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tailscale/client/web/web.go

824 lines
25 KiB
Go

// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
// Package web provides the Tailscale client for web.
package web
import (
"context"
"crypto/rand"
"encoding/json"
"errors"
"fmt"
"io"
"log"
"net/http"
"net/netip"
"os"
"path/filepath"
"slices"
"strings"
"sync"
"time"
"github.com/gorilla/csrf"
"tailscale.com/client/tailscale"
"tailscale.com/client/tailscale/apitype"
"tailscale.com/envknob"
"tailscale.com/ipn"
"tailscale.com/ipn/ipnstate"
"tailscale.com/licenses"
"tailscale.com/net/netutil"
"tailscale.com/net/tsaddr"
"tailscale.com/tailcfg"
"tailscale.com/types/logger"
"tailscale.com/util/httpm"
"tailscale.com/version/distro"
)
// ListenPort is the static port used for the web client when run inside tailscaled.
// (5252 are the numbers above the letters "TSTS" on a qwerty keyboard.)
const ListenPort = 5252
// Server is the backend server for a Tailscale web client.
type Server struct {
mode ServerMode
logf logger.Logf
lc *tailscale.LocalClient
timeNow func() time.Time
// devMode indicates that the server run with frontend assets
// served by a Vite dev server, allowing for local development
// on the web client frontend.
devMode bool
cgiMode bool
pathPrefix string
apiHandler http.Handler // serves api endpoints; csrf-protected
assetsHandler http.Handler // serves frontend assets
assetsCleanup func() // called from Server.Shutdown
// browserSessions is an in-memory cache of browser sessions for the
// full management web client, which is only accessible over Tailscale.
//
// Users obtain a valid browser session by connecting to the web client
// over Tailscale and verifying their identity by authenticating on the
// control server.
//
// browserSessions get reset on every Server restart.
//
// The map provides a lookup of the session by cookie value
// (browserSession.ID => browserSession).
browserSessions sync.Map
}
// ServerMode specifies the mode of a running web.Server.
type ServerMode string
const (
// LoginServerMode serves a readonly login client for logging a
// node into a tailnet, and viewing a readonly interface of the
// node's current Tailscale settings.
//
// In this mode, API calls are authenticated via platform auth.
LoginServerMode ServerMode = "login"
// ManageServerMode serves a management client for editing tailscale
// settings of a node.
//
// This mode restricts the app to only being assessible over Tailscale,
// and API calls are authenticated via browser sessions associated with
// the source's Tailscale identity. If the source browser does not have
// a valid session, a readonly version of the app is displayed.
ManageServerMode ServerMode = "manage"
// LegacyServerMode serves the legacy web client, visible to users
// prior to release of tailscale/corp#14335.
LegacyServerMode ServerMode = "legacy"
)
var (
exitNodeRouteV4 = netip.MustParsePrefix("0.0.0.0/0")
exitNodeRouteV6 = netip.MustParsePrefix("::/0")
)
// ServerOpts contains options for constructing a new Server.
type ServerOpts struct {
// Mode specifies the mode of web client being constructed.
Mode ServerMode
// CGIMode indicates if the server is running as a CGI script.
CGIMode bool
// PathPrefix is the URL prefix added to requests by CGI or reverse proxy.
PathPrefix string
// LocalClient is the tailscale.LocalClient to use for this web server.
// If nil, a new one will be created.
LocalClient *tailscale.LocalClient
// TimeNow optionally provides a time function.
// time.Now is used as default.
TimeNow func() time.Time
// Logf optionally provides a logger function.
// log.Printf is used as default.
Logf logger.Logf
}
// NewServer constructs a new Tailscale web client server.
// If err is empty, s is always non-nil.
// ctx is only required to live the duration of the NewServer call,
// and not the lifespan of the web server.
func NewServer(opts ServerOpts) (s *Server, err error) {
switch opts.Mode {
case LoginServerMode, ManageServerMode, LegacyServerMode:
// valid types
case "":
return nil, fmt.Errorf("must specify a Mode")
default:
return nil, fmt.Errorf("invalid Mode provided")
}
if opts.LocalClient == nil {
opts.LocalClient = &tailscale.LocalClient{}
}
s = &Server{
mode: opts.Mode,
logf: opts.Logf,
devMode: envknob.Bool("TS_DEBUG_WEB_CLIENT_DEV"),
lc: opts.LocalClient,
cgiMode: opts.CGIMode,
pathPrefix: opts.PathPrefix,
timeNow: opts.TimeNow,
}
if s.timeNow == nil {
s.timeNow = time.Now
}
if s.logf == nil {
s.logf = log.Printf
}
s.assetsHandler, s.assetsCleanup = assetsHandler(s.devMode)
var metric string // clientmetric to report on startup
// Create handler for "/api" requests with CSRF protection.
