session.go

/*
(Aliasing securecookie's methods may constitute redistribution, so we
include the original securecookie license in accordance with the BSD-3
clause license terms.)

Copyright (c) 2023 The Gorilla Authors. All rights reserved.

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	 * Redistributions of source code must retain the above copyright
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	 * Redistributions in binary form must reproduce the above
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	 * Neither the name of Google Inc. nor the names of its
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"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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*/

// Package sessions implements HTTP sessions.
//
// (Description TODO)
package sessions

import (
	"bytes"
	"context"
	"encoding/gob"
	"fmt"
	"net/http"
	"sync"
	"time"

	"github.com/gorilla/securecookie"
)

// Version is the released version of the library.
const Version = "1.2.0"

type sessionCtxKeyType struct{}

const (
	defaultSessionName = "_session"
	defaultMaxAge      = 86400 * 365
)

var (
	sessionCtxKey = sessionCtxKeyType{}
)

func init() {
	// Register the encodings used in this package with gob such that we can
	// successfully save session data in the session.
	gob.Register([]interface{}{})
	gob.Register(map[string]interface{}{})
	gob.Register(&session{})
}

// GenerateRandomKey creates a random key with the given length in bytes. On
// failure, returns nil.
//
// Note that keys created using `GenerateRandomKey()` are not automatically
// persisted. New keys will be created when the application is restarted, and
// previously issued cookies will not be able to be decoded.
//
// Callers should explicitly check for the possibility of a nil return, treat
// it as a failure of the system random number generator, and not continue.
//
// This function is an alias of securecookie.GenerateRandomKey, and is
// provided as a convenience method to avoid the additional import of the
// securecookie library.
func GenerateRandomKey(length int) []byte {
	return securecookie.GenerateRandomKey(length)
}

// A Session manages setting and getting data from the cookie that stores the
// session data.
type Session struct {
	sc    *securecookie.SecureCookie
	name  string
	quiet bool
}

// Options to customize the behaviour of the session.
type Options struct {
	// The name of the cookie (default is "_session").
	Name string

	// MaxAge of the cookie before expiry (default is 365 days). Set it to
	// -1 for no expiry.
	MaxAge int

	// Quiet defines whether or not to suppress all error and warning messages
	// from the library. Defaults to false, since when correctly used, these
	// messages should never appear. Setting to true may suppress critical
	// error and warning messages.
	Quiet bool
}

// New creates a new session manager with the given key.
func New(secret []byte, opts ...Options) *Session {
	var o Options
	for _, opt := range opts {
		o = opt
	}

	if o.Name == "" {
		o.Name = defaultSessionName
	}

	switch o.MaxAge {
	case 0:
		// Default to one year, since some browsers don't set their cookies
		// with the same defaults.
		o.MaxAge = defaultMaxAge
	case -1:
		o.MaxAge = 0
	}

	sc := securecookie.New(secret, nil)
	sc.MaxAge(o.MaxAge)

	return &Session{
		sc:    sc,
		name:  o.Name,
		quiet: o.Quiet,
	}
}

// A session holds the session data. It contains two fields:
//
//   - "data" for long-lived session data that persists between requests,
//   - "flashes" for session data that should be deleted as soon as it is shown.
type session struct {
	Data    map[string]interface{}
	Flashes map[string]interface{}
}

// init ensures that both of the underlying maps have been initialized.
func (s *session) init() {
	if s.Data == nil {
		s.Data = make(map[string]interface{})
	}
	if s.Flashes == nil {
		s.Flashes = make(map[string]interface{})
	}
}

// fromReq returns the map of session values from the request. It will
// never return a nil map, instead, the map will be an initialized empty map
// in the case where the session has no data.
func (s *Session) fromReq(r *http.Request) *session {
	// Fastpath: if the context has already been decoded, access the
	// underlying map and return the value associated with the given key.
	v := r.Context().Value(sessionCtxKey)
	if v != nil {
		ss, ok := v.(*session)
		if ok {
			return ss
		}
	}

	cookie, err := r.Cookie(s.name)
	if err != nil {
		// The only error that can be returned by r.Cookie() is ErrNoCookie,
		// so if the error is not nil, that means that the cookie doesn't
		// exist. When that is the case, the value associated with the given
		// key is guaranteed to be nil, so we return nil.
		ss := &session{}
		ss.init()
		return ss
	}

	ss := &session{}
	if err := s.sc.Decode(s.name, cookie.Value, ss); err != nil {
		if !s.quiet {
			fmt.Printf("sessions: [ERROR] failed to decode session from cookie: %+v\n", err)
		}
		ss.init()
		return ss
	}
	return ss
}

