Rearrange the local part syntax checks to put the more likely success conditions first

Author: JoshData

email_validator/rfc_constants.py

@@ -6,6 +6,7 @@
 # characters are permitted in email addresses (not taking into
 # account internationalization):
 ATEXT = r'a-zA-Z0-9_!#\$%&\'\*\+\-/=\?\^`\{\|\}~'
+ATEXT_RE = re.compile('[.' + ATEXT + ']')  # ATEXT plus dots
 
 # A "dot atom text", per RFC 2822 3.2.4:
 DOT_ATOM_TEXT = re.compile('[' + ATEXT + ']+(?:\\.[' + ATEXT + r']+)*\Z')
@@ -15,6 +16,7 @@
 # RFC3629 section 4, which appear to be the Unicode code points from
 # U+0080 to U+10FFFF.
 ATEXT_INTL = ATEXT + u"\u0080-\U0010FFFF"
+ATEXT_INTL_RE = re.compile('[.' + ATEXT_INTL + ']')  # ATEXT_INTL plus dots
 DOT_ATOM_TEXT_INTL = re.compile('[' + ATEXT_INTL + ']+(?:\\.[' + ATEXT_INTL + r']+)*\Z')
 
 # The domain part of the email address, after IDNA (ASCII) encoding,

email_validator/syntax.py

@@ -1,6 +1,6 @@
 from .exceptions_types import EmailSyntaxError
 from .rfc_constants import EMAIL_MAX_LENGTH, LOCAL_PART_MAX_LENGTH, DOMAIN_MAX_LENGTH, \
-    DOT_ATOM_TEXT, DOT_ATOM_TEXT_INTL, ATEXT, ATEXT_INTL, ATEXT_HOSTNAME_INTL, DNS_LABEL_LENGTH_LIMIT, DOT_ATOM_TEXT_HOSTNAME, DOMAIN_NAME_REGEX
+    DOT_ATOM_TEXT, DOT_ATOM_TEXT_INTL, ATEXT_RE, ATEXT_INTL_RE, ATEXT_HOSTNAME_INTL, DNS_LABEL_LENGTH_LIMIT, DOT_ATOM_TEXT_HOSTNAME, DOMAIN_NAME_REGEX
 
 import re
 import unicodedata
@@ -57,44 +57,25 @@ def validate_email_local_part(local, allow_smtputf8=True, allow_empty_local=Fals
         reason = get_length_reason(local, limit=LOCAL_PART_MAX_LENGTH)
         raise EmailSyntaxError("The email address is too long before the @-sign {}.".format(reason))
 
-    # Check for invalid characters.
-    # (RFC 2822 Section 3.2.4 / RFC 5322 Section 3.2.3, plus RFC 6531 section 3.3
-    # if internationalized local parts are allowed)
-    atext_re = re.compile('[.' + (ATEXT if not allow_smtputf8 else ATEXT_INTL) + ']')
-    bad_chars = set(
-        safe_character_display(c)
-        for c in local
-        if not atext_re.match(c)
-    )
-    if bad_chars:
-        raise EmailSyntaxError("The email address contains invalid characters before the @-sign: " + ", ".join(sorted(bad_chars)) + ".")
-
-    # Check for dot errors imposted by the dot-atom rule.
-    # (RFC 2822 3.2.4)
-    check_dot_atom(local, 'An email address cannot start with a {}.', 'An email address cannot have a {} immediately before the @-sign.', is_hostname=False)
-
     # Check the local part against the non-internationalized regular expression.
+    # Most email addresses match this regex so it's probably fastest to check this first.
     # (RFC 2822 3.2.4)
     m = DOT_ATOM_TEXT.match(local)
     if m:
+        # It's valid.
+
         # Return the local part unchanged and flag that SMTPUTF8 is not needed.
         return {
             "local_part": local,
             "ascii_local_part": local,
             "smtputf8": False,
         }
 
-    else:
-        # The local part failed the ASCII check. Now try the extended internationalized requirements.
-        # This should already be handled by the bad_chars and check_dot_atom tests above.
-        # It's the same pattern but with additional characters permitted.
-        m = DOT_ATOM_TEXT_INTL.match(local)
-        if not m:
-            raise EmailSyntaxError("The email address contains invalid characters before the @-sign.")
-        # It would be valid if internationalized characters were allowed by the caller.
-        if not allow_smtputf8:
-            raise EmailSyntaxError("Internationalized characters before the @-sign are not supported.")
-
+    # The local part failed the ASCII check. Try the extended character set
+    # for internationalized addresses. It's the same pattern but with additional
+    # characters permitted.
+    m = DOT_ATOM_TEXT_INTL.match(local)
+    if m and allow_smtputf8:
         # It's valid.
 
         # RFC 6532 section 3.1 also says that Unicode NFC normalization should be applied,
@@ -122,6 +103,27 @@ def validate_email_local_part(local, allow_smtputf8=True, allow_empty_local=Fals
             "smtputf8": True,
         }
 
+    # It's not a valid local part either non-internationalized or internationalized.
+    # Let's find out why.
+
+    # Check for invalid characters.
+    # (RFC 2822 Section 3.2.4 / RFC 5322 Section 3.2.3, plus RFC 6531 section 3.3)
+    bad_chars = set(
+        safe_character_display(c)
+        for c in local
+        if not (ATEXT_INTL_RE if allow_smtputf8 else ATEXT_RE).match(c)
+    )
+    if bad_chars:
+        raise EmailSyntaxError("The email address contains invalid characters before the @-sign: " + ", ".join(sorted(bad_chars)) + ".")
+
+    # Check for dot errors imposted by the dot-atom rule.
+    # (RFC 2822 3.2.4)
+    check_dot_atom(local, 'An email address cannot start with a {}.', 'An email address cannot have a {} immediately before the @-sign.', is_hostname=False)
+
+    # All of the reasons should already have been checked, but just in case
+    # we have a fallback message.
+    raise EmailSyntaxError("The email address contains invalid characters before the @-sign.")
+
 
 def check_unsafe_chars(s):
     # Check for unsafe characters or characters that would make the string