ntfy/server/server.go

package server

import (
	"bytes"
	"context"
	"crypto/sha256"
	"embed"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"github.com/emersion/go-smtp"
	"github.com/gorilla/websocket"
	"github.com/prometheus/client_golang/prometheus/promhttp"
	"golang.org/x/sync/errgroup"
	"heckel.io/ntfy/log"
	"heckel.io/ntfy/user"
	"heckel.io/ntfy/util"
	"io"
	"net"
	"net/http"
	"net/http/pprof"
	"net/netip"
	"net/url"
	"os"
	"path"
	"path/filepath"
	"regexp"
	"sort"
	"strconv"
	"strings"
	"sync"
	"time"
	"unicode/utf8"
)

// Server is the main server, providing the UI and API for ntfy
type Server struct {
	config            *Config
	httpServer        *http.Server
	httpsServer       *http.Server
	httpMetricsServer *http.Server
	httpProfileServer *http.Server
	unixListener      net.Listener
	smtpServer        *smtp.Server
	smtpServerBackend *smtpBackend
	smtpSender        mailer
	topics            map[string]*topic
	visitors          map[string]*visitor // ip:<ip> or user:<user>
	firebaseClient    *firebaseClient
	messages          int64
	userManager       *user.Manager                       // Might be nil!
	messageCache      *messageCache                       // Database that stores the messages
	fileCache         *fileCache                          // File system based cache that stores attachments
	stripe            stripeAPI                           // Stripe API, can be replaced with a mock
	priceCache        *util.LookupCache[map[string]int64] // Stripe price ID -> price as cents (USD implied!)
	metricsHandler    http.Handler                        // Handles /metrics if enable-metrics set, and listen-metrics-http not set
	closeChan         chan bool
	mu                sync.Mutex
}

// handleFunc extends the normal http.HandlerFunc to be able to easily return errors
type handleFunc func(http.ResponseWriter, *http.Request, *visitor) error

var (
	// If changed, don't forget to update Android App and auth_sqlite.go
	topicRegex             = regexp.MustCompile(`^[-_A-Za-z0-9]{1,64}$`)               // No /!
	topicPathRegex         = regexp.MustCompile(`^/[-_A-Za-z0-9]{1,64}$`)              // Regex must match JS & Android app!
	externalTopicPathRegex = regexp.MustCompile(`^/[^/]+\.[^/]+/[-_A-Za-z0-9]{1,64}$`) // Extended topic path, for web-app, e.g. /example.com/mytopic
	jsonPathRegex          = regexp.MustCompile(`^/[-_A-Za-z0-9]{1,64}(,[-_A-Za-z0-9]{1,64})*/json$`)
	ssePathRegex           = regexp.MustCompile(`^/[-_A-Za-z0-9]{1,64}(,[-_A-Za-z0-9]{1,64})*/sse$`)
	rawPathRegex           = regexp.MustCompile(`^/[-_A-Za-z0-9]{1,64}(,[-_A-Za-z0-9]{1,64})*/raw$`)
	wsPathRegex            = regexp.MustCompile(`^/[-_A-Za-z0-9]{1,64}(,[-_A-Za-z0-9]{1,64})*/ws$`)
	authPathRegex          = regexp.MustCompile(`^/[-_A-Za-z0-9]{1,64}(,[-_A-Za-z0-9]{1,64})*/auth$`)
	publishPathRegex       = regexp.MustCompile(`^/[-_A-Za-z0-9]{1,64}/(publish|send|trigger)$`)

	webConfigPath                                        = "/config.js"
	accountPath                                          = "/account"
	matrixPushPath                                       = "/_matrix/push/v1/notify"
	metricsPath                                          = "/metrics"
	apiHealthPath                                        = "/v1/health"
	apiTiers                                             = "/v1/tiers"
	apiAccountPath                                       = "/v1/account"
	apiAccountTokenPath                                  = "/v1/account/token"
	apiAccountPasswordPath                               = "/v1/account/password"
	apiAccountSettingsPath                               = "/v1/account/settings"
	apiAccountSubscriptionPath                           = "/v1/account/subscription"
	apiAccountReservationPath                            = "/v1/account/reservation"
	apiAccountBillingPortalPath                          = "/v1/account/billing/portal"
	apiAccountBillingWebhookPath                         = "/v1/account/billing/webhook"
	apiAccountBillingSubscriptionPath                    = "/v1/account/billing/subscription"
	apiAccountBillingSubscriptionCheckoutSuccessTemplate = "/v1/account/billing/subscription/success/{CHECKOUT_SESSION_ID}"
	apiAccountBillingSubscriptionCheckoutSuccessRegex    = regexp.MustCompile(`/v1/account/billing/subscription/success/(.+)$`)
	apiAccountReservationSingleRegex                     = regexp.MustCompile(`/v1/account/reservation/([-_A-Za-z0-9]{1,64})$`)
	staticRegex                                          = regexp.MustCompile(`^/static/.+`)
	docsRegex                                            = regexp.MustCompile(`^/docs(|/.*)$`)
	fileRegex                                            = regexp.MustCompile(`^/file/([-_A-Za-z0-9]{1,64})(?:\.[A-Za-z0-9]{1,16})?$`)
	urlRegex                                             = regexp.MustCompile(`^https?://`)

	//go:embed site
	webFs        embed.FS
	webFsCached  = &util.CachingEmbedFS{ModTime: time.Now(), FS: webFs}
	webSiteDir   = "/site"
	webHomeIndex = "/home.html" // Landing page, only if "web-root: home"
	webAppIndex  = "/app.html"  // React app

	//go:embed docs
	docsStaticFs     embed.FS
	docsStaticCached = &util.CachingEmbedFS{ModTime: time.Now(), FS: docsStaticFs}
)

const (
	firebaseControlTopic     = "~control"                // See Android if changed
	firebasePollTopic        = "~poll"                   // See iOS if changed
	emptyMessageBody         = "triggered"               // Used if message body is empty
	newMessageBody           = "New message"             // Used in poll requests as generic message
	defaultAttachmentMessage = "You received a file: %s" // Used if message body is empty, and there is an attachment
	encodingBase64           = "base64"                  // Used mainly for binary UnifiedPush messages
	jsonBodyBytesLimit       = 16384
	unifiedPushTopicPrefix   = "up" // Temporarily, we rate limit all "up*" topics based on the subscriber
	unifiedPushTopicLength   = 14
)

// WebSocket constants
const (
	wsWriteWait  = 2 * time.Second
	wsBufferSize = 1024
	wsReadLimit  = 64 // We only ever receive PINGs
	wsPongWait   = 15 * time.Second
)

// New instantiates a new Server. It creates the cache and adds a Firebase
// subscriber (if configured).
func New(conf *Config) (*Server, error) {
	var mailer mailer
	if conf.SMTPSenderAddr != "" {
		mailer = &smtpSender{config: conf}
	}
	var stripe stripeAPI
	if conf.StripeSecretKey != "" {
		stripe = newStripeAPI()
	}
	messageCache, err := createMessageCache(conf)
	if err != nil {
		return nil, err
	}
	topics, err := messageCache.Topics()
	if err != nil {
		return nil, err
	}
	var fileCache *fileCache
	if conf.AttachmentCacheDir != "" {
		fileCache, err = newFileCache(conf.AttachmentCacheDir, conf.AttachmentTotalSizeLimit)
		if err != nil {
			return nil, err
		}
	}
	var userManager *user.Manager
	if conf.AuthFile != "" {
		userManager, err = user.NewManager(conf.AuthFile, conf.AuthStartupQueries, conf.AuthDefault, conf.AuthBcryptCost, conf.AuthStatsQueueWriterInterval)
		if err != nil {
			return nil, err
		}
	}
	var firebaseClient *firebaseClient
	if conf.FirebaseKeyFile != "" {
		sender, err := newFirebaseSender(conf.FirebaseKeyFile)
		if err != nil {
			return nil, err
		}
		// This awkward logic is required because Go is weird about nil types and interfaces.
		// See issue #641, and https://go.dev/play/p/uur1flrv1t3 for an example
		var auther user.Auther
		if userManager != nil {
			auther = userManager
		}
		firebaseClient = newFirebaseClient(sender, auther)
	}
	s := &Server{
		config:         conf,
		messageCache:   messageCache,
		fileCache:      fileCache,
		firebaseClient: firebaseClient,
		smtpSender:     mailer,
		topics:         topics,
		userManager:    userManager,
		visitors:       make(map[string]*visitor),
		stripe:         stripe,
	}
	s.priceCache = util.NewLookupCache(s.fetchStripePrices, conf.StripePriceCacheDuration)
	return s, nil
}

func createMessageCache(conf *Config) (*messageCache, error) {
	if conf.CacheDuration == 0 {
		return newNopCache()
	} else if conf.CacheFile != "" {
		return newSqliteCache(conf.CacheFile, conf.CacheStartupQueries, conf.CacheDuration, conf.CacheBatchSize, conf.CacheBatchTimeout, false)
	}
	return newMemCache()
}

