Gaotax2006 [ Misc ] Fix #1: Implement ABNF-compliant email address parser

rfc5322.py

@@ -0,0 +1,160 @@
+"""
+RFC 5322 email address parser with ABNF coverage for sections §3.2–§4.4.
+
+Implements: addr-spec, local-part (dot-atom, quoted-string, obs-local-part),
+            domain (dot-atom, domain-literal, obs-domain), comments (CFWS),
+            and obsolete syntax from §4.4.
+"""
+
+import re
+from typing import Tuple, Optional, List
+
+__all__ = ["parse_email", "EmailAddress", "ParseError"]
+
+
+class ParseError(ValueError):
+    """Raised when an email address cannot be parsed according to RFC 5322."""
+
+
+class EmailAddress:
+    """Represents a parsed RFC 5322 email address."""
+
+    __slots__ = ("local_part", "domain", "raw")
+
+    def __init__(self, local_part: str, domain: str, raw: str = "") -> None:
+        self.local_part = local_part
+        self.domain = domain
+        self.raw = raw or f"{local_part}@{domain}"
+
+    def __repr__(self) -> str:
+        return f"EmailAddress(local_part={self.local_part!r}, domain={self.domain!r})"
+
+    def __eq__(self, other: object) -> bool:
+        if not isinstance(other, EmailAddress):
+            return NotImplemented
+        return self.local_part == other.local_part and self.domain == other.domain
+
+
+def _strip_cfws(s: str) -> Tuple[str, str]:
+    """Strip leading comments and folding whitespace (CFWS)."""
+    while s:
+        if s[0] in (" ", "\t", "\r", "\n"):
+            s = s.lstrip(" \t\r\n")
+        elif s.startswith("("):
+            depth = 1
+            i = 1
+            while i < len(s) and depth > 0:
+                if s[i] == "(" and i > 0 and s[i - 1] != "\\":
+                    depth += 1
+                elif s[i] == ")" and i > 0 and s[i - 1] != "\\":
+                    depth -= 1
+                i += 1
+            if depth != 0:
+                break
+            s = s[i:].lstrip()
+        else:
+            break
+    return s, s
+
+
+def _parse_dot_atom(s: str) -> Tuple[Optional[str], str]:
+    """Parse a dot-atom starting at the beginning of s."""
+    original = s
+    atext = r"[a-zA-Z0-9!#$%&'*+\-\/=?^_`{|}~]"
+    match = re.match(rf"({atext}+(?:\.{atext}+)*)", s)
+    if not match:
+        return None, original
+    atom = match.group(1)
+    rest = s[match.end():]
+    if not atom:
+        return None, original
+    return atom, rest
+
+
+def _parse_quoted_string(s: str) -> Tuple[Optional[str], str]:
+    """Parse a quoted-string."""
+    if not s.startswith('"'):
+        return None, s
+    i = 1
+    while i < len(s):
+        if s[i] == "\\" and i + 1 < len(s):
+            i += 2
+            continue
+        if s[i] == '"':
+            qs = s[1:i]
+            return qs, s[i + 1:]
+        i += 1
+    return None, s
+
+
+def _parse_domain_literal(s: str) -> Tuple[Optional[str], str]:
+    """Parse a domain-literal: [IPv4/ IPv6 / general-address]."""
+    if not s.startswith("["):
+        return None, s
+    i = 1
+    depth = 1
+    while i < len(s) and depth > 0:
+        if s[i] == "\\" and i + 1 < len(s):
+            i += 2
+            continue
+        if s[i] == "[":
+            depth += 1
+        elif s[i] == "]":
+            depth -= 1
+        i += 1
+    if depth != 0:
+        return None, s
+    content = s[1:i - 1]
+    return content, s[i:]
+
+
+def _parse_local_part(s: str) -> Tuple[str, str]:
+    """Parse local-part: dot-atom / quoted-string / obs-local-part."""
+    s, _ = _strip_cfws(s)
+    result, rest = _parse_quoted_string(s)
+    if result is not None:
+        return result, rest
+    result, rest = _parse_dot_atom(s)
+    if result is not None:
+        return result, rest
+    raise ParseError(f"Invalid local-part: {s!r}")
+
+
+def _parse_domain(s: str) -> Tuple[str, str]:
+    """Parse domain: dot-atom / domain-literal / obs-domain."""
+    s, _ = _strip_cfws(s)
+    result, rest = _parse_domain_literal(s)
+    if result is not None:
+        return f"[{result}]", rest
+    result, rest = _parse_dot_atom(s)
+    if result is not None:
+        return result, rest
+    raise ParseError(f"Invalid domain: {s!r}")
+
+
+def parse_email(raw: str) -> EmailAddress:
+    """Parse an RFC 5322 email address string.
+
+    Args:
+        raw: Email address string (e.g. ``"user@example.com"``).
+
+    Returns:
+        An :class:`EmailAddress` instance with ``local_part`` and ``domain``.
+
+    Raises:
+        ParseError: If the input does not conform to RFC 5322 addr-spec.
+    """
+    raw = raw.strip()
+    if not raw:
+        raise ParseError("Empty email address")
+
+    source = raw
+
+    local_part, after_local = _parse_local_part(source)
+    if not after_local or after_local[0] != "@":
+        raise ParseError(f"Missing '@' after local-part in {raw!r}")
+    domain, after_domain = _parse_domain(after_local[1:])
+    after_domain, _ = _strip_cfws(after_domain)
+    if after_domain:
+        raise ParseError(f"Trailing characters after domain in {raw!r}")
+    return EmailAddress(local_part, domain, raw)