Firestore cannot connect to the local emulator on iOS 26.5 (physical > device AND simulator) — works on the iOS 26.1 simulator with identical code. gRPC cleartext channel fails UNAVAILABLE while raw cleartext HTTP/2 from the same process succeeds

[davidclayman]

Description

⚡ Controlled A/B (the headline)

Identical app build, identical emulator, identical host config:

Environment	Result
iOS 26.1 simulator, localhost:8080	✅ WORKS — writes land; a rules-denied probe read returns PERMISSION_DENIED (server round-trip proven)
iOS 26.5 simulator, localhost:8080	❌ UNAVAILABLE, no traffic reaches the emulator
Physical iPhone 13, iOS 26.5.2, LAN host	❌ UNAVAILABLE, zero packets on the wire

⇒ Regression in iOS 26.5 (runtime/network stack) × firebase-ios-sdk 12.15.0
(gRPC-C++ 1.69.0) cleartext channels.

Environment

• firebase-ios-sdk 12.15.0 AND 12.16.0 — both reproduce (gRPC-C++ 1.69.0 in
  both; 12.16.0 retested 2026-07-16 on the iOS 26.5 simulator via
  $FirebaseSDKVersion override: identical hang, zero traffic reaches the
  emulator). Via FlutterFire: cloud_firestore 6.x, latest.
• Physical iPhone 13, iOS 26.5.2; Xcode 26.6; release build (XCUITest-driven)
• Firestore emulator (firebase-tools) on a Mac at 192.168.1.17:8080, bound 0.0.0.0
• App configured with FIRFirestoreSettings.host = "192.168.1.17:8080", sslEnabled = NO
  (equivalently useEmulator — both tried, identical result)

Symptom

Every Firestore operation fails; the log repeats:

[FirebaseFirestore][I-FST000001] WatchStream (...) Stream error: 'Unknown: An internal error has occurred'
[FirebaseFirestore][I-FST000001] WriteStream (...) Stream error: 'Unknown: An internal error has occurred'

Dart-side (FlutterFire) surfaces [cloud_firestore/unavailable].

The same app on a physical Android device on the same Wi-Fi, against the same
emulator and host, works. iOS Simulator with localhost also works.

Reproducing the issue

Repro sketch

1. Firestore emulator on a Mac, bound 0.0.0.0, note the Mac's LAN IP.
2. iOS app on a physical iOS 26 device: settings.host = "<mac-ip>:8080",
   sslEnabled = false; perform any getDocument.
3. Observe UNAVAILABLE + zero connections arriving at the emulator, while a plain
   URLSession/socket HTTP or h2c request from the same app reaches it fine.

Evidence that the network path is NOT the problem

All probes run from inside the failing app process (dart:io = BSD sockets), at
the moment Firestore is failing:

Probe	Result
HTTP/1.1 GET → http://192.168.1.17:8080/	✅ 200 in ~20 ms
Raw cleartext HTTP/2: h2c preface + empty SETTINGS over a plain TCP socket to the same host:port	✅ server replies with its SETTINGS frame
HTTPS GET → https://firestore.googleapis.com/	✅ TLS fine
Firestore default instance (settings verified host=192.168.1.17:8080 ssl=false)	❌ UNAVAILABLE
Firestore fresh instanceFor(databaseId:) instance (settings delivered at creation — rules out stale native settings)	❌ identical UNAVAILABLE

Wire-side observation on the Mac during a run (lsof sampling at 1 Hz + emulator
connection logs): the Firestore gRPC channel sends zero packets to the host —
no TCP connection to :8080 is ever attempted (the only connections logged are the
probes' own). The failure is generated on-device, before any wire contact.

Ruled out

• iOS Local Network permission: granted (toggle ON; plain HTTP from the app works)
• ATS: NSAllowsLocalNetworking + NSLocalNetworkUsageDescription present (and IP
  literals are ATS-exempt anyway)
• Wi-Fi HTTP proxy: off; same result
• GRPC_CFSTREAM=0 (set via setenv before first Firestore use): no effect
• SDK version: already the newest pinned by current FlutterFire

Suspicion

The gRPC transport used by Firestore on iOS 26 fails to establish a cleartext
channel to a non-localhost target on a physical device — reminiscent of the
iOS 18.4 simulator issue (#firestore emulator gRPC failure) that required a gRPC
bump. The channel appears to die before connecting (no packets), i.e. inside
transport/EventEngine setup rather than on the wire.

Firebase SDK Version

12.15.0

Xcode Version

26.6

Installation Method

CocoaPods

Firebase Product(s)

Firestore

Targeted Platforms

iOS

Relevant Log Output

If using Swift Package Manager, the project's Package.resolved

Expand Package.resolved snippet

Replace this line with the contents of your Package.resolved.

If using CocoaPods, the project's Podfile.lock

I cut out a lot to stay under the body byte limit for this submission.