// Run executes the main server. It listens on HTTP (+ HTTPS, if configured), and starts
// a manager go routine to print stats and prune messages.
func (s *Server) Run() error {
	var listenStr string
	if s.config.ListenHTTP != "" {
		listenStr += fmt.Sprintf(" %s[http]", s.config.ListenHTTP)
	}
	if s.config.ListenHTTPS != "" {
		listenStr += fmt.Sprintf(" %s[https]", s.config.ListenHTTPS)
	}
	if s.config.ListenUnix != "" {
		listenStr += fmt.Sprintf(" %s[unix]", s.config.ListenUnix)
	}
	if s.config.SMTPServerListen != "" {
		listenStr += fmt.Sprintf(" %s[smtp]", s.config.SMTPServerListen)
	}
	if s.config.MetricsListenHTTP != "" {
		listenStr += fmt.Sprintf(" %s[http/metrics]", s.config.MetricsListenHTTP)
	}
	if s.config.ProfileListenHTTP != "" {
		listenStr += fmt.Sprintf(" %s[http/profile]", s.config.ProfileListenHTTP)
	}
	log.Tag(tagStartup).Info("Listening on%s, ntfy %s, log level is %s", listenStr, s.config.Version, log.CurrentLevel().String())
	if log.IsFile() {
		fmt.Fprintf(os.Stderr, "Listening on%s, ntfy %s\n", listenStr, s.config.Version)
		fmt.Fprintf(os.Stderr, "Logs are written to %s\n", log.File())
	}
	mux := http.NewServeMux()
	mux.HandleFunc("/", s.handle)
	errChan := make(chan error)
	s.mu.Lock()
	s.closeChan = make(chan bool)
	if s.config.ListenHTTP != "" {
		s.httpServer = &http.Server{Addr: s.config.ListenHTTP, Handler: mux}
		go func() {
			errChan <- s.httpServer.ListenAndServe()
		}()
	}
	if s.config.ListenHTTPS != "" {
		s.httpsServer = &http.Server{Addr: s.config.ListenHTTPS, Handler: mux}
		go func() {
			errChan <- s.httpsServer.ListenAndServeTLS(s.config.CertFile, s.config.KeyFile)
		}()
	}
	if s.config.ListenUnix != "" {
		go func() {
			var err error
			s.mu.Lock()
			os.Remove(s.config.ListenUnix)
			s.unixListener, err = net.Listen("unix", s.config.ListenUnix)
			if err != nil {
				s.mu.Unlock()
				errChan <- err
				return
			}
			defer s.unixListener.Close()
			if s.config.ListenUnixMode > 0 {
				if err := os.Chmod(s.config.ListenUnix, s.config.ListenUnixMode); err != nil {
					s.mu.Unlock()
					errChan <- err
					return
				}
			}
			s.mu.Unlock()
			httpServer := &http.Server{Handler: mux}
			errChan <- httpServer.Serve(s.unixListener)
		}()
	}
	if s.config.MetricsListenHTTP != "" {
		initMetrics()
		s.httpMetricsServer = &http.Server{Addr: s.config.MetricsListenHTTP, Handler: promhttp.Handler()}
		go func() {
			errChan <- s.httpMetricsServer.ListenAndServe()
		}()
	} else if s.config.EnableMetrics {
		initMetrics()
		s.metricsHandler = promhttp.Handler()
	}
	if s.config.ProfileListenHTTP != "" {
		profileMux := http.NewServeMux()
		profileMux.HandleFunc("/debug/pprof/", pprof.Index)
		profileMux.HandleFunc("/debug/pprof/cmdline", pprof.Cmdline)
		profileMux.HandleFunc("/debug/pprof/profile", pprof.Profile)
		profileMux.HandleFunc("/debug/pprof/symbol", pprof.Symbol)
		profileMux.HandleFunc("/debug/pprof/trace", pprof.Trace)
		s.httpProfileServer = &http.Server{Addr: s.config.ProfileListenHTTP, Handler: profileMux}
		go func() {
			errChan <- s.httpProfileServer.ListenAndServe()
		}()
	}
	if s.config.SMTPServerListen != "" {
		go func() {
			errChan <- s.runSMTPServer()
		}()
	}
	s.mu.Unlock()
	go s.runManager()
	go s.runStatsResetter()
	go s.runDelayedSender()
	go s.runFirebaseKeepaliver()

	return <-errChan
}

// Stop stops HTTP (+HTTPS) server and all managers
func (s *Server) Stop() {
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.httpServer != nil {
		s.httpServer.Close()
	}
	if s.httpsServer != nil {
		s.httpsServer.Close()
	}
	if s.unixListener != nil {
		s.unixListener.Close()
	}
	if s.smtpServer != nil {
		s.smtpServer.Close()
	}
	s.closeDatabases()
	close(s.closeChan)
}

func (s *Server) closeDatabases() {
	if s.userManager != nil {
		s.userManager.Close()
	}
	s.messageCache.Close()
}

// handle is the main entry point for all HTTP requests
func (s *Server) handle(w http.ResponseWriter, r *http.Request) {
	v, err := s.maybeAuthenticate(r) // Note: Always returns v, even when error is returned
	if err != nil {
		s.handleError(w, r, v, err)
		return
	}
	ev := logvr(v, r)
	if ev.IsTrace() {
		ev.Field("http_request", renderHTTPRequest(r)).Trace("HTTP request started")
	} else if logvr(v, r).IsDebug() {
		ev.Debug("HTTP request started")
	}
	logvr(v, r).
		Timing(func() {
			if err := s.handleInternal(w, r, v); err != nil {
				s.handleError(w, r, v, err)
				return
			}
			if metricHTTPRequests != nil {
				metricHTTPRequests.WithLabelValues("200", "20000", r.Method).Inc()
			}
		}).
		Debug("HTTP request finished")
}

func (s *Server) handleError(w http.ResponseWriter, r *http.Request, v *visitor, err error) {
	httpErr, ok := err.(*errHTTP)
	if !ok {
		httpErr = errHTTPInternalError
	}
	if metricHTTPRequests != nil {
		metricHTTPRequests.WithLabelValues(fmt.Sprintf("%d", httpErr.HTTPCode), fmt.Sprintf("%d", httpErr.Code), r.Method).Inc()
	}
	isRateLimiting := util.Contains(rateLimitingErrorCodes, httpErr.HTTPCode)
	isNormalError := strings.Contains(err.Error(), "i/o timeout") || util.Contains(normalErrorCodes, httpErr.HTTPCode)
	ev := logvr(v, r).Err(err)
	if websocket.IsWebSocketUpgrade(r) {
		ev.Tag(tagWebsocket).Fields(websocketErrorContext(err))
		if isNormalError {
			ev.Debug("WebSocket error (this error is okay, it happens a lot): %s", err.Error())
		} else {
			ev.Info("WebSocket error: %s", err.Error())
		}
		return // Do not attempt to write to upgraded connection
	}
	if isNormalError {
		ev.Debug("Connection closed with HTTP %d (ntfy error %d)", httpErr.HTTPCode, httpErr.Code)
	} else {
		ev.Info("Connection closed with HTTP %d (ntfy error %d)", httpErr.HTTPCode, httpErr.Code)
	}
	if isRateLimiting && s.config.StripeSecretKey != "" {
		u := v.User()
		if u == nil || u.Tier == nil {
			httpErr = httpErr.Wrap("increase your limits with a paid plan, see %s", s.config.BaseURL)
		}
	}
	w.Header().Set("Content-Type", "application/json")
	w.Header().Set("Access-Control-Allow-Origin", s.config.AccessControlAllowOrigin) // CORS, allow cross-origin requests
	w.WriteHeader(httpErr.HTTPCode)
	io.WriteString(w, httpErr.JSON()+"\n")
}

