From ad7e364fde3cf9cabe4d68972ea45dfe6941cb22 Mon Sep 17 00:00:00 2001
From: Felix Pojtinger <felix@pojtinger.com>
Date: Sun, 5 Dec 2021 21:07:03 +0100
Subject: [PATCH] feat: Add support for tape drives to Zstandard compressor

---
 cmd/stbak/cmd/archive.go | 29 +++++++++++++++++++++++++----
 cmd/stbak/cmd/update.go  |  2 +-
 2 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/cmd/stbak/cmd/archive.go b/cmd/stbak/cmd/archive.go
index 79e2c78..cdbe6a2 100644
--- a/cmd/stbak/cmd/archive.go
+++ b/cmd/stbak/cmd/archive.go
@@ -12,6 +12,7 @@ import (
 	"io"
 	"io/fs"
 	"io/ioutil"
+	"math"
 	"os"
 	"path/filepath"
 	"strconv"
@@ -788,6 +789,7 @@ func compress(
 	case compressionFormatGZipKey:
 		fallthrough
 	case compressionFormatParallelGZipKey:
+		// TODO: Add support for tape drives
 		if compressionFormat == compressionFormatGZipKey {
 			l := gzip.DefaultCompression
 			switch compressionLevel {
@@ -818,6 +820,7 @@ func compress(
 
 		return pgzip.NewWriterLevel(dst, l)
 	case compressionFormatLZ4Key:
+		// TODO: Add support for tape drives
 		l := lz4.Level5
 		switch compressionLevel {
 		case compressionLevelFastest:
@@ -849,13 +852,24 @@ func compress(
 			return nil, errUnsupportedCompressionLevel
 		}
 
-		zz, err := zstd.NewWriter(dst, zstd.WithEncoderLevel(l))
-		if err != nil {
-			return nil, err
+		var zz *zstd.Encoder
+		if isRegular {
+			z, err := zstd.NewWriter(dst, zstd.WithEncoderLevel(l))
+			if err != nil {
+				return nil, err
+			}
+			zz = z
+		} else {
+			z, err := zstd.NewWriter(dst, zstd.WithWindowSize(getNearestPowerOf2Lower(controllers.BlockSize*recordSize)))
+			if err != nil {
+				return nil, err
+			}
+			zz = z
 		}
 
 		return zz, nil
 	case compressionFormatBrotliKey:
+		// TODO: Add support for tape drives
 		l := brotli.DefaultCompression
 		switch compressionLevel {
 		case compressionLevelFastest:
@@ -874,6 +888,7 @@ func compress(
 	case compressionFormatBzip2Key:
 		fallthrough
 	case compressionFormatBzip2ParallelKey:
+		// TODO: Add support for tape drives
 		l := bzip2.DefaultCompression
 		switch compressionLevel {
 		case compressionLevelFastest:
@@ -901,11 +916,17 @@ func compress(
 	}
 }
 
+func getNearestPowerOf2Lower(n int) int {
+	power := int(math.Log2(float64(n))) // Truncation is intentional, see https://www.geeksforgeeks.org/highest-power-2-less-equal-given-number/
+
+	return int(math.Pow(2, float64(power))) // Truncation is intentional, see https://www.geeksforgeeks.org/highest-power-2-less-equal-given-number/
+}
+
 func init() {
 	archiveCmd.PersistentFlags().IntP(recordSizeFlag, "z", 20, "Amount of 512-bit blocks per record")
 	archiveCmd.PersistentFlags().StringP(fromFlag, "f", ".", "File or directory to archive")
 	archiveCmd.PersistentFlags().BoolP(overwriteFlag, "o", false, "Start writing from the start instead of from the end of the tape or tar file")
-	archiveCmd.PersistentFlags().StringP(compressionLevelFlag, "l", compressionLevelBalanced, fmt.Sprintf("Compression level to use (default %v, available are %v)", compressionLevelBalanced, knownCompressionLevels))
+	archiveCmd.PersistentFlags().StringP(compressionLevelFlag, "l", compressionLevelBalanced, fmt.Sprintf("Compression level to use (default %v, available are %v). Has no effect when on tape, where --record-size is used instead.", compressionLevelBalanced, knownCompressionLevels))
 	archiveCmd.PersistentFlags().StringP(recipientFlag, "r", "", "Path to public key of recipient to encrypt for")
 	archiveCmd.PersistentFlags().StringP(identityFlag, "i", "", "Path to private key to sign with")
 	archiveCmd.PersistentFlags().StringP(passwordFlag, "p", "", "Password for the private key")
diff --git a/cmd/stbak/cmd/update.go b/cmd/stbak/cmd/update.go
index 3e3c662..1576f8f 100644
--- a/cmd/stbak/cmd/update.go
+++ b/cmd/stbak/cmd/update.go
@@ -365,7 +365,7 @@ func init() {
 	updateCmd.PersistentFlags().IntP(recordSizeFlag, "z", 20, "Amount of 512-bit blocks per record")
 	updateCmd.PersistentFlags().StringP(fromFlag, "f", "", "Path of the file or directory to update")
 	updateCmd.PersistentFlags().BoolP(overwriteFlag, "o", false, "Replace the content on the tape or tar file")
-	updateCmd.PersistentFlags().StringP(compressionLevelFlag, "l", compressionLevelBalanced, fmt.Sprintf("Compression level to use (default %v, available are %v)", compressionLevelBalanced, knownCompressionLevels))
+	updateCmd.PersistentFlags().StringP(compressionLevelFlag, "l", compressionLevelBalanced, fmt.Sprintf("Compression level to use (default %v, available are %v). Has no effect when on tape, where --record-size is used instead.", compressionLevelBalanced, knownCompressionLevels))
 	updateCmd.PersistentFlags().StringP(recipientFlag, "r", "", "Path to public key of recipient to encrypt for")
 	updateCmd.PersistentFlags().StringP(identityFlag, "i", "", "Path to private key to sign with")
 	updateCmd.PersistentFlags().StringP(passwordFlag, "p", "", "Password for the private key")