// We don't require secure cookies, since the web client is regularly used
// on network appliances that are served on local non-https URLs.
// The client is secured by limiting the interface it listens on,
// or by authenticating requests before they reach the web client.
csrfProtect := csrf.Protect(s.csrfKey(), csrf.Secure(false))
if s.mode == LoginServerMode {
s.apiHandler = csrfProtect(http.HandlerFunc(s.serveLoginAPI))
metric = "web_login_client_initialization"
} else {
s.apiHandler = csrfProtect(http.HandlerFunc(s.serveAPI))
metric = "web_client_initialization"
}
// Don't block startup on reporting metric.
// Report in separate go routine with 5 second timeout.
go func() {
ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
defer cancel()
s.lc.IncrementCounter(ctx, metric, 1)
}()
return s, nil
}
func (s *Server) Shutdown() {
s.logf("web.Server: shutting down")
if s.assetsCleanup != nil {
s.assetsCleanup()
}
}
// ServeHTTP processes all requests for the Tailscale web client.
func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
handler := s.serve
// if path prefix is defined, strip it from requests.
if s.pathPrefix != "" {
handler = enforcePrefix(s.pathPrefix, handler)
}
handler(w, r)
}
func (s *Server) serve(w http.ResponseWriter, r *http.Request) {
if s.mode == ManageServerMode {
// In manage mode, requests must be sent directly to the bare Tailscale IP address.
// If a request comes in on any other hostname, redirect.
if s.requireTailscaleIP(w, r) {
return // user was redirected
}
// serve HTTP 204 on /ok requests as connectivity check
if r.Method == httpm.GET && r.URL.Path == "/ok" {
w.WriteHeader(http.StatusNoContent)
return
}
if !s.devMode {
w.Header().Set("X-Frame-Options", "DENY")
// TODO: use CSP nonce or hash to eliminate need for unsafe-inline
w.Header().Set("Content-Security-Policy", "default-src 'self' 'unsafe-inline'; img-src * data:")
w.Header().Set("Cross-Origin-Resource-Policy", "same-origin")
}
}
if strings.HasPrefix(r.URL.Path, "/api/") {
switch {
case r.URL.Path == "/api/auth" && r.Method == httpm.GET:
s.serveAPIAuth(w, r) // serve auth status
return
case r.URL.Path == "/api/auth/session/new" && r.Method == httpm.GET:
s.serveAPIAuthSessionNew(w, r) // create new session
return
case r.URL.Path == "/api/auth/session/wait" && r.Method == httpm.GET:
s.serveAPIAuthSessionWait(w, r) // wait for session to be authorized
return
}
if ok := s.authorizeRequest(w, r); !ok {
http.Error(w, "not authorized", http.StatusUnauthorized)
return
}
// Pass API requests through to the API handler.
s.apiHandler.ServeHTTP(w, r)
return
}
if !s.devMode {
s.lc.IncrementCounter(r.Context(), "web_client_page_load", 1)
}
s.assetsHandler.ServeHTTP(w, r)
}
// requireTailscaleIP redirects an incoming request if the HTTP request was not made to a bare Tailscale IP address.
// The request will be redirected to the Tailscale IP, port 5252, with the original request path.
// This allows any custom hostname to be used to access the device, but protects against DNS rebinding attacks.
