Fix #216: Enable to call binding multiple times in some formats (#1341)

* Add interface to read body bytes in binding

* Add BindingBody implementation for some binding

* Fix to use `BindBodyBytesKey` for key

* Revert "Fix to use `BindBodyBytesKey` for key"

This reverts commit 2c82901ceab6ae53730a3cfcd9839bee11a08f13.

* Use private-like key for body bytes

* Add tests for BindingBody & ShouldBindBodyWith

* Add note for README

* Remove redundant space between sentences

binding/binding_body_test.go

@@ -0,0 +1,67 @@
+package binding
+
+import (
+	"bytes"
+	"io/ioutil"
+	"testing"
+
+	"github.com/gin-gonic/gin/binding/example"
+	"github.com/golang/protobuf/proto"
+	"github.com/stretchr/testify/assert"
+	"github.com/ugorji/go/codec"
+)
+
+func TestBindingBody(t *testing.T) {
+	for _, tt := range []struct {
+		name    string
+		binding BindingBody
+		body    string
+		want    string
+	}{
+		{
+			name:    "JSON bidning",
+			binding: JSON,
+			body:    `{"foo":"FOO"}`,
+		},
+		{
+			name:    "XML bidning",
+			binding: XML,
+			body: `<?xml version="1.0" encoding="UTF-8"?>
+<root>
+   <foo>FOO</foo>
+</root>`,
+		},
+		{
+			name:    "MsgPack binding",
+			binding: MsgPack,
+			body:    msgPackBody(t),
+		},
+	} {
+		t.Logf("testing: %s", tt.name)
+		req := requestWithBody("POST", "/", tt.body)
+		form := FooStruct{}
+		body, _ := ioutil.ReadAll(req.Body)
+		assert.NoError(t, tt.binding.BindBody(body, &form))
+		assert.Equal(t, FooStruct{"FOO"}, form)
+	}
+}
+
+func msgPackBody(t *testing.T) string {
+	test := FooStruct{"FOO"}
+	h := new(codec.MsgpackHandle)
+	buf := bytes.NewBuffer(nil)
+	assert.NoError(t, codec.NewEncoder(buf, h).Encode(test))
+	return buf.String()
+}
+
+func TestBindingBodyProto(t *testing.T) {
+	test := example.Test{
+		Label: proto.String("FOO"),
+	}
+	data, _ := proto.Marshal(&test)
+	req := requestWithBody("POST", "/", string(data))
+	form := example.Test{}
+	body, _ := ioutil.ReadAll(req.Body)
+	assert.NoError(t, ProtoBuf.BindBody(body, &form))
+	assert.Equal(t, test, form)
+}