# binding

**Repository Path**: JeffreyBool/binding

## Basic Information

- **Project Name**: binding
- **Description**: No description available
- **Primary Language**: Go
- **License**: MIT
- **Default Branch**: main
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 0
- **Created**: 2020-12-15
- **Last Updated**: 2020-12-19

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

# binding

# binding

### Model binding and validation

To bind a request body into a type, use model binding. We currently support binding of JSON, XML, YAML and standard form values (foo=bar&boo=baz).

Gin uses [**go-playground/validator/v10**](https://github.com/go-playground/validator) for validation. Check the full docs on tags usage [here](https://godoc.org/github.com/go-playground/validator#hdr-Baked_In_Validators_and_Tags).

Note that you need to set the corresponding binding tag on all fields you want to bind. For example, when binding from JSON, set `json:"fieldname"`.

Also, Gin provides two sets of methods for binding:
- **Type** - Must bind
  - **Methods** - `Bind`, `BindJSON`, `BindXML`, `BindQuery`, `BindYAML`, `BindHeader`
  - **Behavior** - These methods use `MustBindWith` under the hood. If there is a binding error, the request is aborted with `c.AbortWithError(400, err).SetType(ErrorTypeBind)`. This sets the response status code to 400 and the `Content-Type` header is set to `text/plain; charset=utf-8`. Note that if you try to set the response code after this, it will result in a warning `[GIN-debug] [WARNING] Headers were already written. Wanted to override status code 400 with 422`. If you wish to have greater control over the behavior, consider using the `ShouldBind` equivalent method.
- **Type** - Should bind
  - **Methods** - `ShouldBind`, `ShouldBindJSON`, `ShouldBindXML`, `ShouldBindQuery`, `ShouldBindYAML`, `ShouldBindHeader`
  - **Behavior** - These methods use `ShouldBindWith` under the hood. If there is a binding error, the error is returned and it is the developer's responsibility to handle the request and error appropriately.

When using the Bind-method, Gin tries to infer the binder depending on the Content-Type header. If you are sure what you are binding, you can use `MustBindWith` or `ShouldBindWith`.

You can also specify that specific fields are required. If a field is decorated with `binding:"required"` and has a empty value when binding, an error will be returned.

```go
// Binding from JSON
type Login struct {
	User     string `form:"user" json:"user" xml:"user"  binding:"required"`
	Password string `form:"password" json:"password" xml:"password" binding:"required"`
}

func main() {
	router := gin.Default()

	// Example for binding JSON ({"user": "manu", "password": "123"})
	router.POST("/loginJSON", func(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"})
	})

	// Example for binding XML (
	//	<?xml version="1.0" encoding="UTF-8"?>
	//	<root>
	//		<user>user</user>
	//		<password>123</password>
	//	</root>)
	router.POST("/loginXML", func(c *gin.Context) {
		var xml Login
		if err := c.ShouldBindXML(&xml); err != nil {
			c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
			return
		}
		
		if xml.User != "manu" || xml.Password != "123" {
			c.JSON(http.StatusUnauthorized, gin.H{"status": "unauthorized"})
			return
		} 
		
		c.JSON(http.StatusOK, gin.H{"status": "you are logged in"})
	})

	// Example for binding a HTML form (user=manu&password=123)
	router.POST("/loginForm", func(c *gin.Context) {
		var form Login
		// This will infer what binder to use depending on the content-type header.
		if err := c.ShouldBind(&form); err != nil {
			c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
			return
		}
		
		if form.User != "manu" || form.Password != "123" {
			c.JSON(http.StatusUnauthorized, gin.H{"status": "unauthorized"})
			return
		} 
		
		c.JSON(http.StatusOK, gin.H{"status": "you are logged in"})
	})

	// Listen and serve on 0.0.0.0:8080
	router.Run(":8080")
}
```

**Sample request**
```shell
$ curl -v -X POST \
  http://localhost:8080/loginJSON \
  -H 'content-type: application/json' \
  -d '{ "user": "manu" }'
> POST /loginJSON HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.51.0
> Accept: */*
> content-type: application/json
> Content-Length: 18
>
* upload completely sent off: 18 out of 18 bytes
< HTTP/1.1 400 Bad Request
< Content-Type: application/json; charset=utf-8
< Date: Fri, 04 Aug 2017 03:51:31 GMT
< Content-Length: 100
<
{"error":"Key: 'Login.Password' Error:Field validation for 'Password' failed on the 'required' tag"}
```

**Skip validate**

When running the above example using the above the `curl` command, it returns error. Because the example use `binding:"required"` for `Password`. If use `binding:"-"` for `Password`, then it will not return error when running the above example again.

