mc: compute default MOTD based on the given type and version

minecraft-server/Dockerfile

@@ -41,7 +41,6 @@ WORKDIR /data
 ENTRYPOINT [ "/start" ]
 
 ENV UID=1000 GID=1000 \
-    MOTD="A Minecraft Server Powered by Docker" \
     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 \

minecraft-server/README.md

@@ -628,8 +628,14 @@ The message of the day, shown below each server entry in the UI, can be changed
 
     docker run -d -e 'MOTD=My Server' ...
 
-If you leave it off, the last used or default message will be used. _The example shows how to specify a server
-message of the day that contains spaces by putting quotes around the whole thing._
+If you leave it off, a default is computed from the server type and version, such as
+
+    A Paper Minecraft Server powered by Docker
+    
+when `TYPE` is `PAPER`. That way you can easily differentiate between several servers you may have started.
+
+_The example shows how to specify a server message of the day that contains spaces by putting quotes 
+around the whole thing._
 
 ### PVP Mode
 

minecraft-server/start-configuration

@@ -58,6 +58,8 @@ esac
 
 cd /data
 
+export ORIGINAL_TYPE=${TYPE}
+
 echo "Checking type information."
 case "$TYPE" in
   *BUKKIT|*bukkit|SPIGOT|spigot)

minecraft-server/start-finalSetup04ServerProperties

@@ -34,6 +34,22 @@ if [ ! -e $SERVER_PROPERTIES ]; then
     setServerProp "white-list" "true"
   fi
 
+  # If not provided, generate a reasonable default message-of-the-day,
+  # which shows up in the server listing in the client
+  if [ -z $MOTD ]; then
+    # snapshot is the odd case where we have to look at version to identify that label
+    if [[ ${ORIGINAL_TYPE} == "VANILLA" && ${VERSION} == "SNAPSHOT" ]]; then
+      label=SNAPSHOT
+    else
+      label=${ORIGINAL_TYPE}
+    fi
+
+    # Convert label to title-case
+    label=${label,,}
+    label=${label^}
+    MOTD="A ${label} Minecraft Server powered by Docker"
+  fi
+
   setServerProp "server-port" "$SERVER_PORT"
   setServerProp "motd" "$MOTD"
   setServerProp "allow-nether" "$ALLOW_NETHER"