Better support for reading/writing non-ASCII xattr values from/to tar

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

1 files changed, 29 insertions, 10 deletions

diff --git a/lib/tar/base64.c b/lib/tar/base64.c
index 0ccf3c4..f88444a 100644
--- a/lib/tar/base64.c
+++ b/lib/tar/base64.c
@@ -23,18 +23,37 @@ static sqfs_u8 convert(char in)
 	return 0;
 }
 
-void base64_decode(sqfs_u8 *out, const char *in)
+size_t base64_decode(sqfs_u8 *out, const char *in, size_t len)
 {
-	char temp[4];
+	sqfs_u8 *start = out;
 
-	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++));
+	while (len > 0) {
+		unsigned int diff = 0, value = 0;
 
-		*(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);
+		while (diff < 4 && len > 0) {
+			if (*in == '=' || *in == '_' || *in == '\0') {
+				len = 0;
+			} else {
+				value = (value << 6) | convert(*(in++));
+				--len;
+				++diff;
+			}
+		}
+
+		if (diff < 2)
+			break;
+
+		value <<= 6 * (4 - diff);
+
+		switch (diff) {
+		case 4:  out[2] = value & 0xff; /* fall-through */
+		case 3:  out[1] = (value >> 8) & 0xff; /* fall-through */
+		default: out[0] = (value >> 16) & 0xff;
+		}
+
+		out += (diff * 3) / 4;
 	}
+
+	*out = '\0';
+	return out - start;
 }