Remove dead domain codec helpers and tighten certhash decoding

multiaddr/codecs/certhash.py

@@ -1,4 +1,4 @@
-from typing import Any, cast
+from typing import Any
 
 import multibase
 import multihash
@@ -52,12 +52,22 @@ def to_bytes(self, proto: Any, string: str) -> bytes:
         Raises:
             ValueError: If the string is not valid multibase or not a multihash.
         """
+        if not string.startswith("u"):
+            raise ValueError("certhash must use base64url multibase prefix 'u'")
+
         try:
             # Decode the multibase string to get the raw multihash bytes.
-            decoded_bytes = cast(bytes, multibase.decode(string))
+            decoded = multibase.decode(string)
         except Exception as e:
             raise ValueError(f"Failed to decode multibase string: {string}") from e
 
+        # Some multibase implementations expose decode metadata as a tuple.
+        # Normalize to raw bytes for consistent validation and return type.
+        decoded_bytes = decoded[1] if isinstance(decoded, tuple) else decoded
+        if not isinstance(decoded_bytes, (bytes, bytearray)):
+            raise ValueError("Failed to decode multibase string to bytes")
+        decoded_bytes = bytes(decoded_bytes)
+
         # Validate that the decoded bytes are a valid multihash.
         self.validate(decoded_bytes)
         return decoded_bytes

multiaddr/codecs/domain.py

@@ -37,16 +37,3 @@ def to_string(self, proto: Any, buf: bytes) -> str:
             return value
         except (UnicodeDecodeError, idna.IDNAError) as e:
             raise BinaryParseError(f"Invalid domain name encoding: {e!s}", buf, proto.name, e)
-
-
-def to_bytes(proto: Any, string: str) -> bytes:
-    # Validate using IDNA, but store as UTF-8
-    idna.encode(string, uts46=True)
-    return string.encode("utf-8")
-
-
-def to_string(proto: Any, buf: bytes) -> str:
-    string = buf.decode("utf-8")
-    # Validate using IDNA
-    idna.encode(string, uts46=True)
-    return string

newsfragments/100.removal.rst

@@ -0,0 +1,2 @@
+Removed the module-level ``to_bytes`` and ``to_string`` helpers from ``multiaddr.codecs.domain``.
+Domain codec behavior remains available through ``multiaddr.codecs.domain.Codec``.