context.go

// 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.

package gin

import (
	"errors"
	"io"
	"math"
	"net/http"
	"strings"
	"time"

	"github.com/gin-gonic/gin/binding"
	"github.com/gin-gonic/gin/render"
	"github.com/manucorporat/sse"
	"golang.org/x/net/context"
)

// 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
)

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     map[string]interface{}
	Errors   errorMsgs
	Accepted []string
}

var _ context.Context = &Context{}

/************************************/
/********** 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 have to be used then the context has to be passed to a goroutine.
func (c *Context) Copy() *Context {
	var cp Context = *c
	cp.writermem.ResponseWriter = nil
	cp.Writer = &cp.writermem
	cp.index = abortIndex
	cp.handlers = nil
	return &cp
}

// HandlerName returns the main handle'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())
}

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

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

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

// Abort stops the system to continue calling the pending handlers in the chain.
// Let's say you have an authorization middleware that validates if the request is authorized
// if the authorization fails (the password does not match). This method (Abort()) should be called
// in order to stop the execution of the actual handler.
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 authentificate a request could use: context.AbortWithStatus(401).
func (c *Context) AbortWithStatus(code int) {
	c.Writer.WriteHeader(code)
	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 *********/
/************************************/

// 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.
func (c *Context) Error(err error) *Error {
	var parsedError *Error
	switch err.(type) {
	case *Error:
		parsedError = err.(*Error)
	default:
		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 exclusivelly 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) {
	if c.Keys != nil {
		value, exists = c.Keys[key]
	}
	return
}

// 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")
}

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

// Query is a shortcut for c.Request.URL.Query().Get(key)
// It is used to return the url query values.
// ?id=1234&name=Manu
// c.Query("id") == "1234"
// c.Query("name") == "Manu"
// c.Query("wtf") == ""
func (c *Context) Query(key string) (va string) {
	va, _ = c.query(key)
	return
}

// PostForm is a shortcut for c.Request.PostFormValue(key)
func (c *Context) PostForm(key string) (va string) {
	va, _ = c.postForm(key)
	return
}

// Param is a shortcut for c.Params.ByName(key)
func (c *Context) Param(key string) string {
	return c.Params.ByName(key)
}

func (c *Context) DefaultPostForm(key, defaultValue string) string {
	if va, ok := c.postForm(key); ok {
		return va
	}
	return defaultValue
}

// DefaultQuery returns the keyed url query value if it exists, othewise it returns the
// specified defaultValue.
// ```
// /?name=Manu
// c.DefaultQuery("name", "unknown") == "Manu"
// c.DefaultQuery("id", "none") == "none"
// ```
func (c *Context) DefaultQuery(key, defaultValue string) string {
	if va, ok := c.query(key); ok {
		return va
	}
	return defaultValue
}

func (c *Context) query(key string) (string, bool) {
	req := c.Request
	if values, ok := req.URL.Query()[key]; ok && len(values) > 0 {
		return values[0], true
	}
	return "", false
}

func (c *Context) postForm(key string) (string, bool) {
	req := c.Request
	req.ParseMultipartForm(32 << 20) // 32 MB
	if values := req.PostForm[key]; len(values) > 0 {
		return values[0], true
	}
	if req.MultipartForm != nil && req.MultipartForm.File != nil {
		if values := req.MultipartForm.Value[key]; len(values) > 0 {
			return values[0], true
		}
	}
	return "", false
}

// 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
// If 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 ParseBody() but this method also writes a 400 error if the json is not valid.
func (c *Context) Bind(obj interface{}) error {
	b := binding.Default(c.Request.Method, c.ContentType())
	return c.BindWith(obj, b)
}

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

// 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 {
	if err := b.Bind(c.Request, obj); err != nil {
		c.AbortWithError(400, err).SetType(ErrorTypeBind)
		return err
	}
	return nil
}