func (s *Server) handleInternal(w http.ResponseWriter, r *http.Request, v *visitor) error {
	if r.Method == http.MethodGet && r.URL.Path == "/" {
		return s.ensureWebEnabled(s.handleHome)(w, r, v)
	} else if r.Method == http.MethodHead && r.URL.Path == "/" {
		return s.ensureWebEnabled(s.handleEmpty)(w, r, v)
	} else if r.Method == http.MethodGet && r.URL.Path == apiHealthPath {
		return s.handleHealth(w, r, v)
	} else if r.Method == http.MethodGet && r.URL.Path == webConfigPath {
		return s.ensureWebEnabled(s.handleWebConfig)(w, r, v)
	} else if r.Method == http.MethodPost && r.URL.Path == apiAccountPath {
		return s.ensureUserManager(s.handleAccountCreate)(w, r, v)
	} else if r.Method == http.MethodGet && r.URL.Path == apiAccountPath {
		return s.handleAccountGet(w, r, v) // Allowed by anonymous
	} else if r.Method == http.MethodDelete && r.URL.Path == apiAccountPath {
		return s.ensureUser(s.withAccountSync(s.handleAccountDelete))(w, r, v)
	} else if r.Method == http.MethodPost && r.URL.Path == apiAccountPasswordPath {
		return s.ensureUser(s.handleAccountPasswordChange)(w, r, v)
	} else if r.Method == http.MethodPost && r.URL.Path == apiAccountTokenPath {
		return s.ensureUser(s.withAccountSync(s.handleAccountTokenCreate))(w, r, v)
	} else if r.Method == http.MethodPatch && r.URL.Path == apiAccountTokenPath {
		return s.ensureUser(s.withAccountSync(s.handleAccountTokenUpdate))(w, r, v)
	} else if r.Method == http.MethodDelete && r.URL.Path == apiAccountTokenPath {
		return s.ensureUser(s.withAccountSync(s.handleAccountTokenDelete))(w, r, v)
	} else if r.Method == http.MethodPatch && r.URL.Path == apiAccountSettingsPath {
		return s.ensureUser(s.withAccountSync(s.handleAccountSettingsChange))(w, r, v)
	} else if r.Method == http.MethodPost && r.URL.Path == apiAccountSubscriptionPath {
		return s.ensureUser(s.withAccountSync(s.handleAccountSubscriptionAdd))(w, r, v)
	} else if r.Method == http.MethodPatch && r.URL.Path == apiAccountSubscriptionPath {
		return s.ensureUser(s.withAccountSync(s.handleAccountSubscriptionChange))(w, r, v)
	} else if r.Method == http.MethodDelete && r.URL.Path == apiAccountSubscriptionPath {
		return s.ensureUser(s.withAccountSync(s.handleAccountSubscriptionDelete))(w, r, v)
	} else if r.Method == http.MethodPost && r.URL.Path == apiAccountReservationPath {
		return s.ensureUser(s.withAccountSync(s.handleAccountReservationAdd))(w, r, v)
	} else if r.Method == http.MethodDelete && apiAccountReservationSingleRegex.MatchString(r.URL.Path) {
		return s.ensureUser(s.withAccountSync(s.handleAccountReservationDelete))(w, r, v)
	} else if r.Method == http.MethodPost && r.URL.Path == apiAccountBillingSubscriptionPath {
		return s.ensurePaymentsEnabled(s.ensureUser(s.handleAccountBillingSubscriptionCreate))(w, r, v) // Account sync via incoming Stripe webhook
	} else if r.Method == http.MethodGet && apiAccountBillingSubscriptionCheckoutSuccessRegex.MatchString(r.URL.Path) {
		return s.ensurePaymentsEnabled(s.ensureUserManager(s.handleAccountBillingSubscriptionCreateSuccess))(w, r, v) // No user context!
	} else if r.Method == http.MethodPut && r.URL.Path == apiAccountBillingSubscriptionPath {
		return s.ensurePaymentsEnabled(s.ensureStripeCustomer(s.handleAccountBillingSubscriptionUpdate))(w, r, v) // Account sync via incoming Stripe webhook
	} else if r.Method == http.MethodDelete && r.URL.Path == apiAccountBillingSubscriptionPath {
		return s.ensurePaymentsEnabled(s.ensureStripeCustomer(s.handleAccountBillingSubscriptionDelete))(w, r, v) // Account sync via incoming Stripe webhook
	} else if r.Method == http.MethodPost && r.URL.Path == apiAccountBillingPortalPath {
		return s.ensurePaymentsEnabled(s.ensureStripeCustomer(s.handleAccountBillingPortalSessionCreate))(w, r, v)
	} else if r.Method == http.MethodPost && r.URL.Path == apiAccountBillingWebhookPath {
		return s.ensurePaymentsEnabled(s.ensureUserManager(s.handleAccountBillingWebhook))(w, r, v) // This request comes from Stripe!
	} else if r.Method == http.MethodGet && r.URL.Path == apiTiers {
		return s.ensurePaymentsEnabled(s.handleBillingTiersGet)(w, r, v)
	} else if r.Method == http.MethodGet && r.URL.Path == matrixPushPath {
		return s.handleMatrixDiscovery(w)
	} else if r.Method == http.MethodGet && r.URL.Path == metricsPath && s.metricsHandler != nil {
		return s.handleMetrics(w, r, v)
	} else if r.Method == http.MethodGet && staticRegex.MatchString(r.URL.Path) {
		return s.ensureWebEnabled(s.handleStatic)(w, r, v)
	} else if r.Method == http.MethodGet && docsRegex.MatchString(r.URL.Path) {
		return s.ensureWebEnabled(s.handleDocs)(w, r, v)
	} else if (r.Method == http.MethodGet || r.Method == http.MethodHead) && fileRegex.MatchString(r.URL.Path) && s.config.AttachmentCacheDir != "" {
		return s.limitRequests(s.handleFile)(w, r, v)
	} else if r.Method == http.MethodOptions {
		return s.limitRequests(s.handleOptions)(w, r, v) // Should work even if the web app is not enabled, see #598
	} else if (r.Method == http.MethodPut || r.Method == http.MethodPost) && r.URL.Path == "/" {
		return s.transformBodyJSON(s.limitRequestsWithTopic(s.authorizeTopicWrite(s.handlePublish)))(w, r, v)
	} else if r.Method == http.MethodPost && r.URL.Path == matrixPushPath {
		return s.transformMatrixJSON(s.limitRequestsWithTopic(s.authorizeTopicWrite(s.handlePublishMatrix)))(w, r, v)
	} else if (r.Method == http.MethodPut || r.Method == http.MethodPost) && topicPathRegex.MatchString(r.URL.Path) {
		return s.limitRequestsWithTopic(s.authorizeTopicWrite(s.handlePublish))(w, r, v)
	} else if r.Method == http.MethodGet && publishPathRegex.MatchString(r.URL.Path) {
		return s.limitRequestsWithTopic(s.authorizeTopicWrite(s.handlePublish))(w, r, v)
	} else if r.Method == http.MethodGet && jsonPathRegex.MatchString(r.URL.Path) {
		return s.limitRequests(s.authorizeTopicRead(s.handleSubscribeJSON))(w, r, v)
	} else if r.Method == http.MethodGet && ssePathRegex.MatchString(r.URL.Path) {
		return s.limitRequests(s.authorizeTopicRead(s.handleSubscribeSSE))(w, r, v)
	} else if r.Method == http.MethodGet && rawPathRegex.MatchString(r.URL.Path) {
		return s.limitRequests(s.authorizeTopicRead(s.handleSubscribeRaw))(w, r, v)
	} else if r.Method == http.MethodGet && wsPathRegex.MatchString(r.URL.Path) {
		return s.limitRequests(s.authorizeTopicRead(s.handleSubscribeWS))(w, r, v)
	} else if r.Method == http.MethodGet && authPathRegex.MatchString(r.URL.Path) {
		return s.limitRequests(s.authorizeTopicRead(s.handleTopicAuth))(w, r, v)
	} else if r.Method == http.MethodGet && (topicPathRegex.MatchString(r.URL.Path) || externalTopicPathRegex.MatchString(r.URL.Path)) {
		return s.ensureWebEnabled(s.handleTopic)(w, r, v)
	}
	return errHTTPNotFound
}

func (s *Server) handleHome(w http.ResponseWriter, r *http.Request, v *visitor) error {
	if s.config.WebRootIsApp {
		r.URL.Path = webAppIndex
	} else {
		r.URL.Path = webHomeIndex
	}
	return s.handleStatic(w, r, v)
}

func (s *Server) handleTopic(w http.ResponseWriter, r *http.Request, v *visitor) error {
	unifiedpush := readBoolParam(r, false, "x-unifiedpush", "unifiedpush", "up") // see PUT/POST too!
	if unifiedpush {
		w.Header().Set("Content-Type", "application/json")
		w.Header().Set("Access-Control-Allow-Origin", s.config.AccessControlAllowOrigin) // CORS, allow cross-origin requests
		_, err := io.WriteString(w, `{"unifiedpush":{"version":1}}`+"\n")
		return err
	}
	r.URL.Path = webAppIndex
	return s.handleStatic(w, r, v)
}

func (s *Server) handleEmpty(_ http.ResponseWriter, _ *http.Request, _ *visitor) error {
	return nil
}

func (s *Server) handleTopicAuth(w http.ResponseWriter, _ *http.Request, _ *visitor) error {
	return s.writeJSON(w, newSuccessResponse())
}

func (s *Server) handleHealth(w http.ResponseWriter, _ *http.Request, _ *visitor) error {
	response := &apiHealthResponse{
		Healthy: true,
	}
	return s.writeJSON(w, response)
}

func (s *Server) handleWebConfig(w http.ResponseWriter, _ *http.Request, _ *visitor) error {
	appRoot := "/"
	if !s.config.WebRootIsApp {
		appRoot = "/app"
	}
	response := &apiConfigResponse{
		BaseURL:            "", // Will translate to window.location.origin
		AppRoot:            appRoot,
		EnableLogin:        s.config.EnableLogin,
		EnableSignup:       s.config.EnableSignup,
		EnablePayments:     s.config.StripeSecretKey != "",
		EnableReservations: s.config.EnableReservations,
		BillingContact:     s.config.BillingContact,
		DisallowedTopics:   s.config.DisallowedTopics,
	}
	b, err := json.MarshalIndent(response, "", "  ")
	if err != nil {
		return err
	}
	w.Header().Set("Content-Type", "text/javascript")
	_, err = io.WriteString(w, fmt.Sprintf("// Generated server configuration\nvar config = %s;\n", string(b)))
	return err
}

// handleMetrics returns Prometheus metrics. This endpoint is only called if enable-metrics is set,
// and listen-metrics-http is not set.
func (s *Server) handleMetrics(w http.ResponseWriter, r *http.Request, _ *visitor) error {
	s.metricsHandler.ServeHTTP(w, r)
	return nil
}

func (s *Server) handleStatic(w http.ResponseWriter, r *http.Request, _ *visitor) error {
	r.URL.Path = webSiteDir + r.URL.Path
	util.Gzip(http.FileServer(http.FS(webFsCached))).ServeHTTP(w, r)
	return nil
}

func (s *Server) handleDocs(w http.ResponseWriter, r *http.Request, _ *visitor) error {
	util.Gzip(http.FileServer(http.FS(docsStaticCached))).ServeHTTP(w, r)
	return nil
}

