Fix loss of undercores in domain names when using libidn2.

libidn2 strips underscores from international domain names
when encoding them. Indeed, it strips underscores even if
no encoding is necessary, which breaks SRV records.

Don't submit domain names to IDN encoding if they contain
one or more underscores to fix this.

src/util.c

@@ -111,6 +111,7 @@ u64 rand64(void)
   return (u64)out[outleft+1] + (((u64)out[outleft]) << 32);
 }
 
+/* returns 2 if names is OK but contains one or more underscores */
 static int check_name(char *in)
 {
   /* remove trailing . 
@@ -118,6 +119,7 @@ static int check_name(char *in)
   size_t dotgap = 0, l = strlen(in);
   char c;
   int nowhite = 0;
+  int hasuscore = 0;
   
   if (l == 0 || l > MAXDNAME) return 0;
   
@@ -141,13 +143,17 @@ static int check_name(char *in)
 	return 0;
 #endif
       else if (c != ' ')
+	{
 	  nowhite = 1;
+	  if (c == '_')
+	    hasuscore = 1;
+	}
     }
 
   if (!nowhite)
     return 0;
 
-  return 1;
+  return hasuscore ? 2 : 1;
 }
 
 /* Hostnames have a more limited valid charset than domain names
@@ -186,17 +192,19 @@ int legal_hostname(char *name)
 char *canonicalise(char *in, int *nomem)
 {
   char *ret = NULL;
-#if defined(HAVE_IDN) || defined(HAVE_LIBIDN2)
   int rc;
-#endif
   
   if (nomem)
     *nomem = 0;
   
-  if (!check_name(in))
+  if (!(rc = check_name(in)))
     return NULL;
   
 #if defined(HAVE_IDN) || defined(HAVE_LIBIDN2)
+  /* libidn2 strips underscores, so don't do IDN processing
+     if the name has an underscore (check_name() returned 2) */
+  if (rc != 2)
+    {
 #ifdef HAVE_LIBIDN2
       rc = idn2_to_ascii_lz(in, &ret, IDN2_NONTRANSITIONAL);
       if (rc == IDN2_DISALLOWED)
@@ -217,12 +225,15 @@ char *canonicalise(char *in, int *nomem)
 	  
 	  return NULL;
 	}
-#else
+      
+      return ret;
+    }
+#endif
+  
   if ((ret = whine_malloc(strlen(in)+1)))
     strcpy(ret, in);
   else if (nomem)
     *nomem = 1;    
-#endif
 
   return ret;
 }