// saveCtx saves a map of session data in the current request's context. It
// also updates the Set-Cookie header of the
func (s *Session) saveCtx(w http.ResponseWriter, r *http.Request, session *session) {
	ctx := context.WithValue(r.Context(), sessionCtxKey, session)
	r2 := r.Clone(ctx)
	*r = *r2

	encoded, err := s.sc.Encode(s.name, session)
	if err != nil {
		if !s.quiet {
			fmt.Printf("sessions: [ERROR} failed to encode cookie: %+v\n", err)
		}
		return
	}

	http.SetCookie(w, &http.Cookie{
		Name:     s.name,
		MaxAge:   defaultMaxAge,
		Expires:  time.Now().UTC().Add(time.Duration(defaultMaxAge * time.Second)),
		Value:    encoded,
		Path:     "/",
		HttpOnly: true,
		Secure:   true,
	})
}

// Session creates a new session from the given HTTP request. If the
// request already has a cookie with an associated session, the session data
// is created from the cookie. If not, a new session is created.
func (s *Session) Get(r *http.Request, key string) interface{} {
	data := s.fromReq(r)
	return data.Data[key]
}

// List returns all key value pairs of session data from the given request.
func (s *Session) List(r *http.Request) map[string]interface{} {
	return s.fromReq(r).Data
}

// Set sets or updates the given value on the session.
func (s *Session) Set(w http.ResponseWriter, r *http.Request, key string, value interface{}) {
	data := s.fromReq(r)
	data.Data[key] = value
	s.saveCtx(w, r, data)
}

// Delete deletes and returns the session value with the given key.
func (s *Session) Delete(w http.ResponseWriter, r *http.Request, key string) interface{} {
	data := s.fromReq(r)
	value := data.Data[key]
	delete(data.Data, key)
	s.saveCtx(w, r, data)
	return value
}

// Reset resets the session, deleting all values.
func (s *Session) Reset(w http.ResponseWriter, r *http.Request) {
	s.saveCtx(w, r, &session{
		Data:    make(map[string]interface{}),
		Flashes: make(map[string]interface{}),
	})
}

// Flash sets a flash message on a request.
func (s *Session) Flash(w http.ResponseWriter, r *http.Request, key string, value interface{}) {
	data := s.fromReq(r)
	data.Flashes[key] = value
	s.saveCtx(w, r, data)
}

// Flashes returns all flash messages, clearing all saved flashes.
func (s *Session) Flashes(w http.ResponseWriter, r *http.Request) map[string]interface{} {
	data := s.fromReq(r)

	// Copy the map before clearing it from the session.
	values := make(map[string]interface{})
	for k, v := range data.Flashes {
		values[k] = v
	}

	data.Flashes = make(map[string]interface{})

	s.saveCtx(w, r, data)
	return values
}

type responseWrapper struct {
	b *bytes.Buffer       // Buffer to write to.
	c int                 // Storage for status code.
	w http.ResponseWriter // Underlying response writer.
}

func (rw *responseWrapper) Header() http.Header {
	return rw.w.Header()
}

func (rw *responseWrapper) Write(data []byte) (int, error) {
	return rw.b.Write(data)
}

func (rw *responseWrapper) WriteHeader(statusCode int) {
	rw.c = statusCode
}

func (rw *responseWrapper) Flush() (int64, error) {
	rw.w.WriteHeader(rw.c)
	return rw.b.WriteTo(rw.w)
}

// TemplMiddleware ensures that the session data is always available on the
// request context for any handler wrapped by the middleware.
//
// This is in contrast to the default behaviour of the library, which is to
// lazily extract the session data from the cookie into the request context
// whenever any session methods are called.
//
// This method makes it possible to access session data in templ's global ctx
// instance, for example, you can use the sessions.FlashesCtx method:
//
//	for key, val := range session.FlashesCtx(ctx) {
//		<div>{ key }: { fmt.Sprintf("%v", val) }</div>
//	}
func (s *Session) TemplMiddleware(next http.Handler) http.Handler {
	pool := &sync.Pool{
		New: func() interface{} {
			return new(bytes.Buffer)
		},
	}

