forked from TrueCloudLab/distribution
82 lines
2.4 KiB
Go
82 lines
2.4 KiB
Go
// Copyright 2012 The Gorilla Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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/*
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Package context stores values shared during a request lifetime.
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For example, a router can set variables extracted from the URL and later
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application handlers can access those values, or it can be used to store
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sessions values to be saved at the end of a request. There are several
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others common uses.
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The idea was posted by Brad Fitzpatrick to the go-nuts mailing list:
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http://groups.google.com/group/golang-nuts/msg/e2d679d303aa5d53
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Here's the basic usage: first define the keys that you will need. The key
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type is interface{} so a key can be of any type that supports equality.
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Here we define a key using a custom int type to avoid name collisions:
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package foo
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import (
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"github.com/gorilla/context"
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)
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type key int
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const MyKey key = 0
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Then set a variable. Variables are bound to an http.Request object, so you
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need a request instance to set a value:
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context.Set(r, MyKey, "bar")
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The application can later access the variable using the same key you provided:
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func MyHandler(w http.ResponseWriter, r *http.Request) {
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// val is "bar".
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val := context.Get(r, foo.MyKey)
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// returns ("bar", true)
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val, ok := context.GetOk(r, foo.MyKey)
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// ...
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}
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And that's all about the basic usage. We discuss some other ideas below.
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Any type can be stored in the context. To enforce a given type, make the key
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private and wrap Get() and Set() to accept and return values of a specific
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type:
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type key int
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const mykey key = 0
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// GetMyKey returns a value for this package from the request values.
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func GetMyKey(r *http.Request) SomeType {
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if rv := context.Get(r, mykey); rv != nil {
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return rv.(SomeType)
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}
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return nil
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}
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// SetMyKey sets a value for this package in the request values.
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func SetMyKey(r *http.Request, val SomeType) {
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context.Set(r, mykey, val)
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}
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Variables must be cleared at the end of a request, to remove all values
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that were stored. This can be done in an http.Handler, after a request was
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served. Just call Clear() passing the request:
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context.Clear(r)
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...or use ClearHandler(), which conveniently wraps an http.Handler to clear
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variables at the end of a request lifetime.
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The Routers from the packages gorilla/mux and gorilla/pat call Clear()
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so if you are using either of them you don't need to clear the context manually.
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*/
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package context
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