feat(minecraft-server): replace environment variables in configs

Add additional setup script that replaces environment variables inside
config files.

Closes #298

minecraft-server/Dockerfile

@@ -3,19 +3,19 @@ FROM openjdk:8u171-jre-alpine
 LABEL maintainer "itzg"
 
 RUN apk add --no-cache -U \
-          openssl \
-          imagemagick \
-          lsof \
-          su-exec \
-          shadow \
-          bash \
-          curl iputils wget \
-          git \
-          jq \
-          mysql-client \
-          tzdata \
-          rsync \
-          python python-dev py2-pip
+  openssl \
+  imagemagick \
+  lsof \
+  su-exec \
+  shadow \
+  bash \
+  curl iputils wget \
+  git \
+  jq \
+  mysql-client \
+  tzdata \
+  rsync \
+  python python-dev py2-pip
 
 RUN pip install mcstatus
 
@@ -71,7 +71,8 @@ ENV UID=1000 GID=1000 \
   JVM_XX_OPTS="-XX:+UseG1GC" MEMORY="1G" \
   TYPE=VANILLA VERSION=LATEST FORGEVERSION=RECOMMENDED SPONGEBRANCH=STABLE SPONGEVERSION= LEVEL=world \
   PVP=true DIFFICULTY=easy ENABLE_RCON=true RCON_PORT=25575 RCON_PASSWORD=minecraft \
-  LEVEL_TYPE=DEFAULT GENERATOR_SETTINGS= WORLD= MODPACK= MODS= SERVER_PORT=25565 ONLINE_MODE=TRUE CONSOLE=true SERVER_NAME="Dedicated Server"
+  LEVEL_TYPE=DEFAULT GENERATOR_SETTINGS= WORLD= MODPACK= MODS= SERVER_PORT=25565 ONLINE_MODE=TRUE CONSOLE=true SERVER_NAME="Dedicated Server" \
+  REPLACE_ENV_VARIABLES="FALSE" ENV_VARIABLE_PREFIX="CFG_"
 
 COPY start* /
 RUN dos2unix /start* && chmod +x /start*

minecraft-server/start-finalSetup04ServerProperties

@@ -132,4 +132,4 @@ else
   echo "server.properties already created, skipping"
 fi
 
-exec /start-minecraftFinalSetup $@
+exec /start-finalSetup05EnvVariables $@

minecraft-server/start-finalSetup05EnvVariables

@@ -0,0 +1,15 @@
+#!/bin/bash
+
+if [ "$REPLACE_ENV_VARIABLES" = "TRUE" ]; then
+  echo "Replacing env variables in configs that match the prefix $ENV_VARIABLE_PREFIX..."
+  while IFS='=' read -r name value ; do
+    # check if name of env variable matches the prefix
+    # sanity check environment variables to avoid code injections
+    if [[ "$name" = $ENV_VARIABLE_PREFIX* ]] && [[ $value =~ ^[0-9a-zA-Z_\-:/=?.+]*$ ]] && [[ $name =~ ^[0-9a-zA-Z_\-]*$ ]]; then
+        echo "$name = $value"
+        find /data/ -type f -exec sed -i 's#${'"$name"'}#'"$value"'#g' {} \;
+    fi
+  done < <(env)
+fi
+
+exec /start-minecraftFinalSetup $@