mc: add support for custom server JARs

For #238

minecraft-server/README.md

@@ -402,6 +402,15 @@ Just change it with `SPONGEBRANCH`, such as:
     $ docker run -d -v /path/on/host:/data ... \
         -e TYPE=SPONGEVANILLA -e SPONGEBRANCH=EXPERIMENTAL ...
 
+## Running with a custom server JAR
+
+If you would like to run a custom server JAR, set `-e TYPE=CUSTOM` and pass the custom server
+JAR via `CUSTOM_SERVER`. It can either be a URL or a container path to an existing JAR file. 
+
+If it is a URL, it will only be downloaded into the `/data` directory if it wasn't already. As
+such, if you need to upgrade or re-download the JAR, then you will need to stop the container,
+remove the file from the container's `/data` directory, and start again. 
+
 ## Using Docker Compose
 
 Rather than type the server options below, the port mappings above, etc

minecraft-server/start-configuration

@@ -89,6 +89,10 @@ case "${TYPE^^}" in
     exec /start-deploySpongeVanilla $@
   ;;
 
+  CUSTOM)
+    exec /start-deployCustom $@
+  ;;
+
   *)
       echo "Invalid type: '$TYPE'"
       echo "Must be: VANILLA, FORGE, BUKKIT, SPIGOT, PAPER, FTB, CURSEFORGE, SPONGEVANILLA"

minecraft-server/start-deployCustom

@@ -0,0 +1,29 @@
+#!/bin/bash
+
+. /start-utils
+
+if isURL ${CUSTOM_SERVER}; then
+  filename=$(basename ${CUSTOM_SERVER})
+  export SERVER=/data/${filename}
+
+  if [[ -f ${SERVER} ]]; then
+    echo "Using previously downloaded jar at ${SERVER}"
+  else
+   echo "Downloading custom server jar from ${CUSTOM_SERVER} ..."
+   if ! curl -sSL -o ${SERVER} ${CUSTOM_SERVER}; then
+      echo "Failed to download from ${CUSTOM_SERVER}"
+      exit 2
+    fi
+  fi
+
+elif [[ -f ${CUSTOM_SERVER} ]]; then
+  echo "Using custom server jar at ${CUSTOM_SERVER} ..."
+  export SERVER=${CUSTOM_SERVER}
+
+else
+  echo "CUSTOM_SERVER is not properly set to a URL or existing jar file"
+  exit 2
+fi
+
+# Continue to Final Setup
+exec /start-finalSetup01World $@