feat: add zstd in-transfer compression support

* clean up trailing whitespace
* update README.md and add a standalone Credits section

README.md

@@ -1,8 +1,10 @@
 # btrfs-sync
 
-Smart and easy sync of BTRFS snapshots, locally or through SSH. 
+> **Note**: This fork simply adds in-transfer `zstd` compression support
 
-![Example](resources/btrfs-sync.gif)
+Smart and easy sync of BTRFS snapshots, locally or through SSH.
+
+See example [gif](resources/btrfs-sync.gif).
 
 Can be used in conjunction with [btrfs-snp](https://ownyourbits.com/2017/12/27/schedule-btrfs-snapshots-with-btrfs-snp/)
 
@@ -31,8 +33,8 @@ Delete subvolume (no-commit): '/media/USBdrive/home-snapshots/hourly_2018-03-08_
 ## Features
 
 - Simple syntax
-- Progress indication
-- Support for _xz_ or _pbzip2_ compression in order to save bandwidth.
+- Optional progress indication (using `pv`)
+- Support for `zstd`, `xz` or `pbzip2` compression in order to save bandwidth.
 - Retention policy
 - Automatic incremental synchronization
 - Cron friendly
@@ -49,6 +51,7 @@ Usage:
   -d|--delete       delete snapshots in <dst> that don't exist in <src>
   -z|--xz           use xz     compression. Saves bandwidth, but uses one CPU
   -Z|--pbzip2       use pbzip2 compression. Saves bandwidth, but uses all CPUs
+  -s|--zstd         use zstd compression.
   -q|--quiet        don't display progress
   -v|--verbose      display more information
   -h|--help         show usage
@@ -57,7 +60,7 @@ Usage:
 <user> requires privileged permissions at <host> for the 'btrfs' command
 ```
 
-## Examples 
+## Examples
 
 ### Manual
 
@@ -85,7 +88,7 @@ Synchronize only monthly snapshots of _home_ to a USB drive in another machine
 # btrfs-sync /home/user/.snapshots/monthly_* user@server:/media/USBdrive/home-snapshots
 ```
 
-### Cron 
+### Cron
 
 Daily synchronization over the internet, keep only last 50
 
@@ -107,4 +110,8 @@ EOF
 chmod +x /etc/cron.daily/btrfs-sync
 ```
 
-More at [ownyourbits.com](https://ownyourbits.com/2018/03/09/easy-sync-of-btrfs-snapshots-with-btrfs-sync/)
+### Credits
+
+Original work by *nachoparker* of [ownyourbits.com](https://ownyourbits.com/2018/03/09/easy-sync-of-btrfs-snapshots-with-btrfs-sync/)
+
+zstd compression support added by wanderer of [dotya.ml](https://git.dotya.ml/wanderer)

btrfs-sync

@@ -43,6 +43,7 @@ print_usage() {
   -d|--delete       delete snapshots in <dst> that don't exist in <src>
   -z|--xz           use xz     compression. Saves bandwidth, but uses one CPU
   -Z|--pbzip2       use pbzip2 compression. Saves bandwidth, but uses all CPUs
+  -s|--zstd         use zstd compression.
   -p|--port         SSH port. Default 22
   -q|--quiet        don't display progress
   -v|--verbose      display more information
@@ -76,7 +77,7 @@ PORT=22
 ZIP=cat PIZ=cat
 SILENT=">/dev/null"
 
-OPTS=$( getopt -o hqzZk:p:dv -l quiet -l help -l xz -l pbzip2 -l keep: -l port: -l delete -l verbose -- "$@" 2>/dev/null )
+OPTS=$( getopt -o hqzZsk:p:dv -l quiet -l help -l xz -l pbzip2 -l zstd -l keep: -l port: -l delete -l verbose -- "$@" 2>/dev/null )
 [[ $? -ne 0 ]] && { echo "error parsing arguments"; exit 1; }
 eval set -- "$OPTS"
 
@@ -89,6 +90,7 @@ while true; do
     -p|--port   ) PORT=$2    ; shift 2 ;;
     -z|--xz     ) ZIP=xz     PIZ=( xz     -d ); shift 1 ;;
     -Z|--pbzip2 ) ZIP=pbzip2 PIZ=( pbzip2 -d ); shift 1 ;;
+    -s|--zstd   ) ZIP=zstd   PIZ=( zstd   -d ); shift 1 ;;
     -v|--verbose) SILENT=""  VERBOSE=1        ; shift 1 ;;
     --)                shift;  break   ;;
   esac
@@ -160,6 +162,15 @@ while read entry; do SRCS+=( "$entry" ); done < <(
   }
 }
 
+## check zstd
+[[ "$ZIP" == "zstd" ]] && {
+    "${SRC_CMD[@]}" type zstd &>/dev/null && \
+    "${DST_CMD[@]}" type zstd &>/dev/null || {
+      echo "INFO: 'zstd' not installed on both ends, fallback to 'xz'"
+      ZIP=xz PIZ=unxz
+  }
+}
+
 ## use 'pv' command if available
 PV=( pv -F"time elapsed [%t] | rate %r | total size [%b]" )
 [[ "$QUIET" == "1" ]] && PV=( cat ) || type pv &>/dev/null || {