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server.go
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server.go
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package main
import (
"crypto/rand"
"encoding/hex"
"errors"
"html/template"
"net/http"
"net/url"
"strings"
"time"
"golang.org/x/crypto/bcrypt"
)
// Server is the HTTP server for the to-do list app.
type Server struct {
model Model
logger Logger
location *time.Location
username string
passwordHash string
showLists bool
mux *http.ServeMux
homeTmpl *template.Template
listTmpl *template.Template
}
// Model is the database model interface used by the server.
type Model interface {
GetLists() ([]*List, error)
CreateList(name string) (string, error)
DeleteList(id string) error
GetList(id string) (*List, error)
AddItem(listID, description string) (string, error)
UpdateDone(listID, itemID string, done bool) error
DeleteItem(listID, itemID string) error
CreateSignIn() (string, error)
IsSignInValid(id string) (bool, error)
DeleteSignIn(id string) error
}
// Logger is the logger interface used by the server.
type Logger interface {
Printf(format string, v ...interface{})
}
// NewServer creates a new server with the specified dependencies.
func NewServer(
model Model,
logger Logger,
timezone string,
username string,
passwordHash string,
showLists bool,
) (*Server, error) {
location := time.Local // use server's local time if timezone not specified
if timezone != "" {
var err error
location, err = time.LoadLocation(timezone)
if err != nil {
return nil, err
}
}
s := &Server{
model: model,
logger: logger,
location: location,
username: username,
passwordHash: passwordHash,
showLists: showLists,
mux: http.NewServeMux(),
}
s.addRoutes()
s.addTemplates()
return s, nil
}
func (s *Server) addRoutes() {
s.mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
if r.URL.Path == "/" { // because "/" pattern matches /*
s.home(w, r)
} else {
http.NotFound(w, r)
}
})
s.mux.HandleFunc("/sign-in", csrf(s.signIn))
s.mux.HandleFunc("/sign-out", s.signedIn(csrf(s.signOut)))
s.mux.HandleFunc("/lists/", s.signedIn(s.showList))
s.mux.HandleFunc("/create-list", s.signedIn(csrf(s.createList)))
s.mux.HandleFunc("/delete-list", s.signedIn(csrf(s.deleteList)))
s.mux.HandleFunc("/add-item", s.signedIn(csrf(s.addItem)))
s.mux.HandleFunc("/update-done", s.signedIn(csrf(s.updateDone)))
s.mux.HandleFunc("/delete-item", s.signedIn(csrf(s.deleteItem)))
}
func (s *Server) signedIn(h http.HandlerFunc) http.HandlerFunc {
return func(w http.ResponseWriter, r *http.Request) {
if !s.isSignedIn(r) {
location := "/?return-url=" + url.QueryEscape(r.URL.Path)
http.Redirect(w, r, location, http.StatusFound)
return
}
h(w, r)
}
}
func (s *Server) isSignedIn(r *http.Request) bool {
if s.username == "" {
return true
}
valid, err := s.model.IsSignInValid(getSignInCookie(r))
return err == nil && valid
}
func getSignInCookie(r *http.Request) string {
cookie, err := r.Cookie("sign-in")
if err != nil {
return ""
}
return cookie.Value
}
func (s *Server) addTemplates() {
s.homeTmpl = template.Must(template.New("home").Parse(homeTmpl))
s.listTmpl = template.Must(template.New("list").Parse(listTmpl))
}
// ServeHTTP implements the http.Handler interface.
func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
startTime := time.Now()
w.Header().Set("Cache-Control", "no-cache")
s.mux.ServeHTTP(w, r)
s.logger.Printf("%s %s %v", r.Method, r.URL.Path, time.Since(startTime))
}
func (s *Server) home(w http.ResponseWriter, r *http.Request) {
var lists []*List
if s.showLists {
var err error
lists, err = s.model.GetLists()
if err != nil {
s.internalError(w, "fetching lists", err)
return
}
for _, list := range lists {
// Change UTC timezone to display timezone
list.TimeCreated = list.TimeCreated.In(s.location)
}
}
isSignedIn := s.isSignedIn(r)
var data = struct {
Token string
Lists []*List
ShowSignIn bool
ShowSignOut bool
ReturnURL string
SignInError bool
}{
Token: getCSRFToken(w, r),
Lists: lists,
ShowSignIn: !isSignedIn,
ShowSignOut: s.username != "" && isSignedIn,
ReturnURL: r.URL.Query().Get("return-url"),
SignInError: r.URL.Query().Get("error") == "sign-in",
}
err := s.homeTmpl.Execute(w, data)
if err != nil {
s.internalError(w, "rendering template", err)
return
}
}
func (s *Server) signIn(w http.ResponseWriter, r *http.Request) {
username := strings.TrimSpace(r.FormValue("username"))
password := r.FormValue("password")
returnURL := r.FormValue("return-url")
if returnURL == "" {
returnURL = "/"
}
if username != s.username || bcrypt.CompareHashAndPassword([]byte(s.passwordHash), []byte(password)) != nil {
location := "/?error=sign-in&return-url=" + url.QueryEscape(returnURL)
http.Redirect(w, r, location, http.StatusFound)
return
}
id, err := s.model.CreateSignIn()
if err != nil {
s.internalError(w, "creating sign in", err)
return
}
cookie := &http.Cookie{
Name: "sign-in",
Value: id,
MaxAge: 90 * 24 * 60 * 60,
Path: "/",
Secure: r.URL.Scheme == "https",
HttpOnly: true,
