Allow for custom SERVER_RUNNER (#4182)

docs/configuration/misc-options.md

@@ -202,6 +202,10 @@ Be sure to also increase the shutdown timeout described [here for docker compose
 
 If you are using a host-attached data directory, then you can have the image setup the Minecraft server files and stop prior to launching the server process by setting `SETUP_ONLY` to `true`. 
     
+## Custom server runner
+
+By default, the image finishes startup by exec'ing [mc-server-runner](https://github.com/itzg/mc-server-runner) to run the Minecraft server itself. This can be replaced by setting the environment variable `SERVER_RUNNER`. The arguments passed will start with ones specific to mc-server-runner, followed by `--`, and then the actual `java -jar` arguments or equivalent server entry script, such as `run.sh` for Forge. 
+
 ## Enable Flare Flags
     
 To enable the JVM flags required to fully support the [Flare profiling suite](https://blog.airplane.gg/flare), set the following variable:

scripts/start-finalExec

@@ -3,6 +3,7 @@
 : "${DEBUG_EXEC:=false}"
 : "${SETUP_ONLY:=false}"
 : "${CUSTOM_JAR_EXEC:=}"
+: "${SERVER_RUNNER:=mc-server-runner}"
 
 # shellcheck source=start-utils
 . "$(dirname "$0")/start-utils"
@@ -96,7 +97,7 @@ fi
 if versionLessThan 1.7; then
   : # No patch required here.
 elif versionLessThan 1.18.1; then
-  if isTrue ${SKIP_LOG4J_PATCHER:-false}; then
+  if isTrue "${SKIP_LOG4J_PATCHER:-false}"; then
     log "Skipping Log4jPatcher, make sure you are not affected"
   else
     JVM_OPTS="-javaagent:/image/Log4jPatcher.jar ${JVM_OPTS}"
@@ -496,7 +497,7 @@ if [[ ${TYPE} == "CURSEFORGE" && "${SERVER}" ]]; then
   if isTrue "${DEBUG_EXEC}"; then
     set -x
   fi
-  exec mc-server-runner ${bootstrapArgs} "${mcServerRunnerArgs[@]}" java $JVM_XX_OPTS $JVM_OPTS $expandedDOpts -jar "$(basename "${SERVER}")" "$@" $EXTRA_ARGS
+  exec "${SERVER_RUNNER}" ${bootstrapArgs} "${mcServerRunnerArgs[@]}" -- java $JVM_XX_OPTS $JVM_OPTS $expandedDOpts -jar "$(basename "${SERVER}")" "$@" $EXTRA_ARGS
 elif [[ ${TYPE} == "CURSEFORGE" ]]; then
   mcServerRunnerArgs+=(--shell bash)
 
@@ -550,18 +551,18 @@ fi
       JVM_ARGS=${JVM_ARGS//$'\n'/}
       sed -i "s~JAVA_ARGS=.*~JAVA_ARGS=\"${JVM_ARGS}\"~" "${FTB_DIR}/variables.txt"
   fi
-  exec mc-server-runner "${mcServerRunnerArgs[@]}" "${finalArgs[@]}"
+  exec "${SERVER_RUNNER}" "${mcServerRunnerArgs[@]}" -- "${finalArgs[@]}"
 elif [[ $SERVER =~ run.sh ]]; then
   log "Using Forge supplied run.sh script..."
   echo $JVM_XX_OPTS $JVM_OPTS $expandedDOpts > user_jvm_args.txt
-  if isTrue ${SETUP_ONLY}; then
+  if isTrue "${SETUP_ONLY}"; then
     echo "SETUP_ONLY: bash ${SERVER}"
     exit
   fi
   if isTrue "${DEBUG_EXEC}"; then
     set -x
   fi
-  exec mc-server-runner "${mcServerRunnerArgs[@]}" --shell bash "${SERVER}" $EXTRA_ARGS
+  exec "${SERVER_RUNNER}" "${mcServerRunnerArgs[@]}" --shell bash -- "${SERVER}" $EXTRA_ARGS
 else
   # If we have a bootstrap.txt file... feed that in to the server stdin
   if [ -f $bootstrapPath ]; then
@@ -590,7 +591,7 @@ else
     "$@" $EXTRA_ARGS
   )
 
-  if isTrue ${SETUP_ONLY}; then
+  if isTrue "${SETUP_ONLY}"; then
     echo "SETUP_ONLY: java ${finalArgs[*]}"
     exit
   fi
@@ -599,5 +600,5 @@ else
     set -x
   fi
 
-  exec mc-server-runner ${bootstrapArgs} "${mcServerRunnerArgs[@]}" java "${finalArgs[@]}"
+  exec "${SERVER_RUNNER}" ${bootstrapArgs} "${mcServerRunnerArgs[@]}" -- java "${finalArgs[@]}"
 fi