// handleFile processes the download of attachment files. The method handles GET and HEAD requests against a file.
// Before streaming the file to a client, it locates uploader (m.Sender or m.User) in the message cache, so it
// can associate the download bandwidth with the uploader.
func (s *Server) handleFile(w http.ResponseWriter, r *http.Request, v *visitor) error {
	if s.config.AttachmentCacheDir == "" {
		return errHTTPInternalError
	}
	matches := fileRegex.FindStringSubmatch(r.URL.Path)
	if len(matches) != 2 {
		return errHTTPInternalErrorInvalidPath
	}
	messageID := matches[1]
	file := filepath.Join(s.config.AttachmentCacheDir, messageID)
	stat, err := os.Stat(file)
	if err != nil {
		return errHTTPNotFound.Fields(log.Context{
			"message_id":    messageID,
			"error_context": "filesystem",
		})
	}
	w.Header().Set("Access-Control-Allow-Origin", s.config.AccessControlAllowOrigin) // CORS, allow cross-origin requests
	w.Header().Set("Content-Length", fmt.Sprintf("%d", stat.Size()))
	if r.Method == http.MethodHead {
		return nil
	}
	// Find message in database, and associate bandwidth to the uploader user
	// This is an easy way to
	//   - avoid abuse (e.g. 1 uploader, 1k downloaders)
	//   - and also uses the higher bandwidth limits of a paying user
	m, err := s.messageCache.Message(messageID)
	if err == errMessageNotFound {
		if s.config.CacheBatchTimeout > 0 {
			// Strange edge case: If we immediately after upload request the file (the web app does this for images),
			// and messages are persisted asynchronously, retry fetching from the database
			m, err = util.Retry(func() (*message, error) {
				return s.messageCache.Message(messageID)
			}, s.config.CacheBatchTimeout, 100*time.Millisecond, 300*time.Millisecond, 600*time.Millisecond)
		}
		if err != nil {
			return errHTTPNotFound.Fields(log.Context{
				"message_id":    messageID,
				"error_context": "message_cache",
			})
		}
	} else if err != nil {
		return err
	}
	bandwidthVisitor := v
	if s.userManager != nil && m.User != "" {
		u, err := s.userManager.UserByID(m.User)
		if err != nil {
			return err
		}
		bandwidthVisitor = s.visitor(v.IP(), u)
	} else if m.Sender.IsValid() {
		bandwidthVisitor = s.visitor(m.Sender, nil)
	}
	if !bandwidthVisitor.BandwidthAllowed(stat.Size()) {
		return errHTTPTooManyRequestsLimitAttachmentBandwidth.With(m)
	}
	// Actually send file
	f, err := os.Open(file)
	if err != nil {
		return err
	}
	defer f.Close()
	_, err = io.Copy(util.NewContentTypeWriter(w, r.URL.Path), f)
	return err
}

func (s *Server) handleMatrixDiscovery(w http.ResponseWriter) error {
	if s.config.BaseURL == "" {
		return errHTTPInternalErrorMissingBaseURL
	}
	return writeMatrixDiscoveryResponse(w)
}

func (s *Server) handlePublishInternal(r *http.Request, v *visitor) (*message, error) {
	start := time.Now()
	t, err := fromContext[*topic](r, contextTopic)
	if err != nil {
		return nil, err
	}
	vrate, err := fromContext[*visitor](r, contextRateVisitor)
	if err != nil {
		return nil, err
	}
	body, err := util.Peek(r.Body, s.config.MessageLimit)
	if err != nil {
		return nil, err
	}
	m := newDefaultMessage(t.ID, "")
	cache, firebase, email, unifiedpush, e := s.parsePublishParams(r, m)
	if e != nil {
		return nil, e.With(t)
	}
	if unifiedpush && s.config.VisitorSubscriberRateLimiting && t.RateVisitor() == nil {
		// UnifiedPush clients must subscribe before publishing to allow proper subscriber-based rate limiting (see
		// Rate-Topics header). The 5xx response is because some app servers (in particular Mastodon) will remove
		// the subscription as invalid if any 400-499 code (except 429/408) is returned.
		// See https://github.com/mastodon/mastodon/blob/730bb3e211a84a2f30e3e2bbeae3f77149824a68/app/workers/web/push_notification_worker.rb#L35-L46
		return nil, errHTTPInsufficientStorageUnifiedPush.With(t)
	} else if !util.ContainsIP(s.config.VisitorRequestExemptIPAddrs, v.ip) && !vrate.MessageAllowed() {
		return nil, errHTTPTooManyRequestsLimitMessages.With(t)
	} else if email != "" && !vrate.EmailAllowed() {
		return nil, errHTTPTooManyRequestsLimitEmails.With(t)
	}
	if m.PollID != "" {
		m = newPollRequestMessage(t.ID, m.PollID)
	}
	m.Sender = v.IP()
	m.User = v.MaybeUserID()
	if cache {
		m.Expires = time.Unix(m.Time, 0).Add(v.Limits().MessageExpiryDuration).Unix()
	}
	if err := s.handlePublishBody(r, v, m, body, unifiedpush); err != nil {
		return nil, err
	}
	if m.Message == "" {
		m.Message = emptyMessageBody
	}
	delayed := m.Time > time.Now().Unix()
	ev := logvrm(v, r, m).
		Tag(tagPublish).
		With(t).
		Fields(log.Context{
			"message_delayed":     delayed,
			"message_firebase":    firebase,
			"message_unifiedpush": unifiedpush,
			"message_email":       email,
		})
	if ev.IsTrace() {
		ev.Field("message_body", util.MaybeMarshalJSON(m)).Trace("Received message")
	} else if ev.IsDebug() {
		ev.Debug("Received message")
	}
	if !delayed {
		if err := t.Publish(v, m); err != nil {
			return nil, err
		}
		if s.firebaseClient != nil && firebase {
			go s.sendToFirebase(v, m)
		}
		if s.smtpSender != nil && email != "" {
			go s.sendEmail(v, m, email)
		}
		if s.config.UpstreamBaseURL != "" {
			go s.forwardPollRequest(v, m)
		}
	} else {
		logvrm(v, r, m).Tag(tagPublish).Debug("Message delayed, will process later")
	}
	if cache {
		logvrm(v, r, m).Tag(tagPublish).Debug("Adding message to cache")
		if err := s.messageCache.AddMessage(m); err != nil {
			return nil, err
		}
	}
	u := v.User()
	if s.userManager != nil && u != nil && u.Tier != nil {
		go s.userManager.EnqueueUserStats(u.ID, v.Stats())
	}
	s.mu.Lock()
	s.messages++
	s.mu.Unlock()
	if unifiedpush {
		minc(metricUnifiedPushPublishedSuccess)
	}
	mset(metricMessagePublishDurationMillis, time.Since(start).Milliseconds())
	return m, nil
}

func (s *Server) handlePublish(w http.ResponseWriter, r *http.Request, v *visitor) error {
	m, err := s.handlePublishInternal(r, v)
	if err != nil {
		minc(metricMessagesPublishedFailure)
		return err
	}
	minc(metricMessagesPublishedSuccess)
	return s.writeJSON(w, m)
}

func (s *Server) handlePublishMatrix(w http.ResponseWriter, r *http.Request, v *visitor) error {
	_, err := s.handlePublishInternal(r, v)
	if err != nil {
		minc(metricMessagesPublishedFailure)
		minc(metricMatrixPublishedFailure)
		if e, ok := err.(*errHTTP); ok && e.HTTPCode == errHTTPInsufficientStorageUnifiedPush.HTTPCode {
			topic, err := fromContext[*topic](r, contextTopic)
			if err != nil {
				return err
			}
			pushKey, err := fromContext[string](r, contextMatrixPushKey)
			if err != nil {
				return err
			}
			if time.Since(topic.LastAccess()) > matrixRejectPushKeyForUnifiedPushTopicWithoutRateVisitorAfter {
				return writeMatrixResponse(w, pushKey)
			}
		}
		return err
	}
	minc(metricMessagesPublishedSuccess)
	minc(metricMatrixPublishedSuccess)
	return writeMatrixSuccess(w)
}

func (s *Server) sendToFirebase(v *visitor, m *message) {
	logvm(v, m).Tag(tagFirebase).Debug("Publishing to Firebase")
	if err := s.firebaseClient.Send(v, m); err != nil {
		minc(metricFirebasePublishedFailure)
		if err == errFirebaseTemporarilyBanned {
			logvm(v, m).Tag(tagFirebase).Err(err).Debug("Unable to publish to Firebase: %v", err.Error())
		} else {
			logvm(v, m).Tag(tagFirebase).Err(err).Warn("Unable to publish to Firebase: %v", err.Error())
		}
		return
	}
	minc(metricFirebasePublishedSuccess)
}

func (s *Server) sendEmail(v *visitor, m *message, email string) {
	logvm(v, m).Tag(tagEmail).Field("email", email).Debug("Sending email to %s", email)
	if err := s.smtpSender.Send(v, m, email); err != nil {
		logvm(v, m).Tag(tagEmail).Field("email", email).Err(err).Warn("Unable to send email to %s: %v", email, err.Error())
		minc(metricEmailsPublishedFailure)
		return
	}
	minc(metricEmailsPublishedSuccess)
}

func (s *Server) forwardPollRequest(v *visitor, m *message) {
	topicURL := fmt.Sprintf("%s/%s", s.config.BaseURL, m.Topic)
	topicHash := fmt.Sprintf("%x", sha256.Sum256([]byte(topicURL)))
	forwardURL := fmt.Sprintf("%s/%s", s.config.UpstreamBaseURL, topicHash)
	logvm(v, m).Debug("Publishing poll request to %s", forwardURL)
	req, err := http.NewRequest("POST", forwardURL, strings.NewReader(""))
	if err != nil {
		logvm(v, m).Err(err).Warn("Unable to publish poll request")
		return
	}
	req.Header.Set("X-Poll-ID", m.ID)
	var httpClient = &http.Client{
		Timeout: time.Second * 10,
	}
	response, err := httpClient.Do(req)
	if err != nil {
		logvm(v, m).Err(err).Warn("Unable to publish poll request")
		return
	} else if response.StatusCode != http.StatusOK {
		logvm(v, m).Err(err).Warn("Unable to publish poll request, unexpected HTTP status: %d", response.StatusCode)
		return
	}
}