SameSite: http.SameSiteStrictMode,
}
http.SetCookie(w, cookie)
http.Redirect(w, r, returnURL, http.StatusFound)
}
func (s *Server) signOut(w http.ResponseWriter, r *http.Request) {
cookie := &http.Cookie{
Name: "sign-in",
MaxAge: -1,
Path: "/",
Secure: r.URL.Scheme == "https",
HttpOnly: true,
SameSite: http.SameSiteStrictMode,
}
http.SetCookie(w, cookie)
err := s.model.DeleteSignIn(getSignInCookie(r))
if err != nil {
s.internalError(w, "deleting sign in", err)
return
}
http.Redirect(w, r, "/", http.StatusFound)
}
func (s *Server) showList(w http.ResponseWriter, r *http.Request) {
id := r.URL.Path[len("/lists/"):]
list, err := s.model.GetList(id)
if err != nil {
s.internalError(w, "fetching list", err)
return
}
if list == nil {
http.NotFound(w, r)
return
}
var data = struct {
Token string
List *List
ShowDelete bool
}{
Token: getCSRFToken(w, r),
List: list,
ShowDelete: r.URL.Query().Get("delete") != "",
}
err = s.listTmpl.Execute(w, data)
if err != nil {
s.internalError(w, "rendering template", err)
return
}
}
func (s *Server) createList(w http.ResponseWriter, r *http.Request) {
name := strings.TrimSpace(r.FormValue("name"))
if name == "" {
// Empty list name, just reload home page
http.Redirect(w, r, "/", http.StatusFound)
return
}
listID, err := s.model.CreateList(name)
if err != nil {
s.internalError(w, "creating list", err)
return
}
http.Redirect(w, r, "/lists/"+listID, http.StatusFound)
}
func (s *Server) deleteList(w http.ResponseWriter, r *http.Request) {
id := r.FormValue("list-id")
err := s.model.DeleteList(id)
if err != nil {
s.internalError(w, "deleting list", err)
return
}
http.Redirect(w, r, "/", http.StatusFound)
}
func (s *Server) addItem(w http.ResponseWriter, r *http.Request) {
listID := r.FormValue("list-id")
list, err := s.model.GetList(listID)
if err != nil {
s.internalError(w, "fetching list", err)
return
}
if list == nil {
http.NotFound(w, r)
return
}
description := strings.TrimSpace(r.FormValue("description"))
if description == "" {
// Empty item description, just reload list
http.Redirect(w, r, "/lists/"+list.ID, http.StatusFound)
return
}
_, err = s.model.AddItem(list.ID, description)
if err != nil {
s.internalError(w, "adding item", err)
return
}
http.Redirect(w, r, "/lists/"+list.ID, http.StatusFound)
}
func (s *Server) updateDone(w http.ResponseWriter, r *http.Request) {
listID := r.FormValue("list-id")
itemID := r.FormValue("item-id")
done := r.FormValue("done") == "on"
err := s.model.UpdateDone(listID, itemID, done)
if err != nil {
s.internalError(w, "updating done flag", err)
return
}
http.Redirect(w, r, "/lists/"+listID, http.StatusFound)
}
func (s *Server) deleteItem(w http.ResponseWriter, r *http.Request) {
listID := r.FormValue("list-id")
itemID := r.FormValue("item-id")
err := s.model.DeleteItem(listID, itemID)
if err != nil {
s.internalError(w, "deleting item", err)
return
}
http.Redirect(w, r, "/lists/"+listID, http.StatusFound)
}
func (s *Server) internalError(w http.ResponseWriter, msg string, err error) {
s.logger.Printf("error %s: %v", msg, err)
http.Error(w, "error "+msg, http.StatusInternalServerError)
}
// GeneratePasswordHash generates a bcrypt hash from the given password.
func GeneratePasswordHash(password string) (string, error) {
b, err := bcrypt.GenerateFromPassword([]byte(password), bcrypt.DefaultCost)
return string(b), err
}
// CheckPasswordHash returns a non-nil error if the given password hash is not
// a valid bcrypt hash.
func CheckPasswordHash(passwordHash string) error {
err := bcrypt.CompareHashAndPassword([]byte(passwordHash), []byte("x"))
if errors.Is(err, bcrypt.ErrMismatchedHashAndPassword) {
return nil
}
return err
}
// csrf wraps the given handler, ensuring that the HTTP method is POST and
// that the CSRF token in the "csrf-token" cookie matches the token in the
// "csrf-token" form field.
func csrf(h http.HandlerFunc) http.HandlerFunc {
return func(w http.ResponseWriter, r *http.Request) {
if r.Method != "POST" {
w.Header().Set("Allow", "POST")
http.Error(w, "405 method not allowed", http.StatusMethodNotAllowed)
return
}
token := r.FormValue("csrf-token")
cookie, err := r.Cookie("csrf-token")
if err != nil || token != cookie.Value {
http.Error(w, "invalid CSRF token or cookie", http.StatusBadRequest)
return
}
h(w, r)
}
}
// getCSRFToken returns the current session's CSRF token, generating a new one
// and settings the "csrf-token" cookie if not present.
func getCSRFToken(w http.ResponseWriter, r *http.Request) string {
cookie, err := r.Cookie("csrf-token")
if err == nil && cookie.Value != "" {
return cookie.Value
}
token := generateCSRFToken()
cookie = &http.Cookie{
Name: "csrf-token",
Value: token,
Path: "/",
Secure: r.URL.Scheme == "https",
HttpOnly: true,
SameSite: http.SameSiteStrictMode,
}
http.SetCookie(w, cookie)
return token
}
func generateCSRFToken() string {
b := make([]byte, 16)
_, err := rand.Read(b)
if err != nil { // should never fail
panic(err)
}
return hex.EncodeToString(b)
}