Gin源码之gin.Context结构体及其方法

Gin源码之gin.Context结构体及其方法

本文基于github.com/gin-gonic/gin v1.7.7依赖进行讲解

1.Context结构体

gin.Context

// Context is the most important part of gin. It allows us to pass variables between middleware,
// manage the flow, validate the JSON of a request and render a JSON response for example.
type Context struct {
	writermem responseWriter
	Request   *http.Request
	Writer    ResponseWriter

	Params   Params
	handlers HandlersChain
	index    int8
	fullPath string

	engine       *Engine
	params       *Params
	skippedNodes *[]skippedNode

	// This mutex protect Keys map
	mu sync.RWMutex

	// Keys is a key/value pair exclusively for the context of each request.
	Keys map[string]interface{}

	// Errors is a list of errors attached to all the handlers/middlewares who used this context.
	Errors errorMsgs

	// Accepted defines a list of manually accepted formats for content negotiation.
	Accepted []string

	// queryCache use url.ParseQuery cached the param query result from c.Request.URL.Query()
	queryCache url.Values

	// formCache use url.ParseQuery cached PostForm contains the parsed form data from POST, PATCH,
	// or PUT body parameters.
	formCache url.Values

	// SameSite allows a server to define a cookie attribute making it impossible for
	// the browser to send this cookie along with cross-site requests.
	sameSite http.SameSite
}

2.String方法

// String writes the given string into the response body.
func (c *Context) String(code int, format string, values ...interface{}) {
	c.Render(code, render.String{Format: format, Data: values})
}

3.JSON方法

code是http响应的状态码，比如写200; H是gin中定义的一个类型(type H map[string]interface{}),可以把H理解成一个json格式的

// JSON serializes the given struct as JSON into the response body.
// It also sets the Content-Type as "application/json".
func (c *Context) JSON(code int, obj interface{}) {
	c.Render(code, render.JSON{Data: obj})
}

4.Next方法

// Next should be used only inside middleware.
// It executes the pending handlers in the chain inside the calling handler.
// See example in GitHub.
func (c *Context) Next() {
	c.index++
	for c.index < int8(len(c.handlers)) {
		c.handlers[c.index](c)
		c.index++
	}
}

5.Aborted方法

// Abort prevents pending handlers from being called. Note that this will not stop the current handler.
// Let's say you have an authorization middleware that validates that the current request is authorized.
// If the authorization fails (ex: the password does not match), call Abort to ensure the remaining handlers
// for this request are not called.
func (c *Context) Abort() {
	c.index = abortIndex
}

6.Set方法

// Set is used to store a new key/value pair exclusively for this context.
// It also lazy initializes  c.Keys if it was not used previously.
func (c *Context) Set(key string, value interface{}) {
	c.mu.Lock()
	if c.Keys == nil {
		c.Keys = make(map[string]interface{})
	}

	c.Keys[key] = value
	c.mu.Unlock()
}

7.Get方法

// Get returns the value for the given key, ie: (value, true).
// If the value does not exists it returns (nil, false)
func (c *Context) Get(key string) (value interface{}, exists bool) {
	c.mu.RLock()
	value, exists = c.Keys[key]
	c.mu.RUnlock()
	return
}

8.MustGet方法

// MustGet returns the value for the given key if it exists, otherwise it panics.
func (c *Context) MustGet(key string) interface{} {
	if value, exists := c.Get(key); exists {
		return value
	}
	panic("Key \"" + key + "\" does not exist")
}

9.Query方法

// Query returns the keyed url query value if it exists,
// otherwise it returns an empty string `("")`.
// It is shortcut for `c.Request.URL.Query().Get(key)`
//     GET /path?id=1234&name=Manu&value=
// 	   c.Query("id") == "1234"
// 	   c.Query("name") == "Manu"
// 	   c.Query("value") == ""
// 	   c.Query("wtf") == ""
func (c *Context) Query(key string) string {
	value, _ := c.GetQuery(key)
	return value
}

10.DefaultQuery方法

// DefaultQuery returns the keyed url query value if it exists,
// otherwise it returns the specified defaultValue string.
// See: Query() and GetQuery() for further information.
//     GET /?name=Manu&lastname=
//     c.DefaultQuery("name", "unknown") == "Manu"
//     c.DefaultQuery("id", "none") == "none"
//     c.DefaultQuery("lastname", "none") == ""
func (c *Context) DefaultQuery(key, defaultValue string) string {
	if value, ok := c.GetQuery(key); ok {
		return value
	}
	return defaultValue
}

