见gin源码研究&整理之Context类

// Copyright 2014 Manu Martinez-Almeida.  All rights reserved.
// Use of this source code is governed by a MIT style
// license that can be found in the LICENSE file.

//修改说明：
//1.数据响应方法改为默认Abort且Status为200。修改状态码请在之前调用Status(...)
//2.Negotiate已删除

package gin

import (
    "fmt"
    "github.com/gin-contrib/sse"
    "github.com/gin-gonic/gin/binding"
    "github.com/gin-gonic/gin/render"
    "io"
    "io/ioutil"
    "math"
    "mime/multipart"
    "net"
    "net/http"
    "net/url"
    "os"
    "strings"
    "time"
)

// Content-Type MIME of the most common data formats.
const (
    MIMEJSON              = binding.MIMEJSON
    MIMEHTML              = binding.MIMEHTML
    MIMEXML               = binding.MIMEXML
    MIMEXML2              = binding.MIMEXML2
    MIMEPlain             = binding.MIMEPlain
    MIMEPOSTForm          = binding.MIMEPOSTForm
    MIMEMultipartPOSTForm = binding.MIMEMultipartPOSTForm
    MIMEYAML              = binding.MIMEYAML
)

const abortIndex int8 = math.MaxInt8 / 2

// 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

    engine *Engine

    // 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
}

/************************************/
/********** CONTEXT CREATION ********/
/************************************/

func (c *Context) reset() {
    c.Writer = &c.writermem
    c.Params = c.Params[0:0]
    c.handlers = nil
    c.index = -1
    c.Keys = nil
    c.Errors = c.Errors[0:0]
    c.Accepted = nil
}

// Copy returns a copy of the current context that can be safely used outside the request's scope.
// This has to be used when the context has to be passed to a goroutine.
func (c *Context) Copy() *Context {
    var cp = *c
    cp.writermem.ResponseWriter = nil
    cp.Writer = &cp.writermem
    cp.index = abortIndex
    cp.handlers = nil
    cp.Keys = map[string]interface{}{}
    for k, v := range c.Keys {
        cp.Keys[k] = v
    }
    return &cp
}

// HandlerName returns the main handler's name. For example if the handler is "handleGetUsers()",
// this function will return "main.handleGetUsers".
func (c *Context) HandlerName() string {
    return nameOfFunction(c.handlers.Last())
}

// HandlerNames returns a list of all registered handlers for this context in descending order,
// following the semantics of HandlerName()
func (c *Context) HandlerNames() []string {
    hn := make([]string, 0, len(c.handlers))
    for _, val := range c.handlers {
        hn = append(hn, nameOfFunction(val))
    }
    return hn
}

// Handler returns the main handler.
func (c *Context) Handler() HandlerFunc {
    return c.handlers.Last()
}

/************************************/
/*********** FLOW CONTROL ***********/
/************************************/

// 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++
    }
}

// IsAborted returns true if the current context was aborted.
func (c *Context) IsAborted() bool {
    return c.index >= abortIndex
}

// 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
}

// AbortWithStatus calls `Abort()` and writes the headers with the specified status code.
// For example, a failed attempt to authenticate a request could use: context.AbortWithStatus(401).
func (c *Context) AbortWithStatus(code int) {
    c.Status(code)
    c.Writer.WriteHeaderNow()
    c.Abort()
}


// AbortWithError calls `AbortWithStatus()` and `Error()` internally.
// This method stops the chain, writes the status code and pushes the specified error to `c.Errors`.
// See Context.Error() for more details.
func (c *Context) AbortWithError(code int, err error) *Error {
    c.AbortWithStatus(code)
    return c.Error(err)
}

/************************************/
/********* ERROR MANAGEMENT *********/
/************************************/

// Error attaches an error to the current context. The error is pushed to a list of errors.
// It's a good idea to call Error for each error that occurred during the resolution of a request.
// A middleware can be used to collect all the errors and push them to a database together,
// print a log, or append it in the HTTP response.
// Error will panic if err is nil.
func (c *Context) Error(err error) *Error {
    if err == nil {
        panic("err is nil")
    }

    parsedError, ok := err.(*Error)
    if !ok {
        parsedError = &Error{
            Err:  err,
            Type: ErrorTypePrivate,
        }
    }

    c.Errors = append(c.Errors, parsedError)
    return parsedError
}

/************************************/
/******** METADATA MANAGEMENT********/
/************************************/

// 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{}) {
    if c.Keys == nil {
        c.Keys = make(map[string]interface{})
    }
    c.Keys[key] = value
}

