-			if err := v.validateVar(obj, tag); err != nil {
+			if err := v.validateVar(ctx, obj, tag); err != nil {
 				errs = append(errs, err.(validator.ValidationErrors)...) // nolint: errorlint
 			}
 		}
 
 		count := value.Len()
 		for i := 0; i < count; i++ {
-			if err := v.ValidateStruct(value.Index(i).Interface()); err != nil {
+			if err := v.ValidateStructContext(ctx, value.Index(i).Interface()); err != nil {
 				for _, fieldError := range err.(validator.ValidationErrors) { // nolint: errorlint
 					errs = append(errs, sliceFieldError{fieldError, i})
 				}
@@ -132,13 +137,13 @@ func (v *defaultValidator) ValidateStruct(obj interface{}) error {
 		var errs validator.ValidationErrors
 
 		if tag, ok := validatorTags[value.Type()]; ok {
-			if err := v.validateVar(obj, tag); err != nil {
+			if err := v.validateVar(ctx, obj, tag); err != nil {
 				errs = append(errs, err.(validator.ValidationErrors)...) // nolint: errorlint
 			}
 		}
 
 		for _, key := range value.MapKeys() {
-			if err := v.ValidateStruct(value.MapIndex(key).Interface()); err != nil {
+			if err := v.ValidateStructContext(ctx, value.MapIndex(key).Interface()); err != nil {
 				for _, fieldError := range err.(validator.ValidationErrors) { // nolint: errorlint
 					errs = append(errs, mapFieldError{fieldError, key.Interface()})
 				}
@@ -154,15 +159,15 @@ func (v *defaultValidator) ValidateStruct(obj interface{}) error {
 }
 
 // validateStruct receives struct type
-func (v *defaultValidator) validateStruct(obj interface{}) error {
+func (v *defaultValidator) validateStruct(ctx context.Context, obj interface{}) error {
 	v.lazyinit()
-	return v.validate.Struct(obj)
+	return v.validate.StructCtx(ctx, obj)
 }
 
 // validateStruct receives slice, array, and map types
-func (v *defaultValidator) validateVar(obj interface{}, tag string) error {
+func (v *defaultValidator) validateVar(ctx context.Context, obj interface{}, tag string) error {
 	v.lazyinit()
-	return v.validate.Var(obj, tag)
+	return v.validate.VarCtx(ctx, obj, tag)
 }
 
 // Engine returns the underlying validator engine which powers the default

binding/form.go

@@ -5,6 +5,7 @@
 package binding
 
 import (
+	"context"
 	"errors"
 	"net/http"
 )
@@ -19,7 +20,11 @@ func (formBinding) Name() string {
 	return "form"
 }
 
-func (formBinding) Bind(req *http.Request, obj interface{}) error {
+func (b formBinding) Bind(req *http.Request, obj interface{}) error {
+	return b.BindContext(context.Background(), req, obj)
+}
+
+func (formBinding) BindContext(ctx context.Context, req *http.Request, obj interface{}) error {
 	if err := req.ParseForm(); err != nil {
 		return err
 	}
@@ -29,34 +34,41 @@ func (formBinding) Bind(req *http.Request, obj interface{}) error {
 	if err := mapForm(obj, req.Form); err != nil {
 		return err
 	}
-	return validate(obj)
+	return validateContext(ctx, obj)
 }
 
 func (formPostBinding) Name() string {
 	return "form-urlencoded"
 }
 
-func (formPostBinding) Bind(req *http.Request, obj interface{}) error {
+func (b formPostBinding) Bind(req *http.Request, obj interface{}) error {
+	return b.BindContext(context.Background(), req, obj)
+}
+
+func (formPostBinding) BindContext(ctx context.Context, req *http.Request, obj interface{}) error {
 	if err := req.ParseForm(); err != nil {
 		return err
 	}
 	if err := mapForm(obj, req.PostForm); err != nil {
 		return err
 	}
-	return validate(obj)
+	return validateContext(ctx, obj)
 }
 
 func (formMultipartBinding) Name() string {
 	return "multipart/form-data"
 }
 
-func (formMultipartBinding) Bind(req *http.Request, obj interface{}) error {
+func (b formMultipartBinding) Bind(req *http.Request, obj interface{}) error {
+	return b.BindContext(context.Background(), req, obj)
+}
+
+func (formMultipartBinding) BindContext(ctx context.Context, req *http.Request, obj interface{}) error {
 	if err := req.ParseMultipartForm(defaultMemory); err != nil {
 		return err
 	}
 	if err := mappingByPtr(obj, (*multipartRequest)(req), "form"); err != nil {
 		return err
 	}
-
-	return validate(obj)
+	return validateContext(ctx, obj)
 }

binding/header.go

@@ -1,6 +1,7 @@
 package binding
 
 import (
+	"context"
 	"net/http"
 	"net/textproto"
 	"reflect"
@@ -12,13 +13,15 @@ func (headerBinding) Name() string {
 	return "header"
 }
 
