[ADD/WIP] Start adding a basic IPv6 parser.

It's only missing verification and a little cleanup

src/Parser.c

@@ -126,11 +126,93 @@ ParseIPv4(char **str, char **out)
     return 1;
 }
 static int
+IsIPv6Char(char c)
+{
+    return isxdigit(c) || c == ':' || c == '.';
+}
+static int
 ParseIPv6(char **str, char **out)
 {
-    /* TODO */
-    (void) str;
-    (void) out;
+    char *start;
+    size_t length;
+    char c;
+
+    int filled = 0;
+    int digit = 0;
+    int digits = 0;
+
+    start = *str;
+    length = 0;
+
+    if (Iterate(str) != '[')
+    {
+        goto fail;
+    }
+
+    while ((c = Iterate(str)) && IsIPv6Char(c))
+    {
+        char *ipv4;
+        if (isxdigit(c))
+        {
+            digit++;
+            length++;
+            continue;
+        }
+        if (c == ':')
+        {
+            if (**str == ':')
+            {
+                digit = 0;
+                if (!filled)
+                {
+                    filled = 1;
+                    length++;
+                    c = Iterate(str); /* Skip over the character */
+                    continue;
+                }
+                /* RFC3513 says the following:
+                 * > 'The "::" can only appear once in an address.' */
+                *str = start;
+                return 0;
+            }
+            if (digit < 1 || digit > 4)
+            {
+                goto fail;
+            }
+            /* We do not have to check whenever the digit here is valid, 
+             * because it has to be .*/
+            digit = 0;
+            digits++;
+
+            length++;
+            continue;
+        }
+        /* The only remaining character being '.', we are probably dealing 
+         * with an IPv4 literal. */
+        *str -= digit + 1;
+        length -= digit + 1;
+        if (ParseIPv4(str, &ipv4))
+        {
+            length += strlen(ipv4);
+            Free(ipv4);
+            c = Iterate(str);
+            goto end;
+        }
+    }
+end:
+    --(*str);
+    if (Iterate(str) != ']')
+    {
+        goto fail;
+    }
+
+    length = (size_t) (*str - start);
+    *out = Malloc(length + 1);
+    memcpy(*out, start, length);
+
+    return 1;
+fail:
+    *str = start;
     return 0;
 }
 static int