zstd: Support negative compression-levels

libarchive/archive_write_add_filter_zstd.c

@@ -59,7 +59,15 @@ struct private_data {
 #endif
 };
 
+/* If we don't have the library use default range values (zstdcli.c v1.4.0) */
+#define CLEVEL_MIN -99
+#define CLEVEL_STD_MIN 0 /* prior to 1.3.4 and more recent without using --fast */
+#define CLEVEL_DEFAULT 3
 #define CLEVEL_STD_MAX 19 /* without using --ultra */
+#define CLEVEL_MAX 22
+
+#define MINVER_NEGCLEVEL 10304
+#define MINVER_MINCLEVEL 10306
 
 static int archive_compressor_zstd_options(struct archive_write_filter *,
 		    const char *, const char *);
@@ -98,7 +106,7 @@ archive_write_add_filter_zstd(struct archive *_a)
 	f->free = &archive_compressor_zstd_free;
 	f->code = ARCHIVE_FILTER_ZSTD;
 	f->name = "zstd";
-	data->compression_level = 3; /* Default level used by the zstd CLI */
+	data->compression_level = CLEVEL_DEFAULT;
 #if HAVE_ZSTD_H && HAVE_LIBZSTD
 	data->cstream = ZSTD_createCStream();
 	if (data->cstream == NULL) {
@@ -137,6 +145,31 @@ archive_compressor_zstd_free(struct archive_write_filter *f)
 	return (ARCHIVE_OK);
 }
 
+static int string_is_numeric (const char* value)
+{
+       size_t len = strlen(value);
+       size_t i;
+
+       if (len == 0) {
+               return (ARCHIVE_WARN);
+       }
+       else if (len == 1 && !(value[0] >= '0' && value[0] <= '9')) {
+               return (ARCHIVE_WARN);
+       }
+       else if (!(value[0] >= '0' && value[0] <= '9') &&
+                value[0] != '-' && value[0] != '+') {
+               return (ARCHIVE_WARN);
+       }
+
+       for (i = 1; i < len; i++) {
+               if (!(value[i] >= '0' && value[i] <= '9')) {
+                       return (ARCHIVE_WARN);
+               }
+       }
+
+       return (ARCHIVE_OK);
+}
+
 /*
  * Set write options.
  */
@@ -148,12 +181,24 @@ archive_compressor_zstd_options(struct archive_write_filter *f, const char *key,
 
 	if (strcmp(key, "compression-level") == 0) {
 		int level = atoi(value);
-#if HAVE_ZSTD_H && HAVE_LIBZSTD
-		if (level < 1 || level > ZSTD_maxCLevel()) {
-#else
 		/* If we don't have the library, hard-code the max level */
-		if (level < 1 || level > 22) {
+		int minimum = CLEVEL_MIN;
+		int maximum = CLEVEL_MAX;
+		if (string_is_numeric(value) != ARCHIVE_OK) {
+			return (ARCHIVE_WARN);
+		}
+#if HAVE_ZSTD_H && HAVE_LIBZSTD
+		maximum = ZSTD_maxCLevel();
+#endif
+#if HAVE_ZSTD_H && HAVE_LIBZSTD && ZSTD_VERSION_NUMBER >= MINVER_MINCLEVEL
+		if (ZSTD_versionNumber() >= MINVER_MINCLEVEL) {
+			minimum = ZSTD_minCLevel();
+		}
+		else if (ZSTD_versionNumber() < MINVER_NEGCLEVEL) {
+			minimum = CLEVEL_STD_MIN;
+		}
 #endif
+		if (level < minimum || level > maximum) {
 			return (ARCHIVE_WARN);
 		}
 		data->compression_level = level;
@@ -300,7 +345,21 @@ archive_compressor_zstd_open(struct archive_write_filter *f)
 
 	archive_string_init(&as);
 	/* --no-check matches library default */
-	archive_string_sprintf(&as, "zstd -%d --no-check", data->compression_level);
+	archive_strcpy(&as, "zstd --no-check");
+
+	if (data->compression_level < CLEVEL_STD_MIN) {
+		struct archive_string as2;
+		archive_string_init(&as2);
+		archive_string_sprintf(&as2, " --fast=%d", -data->compression_level);
+		archive_string_concat(&as, &as2);
+		archive_string_free(&as2);
+	} else {
+		struct archive_string as2;
+		archive_string_init(&as2);
+		archive_string_sprintf(&as2, " -%d", data->compression_level);
+		archive_string_concat(&as, &as2);
+		archive_string_free(&as2);
+	}
 
 	if (data->compression_level > CLEVEL_STD_MAX) {
 		archive_strcat(&as, " --ultra");

libarchive/archive_write_set_options.3

@@ -255,7 +255,8 @@ If supported, the default value is read from
 .Bl -tag -compact -width indent
 .It Cm compression-level
 The value is interpreted as a decimal integer specifying the
-compression level. Supported values are from 1 to 22.
+compression level. Supported values depend on the library version,
+common values are from 1 to 22.
 .El
 .It Format 7zip
 .Bl -tag -compact -width indent

libarchive/test/test_write_filter_zstd.c

@@ -124,6 +124,9 @@ DEFINE_TEST(test_write_filter_zstd)
 	    archive_write_set_filter_option(a, NULL, "compression-level", "25")); /* too big */
 	assertEqualIntA(a, ARCHIVE_OK,
 	    archive_write_set_filter_option(a, NULL, "compression-level", "9"));
+	/* Following is disabled as it will fail on library versions < 1.3.4 */
+	/* assertEqualIntA(a, ARCHIVE_OK,
+	    archive_write_set_filter_option(a, NULL, "compression-level", "-1")); */
 	assertEqualIntA(a, ARCHIVE_OK,
 	    archive_write_set_filter_option(a, NULL, "compression-level", "7"));
 	assertEqualIntA(a, ARCHIVE_OK, archive_write_open_memory(a, buff, buffsize, &used2));

tar/bsdtar.1

@@ -631,7 +631,8 @@ A decimal integer from 4 to 7 specifying the lz4 compression block size
 Use the previous block of the block being compressed for
 a compression dictionary to improve compression ratio.
 .It Cm zstd:compression-level
-A decimal integer from 1 to 22 specifying the zstd compression level.
+A decimal integer specifying the zstd compression level. Supported values depend
+on the library version, common values are from 1 to 22.
 .It Cm lzop:compression-level
 A decimal integer from 1 to 9 specifying the lzop compression level.
 .It Cm xz:compression-level