Gin源码分析 – Context之Bind
•
Gin框架
1 介绍
本小节主要介绍上下文的Bind相关函数。Bind函数的主要目的是自动提取HTTP请求中的各种参数到结构体中。下面给出了一个例子，该列子中调用Context.ShouldBindJSON自动将HTTP的JSON格式的参数绑定到Login结构体中，Gin的Bind存在两大类，一类是ShouldBindXXX，另一类是MustBindXXX，后面分别进行详细介绍。
package main
import (
"github.com/gin-gonic/gin"
"net/http"
)
// 定义可绑定的数据结果，支持form，JSON，XML等格式
type Login struct {
User string `form:"user" json:"user" xml:"user" binding:"required"`
Password string `form:"password" json:"password" xml:"password" binding:"required"`
}
// binding JSON ({"user": "manu", "password": "123"})
func loginJSONHandler(c *gin.Context) {
var json Login
if err := c.ShouldBindJSON(&json); err != nil {
c.JSON(http.StatusBadRequest, gin.H{
"error":err.Error(),
})
return
}
if json.User != "manu" || json.Password != "123" {
c.JSON(http.StatusUnauthorized, gin.H{
"status":"unauthorized",
})
return
}
c.JSON(http.StatusOK, gin.H {
"status":"you are logged in",
})
}
func main() {
router := gin.Default()
router.POST("/loginJSON", loginJSONHandler)
router.Run()
}
2 MustBind
MustBind如果绑定发生了错误，则请求终止，并响应400状态码，包括一组函数，核心的函数是MustBindWith，函数定义入。
// MustBindWith binds the passed struct pointer using the specified binding engine.
// It will abort the request with HTTP 400 if any error occurs.
// See the binding package.
func (c *Context) MustBindWith(obj interface{}, b binding.Binding) error {
if err := c.ShouldBindWith(obj, b); err != nil {
c.AbortWithError(http.StatusBadRequest, err).SetType(ErrorTypeBind) // nolint: errcheck
return err
}
return nil
}
内部调用ShouldBindWith，但是当出现异常后，直接调用AbortWithError返回400异常，ShouldBindWith的实现在下一小节将进行详细的介绍。
binding.Binding 是Gin实现的绑定组件，详细注释见本小节附录1。在Context封装了如下的快捷调用函数，包括：BindJSON，BindXML，BindQuery，BindYAML，BindHeader。
// BindJSON is a shortcut for c.MustBindWith(obj, binding.JSON).
func (c *Context) BindJSON(obj interface{}) error {
return c.MustBindWith(obj, binding.JSON)
}
// BindXML is a shortcut for c.MustBindWith(obj, binding.BindXML).
func (c *Context) BindXML(obj interface{}) error {
return c.MustBindWith(obj, binding.XML)
}
// BindYAML is a shortcut for c.MustBindWith(obj, binding.YAML).
func (c *Context) BindYAML(obj interface{}) error {
return c.MustBindWith(obj, binding.YAML)
}
// BindQuery is a shortcut for c.MustBindWith(obj, binding.Query).
func (c *Context) BindQuery(obj interface{}) error {
return c.MustBindWith(obj, binding.Query)
}
// BindHeader is a shortcut for c.MustBindWith(obj, binding.Header).
func (c *Context) BindHeader(obj interface{}) error {
return c.MustBindWith(obj, binding.Header)
}
另外Bind根据ContentType进行判读，然后调用合适的函数，根据Default实际可以实现的有Form、JSON、XML、YAML、ProtoBuf、MsgPack、FormMultipart这样几种。
func (c *Context) Bind(obj interface{}) error {
b := binding.Default(c.Request.Method, c.ContentType())
return c.MustBindWith(obj, b)
}
附录1 Binding
本小节对binding.go文件进行详细注释说明，具体各绑定引擎的实现见不同的方法
package binding
import "net/http"
// Content-Type MIME of the most common data formats.
const (
MIMEJSON = "application/json"
MIMEHTML = "text/html"
MIMEXML = "application/xml"
MIMEXML2 = "text/xml"
MIMEPlain = "text/plain"
MIMEPOSTForm = "application/x-www-form-urlencoded"
MIMEMultipartPOSTForm = "multipart/form-data"
MIMEPROTOBUF = "application/x-protobuf"
MIMEMSGPACK = "application/x-msgpack"
MIMEMSGPACK2 = "application/msgpack"
MIMEYAML = "application/x-yaml"
)
// Binding describes the interface which needs to be implemented for binding the
// data present in the request such as JSON request body, query parameters or
// the form POST.