-func (headerBinding) Bind(req *http.Request, obj interface{}) error {
+func (b headerBinding) Bind(req *http.Request, obj interface{}) error {
+	return b.BindContext(context.Background(), req, obj)
+}
 
+func (headerBinding) BindContext(ctx context.Context, req *http.Request, obj interface{}) error {
 	if err := mapHeader(obj, req.Header); err != nil {
 		return err
 	}
-
-	return validate(obj)
+	return validateContext(ctx, obj)
 }
 
 func mapHeader(ptr interface{}, h map[string][]string) error {

binding/json.go

@@ -6,6 +6,7 @@ package binding
 
 import (
 	"bytes"
+	"context"
 	"errors"
 	"io"
 	"net/http"
@@ -30,18 +31,26 @@ func (jsonBinding) Name() string {
 	return "json"
 }
 
-func (jsonBinding) Bind(req *http.Request, obj interface{}) error {
+func (b jsonBinding) Bind(req *http.Request, obj interface{}) error {
+	return b.BindContext(context.Background(), req, obj)
+}
+
+func (jsonBinding) BindContext(ctx context.Context, req *http.Request, obj interface{}) error {
 	if req == nil || req.Body == nil {
 		return errors.New("invalid request")
 	}
-	return decodeJSON(req.Body, obj)
+	return decodeJSON(ctx, req.Body, obj)
 }
 
-func (jsonBinding) BindBody(body []byte, obj interface{}) error {
-	return decodeJSON(bytes.NewReader(body), obj)
+func (b jsonBinding) BindBody(body []byte, obj interface{}) error {
+	return b.BindBodyContext(context.Background(), body, obj)
 }
 
-func decodeJSON(r io.Reader, obj interface{}) error {
+func (jsonBinding) BindBodyContext(ctx context.Context, body []byte, obj interface{}) error {
+	return decodeJSON(ctx, bytes.NewReader(body), obj)
+}
+
+func decodeJSON(ctx context.Context, r io.Reader, obj interface{}) error {
 	decoder := json.NewDecoder(r)
 	if EnableDecoderUseNumber {
 		decoder.UseNumber()
@@ -52,5 +61,5 @@ func decodeJSON(r io.Reader, obj interface{}) error {
 	if err := decoder.Decode(obj); err != nil {
 		return err
 	}
-	return validate(obj)
+	return validateContext(ctx, obj)
 }

binding/msgpack.go

@@ -9,6 +9,7 @@ package binding
 
 import (
 	"bytes"
+	"context"
 	"io"
 	"net/http"
 
@@ -21,18 +22,26 @@ func (msgpackBinding) Name() string {
 	return "msgpack"
 }
 
-func (msgpackBinding) Bind(req *http.Request, obj interface{}) error {
-	return decodeMsgPack(req.Body, obj)
+func (b msgpackBinding) Bind(req *http.Request, obj interface{}) error {
+	return b.BindContext(context.Background(), req, obj)
 }
 
-func (msgpackBinding) BindBody(body []byte, obj interface{}) error {
-	return decodeMsgPack(bytes.NewReader(body), obj)
+func (msgpackBinding) BindContext(ctx context.Context, req *http.Request, obj interface{}) error {
+	return decodeMsgPack(ctx, req.Body, obj)
 }
 
