[mc] Adding MODPACK download option similar to WORLD

minecraft-server/Dockerfile

@@ -36,4 +36,4 @@ ENV UID=1000
 ENV MOTD A Minecraft Server Powered by Docker
 ENV JVM_OPTS -Xmx1024M -Xms1024M
 ENV TYPE=VANILLA VERSION=LATEST FORGEVERSION=RECOMMENDED LEVEL=world PVP=true DIFFICULTY=easy \
-  LEVEL_TYPE=DEFAULT GENERATOR_SETTINGS= WORLD=
+  LEVEL_TYPE=DEFAULT GENERATOR_SETTINGS= WORLD= MODPACK=

minecraft-server/README.md

@@ -301,6 +301,17 @@ will be deleted when the container is deleted.
 you should use an IP address or a globally resolveable FQDN, or else the
 name of a linked container.
 
+### Downloadable mod pack
+
+Like the `WORLD` option above, you can specify the URL of a "mod pack"
+to download and install into the `mods` directory. To use this option
+pass the environment variable `MODPACK`, such as
+
+    docker run -d -e MODPACK=http://www.example.com/mods/modpack.zip ...
+
+**NOTE:** The referenced URL must be a zip file with one or more Forge jar files at the
+top level of the zip archive.
+
 ## JVM Configuration
 
 ### Memory Limit

minecraft-server/start-minecraft.sh

@@ -90,6 +90,7 @@ case "$TYPE" in
 esac
 
 # If supplied with a URL for a world, download it and unpack
+if [[ "$WORLD" ]]; then
 case "X$WORLD" in
   X[Hh][Tt][Tt][Pp]*[Zz][iI][pP])
     echo "Downloading world via HTTP"
@@ -113,6 +114,24 @@ case "X$WORLD" in
     echo "Invalid URL given for world: Must be HTTP or HTTPS and a ZIP file"
     ;;
 esac
+fi
+
+# If supplied with a URL for a modpack (simple zip of jars), download it and unpack
+if [[ "$MODPACK" ]]; then
+case "X$MODPACK" in
+  X[Hh][Tt][Tt][Pp]*[Zz][iI][pP])
+    echo "Downloading mod pack via HTTP"
+    echo "$MODPACK"
+    mkdir -p /data/mods
+    wget -q -O /tmp/modpack.zip "$MODPACK"
+    unzip -d /data/mods /tmp/modpack.zip
+    rm -f /tmp/modpack.zip
+    ;;
+  *)
+    echo "Invalid URL given for modpack: Must be HTTP or HTTPS and a ZIP file"
+    ;;
+esac
+fi
 
 if [ ! -e server.properties ]; then
   cp /tmp/server.properties .