#!/bin/bash

set -e

function die() {
	echo "$@"
	exit 2
}

OUTPUT_FILE="mtd_backup.tgz"

OPENWRT="ubnt@192.168.1.1"

TMPDIR=$(mktemp -d)
BACKUP_DIR="$TMPDIR/mtd_backup"
mkdir -p "$BACKUP_DIR"
SSH_CONTROL="$TMPDIR/ssh_control"

function cleanup() {
	set +e

	echo "Closing master SSH connection"
	"${SSH_CMD[@]}" -O stop

	echo "Removing temporary backup files"
	rm -r "$TMPDIR"
}
trap cleanup EXIT

# Open master ssh connection, to avoid the need to authenticate multiple times
echo "Opening master SSH connection"
ssh -oControlMaster=yes -oControlPath="$SSH_CONTROL" -o ControlPersist=10 -n -N "$OPENWRT"

# This is the command we'll use to reuse the master connection
SSH_CMD=(ssh -oControlMaster=no -oControlPath="$SSH_CONTROL" -n "$OPENWRT")

# List remote mtd devices from /proc/mtd. The first line is just a table
# header, so skip it (using tail)
"${SSH_CMD[@]}" 'cat /proc/mtd' | tail -n+2 | while read; do
	MTD_DEV=$(echo $REPLY | cut -f1 -d:)
	MTD_NAME=$(echo $REPLY | cut -f2 -d\")
	echo "Backing up $MTD_DEV ($MTD_NAME)"
	# It's important that the remote command only prints the actual file
	# contents to stdout, otherwise our backup files will be corrupted. Other
	# info must be printed to stderr instead. Luckily, this is how the dd
	# command already behaves by default, so no additional flags are needed.
	"${SSH_CMD[@]}" "sudo dd if='/dev/${MTD_DEV}ro'" > "${BACKUP_DIR}/${MTD_DEV}_${MTD_NAME}.backup" || die "dd failed, aborting..."
done

# Use gzip and tar to compress the backup files
echo "Compressing backup files to \"$OUTPUT_FILE\""
(cd "$TMPDIR" && tar czf - "$(basename "$BACKUP_DIR")") > "$OUTPUT_FILE" || die 'tar failed, aborting...'

# Clean up a little earlier, so the completion message is the last thing the user sees
cleanup
# Reset signal handler
trap EXIT

echo -e "\nMTD backup complete. Extract the files using:\ntar xzf \"$OUTPUT_FILE\""