func (s *Server) parsePublishParams(r *http.Request, m *message) (cache bool, firebase bool, email string, unifiedpush bool, err *errHTTP) {
	cache = readBoolParam(r, true, "x-cache", "cache")
	firebase = readBoolParam(r, true, "x-firebase", "firebase")
	m.Title = readParam(r, "x-title", "title", "t")
	m.Click = readParam(r, "x-click", "click")
	icon := readParam(r, "x-icon", "icon")
	filename := readParam(r, "x-filename", "filename", "file", "f")
	attach := readParam(r, "x-attach", "attach", "a")
	if attach != "" || filename != "" {
		m.Attachment = &attachment{}
	}
	if filename != "" {
		m.Attachment.Name = filename
	}
	if attach != "" {
		if !urlRegex.MatchString(attach) {
			return false, false, "", false, errHTTPBadRequestAttachmentURLInvalid
		}
		m.Attachment.URL = attach
		if m.Attachment.Name == "" {
			u, err := url.Parse(m.Attachment.URL)
			if err == nil {
				m.Attachment.Name = path.Base(u.Path)
				if m.Attachment.Name == "." || m.Attachment.Name == "/" {
					m.Attachment.Name = ""
				}
			}
		}
		if m.Attachment.Name == "" {
			m.Attachment.Name = "attachment"
		}
	}
	if icon != "" {
		if !urlRegex.MatchString(icon) {
			return false, false, "", false, errHTTPBadRequestIconURLInvalid
		}
		m.Icon = icon
	}
	email = readParam(r, "x-email", "x-e-mail", "email", "e-mail", "mail", "e")
	if s.smtpSender == nil && email != "" {
		return false, false, "", false, errHTTPBadRequestEmailDisabled
	}
	messageStr := strings.ReplaceAll(readParam(r, "x-message", "message", "m"), "\\n", "\n")
	if messageStr != "" {
		m.Message = messageStr
	}
	var e error
	m.Priority, e = util.ParsePriority(readParam(r, "x-priority", "priority", "prio", "p"))
	if e != nil {
		return false, false, "", false, errHTTPBadRequestPriorityInvalid
	}
	m.Tags = readCommaSeparatedParam(r, "x-tags", "tags", "tag", "ta")
	delayStr := readParam(r, "x-delay", "delay", "x-at", "at", "x-in", "in")
	if delayStr != "" {
		if !cache {
			return false, false, "", false, errHTTPBadRequestDelayNoCache
		}
		if email != "" {
			return false, false, "", false, errHTTPBadRequestDelayNoEmail // we cannot store the email address (yet)
		}
		delay, err := util.ParseFutureTime(delayStr, time.Now())
		if err != nil {
			return false, false, "", false, errHTTPBadRequestDelayCannotParse
		} else if delay.Unix() < time.Now().Add(s.config.MinDelay).Unix() {
			return false, false, "", false, errHTTPBadRequestDelayTooSmall
		} else if delay.Unix() > time.Now().Add(s.config.MaxDelay).Unix() {
			return false, false, "", false, errHTTPBadRequestDelayTooLarge
		}
		m.Time = delay.Unix()
	}
	actionsStr := readParam(r, "x-actions", "actions", "action")
	if actionsStr != "" {
		m.Actions, e = parseActions(actionsStr)
		if e != nil {
			return false, false, "", false, errHTTPBadRequestActionsInvalid.Wrap(e.Error())
		}
	}
	unifiedpush = readBoolParam(r, false, "x-unifiedpush", "unifiedpush", "up") // see GET too!
	if unifiedpush {
		firebase = false
		unifiedpush = true
	}
	m.PollID = readParam(r, "x-poll-id", "poll-id")
	if m.PollID != "" {
		unifiedpush = false
		cache = false
		email = ""
	}
	return cache, firebase, email, unifiedpush, nil
}

// handlePublishBody consumes the PUT/POST body and decides whether the body is an attachment or the message.
//
//  1. curl -X POST -H "Poll: 1234" ntfy.sh/...
//     If a message is flagged as poll request, the body does not matter and is discarded
//  2. curl -T somebinarydata.bin "ntfy.sh/mytopic?up=1"
//     If body is binary, encode as base64, if not do not encode
//  3. curl -H "Attach: http://example.com/file.jpg" ntfy.sh/mytopic
//     Body must be a message, because we attached an external URL
//  4. curl -T short.txt -H "Filename: short.txt" ntfy.sh/mytopic
//     Body must be attachment, because we passed a filename
//  5. curl -T file.txt ntfy.sh/mytopic
//     If file.txt is <= 4096 (message limit) and valid UTF-8, treat it as a message
//  6. curl -T file.txt ntfy.sh/mytopic
//     If file.txt is > message limit, treat it as an attachment
func (s *Server) handlePublishBody(r *http.Request, v *visitor, m *message, body *util.PeekedReadCloser, unifiedpush bool) error {
	if m.Event == pollRequestEvent { // Case 1
		return s.handleBodyDiscard(body)
	} else if unifiedpush {
		return s.handleBodyAsMessageAutoDetect(m, body) // Case 2
	} else if m.Attachment != nil && m.Attachment.URL != "" {
		return s.handleBodyAsTextMessage(m, body) // Case 3
	} else if m.Attachment != nil && m.Attachment.Name != "" {
		return s.handleBodyAsAttachment(r, v, m, body) // Case 4
	} else if !body.LimitReached && utf8.Valid(body.PeekedBytes) {
		return s.handleBodyAsTextMessage(m, body) // Case 5
	}
	return s.handleBodyAsAttachment(r, v, m, body) // Case 6
}

func (s *Server) handleBodyDiscard(body *util.PeekedReadCloser) error {
	_, err := io.Copy(io.Discard, body)
	_ = body.Close()
	return err
}

func (s *Server) handleBodyAsMessageAutoDetect(m *message, body *util.PeekedReadCloser) error {
	if utf8.Valid(body.PeekedBytes) {
		m.Message = string(body.PeekedBytes) // Do not trim
	} else {
		m.Message = base64.StdEncoding.EncodeToString(body.PeekedBytes)
		m.Encoding = encodingBase64
	}
	return nil
}

func (s *Server) handleBodyAsTextMessage(m *message, body *util.PeekedReadCloser) error {
	if !utf8.Valid(body.PeekedBytes) {
		return errHTTPBadRequestMessageNotUTF8.With(m)
	}
	if len(body.PeekedBytes) > 0 { // Empty body should not override message (publish via GET!)
		m.Message = strings.TrimSpace(string(body.PeekedBytes)) // Truncates the message to the peek limit if required
	}
	if m.Attachment != nil && m.Attachment.Name != "" && m.Message == "" {
		m.Message = fmt.Sprintf(defaultAttachmentMessage, m.Attachment.Name)
	}
	return nil
}

func (s *Server) handleBodyAsAttachment(r *http.Request, v *visitor, m *message, body *util.PeekedReadCloser) error {
	if s.fileCache == nil || s.config.BaseURL == "" || s.config.AttachmentCacheDir == "" {
		return errHTTPBadRequestAttachmentsDisallowed.With(m)
	}
	vinfo, err := v.Info()
	if err != nil {
		return err
	}
	attachmentExpiry := time.Now().Add(vinfo.Limits.AttachmentExpiryDuration).Unix()
	if m.Time > attachmentExpiry {
		return errHTTPBadRequestAttachmentsExpiryBeforeDelivery.With(m)
	}
	contentLengthStr := r.Header.Get("Content-Length")
	if contentLengthStr != "" { // Early "do-not-trust" check, hard limit see below
		contentLength, err := strconv.ParseInt(contentLengthStr, 10, 64)
		if err == nil && (contentLength > vinfo.Stats.AttachmentTotalSizeRemaining || contentLength > vinfo.Limits.AttachmentFileSizeLimit) {
			return errHTTPEntityTooLargeAttachment.With(m).Fields(log.Context{
				"message_content_length":          contentLength,
				"attachment_total_size_remaining": vinfo.Stats.AttachmentTotalSizeRemaining,
				"attachment_file_size_limit":      vinfo.Limits.AttachmentFileSizeLimit,
			})
		}
	}
	if m.Attachment == nil {
		m.Attachment = &attachment{}
	}
	var ext string
	m.Attachment.Expires = attachmentExpiry
	m.Attachment.Type, ext = util.DetectContentType(body.PeekedBytes, m.Attachment.Name)
	m.Attachment.URL = fmt.Sprintf("%s/file/%s%s", s.config.BaseURL, m.ID, ext)
	if m.Attachment.Name == "" {
		m.Attachment.Name = fmt.Sprintf("attachment%s", ext)
	}
	if m.Message == "" {
		m.Message = fmt.Sprintf(defaultAttachmentMessage, m.Attachment.Name)
	}
	limiters := []util.Limiter{
		v.BandwidthLimiter(),
		util.NewFixedLimiter(vinfo.Limits.AttachmentFileSizeLimit),
		util.NewFixedLimiter(vinfo.Stats.AttachmentTotalSizeRemaining),
	}
	m.Attachment.Size, err = s.fileCache.Write(m.ID, body, limiters...)
	if err == util.ErrLimitReached {
		return errHTTPEntityTooLargeAttachment.With(m)
	} else if err != nil {
		return err
	}
	return nil
}

func (s *Server) handleSubscribeJSON(w http.ResponseWriter, r *http.Request, v *visitor) error {
	encoder := func(msg *message) (string, error) {
		var buf bytes.Buffer
		if err := json.NewEncoder(&buf).Encode(&msg); err != nil {
			return "", err
		}
		return buf.String(), nil
	}
	return s.handleSubscribeHTTP(w, r, v, "application/x-ndjson", encoder)
}

func (s *Server) handleSubscribeSSE(w http.ResponseWriter, r *http.Request, v *visitor) error {
	encoder := func(msg *message) (string, error) {
		var buf bytes.Buffer
		if err := json.NewEncoder(&buf).Encode(&msg); err != nil {
			return "", err
		}
		if msg.Event != messageEvent {
			return fmt.Sprintf("event: %s\ndata: %s\n", msg.Event, buf.String()), nil // Browser's .onmessage() does not fire on this!
		}
		return fmt.Sprintf("data: %s\n", buf.String()), nil
	}
	return s.handleSubscribeHTTP(w, r, v, "text/event-stream", encoder)
}

