From 999bf8d5d61a8d87f4f4cc53e132b095ac707bec Mon Sep 17 00:00:00 2001
From: 0x1eef <0x1eef@protonmail.com>
Date: Fri, 22 Sep 2023 01:20:52 -0300
Subject: [PATCH] Address 2.2.1 of RFC 4291

Treat `2001:DB8:0:0:8:800:200C:417A` as valid.
---
 src/isinetaddr6.c       | 22 +++++++---------------
 test/isinetaddr6_test.c |  5 ++++-
 2 files changed, 11 insertions(+), 16 deletions(-)

diff --git a/src/isinetaddr6.c b/src/isinetaddr6.c
index d623a3d..b5ac714 100644
--- a/src/isinetaddr6.c
+++ b/src/isinetaddr6.c
@@ -30,28 +30,20 @@ isinetaddr6(const char *str)
       char new_str[MAX_STRLEN];
       return isinetaddr6(expand(str, len, new_str, i));
     } else if (str[i] == SEP) {
-      if (digitlen < MAX_DIGITLEN) {
-        return 0;
-      } else {
-        digitlen = 0;
-        hextets++;
-      }
+      digitlen = 0;
     } else if (isxdigit(str[i])) {
-      if (digitlen == MAX_DIGITLEN) {
+      digitlen++;
+      hexdigits++;
+      if (digitlen > MAX_DIGITLEN) {
         return 0;
-      } else {
-        digitlen++;
-        hexdigits++;
+      } else if (str[i-1] == SEP) {
+        hextets++;
       }
     } else {
       return 0;
     }
   }
-  if (hextets == MAX_HEXTETS) {
-    return hexdigits <= MAX_HEXDIGITS && digitlen == MAX_DIGITLEN;
-  } else {
-    return 0;
-  }
+  return hextets == MAX_HEXTETS && hexdigits <= MAX_HEXDIGITS;
 }
 
 static int
diff --git a/test/isinetaddr6_test.c b/test/isinetaddr6_test.c
index 7e4fe11..1781b49 100644
--- a/test/isinetaddr6_test.c
+++ b/test/isinetaddr6_test.c
@@ -12,6 +12,9 @@ const char *valid[] = {
   "1234:5678:9abc:def0:face:face:b00c:0ffe",
   "2001:19f0:5401:0000:0000:ffff:1e61:face",
   "dead:beef:cafe:babe:affe:8a2e:0370:7334",
+  "2001:DB8:0:0:8:800:200C:417A",
+  "0000:0000:0000:0000:0000:0000:0000:0",
+  "FEDC:BA98:7654:3210:FEDC:BA98:7654:3210",
 
   /* valid IPv6 (double colon) */
   "fe80::c001:a0ff:fe12:3456",
@@ -34,8 +37,8 @@ const char *valid[] = {
 const char *invalid[] = {
   /* invalid IPv6 (single colon) */
   "0000:0000:0000:0000:0000:0000:0000:000Z",
-  "0000:0000:0000:0000:0000:0000:0000:0",
   "0000:0000:0000:0000:0000:0000:0000:",
+  "2001:DB8:0:Z:8:800:200C:417A",
 
   /* invalid IPv6 (double colon) */
   ":::", "2001:::1", "2001:::1::",