// Returns true if the request has been fully handled, either be returning a redirect or an HTTP error.
func (s *Server) requireTailscaleIP(w http.ResponseWriter, r *http.Request) (handled bool) {
const (
ipv4ServiceHost = tsaddr.TailscaleServiceIPString
ipv6ServiceHost = "[" + tsaddr.TailscaleServiceIPv6String + "]"
)
// allow requests on quad-100 (or ipv6 equivalent)
if r.Host == ipv4ServiceHost || r.Host == ipv6ServiceHost {
return false
}
st, err := s.lc.StatusWithoutPeers(r.Context())
if err != nil {
s.logf("error getting status: %v", err)
http.Error(w, "internal error", http.StatusInternalServerError)
return true
}
var ipv4 string // store the first IPv4 address we see for redirect later
for _, ip := range st.Self.TailscaleIPs {
if ip.Is4() {
if r.Host == fmt.Sprintf("%s:%d", ip, ListenPort) {
return false
}
ipv4 = ip.String()
}
if ip.Is6() && r.Host == fmt.Sprintf("[%s]:%d", ip, ListenPort) {
return false
}
}
newURL := *r.URL
newURL.Host = fmt.Sprintf("%s:%d", ipv4, ListenPort)
http.Redirect(w, r, newURL.String(), http.StatusMovedPermanently)
return true
}
// authorizeRequest reports whether the request from the web client
// is authorized to be completed.
// It reports true if the request is authorized, and false otherwise.
// authorizeRequest manages writing out any relevant authorization
// errors to the ResponseWriter itself.
func (s *Server) authorizeRequest(w http.ResponseWriter, r *http.Request) (ok bool) {
if s.mode == ManageServerMode { // client using tailscale auth
_, err := s.lc.WhoIs(r.Context(), r.RemoteAddr)
switch {
case err != nil:
// All requests must be made over tailscale.
http.Error(w, "must access over tailscale", http.StatusUnauthorized)
return false
case r.URL.Path == "/api/data" && r.Method == httpm.GET:
// Readonly endpoint allowed without browser session.
return true
case strings.HasPrefix(r.URL.Path, "/api/"):
// All other /api/ endpoints require a valid browser session.
//
// TODO(sonia): s.getSession calls whois again,
// should try and use the above call instead of running another
// localapi request.
session, _, err := s.getSession(r)
if err != nil || !session.isAuthorized(s.timeNow()) {
http.Error(w, "no valid session", http.StatusUnauthorized)
return false
}
return true
default:
// No additional auth on non-api (assets, index.html, etc).
return true
}
}
// Client using system-specific auth.
switch distro.Get() {
case distro.Synology:
resp, _ := authorizeSynology(r)
return resp.OK
case distro.QNAP:
resp, _ := authorizeQNAP(r)
return resp.OK
default:
return true // no additional auth for this distro
}
}
// serveLoginAPI serves requests for the web login client.
// It should only be called by Server.ServeHTTP, via Server.apiHandler,
// which protects the handler using gorilla csrf.
func (s *Server) serveLoginAPI(w http.ResponseWriter, r *http.Request) {
w.Header().Set("X-CSRF-Token", csrf.Token(r))
if r.URL.Path != "/api/data" { // only endpoint allowed for login client
http.Error(w, "invalid endpoint", http.StatusNotFound)
return
}
switch r.Method {
case httpm.GET:
// TODO(soniaappasamy): we may want a minimal node data response here
s.serveGetNodeData(w, r)
return
}
http.Error(w, "invalid endpoint", http.StatusNotFound)
return
}
type authType string
var (
synoAuth authType = "synology" // user needs a SynoToken for subsequent API calls
tailscaleAuth authType = "tailscale" // user needs to complete Tailscale check mode
)
type authResponse struct {
OK bool `json:"ok"` // true when user has valid auth session
AuthNeeded authType `json:"authNeeded,omitempty"` // filled when user needs to complete a specific type of auth
}
// serverAPIAuth handles requests to the /api/auth endpoint
// and returns an authResponse indicating the current auth state and any steps the user needs to take.
func (s *Server) serveAPIAuth(w http.ResponseWriter, r *http.Request) {
var resp authResponse
session, _, err := s.getSession(r)
switch {
case err != nil && errors.Is(err, errNotUsingTailscale):
// not using tailscale, so perform platform auth
switch distro.Get() {
case distro.Synology:
resp, err = authorizeSynology(r)
if err != nil {
http.Error(w, err.Error(), http.StatusUnauthorized)
return
}
case distro.QNAP:
resp, err = authorizeQNAP(r)
if err != nil {
http.Error(w, err.Error(), http.StatusUnauthorized)
return
}
default:
resp.OK = true // no additional auth for this distro
}
case err != nil && (errors.Is(err, errNotOwner) ||
errors.Is(err, errNotUsingTailscale) ||
errors.Is(err, errTaggedLocalSource) ||
errors.Is(err, errTaggedRemoteSource)):
// These cases are all restricted to the readonly view.