// 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) {
    value, exists = c.Keys[key]
    return
}

// 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")
}

// GetString returns the value associated with the key as a string.
func (c *Context) GetString(key string) (s string) {
    if val, ok := c.Get(key); ok && val != nil {
        s, _ = val.(string)
    }
    return
}

// GetBool returns the value associated with the key as a boolean.
func (c *Context) GetBool(key string) (b bool) {
    if val, ok := c.Get(key); ok && val != nil {
        b, _ = val.(bool)
    }
    return
}

// GetInt returns the value associated with the key as an integer.
func (c *Context) GetInt(key string) (i int) {
    if val, ok := c.Get(key); ok && val != nil {
        i, _ = val.(int)
    }
    return
}

// GetInt64 returns the value associated with the key as an integer.
func (c *Context) GetInt64(key string) (i64 int64) {
    if val, ok := c.Get(key); ok && val != nil {
        i64, _ = val.(int64)
    }
    return
}

// GetFloat64 returns the value associated with the key as a float64.
func (c *Context) GetFloat64(key string) (f64 float64) {
    if val, ok := c.Get(key); ok && val != nil {
        f64, _ = val.(float64)
    }
    return
}

// GetTime returns the value associated with the key as time.
func (c *Context) GetTime(key string) (t time.Time) {
    if val, ok := c.Get(key); ok && val != nil {
        t, _ = val.(time.Time)
    }
    return
}

// GetDuration returns the value associated with the key as a duration.
func (c *Context) GetDuration(key string) (d time.Duration) {
    if val, ok := c.Get(key); ok && val != nil {
        d, _ = val.(time.Duration)
    }
    return
}

// GetStringSlice returns the value associated with the key as a slice of strings.
func (c *Context) GetStringSlice(key string) (ss []string) {
    if val, ok := c.Get(key); ok && val != nil {
        ss, _ = val.([]string)
    }
    return
}

// GetStringMap returns the value associated with the key as a map of interfaces.
func (c *Context) GetStringMap(key string) (sm map[string]interface{}) {
    if val, ok := c.Get(key); ok && val != nil {
        sm, _ = val.(map[string]interface{})
    }
    return
}

// GetStringMapString returns the value associated with the key as a map of strings.
func (c *Context) GetStringMapString(key string) (sms map[string]string) {
    if val, ok := c.Get(key); ok && val != nil {
        sms, _ = val.(map[string]string)
    }
    return
}

// GetStringMapStringSlice returns the value associated with the key as a map to a slice of strings.
func (c *Context) GetStringMapStringSlice(key string) (smss map[string][]string) {
    if val, ok := c.Get(key); ok && val != nil {
        smss, _ = val.(map[string][]string)
    }
    return
}

/************************************/
/************ INPUT DATA ************/
/************************************/

// Param returns the value of the URL param.
// It is a shortcut for c.Params.ByName(key)
//     router.GET("/user/:id", func(c *gin.Context) {
//         // a GET request to /user/john
//         id := c.Param("id") // id == "john"
//     })
func (c *Context) Param(key string) string {
    return c.Params.ByName(key)
}

// 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
}

// 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
}

// 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
}

// QueryArray returns a slice of strings for a given query key.
// The length of the slice depends on the number of params with the given key.
func (c *Context) QueryArray(key string) []string {
    values, _ := c.GetQueryArray(key)
    return values
}

// GetQueryArray returns a slice of strings for a given query key, plus
// a boolean value whether at least one value exists for the given key.
func (c *Context) GetQueryArray(key string) ([]string, bool) {
    if values, ok := c.Request.URL.Query()[key]; ok && len(values) > 0 {
        return values, true
    }
    return []string{}, false
}

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

// GetQueryMap returns a map for a given query key, plus a boolean value
// whether at least one value exists for the given key.
func (c *Context) GetQueryMap(key string) (map[string]string, bool) {
    return c.get(c.Request.URL.Query(), key)
}

