build-package.sh: add TERMUX_PKG_SERVICE_SCRIPT var and build script

termux_step_install_service_scripts is run after
termux_step_post_make_install and loops over the new array
TERMUX_PKG_SERVICE_SCRIPT to add service scripts for termux-services.

The service scripts are usually only a one-liner so we might just as
well define it in a variable like TERMUX_PKG_SERVICE_SCRIPT.

TERMUX_PKG_SERVICE_SCRIPT should be an array on the format
("daemon-name" 'script to execute' "another daemon" 'multi\n line\n script'),
i.e. it should be of even length with name + script where the script
part preferably is within single quotes (to avoid accidental expansion
of for example $HOME).

build-package.sh

@@ -159,6 +159,10 @@ termux_step_post_make_install() {
 	return
 }
 
+# Add service scripts from array TERMUX_PKG_SERVICE_SCRIPT, if it is set
+# shellcheck source=scripts/build/termux_step_install_service_scripts.sh
+source "$TERMUX_SCRIPTDIR/scripts/build/termux_step_install_service_scripts.sh"
+
 # Link/copy the LICENSE for the package to $TERMUX_PREFIX/share/$TERMUX_PKG_NAME/
 # shellcheck source=scripts/build/termux_step_install_license.sh
 source "$TERMUX_SCRIPTDIR/scripts/build/termux_step_install_license.sh"
@@ -322,6 +326,7 @@ while (($# > 0)); do
 		termux_step_make_install
 		cd "$TERMUX_PKG_BUILDDIR"
 		termux_step_post_make_install
+                termux_step_install_service_scripts
 		termux_step_install_license
 		cd "$TERMUX_PKG_MASSAGEDIR"
 		termux_step_extract_into_massagedir

scripts/build/termux_step_install_service_scripts.sh

@@ -0,0 +1,26 @@
+termux_step_install_service_scripts() {
+	array_length=${#TERMUX_PKG_SERVICE_SCRIPT[@]}
+	if [ $array_length -eq 0 ]; then return; fi
+
+	# TERMUX_PKG_SERVICE_SCRIPT should have the structure =("daemon name" 'script to execute')
+	if [ $(( $array_length & 1 )) -eq 1 ]; then
+		termux_error_exit "TERMUX_PKG_SERVICE_SCRIPT has to be an array of even length"
+	fi
+
+	mkdir -p $TERMUX_PREFIX/var/service
+	cd $TERMUX_PREFIX/var/service
+	for ((i=0; i<${array_length}; i+=2)); do
+		mkdir -p ${TERMUX_PKG_SERVICE_SCRIPT[$i]}/log
+		echo "#!$TERMUX_PREFIX/bin/sh" > ${TERMUX_PKG_SERVICE_SCRIPT[$i]}/run
+		echo -e ${TERMUX_PKG_SERVICE_SCRIPT[$((i + 1))]} >> ${TERMUX_PKG_SERVICE_SCRIPT[$i]}/run
+
+		TERMUX_PKG_CONFFILES+="
+		var/service/${TERMUX_PKG_SERVICE_SCRIPT[$i]}/run
+		var/service/${TERMUX_PKG_SERVICE_SCRIPT[$i]}/log/run
+		"
+
+		chmod +x ${TERMUX_PKG_SERVICE_SCRIPT[$i]}/run
+		touch ${TERMUX_PKG_SERVICE_SCRIPT[$i]}/down
+		ln -sf $TERMUX_PREFIX/share/termux-services/svlogger ${TERMUX_PKG_SERVICE_SCRIPT[$i]}/log/run
+	done
+}

scripts/build/termux_step_setup_variables.sh

@@ -125,6 +125,7 @@ termux_step_setup_variables() {
 	TERMUX_PKG_SUGGESTS=""
 	TERMUX_PKG_REPLACES=""
 	TERMUX_PKG_PROVIDES="" #https://www.debian.org/doc/debian-policy/#virtual-packages-provides
+        TERMUX_PKG_SERVICE_SCRIPT=() # Fill with entries like: ("daemon name" 'script to execute'). Script is echoed with -e so can contain \n for multiple lines
 	TERMUX_PKG_CONFFILES=""
 	# Set if a host build should be done in TERMUX_PKG_HOSTBUILD_DIR:
 	TERMUX_PKG_HOSTBUILD=false

scripts/lint-packages.sh

@@ -378,6 +378,17 @@ lint_package() {
 			unset file_path_ok
 		fi
 
+		if [ -n "$TERMUX_PKG_SERVICE_SCRIPT" ]; then
+			echo -n "TERMUX_PKG_SERVICE_SCRIPT: "
+			array_length=${#TERMUX_PKG_SERVICE_SCRIPT[@]}
+			if [ $(( $array_length & 1 )) -eq 1 ]; then
+				echo "INVALID (TERMUX_PKG_SERVICE_SCRIPT has to be an array of even length)"
+				pkg_lint_error=true
+			else
+				echo "PASS"
+			fi
+		fi
+
 		if $pkg_lint_error; then
 			exit 1
 		else