From 875b0af73ff25c6f85097b05820ae9f0c0894486 Mon Sep 17 00:00:00 2001
From: "Steinar H. Gunderson" <sesse@samfundet.no>
Date: Sun, 9 Dec 2018 22:24:09 +0100
Subject: [PATCH] Support changing compressors (e.g. to get zstd or xz).

---
 backup.sh                  | 26 ++++++++++++++++++--------
 conf/backup.config.example | 11 +++++++++++
 2 files changed, 29 insertions(+), 8 deletions(-)

diff --git a/backup.sh b/backup.sh
index dfe8d45..e64312f 100755
--- a/backup.sh
+++ b/backup.sh
@@ -117,6 +117,13 @@ backup()
 	# a GPG command line.
 	storageprogram=$( findconf storageprogram $computer $sfilesystem )
 
+	# Find compressor and decompressor for this filesystem.
+	fscompressor=$( findconf compressor $computer $filesystem )
+	if [ -z "$fscompressor" ]; then
+		fscompressor=$compressor
+	fi
+	decompressor=$( findconf decompressor $computer $filesystem )
+
 	# We try to run tar on the remote computer
 	#    c create archive
 	#    C change to directory first
@@ -128,8 +135,8 @@ backup()
 	#    Pipe the stuff over ssh to ourselves, run pee to cat the contents to a
 	#    file and build a file list, respectivly.  
 	TARFILE=$DATE.tmp
-	TARCMD="ssh -n $username@$computer \"$nice tar --one-file-system --use-compress-program $compressor -cf - -C $filesystem . $lastcmd \
-		--exclude-from=$remotehome/.backup/exclude\" | pee \"$storageprogram > $TARFILE\" \"tar tzvf -\""
+	TARCMD="ssh -n $username@$computer \"$nice tar --one-file-system --use-compress-program $fscompressor -cf - -C $filesystem . $lastcmd \
+		--exclude-from=$remotehome/.backup/exclude\" | pee \"$storageprogram > $TARFILE\" \"$decompressor | tar tvf -\""
 	infomsg "Running $TARCMD"
 	eval $TARCMD > $DATE.idx
 
@@ -236,12 +243,15 @@ if [ -z "$remotehome" ]; then
 	diemsg "Could not expand ~ for user $username"
 fi
 
-# Check if pigz is available
-if ssh -n $username@$computer "pigz -V 2>/dev/null"; then
-	compressor=pigz
-else
-	infomsg "pigz missing; falling back to gzip."
-	compressor=gzip
+# Check if pigz is available. Note that this may be overridden per-filesystem later.
+compressor=$( findconf compressor $computer )
+if [ -z "$compressor" ]; then
+	if ssh -n $username@$computer "pigz -V 2>/dev/null"; then
+		compressor=pigz
+	else
+		infomsg "pigz missing; falling back to gzip."
+		compressor=gzip
+	fi
 fi
 
 # Check if nice and ionice are available
diff --git a/conf/backup.config.example b/conf/backup.config.example
index 254092d..0324ae7 100644
--- a/conf/backup.config.example
+++ b/conf/backup.config.example
@@ -38,6 +38,17 @@
 	# Otherwise, assume root privileges.
 	nonpriv =
 
+	# If set, use the given program to compress and decompress the backup
+	# (compressor must exist on the host to be backed up, and decompressor
+	# must exist on the backup host). compressor can be unset; if so,
+	# either pigz or gzip (autodetected) will be used. You can give flags
+	# (e.g. -9) if you wish.
+	#
+	# Not used for nonpriv (change output-encrypted-backup instead).
+	# The file will be called .tgz no matter what the compressor is.
+	compressor =
+	decompressor = gzip -d
+
 # Config for a given host
 [pannekake.samfundet.no]
 	maxnumfull = 2
-- 
2.39.2