Add support for accessing internal IP

Pterodactyl/Panel#613

Dockerfile

@@ -13,8 +13,7 @@ RUN apk update \
     && adduser -D -h /home/container container
 
 USER container
-ENV  USER container
-ENV  HOME /home/container
+ENV  USER=container HOME=/home/container
 
 WORKDIR /home/container
 

entrypoint.sh

@@ -1,11 +1,14 @@
 #!/bin/bash
-sleep 5
+sleep 2
 
 cd /home/container
 
 # Output Current Java Version
 java -version
 
+# Make internal Docker IP address available to processes.
+export INTERNAL_IP=`ip route get 1 | awk '{print $NF;exit}'`
+
 # Replace Startup Variables
 MODIFIED_STARTUP=`eval echo $(echo ${STARTUP} | sed -e 's/{{/${/g' -e 's/}}/}/g')`
 echo ":/home/container$ ${MODIFIED_STARTUP}"