Accepting a final "." at the end of a subdomain (both RFC1035 and Modern Parser).

src/GenericParser/DomainParser.purs

@@ -19,7 +19,7 @@ import GenericParser.Parser (Parser(..)
                             , failureError
                             , current_position
                             , char, letter, parse, string
-                            , try, tryMaybe)
+                            , tryMaybe)
 
 -- | From RFC 1035: <label> ::= <letter> [ [ <ldh-str> ] <let-dig> ]
 -- | In practice, the first character can be an underscore (for example, see `_dmarc.example.com`).
@@ -53,16 +53,18 @@ label = do
          _       -> true
 
 -- | From RFC 1035: <subdomain> ::= <label> | <subdomain> "." <label>
+-- | For implementation details, this accepts a final dot "." as a suffix.
 subdomain :: Parser DomainError String
 subdomain = do
   -- First: read a label. This is bare minimum for a subdomain.
   lab <- label
-  upperlabels <- try do
+  point <- tryMaybe $ char '.'
-    _ <- char '.'
+  case point of
-    sub <- defer \_ -> subdomain
-    pure sub
-  case upperlabels of
     Nothing -> pure lab
+    Just _  -> do
+      upperlabels <- tryMaybe $ defer \_ -> subdomain
+      case upperlabels of
+        Nothing -> pure $ lab <> "."
         Just l  -> pure $ lab <> "." <> l
 
 -- | Test for the domain to be a list of subdomains then an end-of-file.

src/GenericParser/DomainParserRFC1035.purs

@@ -13,13 +13,13 @@ import Data.String as S
 import Data.String.CodeUnits as CU
 
 -- Import all common functions between RFC1035 and modern domain parsing.
-import GenericParser.DomainParser.Common (DomainError(..), eof, ldh_str, let_dig, let_dig_hyp, max_domain_length, max_label_length, Size)
+import GenericParser.DomainParser.Common (DomainError(..), eof, ldh_str, let_dig, max_domain_length, max_label_length)
 
 import GenericParser.Parser (Parser(..)
-                            , success, failureError
+                            , failureError
                             , current_position
-                            , alphanum, char, letter, many1, parse, string
+                            , char, letter, parse, string
-                            , try, tryMaybe)
+                            , tryMaybe)
 
 -- | From RFC 1035: <label> ::= <letter> [ [ <ldh-str> ] <let-dig> ]
 label :: Parser DomainError String
@@ -51,16 +51,18 @@ label = do
          _       -> true
 
 -- | From RFC 1035: <subdomain> ::= <label> | <subdomain> "." <label>
+-- | For implementation details, this accepts a final dot "." as a suffix.
 subdomain :: Parser DomainError String
 subdomain = do
   -- First: read a label. This is bare minimum for a subdomain.
   lab <- label
-  upperlabels <- try do
+  point <- tryMaybe $ char '.'
-    _ <- char '.'
+  case point of
-    sub <- defer \_ -> subdomain
-    pure sub
-  case upperlabels of
     Nothing -> pure lab
+    Just _  -> do
+      upperlabels <- tryMaybe $ defer \_ -> subdomain
+      case upperlabels of
+        Nothing -> pure $ lab <> "."
         Just l  -> pure $ lab <> "." <> l
 
 -- | Test for the domain to be a list of subdomains then an end-of-file.
@@ -68,16 +70,11 @@ subdomain = do
 sub_eof :: Parser DomainError String
 sub_eof = do
   sub <- subdomain
-  maybe_final_point <- tryMaybe $ char '.'
   _ <- eof -- In case there is still some input, it fails.
   pos <- current_position
-  let parsed_domain = did_we_parse_the_final_point maybe_final_point sub
+  if S.length sub > max_domain_length
-  if S.length parsed_domain > max_domain_length
+  then Parser \_ -> failureError pos (Just <<< DomainTooLarge $ S.length sub)
-  then Parser \_ -> failureError pos (Just <<< DomainTooLarge $ S.length parsed_domain)
+  else pure sub
-  else pure parsed_domain
-  where
-    did_we_parse_the_final_point Nothing sub = sub
-    did_we_parse_the_final_point _       sub = sub <> "."
 
 -- | From RFC 1035: <domain> ::= <subdomain> | " "
 -- |

test/Main.purs

@@ -45,19 +45,9 @@ main = do
       "a.x",
       "a2.org",
       "a33.org",
-      "a444.org",
-      "a5555.org",
-      "a66666.org",
-      "a777777.org",
-      "a8888888.org",
       "xblah.a.x",
       "xblah.a2.org",
       "xblah.a33.org",
-      "xblah.a444.org",
-      "xblah.a5555.org",
-      "xblah.a66666.org",
-      "xblah.a777777.org",
-      "xblah.a8888888.org",
       "_dmarc.example.com"
     ]
   test_series "ldh_str" ldh_str fromCharArray showerror domains