// 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.
func (c *Context) ClientIP() string {
	if c.engine.ForwardedByClientIP {
		clientIP := strings.TrimSpace(c.requestHeader("X-Real-Ip"))
		if len(clientIP) > 0 {
			return clientIP
		}
		clientIP = c.requestHeader("X-Forwarded-For")
		if index := strings.IndexByte(clientIP, ','); index >= 0 {
			clientIP = clientIP[0:index]
		}
		clientIP = strings.TrimSpace(clientIP)
		if len(clientIP) > 0 {
			return clientIP
		}
	}
	return strings.TrimSpace(c.Request.RemoteAddr)
}

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

func (c *Context) requestHeader(key string) string {
	if values, _ := c.Request.Header[key]; len(values) > 0 {
		return values[0]
	}
	return ""
}

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

// 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 len(value) == 0 {
		c.Writer.Header().Del(key)
	} else {
		c.Writer.Header().Set(key, value)
	}
}

func (c *Context) Render(code int, r render.Render) {
	c.writermem.WriteHeader(code)
	if err := r.Render(c.Writer); err != nil {
		c.renderError(err)
	}
}

func (c *Context) renderError(err error) {
	debugPrintError(err)
	c.AbortWithError(500, err).SetType(ErrorTypeRender)
}

// 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)
}

// 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 propuses since printing pretty JSON is
// more CPU and bandwidth consuming. Use Context.JSON() instead.
func (c *Context) IndentedJSON(code int, obj interface{}) {
	c.Render(code, render.IndentedJSON{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(code int, obj interface{}) {
	c.writermem.WriteHeader(code)
	if err := render.WriteJSON(c.Writer, obj); err != nil {
		c.renderError(err)
	}
}

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

// String writes the given string into the response body.
func (c *Context) String(code int, format string, values ...interface{}) {
	c.writermem.WriteHeader(code)
	render.WriteString(c.Writer, format, values)
}

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

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

// 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)
}

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

func (c *Context) Stream(step func(w io.Writer) bool) {
	w := c.Writer
	clientGone := w.CloseNotify()
	for {
		select {
		case <-clientGone:
			return
		default:
			keepopen := step(w)
			w.Flush()
			if !keepopen {
				return
			}
		}
	}
}

/************************************/
/******** CONTENT NEGOTIATION *******/
/************************************/

type Negotiate struct {
	Offered  []string
	HTMLName string
	HTMLData interface{}
	JSONData interface{}
	XMLData  interface{}
	Data     interface{}
}

func (c *Context) Negotiate(code int, config Negotiate) {
	switch c.NegotiateFormat(config.Offered...) {
	case binding.MIMEJSON:
		data := chooseData(config.JSONData, config.Data)
		c.JSON(code, data)

	case binding.MIMEHTML:
		data := chooseData(config.HTMLData, config.Data)
		c.HTML(code, config.HTMLName, data)

	case binding.MIMEXML:
		data := chooseData(config.XMLData, config.Data)
		c.XML(code, data)

	default:
		c.AbortWithError(http.StatusNotAcceptable, errors.New("the accepted formats are not offered by the server"))
	}
}

func (c *Context) NegotiateFormat(offered ...string) string {
	if len(offered) == 0 {
		panic("you must provide at least one offer")
	}
	if c.Accepted == nil {
		c.Accepted = parseAccept(c.requestHeader("Accept"))
	}
	if len(c.Accepted) == 0 {
		return offered[0]
	}
	for _, accepted := range c.Accepted {
		for _, offert := range offered {
			if accepted == offert {
				return offert
			}
		}
	}
	return ""
}

func (c *Context) SetAccepted(formats ...string) {
	c.Accepted = formats
}

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

func (c *Context) Deadline() (deadline time.Time, ok bool) {
	return
}

func (c *Context) Done() <-chan struct{} {
	return nil
}

func (c *Context) Err() error {
	return nil
}

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
}