README.md

Introduction

In response to the modifications made to the permissions for accessing system MAC addresses in Android 11, ordinary applications encounter several main issues when using NETLINK sockets:

• Not allowing bind operations on NETLINK sockets.
• Not permitting the use of the RTM_GETLINK functionality.

For detailed information, please refer to: https://developer.android.com/training/articles/user-data-ids#mac-11-plus

As a result of the aforementioned reasons, using net.Interfaces() and net.InterfaceAddrs() from the Go net package in the Android environment leads to the route ip+net: netlinkrib: permission denied error.

You can find specific issue details here: golang/go#40569

To address the issue of using the Go net package in the Android environment, we have made partial modifications to its source code to ensure proper functionality on Android.

I have fully resolved the issues with net.InterfaceAddrs().

However, for net.Interfaces(), we have only addressed some problems, as the following issues still remain:

• It can only return interfaces with IP addresses.
• It cannot return hardware MAC addresses.

Nevertheless, the fixed net.Interfaces() function now aligns with the Android API's NetworkInterface.getNetworkInterfaces() and can be used normally in most scenarios.

The specific fix logic includes:

Removing the Bind() operation on Netlink sockets in the NetlinkRIB() function. Using ioctl based on the Index number returned by RTM_GETADDR to retrieve the network card's name, MTU, and flags.

There are two implementations of the net package: one from the Go standard library and another from the golang.org/x/net module. Both of these implementations have the same issues in the Android environment. The anet package should be compatible with both of them.

Test Code

net.Interface()

use net.Interface():

func RawInterface() {
	interfaces, err := net.Interfaces()
	if err != nil {
		panic(err)
	}

	for _, i := range interfaces {
		log.Println(i)
	}
}

result:

panic: route ip+net: netlinkrib: permission denied

use anet.Interface():

func AnetInterface() {
	interfaces, err := anet.Interfaces()
	if err != nil {
		panic(err)
	}

	for _, i := range interfaces {
		log.Println(i)
	}
}

result:

{1 65536 lo  up|loopback|running}
{15 1400 rmnet_data1  up|running}
{24 1500 wlan0  up|broadcast|multicast|running}
{3 1500 dummy0  up|broadcast|running}
{4 1500 ifb0  up|broadcast|running}
{5 1500 ifb1  up|broadcast|running}
{12 1500 ifb2  up|broadcast|running}
{14 1500 rmnet_data0  up|running}
{16 1400 rmnet_data2  up|running}
{17 1400 rmnet_data3  up|running}

net.InterfaceAddrs()

use net.InterfaceAddrs():

func NetInterfaceAddrs() {
	addrs, err := net.InterfaceAddrs()
	if err != nil {
		panic(err)
	}

	for _, addr := range addrs {
		log.Println(addr)
	}
}

result:

panic: route ip+net: netlinkrib: permission denied

use anet.InterfaceAddrs():

func AnetInterfaceAddrs() {
	addrs, err := anet.InterfaceAddrs()
	if err != nil {
		panic(err)
	}

	for _, addr := range addrs {
		log.Println(addr)
	}
}

result:

127.0.0.1/8
::1/128
...
192.168.6.143/24
fe80::7e4f:4446:eb3:1eb8/64

Other issues due to #40569

• golang/go#68082

How to build with Go 1.23.0 or later

The anet library internally relies on //go:linkname directive. Since the usage of //go:linkname has been restricted since Go 1.23.0 (Go 1.23 Release Notes), it is necessary to specify the -checklinkname=0 linker flag when building the anet package with Go 1.23.0 or later. Without this flag, the following linker error will occur:

link: github.com/wlynxg/anet: invalid reference to net.zoneCache