### Custom Validators

It is also possible to register custom validators. See the [example code](https://github.com/gin-gonic/examples/tree/master/custom-validation/server.go).

```go
package main

import (
	"net/http"
	"time"

	"github.com/gin-gonic/gin"
	"github.com/gin-gonic/gin/binding"
	"github.com/go-playground/validator/v10"
)

// Booking contains binded and validated data.
type Booking struct {
	CheckIn  time.Time `form:"check_in" binding:"required,bookabledate" time_format:"2006-01-02"`
	CheckOut time.Time `form:"check_out" binding:"required,gtfield=CheckIn" time_format:"2006-01-02"`
}

var bookableDate validator.Func = func(fl validator.FieldLevel) bool {
	date, ok := fl.Field().Interface().(time.Time)
	if ok {
		today := time.Now()
		if today.After(date) {
			return false
		}
	}
	return true
}

func main() {
	route := gin.Default()

	if v, ok := binding.Validator.Engine().(*validator.Validate); ok {
		v.RegisterValidation("bookabledate", bookableDate)
	}

	route.GET("/bookable", getBookable)
	route.Run(":8085")
}

func getBookable(c *gin.Context) {
	var b Booking
	if err := c.ShouldBindWith(&b, binding.Query); err == nil {
		c.JSON(http.StatusOK, gin.H{"message": "Booking dates are valid!"})
	} else {
		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
	}
}
```

```console
$ curl "localhost:8085/bookable?check_in=2030-04-16&check_out=2030-04-17"
{"message":"Booking dates are valid!"}

$ curl "localhost:8085/bookable?check_in=2030-03-10&check_out=2030-03-09"
{"error":"Key: 'Booking.CheckOut' Error:Field validation for 'CheckOut' failed on the 'gtfield' tag"}

$ curl "localhost:8085/bookable?check_in=2000-03-09&check_out=2000-03-10"
{"error":"Key: 'Booking.CheckIn' Error:Field validation for 'CheckIn' failed on the 'bookabledate' tag"}%    
```

[Struct level validations](https://github.com/go-playground/validator/releases/tag/v8.7) can also be registered this way.
See the [struct-lvl-validation example](https://github.com/gin-gonic/examples/tree/master/struct-lvl-validations) to learn more.

### Only Bind Query String

`ShouldBindQuery` function only binds the query params and not the post data. See the [detail information](https://github.com/gin-gonic/gin/issues/742#issuecomment-315953017).

```go
package main

import (
	"log"

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

type Person struct {
	Name    string `form:"name"`
	Address string `form:"address"`
}

func main() {
	route := gin.Default()
	route.Any("/testing", startPage)
	route.Run(":8085")
}

func startPage(c *gin.Context) {
	var person Person
	if c.ShouldBindQuery(&person) == nil {
		log.Println("====== Only Bind By Query String ======")
		log.Println(person.Name)
		log.Println(person.Address)
	}
	c.String(200, "Success")
}

```

### Bind Query String or Post Data

See the [detail information](https://github.com/gin-gonic/gin/issues/742#issuecomment-264681292).

```go
package main

import (
	"log"
	"time"

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

type Person struct {
        Name       string    `form:"name"`
        Address    string    `form:"address"`
        Birthday   time.Time `form:"birthday" time_format:"2006-01-02" time_utc:"1"`
        CreateTime time.Time `form:"createTime" time_format:"unixNano"`
        UnixTime   time.Time `form:"unixTime" time_format:"unix"`
}

func main() {
	route := gin.Default()
	route.GET("/testing", startPage)
	route.Run(":8085")
}

func startPage(c *gin.Context) {
	var person Person
	// If `GET`, only `Form` binding engine (`query`) used.
	// If `POST`, first checks the `content-type` for `JSON` or `XML`, then uses `Form` (`form-data`).
	// See more at https://github.com/gin-gonic/gin/blob/master/binding/binding.go#L48
        if c.ShouldBind(&person) == nil {
                log.Println(person.Name)
                log.Println(person.Address)
                log.Println(person.Birthday)
                log.Println(person.CreateTime)
                log.Println(person.UnixTime)
        }

	c.String(200, "Success")
}
```