func (s *Server) handleSubscribeRaw(w http.ResponseWriter, r *http.Request, v *visitor) error {
	encoder := func(msg *message) (string, error) {
		if msg.Event == messageEvent { // only handle default events
			return strings.ReplaceAll(msg.Message, "\n", " ") + "\n", nil
		}
		return "\n", nil // "keepalive" and "open" events just send an empty line
	}
	return s.handleSubscribeHTTP(w, r, v, "text/plain", encoder)
}

func (s *Server) handleSubscribeHTTP(w http.ResponseWriter, r *http.Request, v *visitor, contentType string, encoder messageEncoder) error {
	logvr(v, r).Tag(tagSubscribe).Debug("HTTP stream connection opened")
	defer logvr(v, r).Tag(tagSubscribe).Debug("HTTP stream connection closed")
	if !v.SubscriptionAllowed() {
		return errHTTPTooManyRequestsLimitSubscriptions
	}
	defer v.RemoveSubscription()
	topics, topicsStr, err := s.topicsFromPath(r.URL.Path)
	if err != nil {
		return err
	}
	poll, since, scheduled, filters, rateTopics, err := parseSubscribeParams(r)
	if err != nil {
		return err
	}
	var wlock sync.Mutex
	defer func() {
		// Hack: This is the fix for a horrible data race that I have not been able to figure out in quite some time.
		// It appears to be happening when the Go HTTP code reads from the socket when closing the request (i.e. AFTER
		// this function returns), and causes a data race with the ResponseWriter. Locking wlock here silences the
		// data race detector. See https://github.com/binwiederhier/ntfy/issues/338#issuecomment-1163425889.
		wlock.TryLock()
	}()
	sub := func(v *visitor, msg *message) error {
		if !filters.Pass(msg) {
			return nil
		}
		m, err := encoder(msg)
		if err != nil {
			return err
		}
		wlock.Lock()
		defer wlock.Unlock()
		if _, err := w.Write([]byte(m)); err != nil {
			return err
		}
		if fl, ok := w.(http.Flusher); ok {
			fl.Flush()
		}
		return nil
	}
	if err := s.maybeSetRateVisitors(r, v, topics, rateTopics); err != nil {
		return err
	}
	w.Header().Set("Access-Control-Allow-Origin", s.config.AccessControlAllowOrigin) // CORS, allow cross-origin requests
	w.Header().Set("Content-Type", contentType+"; charset=utf-8")                    // Android/Volley client needs charset!
	if poll {
		for _, t := range topics {
			t.Keepalive()
		}
		return s.sendOldMessages(topics, since, scheduled, v, sub)
	}
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()
	subscriberIDs := make([]int, 0)
	for _, t := range topics {
		subscriberIDs = append(subscriberIDs, t.Subscribe(sub, v.MaybeUserID(), cancel))
	}
	defer func() {
		for i, subscriberID := range subscriberIDs {
			topics[i].Unsubscribe(subscriberID) // Order!
		}
	}()
	if err := sub(v, newOpenMessage(topicsStr)); err != nil { // Send out open message
		return err
	}
	if err := s.sendOldMessages(topics, since, scheduled, v, sub); err != nil {
		return err
	}
	for {
		select {
		case <-ctx.Done():
			return nil
		case <-r.Context().Done():
			return nil
		case <-time.After(s.config.KeepaliveInterval):
			ev := logvr(v, r).Tag(tagSubscribe)
			if len(topics) == 1 {
				ev.With(topics[0]).Trace("Sending keepalive message to %s", topics[0].ID)
			} else {
				ev.Trace("Sending keepalive message to %d topics", len(topics))
			}
			v.Keepalive()
			for _, t := range topics {
				t.Keepalive()
			}
			if err := sub(v, newKeepaliveMessage(topicsStr)); err != nil { // Send keepalive message
				return err
			}
		}
	}
}

func (s *Server) handleSubscribeWS(w http.ResponseWriter, r *http.Request, v *visitor) error {
	if strings.ToLower(r.Header.Get("Upgrade")) != "websocket" {
		return errHTTPBadRequestWebSocketsUpgradeHeaderMissing
	}
	if !v.SubscriptionAllowed() {
		return errHTTPTooManyRequestsLimitSubscriptions
	}
	defer v.RemoveSubscription()
	logvr(v, r).Tag(tagWebsocket).Debug("WebSocket connection opened")
	defer logvr(v, r).Tag(tagWebsocket).Debug("WebSocket connection closed")
	topics, topicsStr, err := s.topicsFromPath(r.URL.Path)
	if err != nil {
		return err
	}
	poll, since, scheduled, filters, rateTopics, err := parseSubscribeParams(r)
	if err != nil {
		return err
	}
	upgrader := &websocket.Upgrader{
		ReadBufferSize:  wsBufferSize,
		WriteBufferSize: wsBufferSize,
		CheckOrigin: func(r *http.Request) bool {
			return true // We're open for business!
		},
	}
	conn, err := upgrader.Upgrade(w, r, nil)
	if err != nil {
		return err
	}
	defer conn.Close()

	// Subscription connections can be canceled externally, see topic.CancelSubscribers
	cancelCtx, cancel := context.WithCancel(context.Background())
	defer cancel()

	// Use errgroup to run WebSocket reader and writer in Go routines
	var wlock sync.Mutex
	g, gctx := errgroup.WithContext(cancelCtx)
	g.Go(func() error {
		pongWait := s.config.KeepaliveInterval + wsPongWait
		conn.SetReadLimit(wsReadLimit)
		if err := conn.SetReadDeadline(time.Now().Add(pongWait)); err != nil {
			return err
		}
		conn.SetPongHandler(func(appData string) error {
			logvr(v, r).Tag(tagWebsocket).Trace("Received WebSocket pong")
			return conn.SetReadDeadline(time.Now().Add(pongWait))
		})
		for {
			_, _, err := conn.NextReader()
			if err != nil {
				return err
			}
			select {
			case <-gctx.Done():
				return nil
			default:
			}
		}
	})
	g.Go(func() error {
		ping := func() error {
			wlock.Lock()
			defer wlock.Unlock()
			if err := conn.SetWriteDeadline(time.Now().Add(wsWriteWait)); err != nil {
				return err
			}
			logvr(v, r).Tag(tagWebsocket).Trace("Sending WebSocket ping")
			return conn.WriteMessage(websocket.PingMessage, nil)
		}
		for {
			select {
			case <-gctx.Done():
				return nil
			case <-cancelCtx.Done():
				logvr(v, r).Tag(tagWebsocket).Trace("Cancel received, closing subscriber connection")
				conn.Close()
				return &websocket.CloseError{Code: websocket.CloseNormalClosure, Text: "subscription was canceled"}
			case <-time.After(s.config.KeepaliveInterval):
				v.Keepalive()
				for _, t := range topics {
					t.Keepalive()
				}
				if err := ping(); err != nil {
					return err
				}
			}
		}
	})
	sub := func(v *visitor, msg *message) error {
		if !filters.Pass(msg) {
			return nil
		}
		wlock.Lock()
		defer wlock.Unlock()
		if err := conn.SetWriteDeadline(time.Now().Add(wsWriteWait)); err != nil {
			return err
		}
		return conn.WriteJSON(msg)
	}
	if err := s.maybeSetRateVisitors(r, v, topics, rateTopics); err != nil {
		return err
	}
	w.Header().Set("Access-Control-Allow-Origin", s.config.AccessControlAllowOrigin) // CORS, allow cross-origin requests
	if poll {
		for _, t := range topics {
			t.Keepalive()
		}
		return s.sendOldMessages(topics, since, scheduled, v, sub)
	}
	subscriberIDs := make([]int, 0)
	for _, t := range topics {
		subscriberIDs = append(subscriberIDs, t.Subscribe(sub, v.MaybeUserID(), cancel))
	}
	defer func() {
		for i, subscriberID := range subscriberIDs {
			topics[i].Unsubscribe(subscriberID) // Order!
		}
	}()
	if err := sub(v, newOpenMessage(topicsStr)); err != nil { // Send out open message
		return err
	}
	if err := s.sendOldMessages(topics, since, scheduled, v, sub); err != nil {
		return err
	}
	err = g.Wait()
	if err != nil && websocket.IsCloseError(err, websocket.CloseNormalClosure, websocket.CloseGoingAway, websocket.CloseAbnormalClosure, websocket.CloseNoStatusReceived) {
		logvr(v, r).Tag(tagWebsocket).Err(err).Fields(websocketErrorContext(err)).Trace("WebSocket connection closed")
		return nil // Normal closures are not errors; note: "1006 (abnormal closure)" is treated as normal, because people disconnect a lot
	}
	return err
}

func parseSubscribeParams(r *http.Request) (poll bool, since sinceMarker, scheduled bool, filters *queryFilter, rateTopics []string, err error) {
	poll = readBoolParam(r, false, "x-poll", "poll", "po")
	scheduled = readBoolParam(r, false, "x-scheduled", "scheduled", "sched")
	since, err = parseSince(r, poll)
	if err != nil {
		return
	}
	filters, err = parseQueryFilters(r)
	if err != nil {
		return
	}
	rateTopics = readCommaSeparatedParam(r, "x-rate-topics", "rate-topics")
	return
}