// 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
}

// 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
}

// 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=mail@example.com  -->  ("mail@example.com", true) := GetPostForm("email") // set email to "mail@example.com"
//     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
}

// PostFormArray returns a slice of strings for a given form key.
// The length of the slice depends on the number of params with the given key.
func (c *Context) PostFormArray(key string) []string {
    values, _ := c.GetPostFormArray(key)
    return values
}

// GetPostFormArray returns a slice of strings for a given form key, plus
// a boolean value whether at least one value exists for the given key.
func (c *Context) GetPostFormArray(key string) ([]string, bool) {
    req := c.Request
    if err := req.ParseMultipartForm(c.engine.MaxMultipartMemory); err != nil {
        if err != http.ErrNotMultipart {
            debugPrint("error on parse multipart form array: %v", err)
        }
    }
    if values := req.PostForm[key]; len(values) > 0 {
        return values, true
    }
    return []string{}, false
}

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

// GetPostFormMap returns a map for a given form key, plus a boolean value
// whether at least one value exists for the given key.
func (c *Context) GetPostFormMap(key string) (map[string]string, bool) {
    req := c.Request
    if err := req.ParseMultipartForm(c.engine.MaxMultipartMemory); err != nil {
        if err != http.ErrNotMultipart {
            debugPrint("error on parse multipart form map: %v", err)
        }
    }
    return c.get(req.PostForm, key)
}

// get is an internal method and returns a map which satisfy conditions.
func (c *Context) get(m map[string][]string, key string) (map[string]string, bool) {
    dicts := make(map[string]string)
    exist := false
    for k, v := range m {
        if i := strings.IndexByte(k, '['); i >= 1 && k[0:i] == key {
            if j := strings.IndexByte(k[i+1:], ']'); j >= 1 {
                exist = true
                dicts[k[i+1:][:j]] = v[0]
            }
        }
    }
    return dicts, exist
}

// FormFile returns the first file for the provided form key.
func (c *Context) FormFile(name string) (*multipart.FileHeader, error) {
    if c.Request.MultipartForm == nil {
        if err := c.Request.ParseMultipartForm(c.engine.MaxMultipartMemory); err != nil {
            return nil, err
        }
    }
    _, fh, err := c.Request.FormFile(name)
    return fh, err
}

// MultipartForm is the parsed multipart form, including file uploads.
func (c *Context) MultipartForm() (*multipart.Form, error) {
    err := c.Request.ParseMultipartForm(c.engine.MaxMultipartMemory)
    return c.Request.MultipartForm, err
}

// SaveUploadedFile uploads the form file to specific dst.
func (c *Context) SaveUploadedFile(file *multipart.FileHeader, dst string) error {
    src, err := file.Open()
    if err != nil {
        return err
    }
    defer src.Close()

    out, err := os.Create(dst)
    if err != nil {
        return err
    }
    defer out.Close()

    _, err = io.Copy(out, src)
    return err
}

// 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)
}

// 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)
}

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

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

// 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
}

// 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
}

// 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)
}

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

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

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

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

// 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)
}

// 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)
}



// ClientIP implements a best effort algorithm to return the real client IP, it parses
// X-Real-IP and X-Forwarded-For in order to work properly with reverse-proxies such us: nginx or haproxy.
// Use X-Forwarded-For before X-Real-Ip as nginx uses X-Real-Ip with the proxy's IP.
func (c *Context) ClientIP() string {
    if c.engine.ForwardedByClientIP {
        clientIP := c.requestHeader("X-Forwarded-For")
        clientIP = strings.TrimSpace(strings.Split(clientIP, ",")[0])
        if clientIP == "" {
            clientIP = strings.TrimSpace(c.requestHeader("X-Real-Ip"))
        }
        if clientIP != "" {
            return clientIP
        }
    }

    if c.engine.AppEngine {
        if addr := c.requestHeader("X-Appengine-Remote-Addr"); addr != "" {
            return addr
        }
    }

    if ip, _, err := net.SplitHostPort(strings.TrimSpace(c.Request.RemoteAddr)); err == nil {
        return ip
    }

    return ""
}

// ContentType returns the Content-Type header of the request.
func (c *Context) ContentType() string {
    return filterFlags(c.requestHeader("Content-Type"))
}