// No auth action to take.
resp = authResponse{OK: false}
case err != nil && !errors.Is(err, errNoSession):
// Any other error.
http.Error(w, err.Error(), http.StatusInternalServerError)
return
case session.isAuthorized(s.timeNow()):
resp = authResponse{OK: true}
default:
resp = authResponse{OK: false, AuthNeeded: tailscaleAuth}
}
writeJSON(w, resp)
}
type newSessionAuthResponse struct {
AuthURL string `json:"authUrl,omitempty"`
}
// serveAPIAuthSessionNew handles requests to the /api/auth/session/new endpoint.
func (s *Server) serveAPIAuthSessionNew(w http.ResponseWriter, r *http.Request) {
session, whois, err := s.getSession(r)
if err != nil && !errors.Is(err, errNoSession) {
// Source associated with request not allowed to create
// a session for this web client.
http.Error(w, err.Error(), http.StatusUnauthorized)
return
}
if session == nil {
// Create a new session.
// If one already existed, we return that authURL rather than creating a new one.
session, err = s.newSession(r.Context(), whois)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
// Set the cookie on browser.
http.SetCookie(w, &http.Cookie{
Name: sessionCookieName,
Value: session.ID,
Raw: session.ID,
Path: "/",
Expires: session.expires(),
})
}
writeJSON(w, newSessionAuthResponse{AuthURL: session.AuthURL})
}
// serveAPIAuthSessionWait handles requests to the /api/auth/session/wait endpoint.
func (s *Server) serveAPIAuthSessionWait(w http.ResponseWriter, r *http.Request) {
session, _, err := s.getSession(r)
if err != nil {
http.Error(w, err.Error(), http.StatusUnauthorized)
return
}
if session.isAuthorized(s.timeNow()) {
return // already authorized
}
if err := s.awaitUserAuth(r.Context(), session); err != nil {
http.Error(w, err.Error(), http.StatusUnauthorized)
return
}
}
// serveAPI serves requests for the web client api.
// It should only be called by Server.ServeHTTP, via Server.apiHandler,
// which protects the handler using gorilla csrf.
func (s *Server) serveAPI(w http.ResponseWriter, r *http.Request) {
w.Header().Set("X-CSRF-Token", csrf.Token(r))
path := strings.TrimPrefix(r.URL.Path, "/api")
switch {
case path == "/data":
switch r.Method {
case httpm.GET:
s.serveGetNodeData(w, r)
case httpm.POST:
s.servePostNodeUpdate(w, r)
default:
http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
}
return
case strings.HasPrefix(path, "/local/"):
s.proxyRequestToLocalAPI(w, r)
return
}
http.Error(w, "invalid endpoint", http.StatusNotFound)
}
type nodeData struct {
Profile tailcfg.UserProfile
Status string
DeviceName string
IP string
AdvertiseExitNode bool
AdvertiseRoutes string
LicensesURL string
TUNMode bool
IsSynology bool
DSMVersion int // 6 or 7, if IsSynology=true
IsUnraid bool
UnraidToken string
IPNVersion string
DebugMode string // empty when not running in any debug mode
URLPrefix string // if set, the URL prefix the client is served behind
}
func (s *Server) serveGetNodeData(w http.ResponseWriter, r *http.Request) {
st, err := s.lc.Status(r.Context())
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
prefs, err := s.lc.GetPrefs(r.Context())
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
profile := st.User[st.Self.UserID]
deviceName := strings.Split(st.Self.DNSName, ".")[0]
versionShort := strings.Split(st.Version, "-")[0]
var debugMode string
if s.mode == ManageServerMode {
debugMode = "full"
} else if s.mode == LoginServerMode {
debugMode = "login"
}
data := &nodeData{
Profile: profile,
Status: st.BackendState,
DeviceName: deviceName,
LicensesURL: licenses.LicensesURL(),
TUNMode: st.TUN,
IsSynology: distro.Get() == distro.Synology || envknob.Bool("TS_FAKE_SYNOLOGY"),
DSMVersion: distro.DSMVersion(),
IsUnraid: distro.Get() == distro.Unraid,
UnraidToken: os.Getenv("UNRAID_CSRF_TOKEN"),
IPNVersion: versionShort,
URLPrefix: strings.TrimSuffix(s.pathPrefix, "/"),
DebugMode: debugMode, // TODO(sonia,will): just pass back s.mode directly?