-func decodeMsgPack(r io.Reader, obj interface{}) error {
+func (b msgpackBinding) BindBody(body []byte, obj interface{}) error {
+	return b.BindBodyContext(context.Background(), body, obj)
+}
+
+func (msgpackBinding) BindBodyContext(ctx context.Context, body []byte, obj interface{}) error {
+	return decodeMsgPack(ctx, bytes.NewReader(body), obj)
+}
+
+func decodeMsgPack(ctx context.Context, r io.Reader, obj interface{}) error {
 	cdc := new(codec.MsgpackHandle)
 	if err := codec.NewDecoder(r, cdc).Decode(&obj); err != nil {
 		return err
 	}
-	return validate(obj)
+	return validateContext(ctx, obj)
 }

binding/query.go

@@ -4,7 +4,10 @@
 
 package binding
 
-import "net/http"
+import (
+	"context"
+	"net/http"
+)
 
 type queryBinding struct{}
 
@@ -12,10 +15,14 @@ func (queryBinding) Name() string {
 	return "query"
 }
 
-func (queryBinding) Bind(req *http.Request, obj interface{}) error {
+func (b queryBinding) Bind(req *http.Request, obj interface{}) error {
+	return b.BindContext(context.Background(), req, obj)
+}
+
+func (queryBinding) BindContext(ctx context.Context, req *http.Request, obj interface{}) error {
 	values := req.URL.Query()
 	if err := mapForm(obj, values); err != nil {
 		return err
 	}
-	return validate(obj)
+	return validateContext(ctx, obj)
 }

binding/uri.go

@@ -4,15 +4,21 @@
 
 package binding
 
+import "context"
+
 type uriBinding struct{}
 
 func (uriBinding) Name() string {
 	return "uri"
 }
 
-func (uriBinding) BindUri(m map[string][]string, obj interface{}) error {
+func (b uriBinding) BindUri(m map[string][]string, obj interface{}) error {
+	return b.BindUriContext(context.Background(), m, obj)
+}
+
+func (uriBinding) BindUriContext(ctx context.Context, m map[string][]string, obj interface{}) error {
 	if err := mapURI(obj, m); err != nil {
 		return err
 	}
-	return validate(obj)
+	return validateContext(ctx, obj)
 }

binding/validate_test.go

@@ -6,6 +6,7 @@ package binding
 
 import (
 	"bytes"
+	"context"
 	"testing"
 	"time"
 
@@ -226,3 +227,7 @@ func TestValidatorEngine(t *testing.T) {
 	// Check that the error matches expectation
 	assert.Error(t, errs, "", "", "notone")
 }
+
+func validate(obj interface{}) error {
+	return validateContext(context.Background(), obj)
+}

binding/xml.go

@@ -6,6 +6,7 @@ package binding
 
 import (
 	"bytes"
+	"context"
 	"encoding/xml"
 	"io"
 	"net/http"
@@ -17,17 +18,26 @@ func (xmlBinding) Name() string {
 	return "xml"
 }
 
-func (xmlBinding) Bind(req *http.Request, obj interface{}) error {
-	return decodeXML(req.Body, obj)
+func (b xmlBinding) Bind(req *http.Request, obj interface{}) error {
+	return b.BindContext(context.Background(), req, obj)
 }
 
-func (xmlBinding) BindBody(body []byte, obj interface{}) error {
-	return decodeXML(bytes.NewReader(body), obj)
+func (xmlBinding) BindContext(ctx context.Context, req *http.Request, obj interface{}) error {
+	return decodeXML(ctx, req.Body, obj)
 }
-func decodeXML(r io.Reader, obj interface{}) error {
+
+func (b xmlBinding) BindBody(body []byte, obj interface{}) error {
+	return b.BindBodyContext(context.Background(), body, obj)
+}
+
+func (xmlBinding) BindBodyContext(ctx context.Context, body []byte, obj interface{}) error {
+	return decodeXML(ctx, bytes.NewReader(body), obj)
+}
+
+func decodeXML(ctx context.Context, r io.Reader, obj interface{}) error {
 	decoder := xml.NewDecoder(r)
 	if err := decoder.Decode(obj); err != nil {
 		return err
 	}
-	return validate(obj)
+	return validateContext(ctx, obj)
 }

binding/yaml.go

@@ -6,6 +6,7 @@ package binding
 
 import (
 	"bytes"
+	"context"
 	"io"
 	"net/http"
 
@@ -18,18 +19,26 @@ func (yamlBinding) Name() string {
 	return "yaml"
 }
 
-func (yamlBinding) Bind(req *http.Request, obj interface{}) error {
-	return decodeYAML(req.Body, obj)
+func (b yamlBinding) Bind(req *http.Request, obj interface{}) error {
+	return b.BindContext(context.Background(), req, obj)
 }
 
