Make the DNS resolver accept domain names with an underscore.
More precisely, this accepts domain labels with an underscore in
the middle (i.e. not at the start or the end of the label). This
is needed to perform complex CNAME chain resolution in certain
VPN networks.
diff --git a/libc/netbsd/resolv/res_comp.c b/libc/netbsd/resolv/res_comp.c
index 6991e8b..77b81b4 100644
--- a/libc/netbsd/resolv/res_comp.c
+++ b/libc/netbsd/resolv/res_comp.c
@@ -147,6 +147,12 @@
* tell us anything about network-format data. The rest of the BIND system
* is not careful about this, but for some reason, we're doing it right here.
*/
+
+/* BIONIC: We also accept underscores in the middle of labels.
+ * This extension is needed to make resolution on some VPN networks
+ * work properly.
+ */
+
#define PERIOD 0x2e
#define hyphenchar(c) ((c) == 0x2d)
#define bslashchar(c) ((c) == 0x5c)
@@ -155,9 +161,10 @@
#define alphachar(c) (((c) >= 0x41 && (c) <= 0x5a) \
|| ((c) >= 0x61 && (c) <= 0x7a))
#define digitchar(c) ((c) >= 0x30 && (c) <= 0x39)
+#define underscorechar(c) ((c) == 0x5f)
#define borderchar(c) (alphachar(c) || digitchar(c))
-#define middlechar(c) (borderchar(c) || hyphenchar(c))
+#define middlechar(c) (borderchar(c) || hyphenchar(c) || underscorechar(c))
#define domainchar(c) ((c) > 0x20 && (c) < 0x7f)
int