}
for _, r := range prefs.AdvertiseRoutes {
if r == exitNodeRouteV4 || r == exitNodeRouteV6 {
data.AdvertiseExitNode = true
} else {
if data.AdvertiseRoutes != "" {
data.AdvertiseRoutes += ","
}
data.AdvertiseRoutes += r.String()
}
}
if len(st.TailscaleIPs) != 0 {
data.IP = st.TailscaleIPs[0].String()
}
writeJSON(w, *data)
}
type nodeUpdate struct {
AdvertiseRoutes string
AdvertiseExitNode bool
Reauthenticate bool
ForceLogout bool
}
func (s *Server) servePostNodeUpdate(w http.ResponseWriter, r *http.Request) {
defer r.Body.Close()
st, err := s.lc.Status(r.Context())
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
var postData nodeUpdate
type mi map[string]any
if err := json.NewDecoder(r.Body).Decode(&postData); err != nil {
w.WriteHeader(400)
json.NewEncoder(w).Encode(mi{"error": err.Error()})
return
}
prefs, err := s.lc.GetPrefs(r.Context())
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
isCurrentlyExitNode := slices.Contains(prefs.AdvertiseRoutes, exitNodeRouteV4) || slices.Contains(prefs.AdvertiseRoutes, exitNodeRouteV6)
if postData.AdvertiseExitNode != isCurrentlyExitNode {
if postData.AdvertiseExitNode {
s.lc.IncrementCounter(r.Context(), "web_client_advertise_exitnode_enable", 1)
} else {
s.lc.IncrementCounter(r.Context(), "web_client_advertise_exitnode_disable", 1)
}
}
routes, err := netutil.CalcAdvertiseRoutes(postData.AdvertiseRoutes, postData.AdvertiseExitNode)
if err != nil {
w.WriteHeader(http.StatusInternalServerError)
json.NewEncoder(w).Encode(mi{"error": err.Error()})
return
}
mp := &ipn.MaskedPrefs{
AdvertiseRoutesSet: true,
WantRunningSet: true,
}
mp.Prefs.WantRunning = true
mp.Prefs.AdvertiseRoutes = routes
s.logf("Doing edit: %v", mp.Pretty())
if _, err := s.lc.EditPrefs(r.Context(), mp); err != nil {
w.WriteHeader(http.StatusInternalServerError)
json.NewEncoder(w).Encode(mi{"error": err.Error()})
return
}
w.Header().Set("Content-Type", "application/json")
var reauth, logout bool
if postData.Reauthenticate {
reauth = true
}
if postData.ForceLogout {
logout = true
}
s.logf("tailscaleUp(reauth=%v, logout=%v) ...", reauth, logout)
url, err := s.tailscaleUp(r.Context(), st, postData)
s.logf("tailscaleUp = (URL %v, %v)", url != "", err)
if err != nil {
w.WriteHeader(http.StatusInternalServerError)
json.NewEncoder(w).Encode(mi{"error": err.Error()})
return
}
if url != "" {
json.NewEncoder(w).Encode(mi{"url": url})
} else {
io.WriteString(w, "{}")
}
}
func (s *Server) tailscaleUp(ctx context.Context, st *ipnstate.Status, postData nodeUpdate) (authURL string, retErr error) {
if postData.ForceLogout {
if err := s.lc.Logout(ctx); err != nil {
return "", fmt.Errorf("Logout error: %w", err)
}
return "", nil
}
origAuthURL := st.AuthURL
isRunning := st.BackendState == ipn.Running.String()
forceReauth := postData.Reauthenticate
if !forceReauth {
if origAuthURL != "" {
return origAuthURL, nil
}
if isRunning {
return "", nil
}
}
// printAuthURL reports whether we should print out the
// provided auth URL from an IPN notify.
printAuthURL := func(url string) bool {
return url != origAuthURL
}
watchCtx, cancelWatch := context.WithCancel(ctx)
defer cancelWatch()
watcher, err := s.lc.WatchIPNBus(watchCtx, 0)
if err != nil {
return "", err
}
defer watcher.Close()
go func() {
if !isRunning {
s.lc.Start(ctx, ipn.Options{})
}
if forceReauth {
s.lc.StartLoginInteractive(ctx)
}
}()
for {
n, err := watcher.Next()
if err != nil {
return "", err
}
if n.ErrMessage != nil {
msg := *n.ErrMessage
return "", fmt.Errorf("backend error: %v", msg)
}
if url := n.BrowseToURL; url != nil && printAuthURL(*url) {
return *url, nil
}
}
}
// proxyRequestToLocalAPI proxies the web API request to the localapi.