11.GetQuery方法

// GetQuery is like Query(), it returns the keyed url query value
// if it exists `(value, true)` (even when the value is an empty string),
// otherwise it returns `("", false)`.
// It is shortcut for `c.Request.URL.Query().Get(key)`
//     GET /?name=Manu&lastname=
//     ("Manu", true) == c.GetQuery("name")
//     ("", false) == c.GetQuery("id")
//     ("", true) == c.GetQuery("lastname")
func (c *Context) GetQuery(key string) (string, bool) {
	if values, ok := c.GetQueryArray(key); ok {
		return values[0], ok
	}
	return "", false
}

12.HTML方法

// HTML renders the HTTP template specified by its file name.
// It also updates the HTTP code and sets the Content-Type as "text/html".
// See http://golang.org/doc/articles/wiki/
func (c *Context) HTML(code int, name string, obj interface{}) {
	instance := c.engine.HTMLRender.Instance(name, obj)
	c.Render(code, instance)
}

13.PostForm方法

// PostForm returns the specified key from a POST urlencoded form or multipart form
// when it exists, otherwise it returns an empty string `("")`.
func (c *Context) PostForm(key string) string {
	value, _ := c.GetPostForm(key)
	return value
}

14.DefaultPostForm方法

// DefaultPostForm returns the specified key from a POST urlencoded form or multipart form
// when it exists, otherwise it returns the specified defaultValue string.
// See: PostForm() and GetPostForm() for further information.
func (c *Context) DefaultPostForm(key, defaultValue string) string {
	if value, ok := c.GetPostForm(key); ok {
		return value
	}
	return defaultValue
}

15.PostFormMap方法

// PostFormMap returns a map for a given form key.
func (c *Context) PostFormMap(key string) map[string]string {
	dicts, _ := c.GetPostFormMap(key)
	return dicts
}

16.GetPostForm方法

// GetPostForm is like PostForm(key). It returns the specified key from a POST urlencoded
// form or multipart form when it exists `(value, true)` (even when the value is an empty string),
// otherwise it returns ("", false).
// For example, during a PATCH request to update the user's email:
//     [email protected]  -->  ("[email protected]", true) := GetPostForm("email") // set email to "[email protected]"
// 	   email=                  -->  ("", true) := GetPostForm("email") // set email to ""
//                             -->  ("", false) := GetPostForm("email") // do nothing with email
func (c *Context) GetPostForm(key string) (string, bool) {
	if values, ok := c.GetPostFormArray(key); ok {
		return values[0], ok
	}
	return "", false
}

17.MustBindWith

Gin 提供了两类绑定方法：MustBindWith和 Should bind。
MustBindWith的方法有 Bind，BindJSON，BindXML，BindQuery，BindYAML，这些方法属于 MustBindWith的具体调用。
Must bind 如果发生绑定错误，则请求终止，并触发 c.AbortWithError(400, err).SetType(ErrorTypeBind)。响应状态码被设置为 400 并且 Content-Type 被设置为 text/plain; charset=utf-8。如果您在此之后尝试设置响应状态码，Gin会输出日志 [GIN-debug] [WARNING] Headers were already written. Wanted to override status code 400 with 422。

Should bind的方法有 ShouldBind，ShouldBindJSON，ShouldBindXML，ShouldBindQuery，ShouldBindYAML，这些方法属于 ShouldBindWith 的具体调用。
Should bind 如果发生绑定错误，Gin 会返回错误并由开发者处理错误和请求。

没有BindWith方法

// 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
}

18.BindWith方法

根据自己指定的Content-Type来进行解析.
ShouldBindWith和BindWith区别就是BindWith会在head中添加400的返回信息(如果解析错误的话，在header中写一个400的状态码)，而ShouldBindWith不会(解析错误直接返回，至于要给客户端返回什么错误状态码有你决定)

// BindWith binds the passed struct pointer using the specified binding engine.
// See the binding package.
func (c *Context) BindWith(obj interface{}, b binding.Binding) error {
	log.Println(`BindWith(\"interface{}, binding.Binding\") error is going to
	be deprecated, please check issue #662 and either use MustBindWith() if you
	want HTTP 400 to be automatically returned if any error occur, or use
	ShouldBindWith() if you need to manage the error.`)
	return c.MustBindWith(obj, b)
}

19.Bind方法

方法内部会自动识别请求中是哪种Content-Type，并以这种方式来去解析
ShouldBind和Bind区别就是Bind会在head中添加400的返回信息(如果解析错误的话，在header中写一个400的状态码)，而ShouldBind不会(解析错误直接返回，至于要给客户端返回什么错误状态码有你决定)

// Bind checks the Content-Type to select a binding engine automatically,
// Depending the "Content-Type" header different bindings are used:
//     "application/json" --> JSON binding
//     "application/xml"  --> XML binding
// otherwise --> returns an error.
// It parses the request's body as JSON if Content-Type == "application/json" using JSON or XML as a JSON input.
// It decodes the json payload into the struct specified as a pointer.
// It writes a 400 error and sets Content-Type header "text/plain" in the response if input is not valid.
func (c *Context) Bind(obj interface{}) error {
	b := binding.Default(c.Request.Method, c.ContentType())
	return c.MustBindWith(obj, b)
}

