allow env variable (#203)

* allow env variable

* look for /etc if /mnt/wsl is not available

* update readme for the new behavior

README.md

@@ -123,6 +123,8 @@ wsl.exe -d wsl-vpnkit --cd /app wsl-vpnkit
 
 `wsl-vpnkit` uses `/mnt/wsl/resolv.conf` to get the WSL 2 gateway IP. If modifying `/etc/resolv.conf` to set a custom DNS configuration, set [`generateResolvConf=false` in `wsl.conf`](https://learn.microsoft.com/en-us/windows/wsl/wsl-config#network-settings).
 
+On older WSL versions where `/mnt/wsl/resolv.conf` is not available, `wsl-vpnkit` will fallback to using `/etc/resolv.conf`. When setup as a standalone script and using a custom DNS configuration for the distro, the `WSL2_GATEWAY_IP` environment variable should be set for `wsl-vpnkit` to use.
+
 #### wsl-gvproxy.exe is not executable due to WSL interop settings or Windows permissions
 
 `wsl-vpnkit` requires that the WSL 2 distro be able to run Windows executables. This [`interop` setting](https://learn.microsoft.com/en-us/windows/wsl/wsl-config#interop-settings) is enabled by default in WSL 2 and in the `wsl-vpnkit` distro.

wsl-vpnkit

@@ -3,10 +3,10 @@
 set -x
 
 # hardcoded in gvisor-tap-vsock
-VPNKIT_GATEWAY_IP="192.168.127.1"
-VPNKIT_HOST_IP="192.168.127.254"
-VPNKIT_LOCAL_IP="192.168.127.2"
-TAP_MAC_ADDR="5a:94:ef:e4:0c:ee"
+VPNKIT_GATEWAY_IP=${VPNKIT_GATEWAY_IP:-192.168.127.1}
+VPNKIT_HOST_IP=${VPNKIT_HOST_IP:-192.168.127.254}
+VPNKIT_LOCAL_IP=${VPNKIT_LOCAL_IP:-192.168.127.2}
+TAP_MAC_ADDR=${TAP_MAC_ADDR:-5a:94:ef:e4:0c:ee}
 
 # overrideable with env
 VMEXEC_PATH=${VMEXEC_PATH:-/app/wsl-vm}
@@ -19,9 +19,14 @@ DEBUG=${DEBUG:-0}
 set +x
 
 # WSL2 default values
-WSL2_TAP_NAME="eth0"
-WSL2_RESOLVCONF="/mnt/wsl/resolv.conf"
-WSL2_GATEWAY_IP="$(cat $WSL2_RESOLVCONF | awk '/^nameserver/ {print $2}')"
+WSL2_TAP_NAME=${WSL2_TAP_NAME:-eth0}
+WSL2_RESOLVCONF_DEFAULT="/mnt/wsl/resolv.conf"
+if [ ! -f "$WSL2_RESOLVCONF_DEFAULT" ]; then
+    WSL2_RESOLVCONF_DEFAULT="/etc/resolv.conf"
+fi
+WSL2_RESOLVCONF=${WSL2_RESOLVCONF:-$WSL2_RESOLVCONF_DEFAULT}
+WSL2_GATEWAY_IP_FROM_RESOLVCONF="$(cat $WSL2_RESOLVCONF | awk '/^nameserver/ {print $2}')"
+WSL2_GATEWAY_IP=${WSL2_GATEWAY_IP:-$WSL2_GATEWAY_IP_FROM_RESOLVCONF}
 
 set -x
 
@@ -142,7 +147,6 @@ fi
 cat $WSL2_RESOLVCONF | grep "automatically generated by WSL" >/dev/null
 if [ $? -eq 1 ]; then
     echo "resolv.conf has been modified without setting generateResolvConf"
-    exit 1
 fi
 $GVPROXY_PATH -help 2>/dev/null
 if [ $? -eq 1 ]; then