// IsWebsocket returns true if the request headers indicate that a websocket
// handshake is being initiated by the client.
func (c *Context) IsWebsocket() bool {
    if strings.Contains(strings.ToLower(c.requestHeader("Connection")), "upgrade") &&
        strings.ToLower(c.requestHeader("Upgrade")) == "websocket" {
        return true
    }
    return false
}

func (c *Context) requestHeader(key string) string {
    return c.Request.Header.Get(key)
}

/************************************/
/******** RESPONSE RENDERING ********/
/************************************/

// bodyAllowedForStatus is a copy of http.bodyAllowedForStatus non-exported function.
func bodyAllowedForStatus(status int) bool {
    switch {
    case status >= 100 && status <= 199:
        return false
    case status == http.StatusNoContent:
        return false
    case status == http.StatusNotModified:
        return false
    }
    return true
}

// Status sets the HTTP response code.
func (c *Context) Status(code int) *Context{
    c.writermem.WriteHeader(code)
    return c
}

// Header is a intelligent shortcut for c.Writer.Header().Set(key, value).
// It writes a header in the response.
// If value == "", this method removes the header `c.Writer.Header().Del(key)`
func (c *Context) Header(key, value string) {
    if value == "" {
        c.Writer.Header().Del(key)
        return
    }
    c.Writer.Header().Set(key, value)
}

// GetHeader returns value from request headers.
func (c *Context) GetHeader(key string) string {
    return c.requestHeader(key)
}

// GetRawData return stream data.
func (c *Context) GetRawData() ([]byte, error) {
    return ioutil.ReadAll(c.Request.Body)
}

// SetCookie adds a Set-Cookie header to the ResponseWriter's headers.
// The provided cookie must have a valid Name. Invalid cookies may be
// silently dropped.
func (c *Context) SetCookie(name, value string, maxAge int, path, domain string, secure, httpOnly bool) {
    if path == "" {
        path = "/"
    }
    http.SetCookie(c.Writer, &http.Cookie{
        Name:     name,
        Value:    url.QueryEscape(value),
        MaxAge:   maxAge,
        Path:     path,
        Domain:   domain,
        Secure:   secure,
        HttpOnly: httpOnly,
    })
}

// Cookie returns the named cookie provided in the request or
// ErrNoCookie if not found. And return the named cookie is unescaped.
// If multiple cookies match the given name, only one cookie will
// be returned.
func (c *Context) Cookie(name string) (string, error) {
    cookie, err := c.Request.Cookie(name)
    if err != nil {
        return "", err
    }
    val, _ := url.QueryUnescape(cookie.Value)
    return val, nil
}

// Render writes the response headers and calls render.Render to render data.
func (c *Context) Render(r render.Render) {
    code:=c.writermem.status
    c.Status(code)

    if !bodyAllowedForStatus(code) {
        r.WriteContentType(c.Writer)
        c.Writer.WriteHeaderNow()
        return
    }

    if err := r.Render(c.Writer); err != nil {
        panic(err)
    }
}

// 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(name string, obj interface{}) {
    instance := c.engine.HTMLRender.Instance(name, obj)
    c.Render(instance)
    c.Abort()
}

// IndentedJSON serializes the given struct as pretty JSON (indented + endlines) into the response body.
// It also sets the Content-Type as "application/json".
// WARNING: we recommend to use this only for development purposes since printing pretty JSON is
// more CPU and bandwidth consuming. Use Context.JSON() instead.
func (c *Context) IndentedJSON(obj interface{}) {
    c.Render(render.IndentedJSON{Data: obj})
    c.Abort()
}

// SecureJSON serializes the given struct as Secure JSON into the response body.
// Default prepends "while(1)," to response body if the given struct is array values.
// It also sets the Content-Type as "application/json".
func (c *Context) SecureJSON(obj interface{}) {
    c.Render(render.SecureJSON{Prefix: c.engine.secureJsonPrefix, Data: obj})
    c.Abort()
}

// JSONP serializes the given struct as JSON into the response body.
// It add padding to response body to request data from a server residing in a different domain than the client.
// It also sets the Content-Type as "application/javascript".
func (c *Context) JSONP(obj interface{}) {
    defer c.Abort()
    callback := c.DefaultQuery("callback", "")
    if callback == "" {
        c.Render(render.JSON{Data: obj})
        return
    }
    c.Render(render.JsonpJSON{Callback: callback, Data: obj})
}

