Gin 框架绑定 JSON 参数使用 jsoniter

Gin 框架中，处理 JSON 格式的参数绑定时，默认采用的标准包 encoding/json，然而标准包不能满足我们的一些要求，比如兼容字符串整型、PHP空数组、时间格式等。

最简单的方式

开发 API 时，需要用到 ShouldBindJSON 绑定传入的参数到结构体：

// github.com/gin-gonic/gin@v1.6.3/context.go:643

// ShouldBindJSON is a shortcut for c.ShouldBindWith(obj, binding.JSON).
func (c *Context) ShouldBindJSON(obj interface{}) error {
    return c.ShouldBindWith(obj, binding.JSON)
}

Gin 默认采用 encoding/json 包：

// github.com/gin-gonic/gin@v1.6.3/internal/json/json.go
// +build !jsoniter

package json

import "encoding/json"

var (
    // Marshal is exported by gin/json package.
    Marshal = json.Marshal
    // Unmarshal is exported by gin/json package.
    Unmarshal = json.Unmarshal
    // MarshalIndent is exported by gin/json package.
    MarshalIndent = json.MarshalIndent
    // NewDecoder is exported by gin/json package.
    NewDecoder = json.NewDecoder
    // NewEncoder is exported by gin/json package.
    NewEncoder = json.NewEncoder
)

同时我们看到还支持了 jsoniter

// github.com/gin-gonic/gin@v1.6.3/internal/json/jsoniter.go
// +build jsoniter

package json

import "github.com/json-iterator/go"

var (
    json = jsoniter.ConfigCompatibleWithStandardLibrary
    // Marshal is exported by gin/json package.
    Marshal = json.Marshal
    // Unmarshal is exported by gin/json package.
    Unmarshal = json.Unmarshal
    // MarshalIndent is exported by gin/json package.
    MarshalIndent = json.MarshalIndent
    // NewDecoder is exported by gin/json package.
    NewDecoder = json.NewDecoder
    // NewEncoder is exported by gin/json package.
    NewEncoder = json.NewEncoder
)

那我们怎么才能使用到 jsoniter 呢？源码中已经明确了编译tag：

// +build jsoniter

所以，我们只需在编译时带上这个 tag 就可以了，例如：

go build -tags=jsoniter main.go

// 或者
go run -tags=jsoniter main.go

自定义的方式

Gin 框架支持的 jsoniter 是默认配置 jsoniter.ConfigCompatibleWithStandardLibrary。当我们需要其他配置或添加一些自定义扩展（比如时间处理）时，就难受了。于是我们就要自己动手了~

翻开源码，我们能看到 binding.JSON 其实使用的是 jsonBinding{} 这个结构体：

// github.com/gin-gonic/gin@v1.6.3/binding/binding.go:73

// These implement the Binding interface and can be used to bind the data
// present in the request to struct instances.
var (
    JSON          = jsonBinding{}
    // 其他省略了...
)

翻开 jsonBinding 源码看看：

// github.com/gin-gonic/gin@v1.6.3/binding/json.go

type jsonBinding struct{}

func (jsonBinding) Name() string {
    return "json"
}

func (jsonBinding) Bind(req *http.Request, obj interface{}) error {
    if req == nil || req.Body == nil {
        return fmt.Errorf("invalid request")
    }
    return decodeJSON(req.Body, obj)
}

func (jsonBinding) BindBody(body []byte, obj interface{}) error {
    return decodeJSON(bytes.NewReader(body), obj)
}

发现实现了 BindingBody 这个接口：

// github.com/gin-gonic/gin@v1.6.3/binding/binding.go:36

// 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.
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
}

那接下来就简单了，我们只要实现了这个接口即可，例如：

package custom

import (
    "bytes"
    "fmt"
    "io"
    "net/http"

    jsoniter "github.com/json-iterator/go"

    "github.com/gin-gonic/gin/binding"
)

// BindingJSON 替换Gin默认的binding，支持更丰富JSON功能
var BindingJSON = jsonBinding{}

// 可以自定义jsoniter配置或者添加插件
var json = jsoniter.ConfigCompatibleWithStandardLibrary

type jsonBinding struct{}

func (jsonBinding) Name() string {
    return "json"
}

func (jsonBinding) Bind(req *http.Request, obj interface{}) error {
    if req == nil || req.Body == nil {
        return fmt.Errorf("invalid request")
    }
    return decodeJSON(req.Body, obj)
}

func (jsonBinding) BindBody(body []byte, obj interface{}) error {
    return decodeJSON(bytes.NewReader(body), obj)
}

func decodeJSON(r io.Reader, obj interface{}) error {
    decoder := json.NewDecoder(r)
    if binding.EnableDecoderUseNumber {
        decoder.UseNumber()
    }
    if binding.EnableDecoderDisallowUnknownFields {
        decoder.DisallowUnknownFields()
    }
    if err := decoder.Decode(obj); err != nil {
        return err
    }
    return validate(obj)
}

func validate(obj interface{}) error {
    if binding.Validator == nil {
        return nil
    }
    return binding.Validator.ValidateStruct(obj)
}

自定义 jsonBinding 已经写好了，可使用有2种方式：

// binding.JSON 替换成自定义的
ctx.ShouldBindWith(&params, binding.JSON)
ctx.ShouldBindBodyWith(&params, binding.JSON)

上述自定义的方式，还可以用于其他包，不仅限于 iterator。从这个方面体现出了 Gin 框架良好的接口设计👍

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原文地址: https://shockerli.net/post/gin-binding-jsoniter/