feat: consider session expired with margin on getSession() without auto refresh (#1027)

When `autoRefreshToken` is off (or when a tab is in the background) but
`getSession()` is called -- such as in an active Realtime channel,
`getSession()` might return a JWT which will expire while the message is
travelling over the internet. There is one confirmed case of this
happening.

This PR adjusts this using the established `EXPIRY_MARGIN_MS` constant
(which only applies on initial initialization of the client). The
constant's value is brought in line with the `autoRefreshToken` ticks
which run every 30 seconds and refreshing is attempted 3 ticks prior to
the session expiring.

This means that JWTs with an expiry value **less than 90s** will always
refresh the session; which is acceptable.

Author: hf

src/GoTrueClient.ts

@@ -1,5 +1,12 @@
 import GoTrueAdminApi from './GoTrueAdminApi'
-import { DEFAULT_HEADERS, EXPIRY_MARGIN, GOTRUE_URL, STORAGE_KEY } from './lib/constants'
+import {
+  DEFAULT_HEADERS,
+  EXPIRY_MARGIN_MS,
+  AUTO_REFRESH_TICK_DURATION_MS,
+  AUTO_REFRESH_TICK_THRESHOLD,
+  GOTRUE_URL,
+  STORAGE_KEY,
+} from './lib/constants'
 import {
   AuthError,
   AuthImplicitGrantRedirectError,
@@ -109,13 +116,6 @@ const DEFAULT_OPTIONS: Omit<Required<GoTrueClientOptions>, 'fetch' | 'storage' |
   hasCustomAuthorizationHeader: false,
 }
 
-/** Current session will be checked for refresh at this interval. */
-const AUTO_REFRESH_TICK_DURATION = 30 * 1000
-
-/**
- * A token refresh will be attempted this many ticks before the current session expires. */
-const AUTO_REFRESH_TICK_THRESHOLD = 3
-
 async function lockNoOp<R>(name: string, acquireTimeout: number, fn: () => Promise<R>): Promise<R> {
   return await fn()
 }
@@ -1107,8 +1107,13 @@ export default class GoTrueClient {
         return { data: { session: null }, error: null }
       }
 
+      // A session is considered expired before the access token _actually_
+      // expires. When the autoRefreshToken option is off (or when the tab is
+      // in the background), very eager users of getSession() -- like
+      // realtime-js -- might send a valid JWT which will expire by the time it
+      // reaches the server.
       const hasExpired = currentSession.expires_at
-        ? currentSession.expires_at <= Date.now() / 1000
+        ? currentSession.expires_at * 1000 - Date.now() < EXPIRY_MARGIN_MS
         : false
 
       this._debug(
@@ -1503,7 +1508,7 @@ export default class GoTrueClient {
       }
 
       const actuallyExpiresIn = expiresAt - timeNow
-      if (actuallyExpiresIn * 1000 <= AUTO_REFRESH_TICK_DURATION) {
+      if (actuallyExpiresIn * 1000 <= AUTO_REFRESH_TICK_DURATION_MS) {
         console.warn(
           `@supabase/gotrue-js: Session as retrieved from URL expires in ${actuallyExpiresIn}s, should have been closer to ${expiresIn}s`
         )
@@ -1850,7 +1855,7 @@ export default class GoTrueClient {
             error &&
             isAuthRetryableFetchError(error) &&
             // retryable only if the request can be sent before the backoff overflows the tick duration
-            Date.now() + nextBackOffInterval - startedAt < AUTO_REFRESH_TICK_DURATION
+            Date.now() + nextBackOffInterval - startedAt < AUTO_REFRESH_TICK_DURATION_MS
           )
         }
       )
@@ -1923,12 +1928,12 @@ export default class GoTrueClient {
         return
       }
 
-      const timeNow = Math.round(Date.now() / 1000)
-      const expiresWithMargin = (currentSession.expires_at ?? Infinity) < timeNow + EXPIRY_MARGIN
+      const expiresWithMargin =
+        (currentSession.expires_at ?? Infinity) * 1000 - Date.now() < EXPIRY_MARGIN_MS
 
       this._debug(
         debugName,
-        `session has${expiresWithMargin ? '' : ' not'} expired with margin of ${EXPIRY_MARGIN}s`
+        `session has${expiresWithMargin ? '' : ' not'} expired with margin of ${EXPIRY_MARGIN_MS}s`
       )
 
       if (expiresWithMargin) {
@@ -2101,7 +2106,7 @@ export default class GoTrueClient {
 
     this._debug('#_startAutoRefresh()')
 
-    const ticker = setInterval(() => this._autoRefreshTokenTick(), AUTO_REFRESH_TICK_DURATION)
+    const ticker = setInterval(() => this._autoRefreshTokenTick(), AUTO_REFRESH_TICK_DURATION_MS)
     this.autoRefreshTicker = ticker
 
     if (ticker && typeof ticker === 'object' && typeof ticker.unref === 'function') {
@@ -2208,12 +2213,12 @@ export default class GoTrueClient {
 
               // session will expire in this many ticks (or has already expired if <= 0)
               const expiresInTicks = Math.floor(
-                (session.expires_at * 1000 - now) / AUTO_REFRESH_TICK_DURATION
+                (session.expires_at * 1000 - now) / AUTO_REFRESH_TICK_DURATION_MS
               )
 
               this._debug(
                 '#_autoRefreshTokenTick()',
-                `access token expires in ${expiresInTicks} ticks, a tick lasts ${AUTO_REFRESH_TICK_DURATION}ms, refresh threshold is ${AUTO_REFRESH_TICK_THRESHOLD} ticks`
+                `access token expires in ${expiresInTicks} ticks, a tick lasts ${AUTO_REFRESH_TICK_DURATION_MS}ms, refresh threshold is ${AUTO_REFRESH_TICK_THRESHOLD} ticks`
               )
 
               if (expiresInTicks <= AUTO_REFRESH_TICK_THRESHOLD) {

src/lib/constants.ts

@@ -1,9 +1,21 @@
 import { version } from './version'
+
+/** Current session will be checked for refresh at this interval. */
+export const AUTO_REFRESH_TICK_DURATION_MS = 30 * 1000
+
+/**
+ * A token refresh will be attempted this many ticks before the current session expires. */
+export const AUTO_REFRESH_TICK_THRESHOLD = 3
+
+/*
+ * Earliest time before an access token expires that the session should be refreshed.
+ */
+export const EXPIRY_MARGIN_MS = AUTO_REFRESH_TICK_THRESHOLD * AUTO_REFRESH_TICK_DURATION_MS
+
 export const GOTRUE_URL = 'http://localhost:9999'
 export const STORAGE_KEY = 'supabase.auth.token'
 export const AUDIENCE = ''
 export const DEFAULT_HEADERS = { 'X-Client-Info': `gotrue-js/${version}` }
-export const EXPIRY_MARGIN = 10 // in seconds
 export const NETWORK_FAILURE = {
   MAX_RETRIES: 10,
   RETRY_INTERVAL: 2, // in deciseconds