1// Copyright 2012 The Gorilla Authors. All rights reserved. 2// Use of this source code is governed by a BSD-style 3// license that can be found in the LICENSE file. 4 5/* 6Package sessions provides cookie and filesystem sessions and 7infrastructure for custom session backends. 8 9The key features are: 10 11 * Simple API: use it as an easy way to set signed (and optionally 12 encrypted) cookies. 13 * Built-in backends to store sessions in cookies or the filesystem. 14 * Flash messages: session values that last until read. 15 * Convenient way to switch session persistency (aka "remember me") and set 16 other attributes. 17 * Mechanism to rotate authentication and encryption keys. 18 * Multiple sessions per request, even using different backends. 19 * Interfaces and infrastructure for custom session backends: sessions from 20 different stores can be retrieved and batch-saved using a common API. 21 22Let's start with an example that shows the sessions API in a nutshell: 23 24 import ( 25 "net/http" 26 "github.com/gorilla/sessions" 27 ) 28 29 // Note: Don't store your key in your source code. Pass it via an 30 // environmental variable, or flag (or both), and don't accidentally commit it 31 // alongside your code. Ensure your key is sufficiently random - i.e. use Go's 32 // crypto/rand or securecookie.GenerateRandomKey(32) and persist the result. 33 var store = sessions.NewCookieStore(os.Getenv("SESSION_KEY")) 34 35 func MyHandler(w http.ResponseWriter, r *http.Request) { 36 // Get a session. Get() always returns a session, even if empty. 37 session, err := store.Get(r, "session-name") 38 if err != nil { 39 http.Error(w, err.Error(), http.StatusInternalServerError) 40 return 41 } 42 43 // Set some session values. 44 session.Values["foo"] = "bar" 45 session.Values[42] = 43 46 // Save it before we write to the response/return from the handler. 47 session.Save(r, w) 48 } 49 50First we initialize a session store calling NewCookieStore() and passing a 51secret key used to authenticate the session. Inside the handler, we call 52store.Get() to retrieve an existing session or a new one. Then we set some 53session values in session.Values, which is a map[interface{}]interface{}. 54And finally we call session.Save() to save the session in the response. 55 56Note that in production code, we should check for errors when calling 57session.Save(r, w), and either display an error message or otherwise handle it. 58 59Save must be called before writing to the response, otherwise the session 60cookie will not be sent to the client. 61 62That's all you need to know for the basic usage. Let's take a look at other 63options, starting with flash messages. 64 65Flash messages are session values that last until read. The term appeared with 66Ruby On Rails a few years back. When we request a flash message, it is removed 67from the session. To add a flash, call session.AddFlash(), and to get all 68flashes, call session.Flashes(). Here is an example: 69 70 func MyHandler(w http.ResponseWriter, r *http.Request) { 71 // Get a session. 72 session, err := store.Get(r, "session-name") 73 if err != nil { 74 http.Error(w, err.Error(), http.StatusInternalServerError) 75 return 76 } 77 78 // Get the previous flashes, if any. 79 if flashes := session.Flashes(); len(flashes) > 0 { 80 // Use the flash values. 81 } else { 82 // Set a new flash. 83 session.AddFlash("Hello, flash messages world!") 84 } 85 session.Save(r, w) 86 } 87 88Flash messages are useful to set information to be read after a redirection, 89like after form submissions. 90 91There may also be cases where you want to store a complex datatype within a 92session, such as a struct. Sessions are serialised using the encoding/gob package, 93so it is easy to register new datatypes for storage in sessions: 94 95 import( 96 "encoding/gob" 97 "github.com/gorilla/sessions" 98 ) 99 100 type Person struct { 101 FirstName string 102 LastName string 103 Email string 104 Age int 105 } 106 107 type M map[string]interface{} 108 109 func init() { 110 111 gob.Register(&Person{}) 112 gob.Register(&M{}) 113 } 114 115As it's not possible to pass a raw type as a parameter to a function, gob.Register() 116relies on us passing it a value of the desired type. In the example above we've passed 117it a pointer to a struct and a pointer to a custom type representing a 118map[string]interface. (We could have passed non-pointer values if we wished.) This will 119then allow us to serialise/deserialise values of those types to and from our sessions. 120 121Note that because session values are stored in a map[string]interface{}, there's 122a need to type-assert data when retrieving it. We'll use the Person struct we registered above: 123 124 func MyHandler(w http.ResponseWriter, r *http.Request) { 125 session, err := store.Get(r, "session-name") 126 if err != nil { 127 http.Error(w, err.Error(), http.StatusInternalServerError) 128 return 129 } 130 131 // Retrieve our struct and type-assert it 132 val := session.Values["person"] 133 var person = &Person{} 134 if person, ok := val.(*Person); !ok { 135 // Handle the case that it's not an expected type 136 } 137 138 // Now we can use our person object 139 } 140 141By default, session cookies last for a month. This is probably too long for 142some cases, but it is easy to change this and other attributes during 143runtime. Sessions can be configured individually or the store can be 144configured and then all sessions saved using it will use that configuration. 145We access session.Options or store.Options to set a new configuration. The 146fields are basically a subset of http.Cookie fields. Let's change the 147maximum age of a session to one week: 148 149 session.Options = &sessions.Options{ 150 Path: "/", 151 MaxAge: 86400 * 7, 152 HttpOnly: true, 153 } 154 155Sometimes we may want to change authentication and/or encryption keys without 156breaking existing sessions. The CookieStore supports key rotation, and to use 157it you just need to set multiple authentication and encryption keys, in pairs, 158to be tested in order: 159 160 var store = sessions.NewCookieStore( 161 []byte("new-authentication-key"), 162 []byte("new-encryption-key"), 163 []byte("old-authentication-key"), 164 []byte("old-encryption-key"), 165 ) 166 167New sessions will be saved using the first pair. Old sessions can still be 168read because the first pair will fail, and the second will be tested. This 169makes it easy to "rotate" secret keys and still be able to validate existing 170sessions. Note: for all pairs the encryption key is optional; set it to nil 171or omit it and and encryption won't be used. 172 173Multiple sessions can be used in the same request, even with different 174session backends. When this happens, calling Save() on each session 175individually would be cumbersome, so we have a way to save all sessions 176at once: it's sessions.Save(). Here's an example: 177 178 var store = sessions.NewCookieStore([]byte("something-very-secret")) 179 180 func MyHandler(w http.ResponseWriter, r *http.Request) { 181 // Get a session and set a value. 182 session1, _ := store.Get(r, "session-one") 183 session1.Values["foo"] = "bar" 184 // Get another session and set another value. 185 session2, _ := store.Get(r, "session-two") 186 session2.Values[42] = 43 187 // Save all sessions. 188 sessions.Save(r, w) 189 } 190 191This is possible because when we call Get() from a session store, it adds the 192session to a common registry. Save() uses it to save all registered sessions. 193*/ 194package sessions 195