git_buf_quote/unquote: handle > \177

Parse values up to and including `\377` (`0xff`) when unquoting.
Print octal values as an unsigned char when quoting, lest `printf`
think we're talking about negatives.

src/buffer.c

@@ -901,7 +901,7 @@ int git_buf_quote(git_buf *buf)
 		/* escape anything unprintable as octal */
 		else if (buf->ptr[i] != ' ' &&
 				(buf->ptr[i] < '!' || buf->ptr[i] > '~')) {
-			git_buf_printf(&quoted, "\\%03o", buf->ptr[i]);
+			git_buf_printf(&quoted, "\\%03o", (unsigned char)buf->ptr[i]);
 		}
 
 		/* yay, printable! */
@@ -959,7 +959,7 @@ int git_buf_unquote(git_buf *buf)
 			case 'v': ch = '\v'; break;
 
 			/* \xyz digits convert to the char*/
-			case '0': case '1': case '2':
+			case '0': case '1': case '2': case '3':
 				if (j == buf->size-3) {
 					giterr_set(GITERR_INVALID,
 						"Truncated quoted character \\%c", ch);

tests/buf/quote.c

@@ -25,6 +25,7 @@ void test_buf_quote__quote_succeeds(void)
 	expect_quote_pass("\"foo\\r\\nbar\"", "foo\r\nbar");
 	expect_quote_pass("\"foo\\177bar\"", "foo\177bar");
 	expect_quote_pass("\"foo\\001bar\"", "foo\001bar");
+	expect_quote_pass("\"foo\\377bar\"", "foo\377bar");
 }
 
 static void expect_unquote_pass(const char *expected, const char *quoted)
@@ -64,6 +65,7 @@ void test_buf_quote__unquote_succeeds(void)
 	expect_unquote_pass("foo\r\nbar", "\"foo\\015\\012bar\"");
 	expect_unquote_pass("foo\r\nbar", "\"\\146\\157\\157\\015\\012\\142\\141\\162\"");
 	expect_unquote_pass("newline: \n", "\"newline: \\012\"");
+	expect_unquote_pass("0xff: \377", "\"0xff: \\377\"");
 }
 
 void test_buf_quote__unquote_fails(void)
@@ -76,6 +78,9 @@ void test_buf_quote__unquote_fails(void)
 	expect_unquote_fail("\"invalid escape char \\p\"");
 	expect_unquote_fail("\"invalid \\1 escape char \"");
 	expect_unquote_fail("\"invalid \\14 escape char \"");
+	expect_unquote_fail("\"invalid \\280 escape char\"");
+	expect_unquote_fail("\"invalid \\378 escape char\"");
+	expect_unquote_fail("\"invalid \\380 escape char\"");
 	expect_unquote_fail("\"invalid \\411 escape char\"");
 	expect_unquote_fail("\"truncated escape char \\\"");
 	expect_unquote_fail("\"truncated escape char \\0\"");