20.BindJSON方法

方法会以JSON这种Content-Type这种方式来去去解析
ShouldBindJSON和BindJSON区别就是Bind会在head中添加400的返回信息(如果解析错误的话，在header中写一个400的状态码)，而ShouldBindJSON不会(解析错误直接返回，至于要给客户端返回什么错误状态码有你决定)

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

21.BindXML方法

// BindXML is a shortcut for c.MustBindWith(obj, binding.BindXML).
func (c *Context) BindXML(obj interface{}) error {
	return c.MustBindWith(obj, binding.XML)
}

22.BindQuery方法

// BindQuery is a shortcut for c.MustBindWith(obj, binding.Query).
func (c *Context) BindQuery(obj interface{}) error {
	return c.MustBindWith(obj, binding.Query)
}

23.BindYAML方法

// BindYAML is a shortcut for c.MustBindWith(obj, binding.YAML).
func (c *Context) BindYAML(obj interface{}) error {
	return c.MustBindWith(obj, binding.YAML)
}

24.BindHeader方法

// BindHeader is a shortcut for c.MustBindWith(obj, binding.Header).
func (c *Context) BindHeader(obj interface{}) error {
	return c.MustBindWith(obj, binding.Header)
}

25.BindUri方法

// BindUri binds the passed struct pointer using binding.Uri.
// It will abort the request with HTTP 400 if any error occurs.
func (c *Context) BindUri(obj interface{}) error {
	if err := c.ShouldBindUri(obj); err != nil {
		c.AbortWithError(http.StatusBadRequest, err).SetType(ErrorTypeBind) // nolint: errcheck
		return err
	}
	return nil
}

26.ShouldBindWith方法

注意b.Bind(c.Request, obj)里的Bind方法不是上面我们说的方法了，而是Binding接口的方法

// ShouldBindWith binds the passed struct pointer using the specified binding engine.
// See the binding package.
func (c *Context) ShouldBindWith(obj interface{}, b binding.Binding) error {
	return b.Bind(c.Request, obj)
}

27.ShouldBind方法

为了能够更方便的获取请求相关参数，提高开发效率，我们可以基于请求的Content-Type识别请求数据类型并利用反射机制自动提取请求中QueryString、form表单、JSON、XML等参数到结构体中。ShouldBind()能够基于请求自动提取JSON、form表单和QueryString类型的数据，并把值绑定到指定的结构体对象。

ShouldBind会按照下面的顺序解析请求中的数据完成绑定：
如果是 GET 请求，只使用 “form” tag 绑定query引擎。
如果是 POST 请求，首先检查 content-type 是否为 JSON 或 XML，然后再使用 Form（form-data）。

// ShouldBind checks the Content-Type to select a binding engine automatically,
// Depending the "Content-Type" header different bindings are used:
//     "application/json" --> JSON binding
//     "application/xml"  --> XML binding
// otherwise --> returns an error
// It parses the request's body as JSON if Content-Type == "application/json" using JSON or XML as a JSON input.
// It decodes the json payload into the struct specified as a pointer.
// Like c.Bind() but this method does not set the response status code to 400 and abort if the json is not valid.
func (c *Context) ShouldBind(obj interface{}) error {
	b := binding.Default(c.Request.Method, c.ContentType())
	return c.ShouldBindWith(obj, b)
}

28.ShouldBindJSON方法

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

29.ShouldBindXML方法

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

30.ShouldBindQuery方法

ShouldBindQuery 如果 url 查询参数和 post 数据都存在，函数只绑定 url 查询参数而忽略 post 数据。

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

31. ShouldBindYAML方法

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

32.ShouldBindHeader方法

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

33.ShouldBindUri方法

// ShouldBindUri binds the passed struct pointer using the specified binding engine.
func (c *Context) ShouldBindUri(obj interface{}) error {
	m := make(map[string][]string)
	for _, v := range c.Params {
		m[v.Key] = []string{v.Value}
	}
	return binding.Uri.BindUri(m, obj)
}

34.QueryMap方法

// QueryMap returns a map for a given query key.
func (c *Context) QueryMap(key string) map[string]string {
	dicts, _ := c.GetQueryMap(key)
	return dicts
}

35.HTML方法

// HTML renders the HTTP template specified by its file name.
// It also updates the HTTP code and sets the Content-Type as "text/html".
// See http://golang.org/doc/articles/wiki/
func (c *Context) HTML(code int, name string, obj interface{}) {
	instance := c.engine.HTMLRender.Instance(name, obj)
	c.Render(code, instance)
}