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 TestUriBindingWithNonCtxValidator(t *testing.T) {
+	prev := Validator
+	defer func() {
+		Validator = prev
+	}()
+	Validator = &nonCtxValidator{}
+
+	TestUriBinding(t)
+}
+
+type nonCtxValidator defaultValidator
+
+func (v *nonCtxValidator) ValidateStruct(obj interface{}) error {
+	return (*defaultValidator)(v).ValidateStruct(obj)
+}
+
+func (v *nonCtxValidator) 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)
 }