	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// Get the session from the cookie, if it's present and valid.
		session := &session{}
		if cookie, err := r.Cookie(s.name); err != nil {
			session.init()
		} else {
			if err := s.sc.Decode(s.name, cookie.Value, session); err != nil {
				if !s.quiet {
					fmt.Printf("sessions: [ERROR] failed to decode session from cookie: %+v\n", err)
				}
				session.init()
			}
		}

		// Create a response wrapper instance to execute the handler with.
		b := pool.Get().(*bytes.Buffer)
		b.Reset()
		wrapper := &responseWrapper{
			b: b,
			c: 200,
			w: w,
		}

		// Set the session on the request's context so that it's accessible on
		// the handler.
		ctx := context.WithValue(r.Context(), sessionCtxKey, session)

		// Execute the handler.
		next.ServeHTTP(wrapper, r.WithContext(ctx))

		// Encode the updated session so that we can set it as a cookie.
		encoded, err := s.sc.Encode(s.name, session)
		if err != nil {
			if !s.quiet {
				fmt.Printf("sessions: [ERROR} failed to encode cookie: %+v\n", err)
			}
			return
		}

		http.SetCookie(wrapper, &http.Cookie{
			Name:     s.name,
			MaxAge:   defaultMaxAge,
			Expires:  time.Now().UTC().Add(time.Duration(defaultMaxAge * time.Second)),
			Value:    encoded,
			Path:     "/",
			HttpOnly: true,
			Secure:   true,
		})

		if _, err := wrapper.Flush(); err != nil {
			if !s.quiet {
				fmt.Printf("sessions: [ERROR] failed to write http response in call to sessions.TemplMiddleware: %v\n", err)
			}
		}

		pool.Put(b)
	})
}

// FlashesCtx returns all flash messages as a map[string]interace{} for the
// given context.
//
// This method is intended to be used with the https://github.com/a-h/templ
// library. It requires the use of the sessions.TemplMiddleware, which ensures
// that  every incoming request has the session data decoded into the context.
//
// When called, the flash messages are cleared on subsequent requests.
//
// This method makes it possible to access session data in templ's global ctx
// instance, for example, you can use the sessions.FlashesCtx method:
//
//	for key, val := range session.FlashesCtx(ctx) {
//		<div>{ key }: { fmt.Sprintf("%v", val) }</div>
//	}
func (s *Session) FlashesCtx(ctx context.Context) map[string]interface{} {
	flashes := make(map[string]interface{})
	v := ctx.Value(sessionCtxKey)

	if v != nil {
		ss, ok := v.(*session)
		if ok {
			for k, v := range ss.Flashes {
				flashes[k] = v
			}
			clear(ss.Flashes)
			return flashes
		}
	}

	if !s.quiet {
		fmt.Printf("sessions: [WARNING] FlashesCtx was called but the session is nil - did you remember to wrap your handler in sessions.TemplMiddleware?\n")
	}
	return flashes
}

// FlashesCtx returns all flash messages as a map[string]interace{} for the
// given context.
//
// This method is intended to be used with the https://github.com/a-h/templ
// library. It requires the use of the sessions.TemplMiddleware, which ensures
// that  every incoming request has the session data decoded into the context.
//
// When called, the flash messages are cleared on subsequent requests.
//
// This method makes it possible to access session data in templ's global ctx
// instance, for example, you can use the sessions.FlashesCtx method:
//
//	for key, val := range sessions.FlashesCtx(ctx) {
//		<div>{ key }: { fmt.Sprintf("%v", val) }</div>
//	}
func FlashesCtx(ctx context.Context) map[string]interface{} {
	flashes := make(map[string]interface{})
	v := ctx.Value(sessionCtxKey)

	if v != nil {
		ss, ok := v.(*session)
		if ok {
			for k, v := range ss.Flashes {
				flashes[k] = v
			}
			clear(ss.Flashes)
			return flashes
		}
	}
	return flashes
}