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+// Copyright 2012 The Gorilla Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+/*
+Package gorilla/sessions provides cookie and filesystem sessions and
+infrastructure for custom session backends.
+
+The key features are:
+
+ * Simple API: use it as an easy way to set signed (and optionally
+ encrypted) cookies.
+ * Built-in backends to store sessions in cookies or the filesystem.
+ * Flash messages: session values that last until read.
+ * Convenient way to switch session persistency (aka "remember me") and set
+ other attributes.
+ * Mechanism to rotate authentication and encryption keys.
+ * Multiple sessions per request, even using different backends.
+ * Interfaces and infrastructure for custom session backends: sessions from
+ different stores can be retrieved and batch-saved using a common API.
+
+Let's start with an example that shows the sessions API in a nutshell:
+
+ import (
+ "net/http"
+ "github.com/gorilla/sessions"
+ )
+
+ var store = sessions.NewCookieStore([]byte("something-very-secret"))
+
+ func MyHandler(w http.ResponseWriter, r *http.Request) {
+ // Get a session. We're ignoring the error resulted from decoding an
+ // existing session: Get() always returns a session, even if empty.
+ session, err := store.Get(r, "session-name")
+ if err != nil {
+ http.Error(w, err.Error(), http.StatusInternalServerError)
+ return
+ }
+
+ // Set some session values.
+ session.Values["foo"] = "bar"
+ session.Values[42] = 43
+ // Save it before we write to the response/return from the handler.
+ session.Save(r, w)
+ }
+
+First we initialize a session store calling NewCookieStore() and passing a
+secret key used to authenticate the session. Inside the handler, we call
+store.Get() to retrieve an existing session or a new one. Then we set some
+session values in session.Values, which is a map[interface{}]interface{}.
+And finally we call session.Save() to save the session in the response.
+
+Note that in production code, we should check for errors when calling
+session.Save(r, w), and either display an error message or otherwise handle it.
+
+Save must be called before writing to the response, otherwise the session
+cookie will not be sent to the client.
+
+Important Note: If you aren't using gorilla/mux, you need to wrap your handlers
+with context.ClearHandler as or else you will leak memory! An easy way to do this
+is to wrap the top-level mux when calling http.ListenAndServe:
+
+ http.ListenAndServe(":8080", context.ClearHandler(http.DefaultServeMux))
+
+The ClearHandler function is provided by the gorilla/context package.
+
+That's all you need to know for the basic usage. Let's take a look at other
+options, starting with flash messages.
+
+Flash messages are session values that last until read. The term appeared with
+Ruby On Rails a few years back. When we request a flash message, it is removed
+from the session. To add a flash, call session.AddFlash(), and to get all
+flashes, call session.Flashes(). Here is an example:
+
+ func MyHandler(w http.ResponseWriter, r *http.Request) {
+ // Get a session.
+ session, err := store.Get(r, "session-name")
+ if err != nil {
+ http.Error(w, err.Error(), http.StatusInternalServerError)
+ return
+ }
+
+ // Get the previously flashes, if any.
+ if flashes := session.Flashes(); len(flashes) > 0 {
+ // Use the flash values.
+ } else {
+ // Set a new flash.
+ session.AddFlash("Hello, flash messages world!")
+ }
+ session.Save(r, w)
+ }
+
+Flash messages are useful to set information to be read after a redirection,
+like after form submissions.
+
+There may also be cases where you want to store a complex datatype within a
+session, such as a struct. Sessions are serialised using the encoding/gob package,
+so it is easy to register new datatypes for storage in sessions:
+
+ import(
+ "encoding/gob"
+ "github.com/gorilla/sessions"
+ )
+
+ type Person struct {
+ FirstName string
+ LastName string
+ Email string
+ Age int
+ }
+
+ type M map[string]interface{}
+
+ func init() {
+
+ gob.Register(&Person{})
+ gob.Register(&M{})
+ }
+
+As it's not possible to pass a raw type as a parameter to a function, gob.Register()
+relies on us passing it a value of the desired type. In the example above we've passed
+it a pointer to a struct and a pointer to a custom type representing a
+map[string]interface. (We could have passed non-pointer values if we wished.) This will
+then allow us to serialise/deserialise values of those types to and from our sessions.
+
+Note that because session values are stored in a map[string]interface{}, there's
+a need to type-assert data when retrieving it. We'll use the Person struct we registered above:
+
+ func MyHandler(w http.ResponseWriter, r *http.Request) {
+ session, err := store.Get(r, "session-name")
+ if err != nil {
+ http.Error(w, err.Error(), http.StatusInternalServerError)
+ return
+ }
+
+ // Retrieve our struct and type-assert it
+ val := session.Values["person"]
+ var person = &Person{}
+ if person, ok := val.(*Person); !ok {
+ // Handle the case that it's not an expected type
+ }
+
+ // Now we can use our person object
+ }
+
+By default, session cookies last for a month. This is probably too long for
+some cases, but it is easy to change this and other attributes during
+runtime. Sessions can be configured individually or the store can be
+configured and then all sessions saved using it will use that configuration.
+We access session.Options or store.Options to set a new configuration. The
+fields are basically a subset of http.Cookie fields. Let's change the
+maximum age of a session to one week:
+
+ session.Options = &sessions.Options{
+ Path: "/",
+ MaxAge: 86400 * 7,
+ HttpOnly: true,
+ }
+
+Sometimes we may want to change authentication and/or encryption keys without
+breaking existing sessions. The CookieStore supports key rotation, and to use
+it you just need to set multiple authentication and encryption keys, in pairs,
+to be tested in order:
+
+ var store = sessions.NewCookieStore(
+ []byte("new-authentication-key"),
+ []byte("new-encryption-key"),
+ []byte("old-authentication-key"),
+ []byte("old-encryption-key"),
+ )
+
+New sessions will be saved using the first pair. Old sessions can still be
+read because the first pair will fail, and the second will be tested. This
+makes it easy to "rotate" secret keys and still be able to validate existing
+sessions. Note: for all pairs the encryption key is optional; set it to nil
+or omit it and and encryption won't be used.
+
+Multiple sessions can be used in the same request, even with different
+session backends. When this happens, calling Save() on each session
+individually would be cumbersome, so we have a way to save all sessions
+at once: it's sessions.Save(). Here's an example:
+
+ var store = sessions.NewCookieStore([]byte("something-very-secret"))
+
+ func MyHandler(w http.ResponseWriter, r *http.Request) {
+ // Get a session and set a value.
+ session1, _ := store.Get(r, "session-one")
+ session1.Values["foo"] = "bar"
+ // Get another session and set another value.
+ session2, _ := store.Get(r, "session-two")
+ session2.Values[42] = 43
+ // Save all sessions.
+ sessions.Save(r, w)
+ }
+
+This is possible because when we call Get() from a session store, it adds the
+session to a common registry. Save() uses it to save all registered sessions.
+*/
+package sessions