Programmatically modify essential preferences on start

Dockerfile

@@ -30,6 +30,7 @@ RUN \
 	ocl-icd-libopencl1 \
 	udev \
 	unrar \
+  xmlstarlet \
 	wget && \
  COMP_RT_RELEASE=$(curl -sX GET "https://api.github.com/repos/intel/compute-runtime/releases/latest" | jq -r '.tag_name') && \
  COMP_RT_URLS=$(curl -sX GET "https://api.github.com/repos/intel/compute-runtime/releases/tags/${COMP_RT_RELEASE}" | jq -r '.body' | grep wget | sed 's|wget ||g') && \

Dockerfile.aarch64

@@ -25,6 +25,7 @@ RUN \
 	jq \
 	udev \
 	unrar \
+  xmlstarlet \
 	wget && \
  echo "**** install plex ****" && \
  if [ -z ${PLEX_RELEASE+x} ]; then \

Dockerfile.armhf

@@ -25,6 +25,7 @@ RUN \
 	jq \
 	udev \
 	unrar \
+  xmlstarlet \
 	wget && \
  echo "**** install plex ****" && \
  if [ -z ${PLEX_RELEASE+x} ]; then \

root/etc/cont-init.d/70-plex-modify-preferences

@@ -0,0 +1,72 @@
+#!/usr/bin/with-contenv bash
+
+XML_CONFIG="/config/Library/Application Support/Plex Media Server/Preferences.xml"
+
+# Fallback to ALLOWED_NETWORKS value
+NOAUTH_NETWORKS="${NOAUTH_NETWORKS:-$ALLOWED_NETWORKS}"
+
+update_or_insert_attr() {
+  # Usage: update_or_replace_attr <attribute> <value> <xmlpath>
+
+  local element attribute_name attribute_value xml_path
+  element="/Preferences"
+  attribute_name="${1:?}"
+  attribute_value="${2:?}"
+  xml_path="${3:?}"
+
+  local response
+  response="$(xmlstarlet select --text --template --match "$element" --value-of "@${attribute_name}" "${xml_path}")"
+
+  # Only write to file if the desired value differs from the current
+  if [[ "$response" == "$attribute_value" ]]; then
+     return
+  fi
+
+  xmlstarlet edit --inplace --insert "$element" --type attr --name "$attribute_name" --value "$attribute_value" "$xml_path"
+}
+
+ensure_xml_exists() {
+  # Usage: ensure_xml_exists <xml_path>
+
+  if [[ -e "${1:?}" ]]; then
+     printf '%s\n' "File '$1' already exists. Skipping..."
+     return
+  fi
+
+  local parent
+  parent="$(dirname "${1:?}")"
+
+  if [[ ! -d "$parent" ]]; then
+     mkdir -p "$parent"
+  fi
+
+  printf '%s\n' "<?xml version=\"1.0\" encoding=\"utf-8\"?><Preferences/>" > "$1"
+
+  chown -R abc:abc "$parent"
+}
+
+main() {
+  ensure_xml_exists "$XML_CONFIG"
+
+  # Comma delimited string of ip cidr blocks that should be considered local
+  if [[ -n "$ALLOWED_NETWORKS" ]]; then
+    update_or_insert_attr allowedNetworks "$ALLOWED_NETWORKS" "$XML_CONFIG"
+  fi
+
+  # Comma delimited string of ip cidr blocks that shouldn't require auth
+  if [[ -n "$NOAUTH_NETWORKS" ]]; then
+    update_or_insert_attr LanNetworksBandwidth "$NOAUTH_NETWORKS" "$XML_CONFIG"
+  fi
+
+  # Comma delimited string of https/http urls used to access server
+  if [[ -n "$ADVERTISE_URLS" ]]; then
+    update_or_insert_attr allowedNetworks "$ADVERTISE_URLS" "$XML_CONFIG"
+  fi
+
+  # Human readable name used to identify server on clients
+  if [[ -n "$SERVER_NAME" ]]; then
+    update_or_insert_attr FriendlyName "$SERVER_NAME" "$XML_CONFIG"
+  fi
+}
+
+main