//
// The web API request path is expected to exactly match a localapi path,
// with prefix /api/local/ rather than /localapi/.
//
// If the localapi path is not included in localapiAllowlist,
// the request is rejected.
func (s *Server) proxyRequestToLocalAPI(w http.ResponseWriter, r *http.Request) {
path := strings.TrimPrefix(r.URL.Path, "/api/local")
if r.URL.Path == path { // missing prefix
http.Error(w, "invalid request", http.StatusBadRequest)
return
}
if !slices.Contains(localapiAllowlist, path) {
http.Error(w, fmt.Sprintf("%s not allowed from localapi proxy", path), http.StatusForbidden)
return
}
localAPIURL := "http://" + apitype.LocalAPIHost + "/localapi" + path
req, err := http.NewRequestWithContext(r.Context(), r.Method, localAPIURL, r.Body)
if err != nil {
http.Error(w, "failed to construct request", http.StatusInternalServerError)
return
}
// Make request to tailscaled localapi.
resp, err := s.lc.DoLocalRequest(req)
if err != nil {
http.Error(w, err.Error(), resp.StatusCode)
return
}
defer resp.Body.Close()
// Send response back to web frontend.
w.Header().Set("Content-Type", resp.Header.Get("Content-Type"))
w.WriteHeader(resp.StatusCode)
if _, err := io.Copy(w, resp.Body); err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
}
}
// localapiAllowlist is an allowlist of localapi endpoints the
// web client is allowed to proxy to the client's localapi.
//
// Rather than exposing all localapi endpoints over the proxy,
// this limits to just the ones actually used from the web
// client frontend.
//
// TODO(sonia,will): Shouldn't expand this beyond the existing
// localapi endpoints until the larger web client auth story
// is worked out (tailscale/corp#14335).
var localapiAllowlist = []string{
"/v0/logout",
}
// csrfKey returns a key that can be used for CSRF protection.
// If an error occurs during key creation, the error is logged and the active process terminated.
// If the server is running in CGI mode, the key is cached to disk and reused between requests.
// If an error occurs during key storage, the error is logged and the active process terminated.
func (s *Server) csrfKey() []byte {
csrfFile := filepath.Join(os.TempDir(), "tailscale-web-csrf.key")
// if running in CGI mode, try to read from disk, but ignore errors
if s.cgiMode {
key, _ := os.ReadFile(csrfFile)
if len(key) == 32 {
return key
}
}
// create a new key
key := make([]byte, 32)
if _, err := rand.Read(key); err != nil {
log.Fatalf("error generating CSRF key: %v", err)
}
// if running in CGI mode, try to write the newly created key to disk, and exit if it fails.
if s.cgiMode {
if err := os.WriteFile(csrfFile, key, 0600); err != nil {
log.Fatalf("unable to store CSRF key: %v", err)
}
}
return key
}
// enforcePrefix returns a HandlerFunc that enforces a given path prefix is used in requests,
// then strips it before invoking h.
// Unlike http.StripPrefix, it does not return a 404 if the prefix is not present.
// Instead, it returns a redirect to the prefix path.
func enforcePrefix(prefix string, h http.HandlerFunc) http.HandlerFunc {
if prefix == "" {
return h
}
// ensure that prefix always has both a leading and trailing slash so
// that relative links for JS and CSS assets work correctly.
if !strings.HasPrefix(prefix, "/") {
prefix = "/" + prefix
}
if !strings.HasSuffix(prefix, "/") {
prefix += "/"
}
return func(w http.ResponseWriter, r *http.Request) {
if !strings.HasPrefix(r.URL.Path, prefix) {
http.Redirect(w, r, prefix, http.StatusFound)
return
}
prefix = strings.TrimSuffix(prefix, "/")
http.StripPrefix(prefix, h).ServeHTTP(w, r)
}
}
func writeJSON(w http.ResponseWriter, data any) {
w.Header().Set("Content-Type", "application/json")
if err := json.NewEncoder(w).Encode(data); err != nil {
w.Header().Set("Content-Type", "text/plain")
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
}