rrsync replacement without perl, useful for limited environment like CoreOS

rrysnc.sh

#!/bin/sh

USAGE="Use command=\"$0 [-ro|-wo] SUBDIR\"
	in front of lines in ${HOME}/.ssh/authorized_keys"
LOGFILE="${HOME}/rsync.log"
CMDNAME="$0"


# Die with the given error message.
die() {
	DATETIME="$(LANG=C date '+%F %T')"
	echo "[$DATETIME] $CMDNAME: $1" >>"$LOGFILE"
	echo >>"$LOGFILE"
	exit 2
}

# Die with the given error message.
debug() {
	DATETIME="$(LANG=C date '+%F %T')"
	echo "[$DATETIME][DEBUG] $1" | tr '\n' '\0' | sed -e 's/\0/\n[DEBUG]'"$DATETIME"'/g' >>"$LOGFILE"
}


# Get "only" option.
# It would be "w" for `-wo` (write only), "r" for `-ro` (read only), or empty string (neither `-ro` nor `-wo`).
ONLY=""
while [ "x$1" = "x-ro" -o "x$1" = "x-wo" ] ; do
	if [ "x$1" = "x-ro" ] ; then
		if [ "x$ONLY" = "xw" ] ; then
			die "the -ro and -wo options conflict."
		fi
		ONLY="r"
		shift
	else
		if [ "x$ONLY" = "xr" ] ; then
			die "the -ro and -wo options conflict."
		fi
		ONLY="w"
		shift
	fi
done
# Now "$ONLY" has "r", "w" or "".

# Ensure the subdirectory is given.
if [ $# -lt 1 ] ; then
	die "No subdirectory specified.\n${USAGE}"
fi
ALLOWED_DIR="$1"
cd "$ALLOWED_DIR"

# Ensure the rrsync is invoked via sshd.
if [ -z "$SSH_ORIGINAL_COMMAND" ] ; then
	die "Not invoked via sshd.\n${USAGE}"
fi

# Ensure the rrsync is invoked in server mode via remote rsync.
if ! echo "$SSH_ORIGINAL_COMMAND" | grep -sqE '^rsync\s+--server' ; then
	die "SSH_ORIGINAL_COMMAND='$SSH_ORIGINAL_COMMAND' is not 'rsync --server' or '--server' is not specified first."
fi

# Check whether the rsync server should be sender or receiver.
if echo "$SSH_ORIGINAL_COMMAND" | grep -sqE '^rsync\s+--server\s+--sender\s' ; then
	# The local rsync is sender mode, i.e. files should be sent from local to remote.
	if [ "x$ONLY" = "xw" ] ; then
		die "Sending to read-only server not allowed."
	fi
else
	# The local rsync is receiver mode, i.e. files should be sent from remote to local.
	if [ "x$ONLY" = "xr" ] ; then
		die "Reading to write-only server not allowed."
	fi
fi

# Command line sanity check.
set -f
set -- $SSH_ORIGINAL_COMMAND
# For each argument:
while [ $# -ge 1 ] ; do
	# Collapse continuous slashes in the argument.
	ARG="$(echo "$1" | sed -e 's!///*!/!g')"
	# Ensure the argument has no ".." as argument.
	if echo "$ARG" | grep -sqE '(^(-[a-zA-Z0-9-]+=?)?|/)\.\.(/|$)' ; then
		debug "command line: ${SSH_ORIGINAL_COMMAND}\ndangerous argument: `$1`"
		die "Do not use .. in option argument, anchor the path at the root of your restricted dir."
	fi
	# Ensure the argument has no absolute path.
	if echo "$ARG" | grep -sq '^/' ; then
		debug "command line: ${SSH_ORIGINAL_COMMAND}\ndangerous argument: `$1`"
		die "Do not use absolute path in argument, anchor the path at the root of your restricted dir."
	fi
	shift
done

# Arguments are safe!
# Execute rsync.
exec $SSH_ORIGINAL_COMMAND