Add a wrapper that uses anet on Android, but net on other platforms.
### Purpose
Fixes
https://forum.syncthing.net/t/workaround-for-android-local-discovery/20403/12
### Testing
Run two Syncthing instances with Global Discovery disabled. Pair them
with each other, don't hardcode their addresses, and verify they
connect.
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>
Currently we log on every single one of 10 retries deep in the upnp
stack. However we also return the failure as an error, which is bubbled
up a while until it's logged at debug level. Switch that around, such
that the repeat logging happens at debug level but the top-level happens
at info. There's some chance that this will newly log errors from
nat-pmp that were previously hidden in debug level - I hope those are
useful and not too numerous.
Also potentially this can even close#9324, my (very limited)
understanding of the reports/discussion there is that there's likely no
problem with syncthing beyond the excessive logging, it's some weird
router behaviour.
This pull request allows syncthing to request an IPv6
[pinhole](https://en.wikipedia.org/wiki/Firewall_pinhole), addressing
issue #7406. This helps users who prefer to use IPv6 for hosting their
services or are forced to do so because of
[CGNAT](https://en.wikipedia.org/wiki/Carrier-grade_NAT). Otherwise,
such users would have to configure their firewall manually to allow
syncthing traffic to pass through while IPv4 users can use UPnP to take
care of network configuration already.
### Testing
I have tested this in a virtual machine setup with miniupnpd running on
the virtualized router. It successfully added an IPv6 pinhole when used
with IPv6 only, an IPv4 port mapping when used with IPv4 only and both
when dual-stack (IPv4 and IPv6) is used.
Automated tests could be added for SOAP responses from the router but
automatically testing this with a real network is likely infeasible.
### Documentation
https://docs.syncthing.net/users/firewall.html could be updated to
mention the fact that UPnP now works with IPv6, although this change is
more "behind the scenes".
---------
Co-authored-by: Simon Frei <freisim93@gmail.com>
Co-authored-by: bt90 <btom1990@googlemail.com>
Co-authored-by: André Colomb <github.com@andre.colomb.de>
Marcus B Spencer
Catfriend1andMarcus B Spencer
Simon Frei
Audrius Butkevicius
Jakob Borg
Lars K.W. Gohlke
aviau