-func (yamlBinding) BindBody(body []byte, obj interface{}) error {
-	return decodeYAML(bytes.NewReader(body), obj)
+func (yamlBinding) BindContext(ctx context.Context, req *http.Request, obj interface{}) error {
+	return decodeYAML(ctx, req.Body, obj)
 }
 
-func decodeYAML(r io.Reader, obj interface{}) error {
+func (b yamlBinding) BindBody(body []byte, obj interface{}) error {
+	return b.BindBodyContext(context.Background(), body, obj)
+}
+
+func (yamlBinding) BindBodyContext(ctx context.Context, body []byte, obj interface{}) error {
+	return decodeYAML(ctx, bytes.NewReader(body), obj)
+}
+
+func decodeYAML(ctx context.Context, r io.Reader, obj interface{}) error {
 	decoder := yaml.NewDecoder(r)
 	if err := decoder.Decode(obj); err != nil {
 		return err
 	}
-	return validate(obj)
+	return validateContext(ctx, obj)
 }

context.go

@@ -704,12 +704,15 @@ func (c *Context) ShouldBindUri(obj interface{}) error {
 	for _, v := range c.Params {
 		m[v.Key] = []string{v.Value}
 	}
-	return binding.Uri.BindUri(m, obj)
+	return binding.Uri.BindUriContext(c, m, obj)
 }
 
 // ShouldBindWith binds the passed struct pointer using the specified binding engine.
 // See the binding package.
 func (c *Context) ShouldBindWith(obj interface{}, b binding.Binding) error {
+	if b, ok := b.(binding.ContextBinding); ok {
+		return b.BindContext(c, c.Request, obj)
+	}
 	return b.Bind(c.Request, obj)
 }
 
@@ -732,6 +735,9 @@ func (c *Context) ShouldBindBodyWith(obj interface{}, bb binding.BindingBody) (e
 		}
 		c.Set(BodyBytesKey, body)
 	}
+	if bb, ok := bb.(binding.ContextBindingBody); ok {
+		return bb.BindBodyContext(c, body, obj)
+	}
 	return bb.BindBody(body, obj)
 }
 

context_test.go

@@ -24,6 +24,7 @@ import (
 	"github.com/gin-contrib/sse"
 	"github.com/gin-gonic/gin/binding"
 	testdata "github.com/gin-gonic/gin/testdata/protoexample"
+	"github.com/go-playground/validator/v10"
 	"github.com/stretchr/testify/assert"
 	"google.golang.org/protobuf/proto"
 )
@@ -36,6 +37,16 @@ var _ context.Context = &Context{}
 // BAD case: func (c *Context) Render(code int, render render.Render, obj ...interface{}) {
 // test that information is not leaked when reusing Contexts (using the Pool)
 
+func init() {
+	_ = binding.Validator.Engine().(*validator.Validate).RegisterValidationCtx(
+		"required_if_condition", func(ctx context.Context, fl validator.FieldLevel) bool {
+			if ctx.Value("condition") == true {
+				return !fl.Field().IsZero()
+			}
+			return true
+		})
+}
+
 func createMultipartRequest() *http.Request {
 	boundary := "--testboundary"
 	body := new(bytes.Buffer)
@@ -1543,6 +1554,27 @@ func TestContextBindWithJSON(t *testing.T) {
 	assert.Equal(t, 0, w.Body.Len())
 }
 
+func TestContextBindWithJSONContextual(t *testing.T) {
+	w := httptest.NewRecorder()
+	c, _ := CreateTestContext(w)
+
+	c.Request, _ = http.NewRequest("POST", "/", bytes.NewBufferString("{\"bar\":\"foo\"}"))
+	c.Request.Header.Add("Content-Type", MIMEXML) // set fake content-type
+
+	var obj struct {
+		Foo string `json:"foo" binding:"required_if_condition"`
+		Bar string `json:"bar"`
+	}
+	c.Set("condition", true)
+	assert.Error(t, c.BindJSON(&obj))
+
+	c.Request, _ = http.NewRequest("POST", "/", bytes.NewBufferString("{\"foo\":\"bar\", \"bar\":\"foo\"}"))
+	assert.NoError(t, c.BindJSON(&obj))
+	assert.Equal(t, "foo", obj.Bar)
+	assert.Equal(t, "bar", obj.Foo)
+	assert.Equal(t, 0, w.Body.Len())
+}
+
 func TestContextBindWithXML(t *testing.T) {
 	w := httptest.NewRecorder()
 	c, _ := CreateTestContext(w)
@@ -1672,6 +1704,92 @@ func TestContextShouldBindWithJSON(t *testing.T) {
 	assert.Equal(t, 0, w.Body.Len())
 }
 
