libtar: add support for xattr extensions

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>

1 files changed, 33 insertions, 0 deletions

diff --git a/lib/tar/base64.c b/lib/tar/base64.c
new file mode 100644
index 0000000..313e9f4
--- /dev/null
+++ b/lib/tar/base64.c
@@ -0,0 +1,33 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+#include "internal.h"
+
+static uint8_t convert(char in)
+{
+	if (isupper(in))
+		return in - 'A';
+	if (islower(in))
+		return in - 'a' + 26;
+	if (isdigit(in))
+		return in - '0' + 52;
+	if (in == '+')
+		return 62;
+	if (in == '/' || in == '-')
+		return 63;
+	return 0;
+}
+
+void base64_decode(uint8_t *out, const char *in)
+{
+	char temp[4];
+
+	while (*in != '\0' && *in != '=') {
+		temp[0] = *in == '\0' ? 0 : convert(*(in++));
+		temp[1] = *in == '\0' ? 0 : convert(*(in++));
+		temp[2] = *in == '\0' ? 0 : convert(*(in++));
+		temp[3] = *in == '\0' ? 0 : convert(*(in++));
+
+		*(out++) = ((temp[0] << 2) & 0xFC) | ((temp[1] >> 4) & 0x03);
+		*(out++) = ((temp[1] << 4) & 0xF0) | ((temp[2] >> 2) & 0x0F);
+		*(out++) = ((temp[2] << 6) & 0xC0) | ( temp[3]       & 0x3F);
+	}
+}