// 可以绑定JSON、XML、Query或者Form
type Binding interface {
Name() string
Bind(*http.Request, interface{}) error
}
// BindingBody adds BindBody method to Binding. BindBody is similar with 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 reads the Params.
// BindUri主要用于绑定URL中的Param参数
type BindingUri interface {
Name() string
BindUri(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
// https://github.com/go-playground/validator/tree/v10.6.1.
type StructValidator interface {
// ValidateStruct can receive any kind of type and it should never panic, even if the configuration is not right.
// If the received type is a slice|array, the validation should be performed travel on every element.
// If the received type is not a struct or slice|array, any validation should be skipped and nil must be returned.
// If the received type is a struct or pointer to a struct, the validation should be performed.
// If the struct is not valid or the validation itself fails, a descriptive error should be returned.
// Otherwise nil must be returned.
ValidateStruct(interface{}) error
// Engine returns the underlying validator engine which powers the
// StructValidator implementation.
Engine() interface{}
}
// 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.
var Validator StructValidator = &defaultValidator{}
// These implement the Binding interface and can be used to bind the data
// present in the request to struct instances.
// 入下的变量将实现各类Binding接口
var (
JSON = jsonBinding{}
XML = xmlBinding{}
Form = formBinding{}
Query = queryBinding{}
FormPost = formPostBinding{}
FormMultipart = formMultipartBinding{}
ProtoBuf = protobufBinding{}
MsgPack = msgpackBinding{}
YAML = yamlBinding{}
Uri = uriBinding{}
Header = headerBinding{}
)
// Default returns the appropriate Binding instance based on the HTTP method
// and the content type.
// 根据Content-Type，返回Binding引擎
func Default(method, contentType string) Binding {
// Get方法将默认返回Form绑定
if method == http.MethodGet {
return Form
}
switch contentType {
case MIMEJSON:
return JSON
case MIMEXML, MIMEXML2:
return XML
case MIMEPROTOBUF:
return ProtoBuf
case MIMEMSGPACK, MIMEMSGPACK2:
return MsgPack
case MIMEYAML:
return YAML
case MIMEMultipartPOSTForm:
return FormMultipart
default: // case MIMEPOSTForm:
return Form
}
}
// 对数据进行合法性检查
func validate(obj interface{}) error {
if Validator == nil {
return nil
}
return Validator.ValidateStruct(obj)
}
附录2 json.go
package binding
import (
"bytes"
"errors"
"io"
"net/http"
"github.com/gin-gonic/gin/internal/json"
)
// EnableDecoderUseNumber is used to call the UseNumber method on the JSON
// Decoder instance. UseNumber causes the Decoder to unmarshal a number into an
// interface{} as a Number instead of as a float64.
var EnableDecoderUseNumber = false
// EnableDecoderDisallowUnknownFields is used to call the DisallowUnknownFields method
// on the JSON Decoder instance. DisallowUnknownFields causes the Decoder to
// return an error when the destination is a struct and the input contains object
// keys which do not match any non-ignored, exported fields in the destination.
// 使用允许不能识别的字段，当为false时，如果有不能识别的则返回错误。
var EnableDecoderDisallowUnknownFields = false
type jsonBinding struct{}
func (jsonBinding) Name() string {
return "json"
}
// 将请求的Body绑定到obj中
func (jsonBinding) Bind(req *http.Request, obj interface{}) error {
if req == nil || req.Body == nil {
return errors.New("invalid request")
}
return decodeJSON(req.Body, obj)
}
// 直接将byte数组绑定到obj中
func (jsonBinding) BindBody(body []byte, obj interface{}) error {
return decodeJSON(bytes.NewReader(body), obj)
}
func decodeJSON(r io.Reader, obj interface{}) error {
// 创建json解码器
decoder := json.NewDecoder(r)
// 设置是否能够使用Number
if EnableDecoderUseNumber {
decoder.UseNumber()
}
if EnableDecoderDisallowUnknownFields {
decoder.DisallowUnknownFields()
}
// 进行实际的解码
if err := decoder.Decode(obj); err != nil {
return err
}
// 最后进行合法性检查
return validate(obj)
}