git-annex/doc/design/external_backend_protocol/git-annex-backend-XFOO

#!/bin/sh
# Demo git-annex external backend program.
# 
# Install in PATH as git-annex-backend-XFOO
#
# Copyright 2020 Joey Hess; licenced under the GNU GPL version 3 or higher.

set -e

hashfile () {
	local contentfile="$1"
	# could send PROGRESS while doing this, but it's
	# hard to implement that in shell
	md5sum "$contentfile" | cut -d ' ' -f 1 || echo ''
}

while read line; do
	set -- $line
	case "$1" in
		GETVERSION)
			echo VERSION 1
		;;
		CANVERIFY)
			echo CANVERIFY-YES
		;;
		ISSTABLE)
			echo ISSTABLE-YES
		;;
		ISCRYPTOGRAPHICALLYSECURE)
			# md5 is not cryptographically secure
			echo ISCRYPTOGRAPHICALLYSECURE-NO
		;;
		GENKEY)
			contentfile="$2"
			hash=$(hashfile "$contentfile")
			sz=$(wc -c "$contentfile" | cut -d ' ' -f 1)
			if [ -n "$hash" ]; then
				echo "GENKEY-SUCCESS" "XFOO-s$sz--$hash"
			else
				echo "GENKEY-FAILURE" "md5sum failed"
			fi
		;;
		VERIFYKEYCONTENT)
			key="$2"
			contentfile="$3"
			hash=$(hashfile "$contentfile")
			khash=$(echo "$key" | sed 's/.*--//')
			if [ "$hash" = "$khash" ]; then
				echo "VERIFYKEYCONTENT-SUCCESS"
			else
				echo "VERIFYKEYCONTENT-FAILURE"
			fi
		;;
		*)
			echo ERROR protocol error
		;;
	esac
done