+func TestContextShouldBindWithJSONContextual(t *testing.T) {
+	w := httptest.NewRecorder()
+	c, _ := CreateTestContext(w)
+
+	c.Request, _ = http.NewRequest("POST", "/", bytes.NewBufferString("{\"bar\":\"foo\"}"))
+	c.Request.Header.Add("Content-Type", MIMEXML) // set fake content-type
+
+	var obj struct {
+		Foo string `json:"foo" binding:"required_if_condition"`
+		Bar string `json:"bar"`
+	}
+	c.Set("condition", true)
+	assert.Error(t, c.ShouldBindJSON(&obj))
+
+	c.Request, _ = http.NewRequest("POST", "/", bytes.NewBufferString("{\"foo\":\"bar\", \"bar\":\"foo\"}"))
+	assert.NoError(t, c.ShouldBindJSON(&obj))
+	assert.Equal(t, "foo", obj.Bar)
+	assert.Equal(t, "bar", obj.Foo)
+	assert.Equal(t, 0, w.Body.Len())
+}
+
+func TestContextShouldBindBodyWithJSONContextual(t *testing.T) {
+	w := httptest.NewRecorder()
+	c, _ := CreateTestContext(w)
+
+	var obj struct {
+		Foo string `json:"foo" binding:"required_if_condition"`
+		Bar string `json:"bar"`
+	}
+	c.Set("condition", true)
+	c.Set(BodyBytesKey, []byte("{\"bar\":\"foo\"}"))
+	assert.Error(t, c.ShouldBindBodyWith(&obj, binding.JSON))
+
+	c.Set(BodyBytesKey, []byte("{\"foo\":\"bar\", \"bar\":\"foo\"}"))
+	assert.NoError(t, c.ShouldBindBodyWith(&obj, binding.JSON))
+	assert.Equal(t, "foo", obj.Bar)
+	assert.Equal(t, "bar", obj.Foo)
+	assert.Equal(t, 0, w.Body.Len())
+}
+
+func TestContextShouldBindWithNotContextBinding(t *testing.T) {
+	w := httptest.NewRecorder()
+	c, _ := CreateTestContext(w)
+
+	c.Request, _ = http.NewRequest("POST", "/", bytes.NewBufferString("{\"foo\":\"bar\", \"bar\":\"foo\"}"))
+	c.Request.Header.Add("Content-Type", MIMEXML) // set fake content-type
+
+	var obj struct {
+		Foo string `json:"foo" binding:"required_if_condition"`
+		Bar string `json:"bar"`
+	}
+	assert.NoError(t, c.ShouldBindWith(&obj, notContextBinding{}))
+	assert.Equal(t, "foo", obj.Bar)
+	assert.Equal(t, "bar", obj.Foo)
+	assert.Equal(t, 0, w.Body.Len())
+}
+
+func TestContextShouldBindBodyWithNotContextBinding(t *testing.T) {
+	w := httptest.NewRecorder()
+	c, _ := CreateTestContext(w)
+
+	var obj struct {
+		Foo string `json:"foo"`
+		Bar string `json:"bar"`
+	}
+	c.Set(BodyBytesKey, []byte("{\"foo\":\"bar\", \"bar\":\"foo\"}"))
+	assert.NoError(t, c.ShouldBindBodyWith(&obj, notContextBinding{}))
+	assert.Equal(t, "foo", obj.Bar)
+	assert.Equal(t, "bar", obj.Foo)
+	assert.Equal(t, 0, w.Body.Len())
+}
+
+type notContextBinding struct{}
+
+func (notContextBinding) Name() string {
+	return binding.JSON.Name()
+}
+
+func (b notContextBinding) Bind(req *http.Request, obj interface{}) error {
+	return binding.JSON.Bind(req, obj)
+}
+
+func (b notContextBinding) BindBody(body []byte, obj interface{}) error {
+	return binding.JSON.BindBody(body, obj)
+}
+
 func TestContextShouldBindWithXML(t *testing.T) {
 	w := httptest.NewRecorder()
 	c, _ := CreateTestContext(w)