### Purpose
As discussed on the forum:
https://forum.syncthing.net/t/reviving-nat-pmp-in-v2-x-on-android-14/24554
TL;DR
Android 14+ only lets java code get the gateway IPv4 address which is
used in SyncthingNative’s NAT-PMP feature.
So I’ve added the java code to the wrapper, got the router IP address
and feeded it to SyncthingNative by setting the env var
“FALLBACK_NET_GATEWAY_IPV4”.
This revives the NAT feature:
> [Z36WU] INFO: Detected 1 NAT service
### Testing
Local build and test via Android emulator (AVD 15).
Before:
- Local discovery on Android 10+ is broken. The phone receives local
discovery packets from other devices running Syncthing on the same
network, e.g. a computer. But it doesn't send its own local discovery
packets.
- Startup of the beacon/broadcast.go and beacon/multicast.go "services"
subsequently fail, see the log entries of "service.go" with "2 of 2
failures, backing off".
Root cause:
- Android 10+ restricts determining the network interfaces for privacy
reasons. The interfaces and IP addresses cannot be determined.
- There's a bug in the go "net" library. I can actually get the
interfaces, but the fix was not implemented by the go team.
Workaround:
- The "community" found a workaround by creating a light wrapper around
"net" called "anet" library.
- "anet" adjusts the behaviour on Android 10+ and gets the interfaces
plus their IP addresses, as required by Syncthing.
After:
- By using the "anet" lib, Syncthing is able to get the interface ip
addresses and put them into the "AllAddresses" string array.
- The "AllAddresses" string array is then announced on the local
discovery multicast and broadcast packets, if enabled in Syncthing's
config.
- By correctly getting the interfaces and IP addresses using "anet" in
"beacon/broadcast.go" and "beacon/multicast.go", the services start up
fine again.
Verification:
- I've built "libSyncthingNative.so" with this PR applied for Android
and put it into Syncthing-Fork v1.29.7.5 for testing. My two phones,
Android 10 and Android 15 (arm64-v8a) immediately discovered each other
using local discovery.
- I can see the "sent XX bytes" and "recv XX bytes" on both phones in
the log filtering for "SyncthingNativeCode" :-).
Personal note:
- Please go light on me, and, if it's not demanded too much of your
time, please help me on this. I am no go programmer. Most things you
think are easy or common sense aren't part of my knowledge set. I'd just
like to help and hope we somehow can drive this home together to fix the
problem.
----
ref: https://github.com/Catfriend1/syncthing-android/pull/1501
ref: https://github.com/Catfriend1/syncthing-android/issues/1500
ref: https://github.com/wlynxg/anet/blob/main/interface.go &
https://github.com/wlynxg/anet/blob/main/interface_android.go
With that fix, I can see the broadcast/multicast lines again and my
phone can be discovered by other phones running the Syncthing app which
wasn't possible before on Android 10+.
```
[ET76H] .346892 broadcast.go:107: DEBUG: sent 185 bytes to 192.168.x.255:21027
[ET76H] .347114 multicast.go:86: DEBUG: sent 185 bytes to [ff12::8384]:21027 on wlan0
```
---------
Co-authored-by: Marcus B Spencer <marcus@marcusspencer.us>
Add an id attribute to the submit button shown on the login form. This
allows my password manager's form filling function to interact with the
button after filling in username and password (which already have the id
attribute in place).
Catfriend1