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

// AsciiJSON serializes the given struct as JSON into the response body with unicode to ASCII string.
// It also sets the Content-Type as "application/json".
func (c *Context) AsciiJSON(obj interface{}) {
    c.Render(render.AsciiJSON{Data: obj})
    c.Abort()
}

// PureJSON serializes the given struct as JSON into the response body.
// PureJSON, unlike JSON, does not replace special html characters with their unicode entities.
func (c *Context) PureJSON(obj interface{}) {
    c.Render(render.PureJSON{Data: obj})
    c.Abort()
}

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

// YAML serializes the given struct as YAML into the response body.
func (c *Context) YAML(obj interface{}) {
    c.Render(render.YAML{Data: obj})
}

// ProtoBuf serializes the given struct as ProtoBuf into the response body.
func (c *Context) ProtoBuf(obj interface{}) {
    c.Render(render.ProtoBuf{Data: obj})
}

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

// Redirect returns a HTTP redirect to the specific location.
func (c *Context) Redirect(code int, location string) {
    c.Status(-1)
    c.Render(render.Redirect{
        Code:     code,
        Location: location,
        Request:  c.Request,
    })
}

// Data writes some data into the body stream
func (c *Context) Data(contentType string, data []byte) {
    c.Render(render.Data{
        ContentType: contentType,
        Data:        data,
    })
}

// DataFromReader writes the specified reader into the body stream
func (c *Context) DataFromReader( contentLength int64, contentType string, reader io.Reader, extraHeaders map[string]string) {
    c.Render(render.Reader{
        Headers:       extraHeaders,
        ContentType:   contentType,
        ContentLength: contentLength,
        Reader:        reader,
    })
}

// File writes the specified file into the body stream in a efficient way.
func (c *Context) File(filepath string) {
    http.ServeFile(c.Writer, c.Request, filepath)
}

// FileAttachment writes the specified file into the body stream in an efficient way
// On the client side, the file will typically be downloaded with the given filename
func (c *Context) FileAttachment(filepath, filename string) {
    c.Writer.Header().Set("content-disposition", fmt.Sprintf("attachment; filename=\"%s\"", filename))
    http.ServeFile(c.Writer, c.Request, filepath)
}

// SSEvent writes a Server-Sent Event into the body stream.
func (c *Context) SSEvent(name string, message interface{}) {
    c.Status(-1)
    c.Render(sse.Event{
        Event: name,
        Data:  message,
    })
}

// Stream sends a streaming response and returns a boolean
// indicates "Is client disconnected in middle of stream"
func (c *Context) Stream(step func(w io.Writer) bool) bool {
    w := c.Writer
    clientGone := w.CloseNotify()
    for {
        select {
        case <-clientGone:
            return true
        default:
            keepOpen := step(w)
            w.Flush()
            if !keepOpen {
                return false
            }
        }
    }
}


// SetAccepted sets Accept header data.
func (c *Context) SetAccepted(formats ...string) {
    c.Accepted = formats
}

/************************************/
/***** GOLANG.ORG/X/NET/CONTEXT *****/
/************************************/

// Deadline returns the time when work done on behalf of this context
// should be canceled. Deadline returns ok==false when no deadline is
// set. Successive calls to Deadline return the same results.
func (c *Context) Deadline() (deadline time.Time, ok bool) {
    return
}

// Done returns a channel that's closed when work done on behalf of this
// context should be canceled. Done may return nil if this context can
// never be canceled. Successive calls to Done return the same value.
func (c *Context) Done() <-chan struct{} {
    return nil
}

// Err returns a non-nil error value after Done is closed,
// successive calls to Err return the same error.
// If Done is not yet closed, Err returns nil.
// If Done is closed, Err returns a non-nil error explaining why:
// Canceled if the context was canceled
// or DeadlineExceeded if the context's deadline passed.
func (c *Context) Err() error {
    return nil
}

// Value returns the value associated with this context for key, or nil
// if no value is associated with key. Successive calls to Value with
// the same key returns the same result.
func (c *Context) Value(key interface{}) interface{} {
    if key == 0 {
        return c.Request
    }
    if keyAsString, ok := key.(string); ok {
        val, _ := c.Get(keyAsString)
        return val
    }
    return nil
}