Test it with:
```sh
$ curl -X GET "localhost:8085/testing?name=appleboy&address=xyz&birthday=1992-03-15&createTime=1562400033000000123&unixTime=1562400033"
```

### Bind Uri

See the [detail information](https://github.com/gin-gonic/gin/issues/846).

```go
package main

import "github.com/gin-gonic/gin"

type Person struct {
	ID string `uri:"id" binding:"required,uuid"`
	Name string `uri:"name" binding:"required"`
}

func main() {
	route := gin.Default()
	route.GET("/:name/:id", func(c *gin.Context) {
		var person Person
		if err := c.ShouldBindUri(&person); err != nil {
			c.JSON(400, gin.H{"msg": err})
			return
		}
		c.JSON(200, gin.H{"name": person.Name, "uuid": person.ID})
	})
	route.Run(":8088")
}
```

Test it with:
```sh
$ curl -v localhost:8088/thinkerou/987fbc97-4bed-5078-9f07-9141ba07c9f3
$ curl -v localhost:8088/thinkerou/not-uuid
```

### Bind Header

```go
package main

import (
	"fmt"
	"github.com/gin-gonic/gin"
)

type testHeader struct {
	Rate   int    `header:"Rate"`
	Domain string `header:"Domain"`
}

func main() {
	r := gin.Default()
	r.GET("/", func(c *gin.Context) {
		h := testHeader{}

		if err := c.ShouldBindHeader(&h); err != nil {
			c.JSON(200, err)
		}

		fmt.Printf("%#v\n", h)
		c.JSON(200, gin.H{"Rate": h.Rate, "Domain": h.Domain})
	})

	r.Run()

// client
// curl -H "rate:300" -H "domain:music" 127.0.0.1:8080/
// output
// {"Domain":"music","Rate":300}
}
```

### Bind HTML checkboxes

See the [detail information](https://github.com/gin-gonic/gin/issues/129#issuecomment-124260092)

main.go

```go
...

type myForm struct {
    Colors []string `form:"colors[]"`
}

...

func formHandler(c *gin.Context) {
    var fakeForm myForm
    c.ShouldBind(&fakeForm)
    c.JSON(200, gin.H{"color": fakeForm.Colors})
}

...

```

form.html

```html
<form action="/" method="POST">
    <p>Check some colors</p>
    <label for="red">Red</label>
    <input type="checkbox" name="colors[]" value="red" id="red">
    <label for="green">Green</label>
    <input type="checkbox" name="colors[]" value="green" id="green">
    <label for="blue">Blue</label>
    <input type="checkbox" name="colors[]" value="blue" id="blue">
    <input type="submit">
</form>
```

result:

```
{"color":["red","green","blue"]}
```

### Multipart/Urlencoded binding

```go
type ProfileForm struct {
	Name   string                `form:"name" binding:"required"`
	Avatar *multipart.FileHeader `form:"avatar" binding:"required"`

	// or for multiple files
	// Avatars []*multipart.FileHeader `form:"avatar" binding:"required"`
}

func main() {
	router := gin.Default()
	router.POST("/profile", func(c *gin.Context) {
		// you can bind multipart form with explicit binding declaration:
		// c.ShouldBindWith(&form, binding.Form)
		// or you can simply use autobinding with ShouldBind method:
		var form ProfileForm
		// in this case proper binding will be automatically selected
		if err := c.ShouldBind(&form); err != nil {
			c.String(http.StatusBadRequest, "bad request")
			return
		}

		err := c.SaveUploadedFile(form.Avatar, form.Avatar.Filename)
		if err != nil {
			c.String(http.StatusInternalServerError, "unknown error")
			return
		}

		// db.Save(&form)

		c.String(http.StatusOK, "ok")
	})
	router.Run(":8080")
}
```

Test it with:
```sh
$ curl -X POST -v --form name=user --form "avatar=@./avatar.png" http://localhost:8080/profile
```