Add Feed-The-Beast (FTB) server modpack support

The popular mod site https://www.feed-the-beast.com provides server
modpacks to go with their client modpacks. These server modpacks
include a custom start script that must be used to launch the server.

minecraft-server/README.md

@@ -264,6 +264,65 @@ This works well if you want to have a common set of plugins in a separate
 location, but still have multiple worlds with different server requirements
 in either persistent volumes or a downloadable archive.
 
+## Running a Server with a Feed-The-Beast (FTB) modpack
+
+Enable this server mode by adding a `-e TYPE=FTB` to your command-line,
+but note the following additional steps needed...
+
+You need to specify a modpack to run, using the `FTB_SERVER_MOD` environment
+variable. An FTB server modpack is available together with its respective
+client modpack on https://www.feed-the-beast.com under "Additional Files."
+Because of the interactive delayed download mechanism on that web site, you
+must manually download the server modpack. Copy the modpack to the `/data`
+directory (see "Attaching data directory to host filesystem”).
+
+Now you can add a `-e FTB_SERVER_MOD=name_of_modpack.zip` to your command-line.
+
+    $ docker run -d -v /path/on/host:/data -e TYPE=FTB \
+        -e FTB_SERVER_MOD=FTBPresentsSkyfactory3Server_3.0.6.zip \
+        -p 25565:25565 -e EULA=TRUE --name mc itzg/minecraft-server
+
+### Using the /data volume
+
+You must use a persistent `/data` mount for this type of server.
+
+To do this, you will need to attach the container's `/data` directory
+(see "Attaching data directory to host filesystem”).
+
+If the modpack is updated and you want to run the new version on your
+server, you stop and remove the container:
+
+    docker stop mc
+    docker rm mc
+
+Do not erase anything from your /data directory (unless you know of
+specific mods that have been removed from the modpack). Download the
+updated FTB server modpack and copy it to `/data`. Start a new container
+with `FTB_SERVER_MOD` specifying the updated modpack file.
+
+    $ docker run -d -v /path/on/host:/data -e TYPE=FTB \
+        -e FTB_SERVER_MOD=FTBPresentsSkyfactory3Server_3.0.7.zip \
+        -p 25565:25565 -e EULA=TRUE --name mc itzg/minecraft-server
+
+### FTB server JVM options
+
+An FTB server modpack contains its own startup script that launches the
+JVM and it does not use the `JVM_OPTS` environment variable. Instead
+you can use `MIN_RAM` and `MAX_RAM` variables. These are appended to
+the JVM `-Xms` and `-Xmx` options. For example, `-e MIN_RAM=2G` results
+in `-Xms2G` passed to the JVM.
+
+Additionally, `PERMGEN_SIZE` is passed on to `-XX:PermSize`. Here is an
+example:
+
+    $ docker run -d -v /path/on/host:/data -e TYPE=FTB \
+        -e MIN_RAM=1G -e MAX_RAM=2G -e PERMGEN_SIZE=512M \
+        -e FTB_SERVER_MOD=FTBPresentsSkyfactory3Server_3.0.6.zip \
+        -p 25565:25565 -e EULA=TRUE --name mc itzg/minecraft-server
+
+Note: The FTB server start script will also override other options,
+like `MOTD`.
+
 ## Using Docker Compose
 
 Rather than type the server options below, the port mappings above, etc

minecraft-server/start-minecraft.sh

@@ -157,6 +157,44 @@ function installForge {
   fi
 }
 
+function installFTB {
+  TYPE=FEED-THE-BEAST
+
+  echo "Looking for Feed-The-Beast server modpack."
+  if [[ -z $FTB_SERVER_MOD ]]; then
+      echo "Environment variable FTB_SERVER_MOD not set."
+      echo "Set FTB_SERVER_MOD to the file name of the FTB server modpack."
+      echo "(And place the modpack in the /data directory.)"
+      exit 2
+  fi
+  local srv_modpack=${FTB_SERVER_MOD}
+  if [[ ${srv_modpack:0:5} == "data/" ]]; then
+      # Prepend with "/"
+      srv_modpack=/${srv_modpack}
+  fi
+  if [[ ! ${srv_modpack:0:1} == "/" ]]; then
+      # If not an absolute path, assume file is in "/data"
+      srv_modpack=/data/${srv_modpack}
+  fi
+  if [[ ! -f ${srv_modpack} ]]; then
+      echo "FTB server modpack ${srv_modpack} not found."
+      exit 2
+  fi
+  if [[ ! ${srv_modpack: -4} == ".zip" ]]; then
+      echo "FTB server modpack ${srv_modpack} is not a zip archive."
+      echo "Please set FTB_SERVER_MOD to a file with a .zip extension."
+      exit 2
+  fi
+
+  echo "Unpacking FTB server modpack ${srv_modpack} ..."
+  local ftb_dir=/data/FeedTheBeast
+  mkdir -p ${ftb_dir}
+  unzip -u -o ${srv_modpack} -d ${ftb_dir}
+  cp -f /data/eula.txt ${ftb_dir}/eula.txt
+  FTB_SERVER_START=${ftb_dir}/ServerStart.sh
+  chmod a+x ${FTB_SERVER_START}
+}
+
 function installVanilla {
   SERVER="minecraft_server.$VANILLA_VERSION.jar"
 
@@ -203,6 +241,11 @@ case "$TYPE" in
     installForge
   ;;
 
+  FTB|ftb)
+    TYPE=FEED-THE-BEAST
+    installFTB
+  ;;
+
   VANILLA|vanilla)
     installVanilla
   ;;
@@ -447,6 +490,10 @@ else
   EXTRA_ARGS=""
 fi
 
+if [[ ${TYPE} == "FEED-THE-BEAST" ]]; then
+    echo "Running FTB server modpack start ..."
+    exec sh ${FTB_SERVER_START}
+else
     # If we have a bootstrap.txt file... feed that in to the server stdin
     if [ -f /data/bootstrap.txt ];
     then
@@ -454,3 +501,4 @@ then
     else
         exec java $JVM_OPTS -jar $SERVER "$@" $EXTRA_ARGS
     fi
+fi