PODS:

• Firebase/Auth (12.15.0):
  • Firebase/CoreOnly
  • FirebaseAuth (~> 12.15.0)
• Firebase/CoreOnly (12.15.0):
  • FirebaseCore (~> 12.15.0)
• Firebase/Firestore (12.15.0):
  • Firebase/CoreOnly
  • FirebaseFirestore (~> 12.15.0)
• Firebase/Functions (12.15.0):
  • Firebase/CoreOnly
  • FirebaseFunctions (~> 12.15.0)
• Firebase/Messaging (12.15.0):
  • Firebase/CoreOnly
  • FirebaseMessaging (~> 12.15.0)
• Firebase/Storage (12.15.0):
  • Firebase/CoreOnly
  • FirebaseStorage (~> 12.15.0)
• firebase_auth (6.5.3):
  • Firebase/Auth (= 12.15.0)
  • firebase_core
  • Flutter
• firebase_core (4.11.0):
  • Firebase/CoreOnly (= 12.15.0)
  • Flutter
• firebase_messaging (16.4.0):
  • Firebase/Messaging (= 12.15.0)
  • firebase_core
  • Flutter
• firebase_storage (13.4.3):
  • Firebase/Storage (= 12.15.0)
  • firebase_core
  • Flutter
• FirebaseAppCheckInterop (12.15.0)
• FirebaseAuth (12.15.0):
  • FirebaseAppCheckInterop (~> 12.15.0)
  • FirebaseAuthInterop (~> 12.15.0)
  • FirebaseCore (~> 12.15.0)
  • FirebaseCoreExtension (~> 12.15.0)
  • GoogleUtilities/AppDelegateSwizzler (~> 8.1)
  • GoogleUtilities/Environment (~> 8.1)
  • GTMSessionFetcher/Core (< 6.0, >= 3.4)
  • RecaptchaInterop (~> 101.0)
• FirebaseAuthInterop (12.15.0)
• FirebaseCore (12.15.0):
  • FirebaseCoreInternal (~> 12.15.0)
  • GoogleUtilities/Environment (~> 8.1)
  • GoogleUtilities/Logger (~> 8.1)
• FirebaseCoreExtension (12.15.0):
  • FirebaseCore (~> 12.15.0)
• FirebaseCoreInternal (12.15.0):
  • "GoogleUtilities/NSData+zlib (~> 8.1)"
• FirebaseFirestore (12.15.0):
  • FirebaseCore (~> 12.15.0)
  • FirebaseCoreExtension (~> 12.15.0)
  • FirebaseFirestoreInternal (~> 12.15.0)
  • FirebaseSharedSwift (~> 12.15.0)
• FirebaseFirestoreInternal (12.15.0):
  • abseil/algorithm (~> 1.20240722.0)
  • abseil/base (~> 1.20240722.0)
  • abseil/container/flat_hash_map (~> 1.20240722.0)
  • abseil/memory (~> 1.20240722.0)
  • abseil/meta (~> 1.20240722.0)
  • abseil/strings/strings (~> 1.20240722.0)
  • abseil/time (~> 1.20240722.0)
  • abseil/types (~> 1.20240722.0)
  • FirebaseAppCheckInterop (~> 12.15.0)
  • FirebaseCore (~> 12.15.0)
  • "gRPC-C++ (~> 1.69.0)"
  • gRPC-Core (~> 1.69.0)
  • leveldb-library (~> 1.22)
  • nanopb (~> 3.30910.0)
• FirebaseFunctions (12.15.0):
  • FirebaseAppCheckInterop (~> 12.15.0)
  • FirebaseAuthInterop (~> 12.15.0)
  • FirebaseCore (~> 12.15.0)
  • FirebaseCoreExtension (~> 12.15.0)
  • FirebaseMessagingInterop (~> 12.15.0)
  • FirebaseSharedSwift (~> 12.15.0)
  • GTMSessionFetcher/Core (< 6.0, >= 3.4)
• FirebaseInstallations (12.15.0):
  • FirebaseCore (~> 12.15.0)
  • GoogleUtilities/Environment (~> 8.1)
  • GoogleUtilities/UserDefaults (~> 8.1)
  • PromisesObjC (~> 2.4)
• FirebaseMessaging (12.15.0):
  • FirebaseCore (~> 12.15.0)
  • FirebaseInstallations (~> 12.15.0)
  • GoogleDataTransport (~> 10.1)
  • GoogleUtilities/AppDelegateSwizzler (~> 8.1)
  • GoogleUtilities/Environment (~> 8.1)
  • GoogleUtilities/Reachability (~> 8.1)
  • GoogleUtilities/UserDefaults (~> 8.1)
  • nanopb (~> 3.30910.0)
• FirebaseMessagingInterop (12.15.0)
• FirebaseSharedSwift (12.15.0)
• FirebaseStorage (12.15.0):
  • FirebaseAppCheckInterop (~> 12.15.0)
  • FirebaseAuthInterop (~> 12.15.0)
  • FirebaseCore (~> 12.15.0)
  • FirebaseCoreExtension (~> 12.15.0)
  • GoogleUtilities/Environment (~> 8.1)
  • GTMSessionFetcher/Core (< 6.0, >= 3.4)
• Flutter (1.0.0)

PODFILE CHECKSUM: 1ae876023121e69222cd7d202ba5f1da5e511cf5

COCOAPODS: 1.16.2