// maybeSetRateVisitors sets the rate visitor on a topic (v.SetRateVisitor), indicating that all messages published
// to that topic will be rate limited against the rate visitor instead of the publishing visitor.
//
// Setting the rate visitor is ony allowed if the `visitor-subscriber-rate-limiting` setting is enabled, AND
// - auth-file is not set (everything is open by default)
// - or the topic is reserved, and v.user is the owner
// - or the topic is not reserved, and v.user has write access
//
// Note: This TEMPORARILY also registers all topics starting with "up" (= UnifiedPush). This is to ease the transition
// until the Android app will send the "Rate-Topics" header.
func (s *Server) maybeSetRateVisitors(r *http.Request, v *visitor, topics []*topic, rateTopics []string) error {
	// Bail out if not enabled
	if !s.config.VisitorSubscriberRateLimiting {
		return nil
	}

	// Make a list of topics that we'll actually set the RateVisitor on
	eligibleRateTopics := make([]*topic, 0)
	for _, t := range topics {
		if (strings.HasPrefix(t.ID, unifiedPushTopicPrefix) && len(t.ID) == unifiedPushTopicLength) || util.Contains(rateTopics, t.ID) {
			eligibleRateTopics = append(eligibleRateTopics, t)
		}
	}
	if len(eligibleRateTopics) == 0 {
		return nil
	}

	// If access controls are turned off, v has access to everything, and we can set the rate visitor
	if s.userManager == nil {
		return s.setRateVisitors(r, v, eligibleRateTopics)
	}

	// If access controls are enabled, only set rate visitor if
	// - topic is reserved, and v.user is the owner
	// - topic is not reserved, and v.user has write access
	writableRateTopics := make([]*topic, 0)
	for _, t := range topics {
		ownerUserID, err := s.userManager.ReservationOwner(t.ID)
		if err != nil {
			return err
		}
		if ownerUserID == "" {
			if err := s.userManager.Authorize(v.User(), t.ID, user.PermissionWrite); err == nil {
				writableRateTopics = append(writableRateTopics, t)
			}
		} else if ownerUserID == v.MaybeUserID() {
			writableRateTopics = append(writableRateTopics, t)
		}
	}
	return s.setRateVisitors(r, v, writableRateTopics)
}

func (s *Server) setRateVisitors(r *http.Request, v *visitor, rateTopics []*topic) error {
	for _, t := range rateTopics {
		logvr(v, r).
			Tag(tagSubscribe).
			With(t).
			Debug("Setting visitor as rate visitor for topic %s", t.ID)
		t.SetRateVisitor(v)
	}
	return nil
}

// sendOldMessages selects old messages from the messageCache and calls sub for each of them. It uses since as the
// marker, returning only messages that are newer than the marker.
func (s *Server) sendOldMessages(topics []*topic, since sinceMarker, scheduled bool, v *visitor, sub subscriber) error {
	if since.IsNone() {
		return nil
	}
	messages := make([]*message, 0)
	for _, t := range topics {
		topicMessages, err := s.messageCache.Messages(t.ID, since, scheduled)
		if err != nil {
			return err
		}
		messages = append(messages, topicMessages...)
	}
	sort.Slice(messages, func(i, j int) bool {
		return messages[i].Time < messages[j].Time
	})
	for _, m := range messages {
		if err := sub(v, m); err != nil {
			return err
		}
	}
	return nil
}

// parseSince returns a timestamp identifying the time span from which cached messages should be received.
//
// Values in the "since=..." parameter can be either a unix timestamp or a duration (e.g. 12h), or
// "all" for all messages.
func parseSince(r *http.Request, poll bool) (sinceMarker, error) {
	since := readParam(r, "x-since", "since", "si")

	// Easy cases (empty, all, none)
	if since == "" {
		if poll {
			return sinceAllMessages, nil
		}
		return sinceNoMessages, nil
	} else if since == "all" {
		return sinceAllMessages, nil
	} else if since == "none" {
		return sinceNoMessages, nil
	}

	// ID, timestamp, duration
	if validMessageID(since) {
		return newSinceID(since), nil
	} else if s, err := strconv.ParseInt(since, 10, 64); err == nil {
		return newSinceTime(s), nil
	} else if d, err := time.ParseDuration(since); err == nil {
		return newSinceTime(time.Now().Add(-1 * d).Unix()), nil
	}
	return sinceNoMessages, errHTTPBadRequestSinceInvalid
}

func (s *Server) handleOptions(w http.ResponseWriter, _ *http.Request, _ *visitor) error {
	w.Header().Set("Access-Control-Allow-Methods", "GET, PUT, POST, PATCH, DELETE")
	w.Header().Set("Access-Control-Allow-Origin", s.config.AccessControlAllowOrigin) // CORS, allow cross-origin requests
	w.Header().Set("Access-Control-Allow-Headers", "*")                              // CORS, allow auth via JS // FIXME is this terrible?
	return nil
}

func (s *Server) topicFromPath(path string) (*topic, error) {
	parts := strings.Split(path, "/")
	if len(parts) < 2 {
		return nil, errHTTPBadRequestTopicInvalid
	}
	return s.topicFromID(parts[1])
}

func (s *Server) topicsFromPath(path string) ([]*topic, string, error) {
	parts := strings.Split(path, "/")
	if len(parts) < 2 {
		return nil, "", errHTTPBadRequestTopicInvalid
	}
	topicIDs := util.SplitNoEmpty(parts[1], ",")
	topics, err := s.topicsFromIDs(topicIDs...)
	if err != nil {
		return nil, "", errHTTPBadRequestTopicInvalid
	}
	return topics, parts[1], nil
}

func (s *Server) topicsFromIDs(ids ...string) ([]*topic, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	topics := make([]*topic, 0)
	for _, id := range ids {
		if util.Contains(s.config.DisallowedTopics, id) {
			return nil, errHTTPBadRequestTopicDisallowed
		}
		if _, ok := s.topics[id]; !ok {
			if len(s.topics) >= s.config.TotalTopicLimit {
				return nil, errHTTPTooManyRequestsLimitTotalTopics
			}
			s.topics[id] = newTopic(id)
		}
		topics = append(topics, s.topics[id])
	}
	return topics, nil
}

func (s *Server) topicFromID(id string) (*topic, error) {
	topics, err := s.topicsFromIDs(id)
	if err != nil {
		return nil, err
	}
	return topics[0], nil
}

func (s *Server) runSMTPServer() error {
	s.smtpServerBackend = newMailBackend(s.config, s.handle)
	s.smtpServer = smtp.NewServer(s.smtpServerBackend)
	s.smtpServer.Addr = s.config.SMTPServerListen
	s.smtpServer.Domain = s.config.SMTPServerDomain
	s.smtpServer.ReadTimeout = 10 * time.Second
	s.smtpServer.WriteTimeout = 10 * time.Second
	s.smtpServer.MaxMessageBytes = 1024 * 1024 // Must be much larger than message size (headers, multipart, etc.)
	s.smtpServer.MaxRecipients = 1
	s.smtpServer.AllowInsecureAuth = true
	return s.smtpServer.ListenAndServe()
}

func (s *Server) runManager() {
	for {
		select {
		case <-time.After(s.config.ManagerInterval):
			log.
				Tag(tagManager).
				Timing(s.execManager).
				Debug("Manager finished")
		case <-s.closeChan:
			return
		}
	}
}

// runStatsResetter runs once a day (usually midnight UTC) to reset all the visitor's message and
// email counters. The stats are used to display the counters in the web app, as well as for rate limiting.
func (s *Server) runStatsResetter() {
	for {
		runAt := util.NextOccurrenceUTC(s.config.VisitorStatsResetTime, time.Now())
		timer := time.NewTimer(time.Until(runAt))
		log.Tag(tagResetter).Debug("Waiting until %v to reset visitor stats", runAt)
		select {
		case <-timer.C:
			log.Tag(tagResetter).Debug("Running stats resetter")
			s.resetStats()
		case <-s.closeChan:
			log.Tag(tagResetter).Debug("Stopping stats resetter")
			timer.Stop()
			return
		}
	}
}

func (s *Server) resetStats() {
	log.Info("Resetting all visitor stats (daily task)")
	s.mu.Lock()
	defer s.mu.Unlock() // Includes the database query to avoid races with other processes
	for _, v := range s.visitors {
		v.ResetStats()
	}
	if s.userManager != nil {
		if err := s.userManager.ResetStats(); err != nil {
			log.Tag(tagResetter).Warn("Failed to write to database: %s", err.Error())
		}
	}
}

func (s *Server) runFirebaseKeepaliver() {
	if s.firebaseClient == nil {
		return
	}
	v := newVisitor(s.config, s.messageCache, s.userManager, netip.IPv4Unspecified(), nil) // Background process, not a real visitor, uses IP 0.0.0.0
	for {
		select {
		case <-time.After(s.config.FirebaseKeepaliveInterval):
			s.sendToFirebase(v, newKeepaliveMessage(firebaseControlTopic))
		/*
			FIXME: Disable iOS polling entirely for now due to thundering herd problem (see #677)
			       To solve this, we'd have to shard the iOS poll topics to spread out the polling evenly.
			       Given that it's not really necessary to poll, turning it off for now should not have any impact.

