common: New function to validate domain names.

* common/mbox-util.c (is_valid_domain_name): New.
* common/t-mbox-util.c (run_dns_test): New test.

Signed-off-by: Werner Koch <wk@gnupg.org>

common/mbox-util.c

@@ -241,3 +241,42 @@ is_valid_user_id (const char *uid)
 
   return 1;
 }
+
+
+/* Returns true if STRING is a valid domain name according to the LDH
+ * rule. */
+int
+is_valid_domain_name (const char *string)
+{
+  static char const ldh_chars[] =
+    "01234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-";
+  const char *s;
+
+  /* Note that we do not check the length limit of a label or the
+   * entire name */
+
+  for (s=string; *s; s++)
+    if (*s == '.')
+      {
+        if (string == s)
+          return 0; /* Dot at the start of the string.  */
+                    /* (may also be at the end like in ".") */
+        if (s[1] == '.')
+          return 0; /* No - double dot.  */
+      }
+    else if (!strchr (ldh_chars, *s))
+      return 0;
+    else if (*s == '-')
+      {
+        if (string == s)
+          return 0;  /* Leading hyphen.  */
+        if (s[-1] == '.')
+          return 0;  /* Hyphen at begin of a label.  */
+        if (s[1] == '.')
+          return 0;  /* Hyphen at start of a label.  */
+        if (!s[1])
+          return 0;  /* Trailing hyphen.  */
+      }
+
+  return !!*string;
+}

common/mbox-util.h

@@ -24,6 +24,7 @@ int is_valid_mailbox (const char *name);
 int is_valid_mailbox_mem (const void *buffer, size_t length);
 char *mailbox_from_userid (const char *userid);
 int is_valid_user_id (const char *uid);
+int is_valid_domain_name (const char *string);
 
 
 #endif /*GNUPG_COMMON_MBOX_UTIL_H*/

common/t-mbox-util.c

@@ -33,7 +33,7 @@
 
 
 static void
-run_test (void)
+run_mbox_test (void)
 {
   static struct
   {
@@ -93,13 +93,64 @@ run_test (void)
 }
 
 
+static void
+run_dns_test (void)
+{
+  static struct
+  {
+    const char *name;
+    int valid;
+  } testtbl[] =
+    {
+      { "", 0 },
+      { ".", 0 },
+      { "-", 0 },
+      { "a", 1 },
+      { "ab", 1 },
+      { "a.b", 1 },
+      { "a.b.", 1 },
+      { ".a.b.", 0 },
+      { ".a.b", 0 },
+      { "-a.b", 0 },
+      { "a-.b", 0 },
+      { "a.-b", 0 },
+      { "a.b-", 0 },
+      { "a.b-.", 0 },
+      { "a..b", 0 },
+      { "ab.c", 1 },
+      { "a-b.c", 1 },
+      { "a-b-.c", 0 },
+      { "-a-b.c", 0 },
+      { "example.org", 1 },
+      { "x.example.org", 1 },
+      { "xy.example.org", 1 },
+      { "Xy.example.org", 1 },
+      { "-Xy.example.org", 0 },
+      { "Xy.example-.org", 0 },
+      { "foo.example.org..", 0 },
+      { "foo.example.org.", 1 },
+      { ".foo.example.org.", 0 },
+      { "..foo.example.org.", 0 },
+      { NULL, 0 }
+    };
+  int idx;
+
+  for (idx=0; testtbl[idx].name; idx++)
+    {
+      if (is_valid_domain_name (testtbl[idx].name) != testtbl[idx].valid)
+        fail (idx);
+    }
+}
+
+
 int
 main (int argc, char **argv)
 {
   (void)argc;
   (void)argv;
 
-  run_test ();
+  run_mbox_test ();
+  run_dns_test ();
 
   return 0;
 }