			case <-time.After(s.config.FirebasePollInterval):
				s.sendToFirebase(v, newKeepaliveMessage(firebasePollTopic))
		*/
		case <-s.closeChan:
			return
		}
	}
}

func (s *Server) runDelayedSender() {
	for {
		select {
		case <-time.After(s.config.DelayedSenderInterval):
			if err := s.sendDelayedMessages(); err != nil {
				log.Tag(tagPublish).Err(err).Warn("Error sending delayed messages")
			}
		case <-s.closeChan:
			return
		}
	}
}

func (s *Server) sendDelayedMessages() error {
	messages, err := s.messageCache.MessagesDue()
	if err != nil {
		return err
	}
	for _, m := range messages {
		var u *user.User
		if s.userManager != nil && m.User != "" {
			u, err = s.userManager.UserByID(m.User)
			if err != nil {
				log.With(m).Err(err).Warn("Error sending delayed message")
				continue
			}
		}
		v := s.visitor(m.Sender, u)
		if err := s.sendDelayedMessage(v, m); err != nil {
			logvm(v, m).Err(err).Warn("Error sending delayed message")
		}
	}
	return nil
}

func (s *Server) sendDelayedMessage(v *visitor, m *message) error {
	logvm(v, m).Debug("Sending delayed message")
	s.mu.Lock()
	t, ok := s.topics[m.Topic] // If no subscribers, just mark message as published
	s.mu.Unlock()
	if ok {
		go func() {
			// We do not rate-limit messages here, since we've rate limited them in the PUT/POST handler
			if err := t.Publish(v, m); err != nil {
				logvm(v, m).Err(err).Warn("Unable to publish message")
			}
		}()
	}
	if s.firebaseClient != nil { // Firebase subscribers may not show up in topics map
		go s.sendToFirebase(v, m)
	}
	if s.config.UpstreamBaseURL != "" {
		go s.forwardPollRequest(v, m)
	}
	if err := s.messageCache.MarkPublished(m); err != nil {
		return err
	}
	return nil
}

// transformBodyJSON peeks the request body, reads the JSON, and converts it to headers
// before passing it on to the next handler. This is meant to be used in combination with handlePublish.
func (s *Server) transformBodyJSON(next handleFunc) handleFunc {
	return func(w http.ResponseWriter, r *http.Request, v *visitor) error {
		m, err := readJSONWithLimit[publishMessage](r.Body, s.config.MessageLimit*2, false) // 2x to account for JSON format overhead
		if err != nil {
			return err
		}
		if !topicRegex.MatchString(m.Topic) {
			return errHTTPBadRequestTopicInvalid
		}
		if m.Message == "" {
			m.Message = emptyMessageBody
		}
		r.URL.Path = "/" + m.Topic
		r.Body = io.NopCloser(strings.NewReader(m.Message))
		if m.Title != "" {
			r.Header.Set("X-Title", m.Title)
		}
		if m.Priority != 0 {
			r.Header.Set("X-Priority", fmt.Sprintf("%d", m.Priority))
		}
		if m.Tags != nil && len(m.Tags) > 0 {
			r.Header.Set("X-Tags", strings.Join(m.Tags, ","))
		}
		if m.Attach != "" {
			r.Header.Set("X-Attach", m.Attach)
		}
		if m.Filename != "" {
			r.Header.Set("X-Filename", m.Filename)
		}
		if m.Click != "" {
			r.Header.Set("X-Click", m.Click)
		}
		if m.Icon != "" {
			r.Header.Set("X-Icon", m.Icon)
		}
		if len(m.Actions) > 0 {
			actionsStr, err := json.Marshal(m.Actions)
			if err != nil {
				return errHTTPBadRequestMessageJSONInvalid
			}
			r.Header.Set("X-Actions", string(actionsStr))
		}
		if m.Email != "" {
			r.Header.Set("X-Email", m.Email)
		}
		if m.Delay != "" {
			r.Header.Set("X-Delay", m.Delay)
		}
		return next(w, r, v)
	}
}

func (s *Server) transformMatrixJSON(next handleFunc) handleFunc {
	return func(w http.ResponseWriter, r *http.Request, v *visitor) error {
		newRequest, err := newRequestFromMatrixJSON(r, s.config.BaseURL, s.config.MessageLimit)
		if err != nil {
			logvr(v, r).Tag(tagMatrix).Err(err).Debug("Invalid Matrix request")
			if e, ok := err.(*errMatrixPushkeyRejected); ok {
				return writeMatrixResponse(w, e.rejectedPushKey)
			}
			return err
		}
		if err := next(w, newRequest, v); err != nil {
			logvr(v, r).Tag(tagMatrix).Err(err).Debug("Error handling Matrix request")
			return err
		}
		return nil
	}
}

func (s *Server) authorizeTopicWrite(next handleFunc) handleFunc {
	return s.autorizeTopic(next, user.PermissionWrite)
}

func (s *Server) authorizeTopicRead(next handleFunc) handleFunc {
	return s.autorizeTopic(next, user.PermissionRead)
}

func (s *Server) autorizeTopic(next handleFunc, perm user.Permission) handleFunc {
	return func(w http.ResponseWriter, r *http.Request, v *visitor) error {
		if s.userManager == nil {
			return next(w, r, v)
		}
		topics, _, err := s.topicsFromPath(r.URL.Path)
		if err != nil {
			return err
		}
		u := v.User()
		for _, t := range topics {
			if err := s.userManager.Authorize(u, t.ID, perm); err != nil {
				logvr(v, r).With(t).Err(err).Debug("Access to topic %s not authorized", t.ID)
				return errHTTPForbidden.With(t)
			}
		}
		return next(w, r, v)
	}
}

// maybeAuthenticate reads the "Authorization" header and will try to authenticate the user
// if it is set.
//
//   - If auth-file is not configured, immediately return an IP-based visitor
//   - If the header is not set or not supported (anything non-Basic and non-Bearer),
//     an IP-based visitor is returned
//   - If the header is set, authenticate will be called to check the username/password (Basic auth),
//     or the token (Bearer auth), and read the user from the database
//
// This function will ALWAYS return a visitor, even if an error occurs (e.g. unauthorized), so
// that subsequent logging calls still have a visitor context.
func (s *Server) maybeAuthenticate(r *http.Request) (*visitor, error) {
	// Read "Authorization" header value, and exit out early if it's not set
	ip := extractIPAddress(r, s.config.BehindProxy)
	vip := s.visitor(ip, nil)
	if s.userManager == nil {
		return vip, nil
	}
	header, err := readAuthHeader(r)
	if err != nil {
		return vip, err
	} else if !supportedAuthHeader(header) {
		return vip, nil
	}
	// If we're trying to auth, check the rate limiter first
	if !vip.AuthAllowed() {
		return vip, errHTTPTooManyRequestsLimitAuthFailure // Always return visitor, even when error occurs!
	}
	u, err := s.authenticate(r, header)
	if err != nil {
		vip.AuthFailed()
		logr(r).Err(err).Debug("Authentication failed")
		return vip, errHTTPUnauthorized // Always return visitor, even when error occurs!
	}
	// Authentication with user was successful
	return s.visitor(ip, u), nil
}

// authenticate a user based on basic auth username/password (Authorization: Basic ...), or token auth (Authorization: Bearer ...).
// The Authorization header can be passed as a header or the ?auth=... query param. The latter is required only to
// support the WebSocket JavaScript class, which does not support passing headers during the initial request. The auth
// query param is effectively doubly base64 encoded. Its format is base64(Basic base64(user:pass)).
func (s *Server) authenticate(r *http.Request, header string) (user *user.User, err error) {
	if strings.HasPrefix(header, "Bearer") {
		return s.authenticateBearerAuth(r, strings.TrimSpace(strings.TrimPrefix(header, "Bearer")))
	}
	return s.authenticateBasicAuth(r, header)
}

// readAuthHeader reads the raw value of the Authorization header, either from the actual HTTP header,
// or from the ?auth... query parameter
func readAuthHeader(r *http.Request) (string, error) {
	value := strings.TrimSpace(r.Header.Get("Authorization"))
	queryParam := readQueryParam(r, "authorization", "auth")
	if queryParam != "" {
		a, err := base64.RawURLEncoding.DecodeString(queryParam)
		if err != nil {
			return "", err
		}
		value = strings.TrimSpace(string(a))
	}
	return value, nil
}

// supportedAuthHeader returns true only if the Authorization header value starts
// with "Basic" or "Bearer". In particular, an empty value is not supported, and neither
// are things like "WebPush", or "vapid" (see #629).
func supportedAuthHeader(value string) bool {
	value = strings.ToLower(value)
	return strings.HasPrefix(value, "basic ") || strings.HasPrefix(value, "bearer ")
}

func (s *Server) authenticateBasicAuth(r *http.Request, value string) (user *user.User, err error) {
	r.Header.Set("Authorization", value)
	username, password, ok := r.BasicAuth()
	if !ok {
		return nil, errors.New("invalid basic auth")
	} else if username == "" {
		return s.authenticateBearerAuth(r, password) // Treat password as token
	}
	return s.userManager.Authenticate(username, password)
}

func (s *Server) authenticateBearerAuth(r *http.Request, token string) (*user.User, error) {
	u, err := s.userManager.AuthenticateToken(token)
	if err != nil {
		return nil, err
	}
	ip := extractIPAddress(r, s.config.BehindProxy)
	go s.userManager.EnqueueTokenUpdate(token, &user.TokenUpdate{
		LastAccess: time.Now(),
		LastOrigin: ip,
	})
	return u, nil
}

func (s *Server) visitor(ip netip.Addr, user *user.User) *visitor {
	s.mu.Lock()
	defer s.mu.Unlock()
	id := visitorID(ip, user)
	v, exists := s.visitors[id]
	if !exists {
		s.visitors[id] = newVisitor(s.config, s.messageCache, s.userManager, ip, user)
		return s.visitors[id]
	}
	v.Keepalive()
	v.SetUser(user) // Always update with the latest user, may be nil!
	return v
}

func (s *Server) writeJSON(w http.ResponseWriter, v any) error {
	w.Header().Set("Content-Type", "application/json")
	w.Header().Set("Access-Control-Allow-Origin", s.config.AccessControlAllowOrigin) // CORS, allow cross-origin requests
	if err := json.NewEncoder(w).Encode(v); err != nil {
		return err
	}
	return nil
}