Prohibit custom codecs on domains

Postgres always includes the base type OID in the RowDescription message even if the query is technically returning domain values. This makes custom codecs on domains ineffective, and so prohibit them to avoid confusion and bug reports. See postgres/postgres@d9b679c and https://postgr.es/m/27307.1047485980%40sss.pgh.pa.us for context. Fixes: #457.

Author: elprans

asyncpg/connection.py

@@ -1160,9 +1160,18 @@ async def set_type_codec(self, typename, *,
 self._check_open()
 typeinfo=awaitself._introspect_type(typename, schema)
 ifnotintrospection.is_scalar_type(typeinfo):
-raiseValueError(
+raiseexceptions.InterfaceError(
 'cannot use custom codec on non-scalar type{}.{}'.format(
 schema, typename))
+ifintrospection.is_domain_type(typeinfo):
+raiseexceptions.UnsupportedClientFeatureError(
+'custom codecs on domain types are not supported',
+hint='Set the codec on the base type.',
+detail=(
+'PostgreSQL does not distinguish domains from '
+'their base types in query results at the protocol level.'
+ )
+ )
 
 oid=typeinfo['oid']
 self._protocol.get_settings().add_python_codec(

asyncpg/exceptions/_base.py

@@ -12,7 +12,8 @@
 
 __all__= ('PostgresError', 'FatalPostgresError', 'UnknownPostgresError',
 'InterfaceError', 'InterfaceWarning', 'PostgresLogMessage',
-'InternalClientError', 'OutdatedSchemaCacheError', 'ProtocolError')
+'InternalClientError', 'OutdatedSchemaCacheError', 'ProtocolError',
+'UnsupportedClientFeatureError')
 
 
 def_is_asyncpg_class(cls):
@@ -214,6 +215,10 @@ class DataError(InterfaceError, ValueError):
 """An error caused by invalid query input."""
 
 
+classUnsupportedClientFeatureError(InterfaceError):
+"""Requested feature is unsupported by asyncpg."""
+
+
 classInterfaceWarning(InterfaceMessage, UserWarning):
 """A warning caused by an improper use of asyncpg API."""
 

asyncpg/introspection.py

@@ -168,3 +168,7 @@ def is_scalar_type(typeinfo) -> bool:
 typeinfo['kind'] inSCALAR_TYPE_KINDSand
 nottypeinfo['elemtype']
  )
+
+
+defis_domain_type(typeinfo) ->bool:
+returntypeinfo['kind'] ==b'd'

asyncpg/protocol/codecs/base.pyx

@@ -66,14 +66,14 @@ cdef class Codec:
 self.decoder =<codec_decode_func>&self.decode_array_text
 eliftype== CODEC_RANGE:
 if format != PG_FORMAT_BINARY:
-raiseNotImplementedError(
+raiseexceptions.UnsupportedClientFeatureError(
 'cannot decode type "{}"."{}": text encoding of '
 'range types is not supported'.format(schema, name))
 self.encoder =<codec_encode_func>&self.encode_range
 self.decoder =<codec_decode_func>&self.decode_range
 eliftype== CODEC_COMPOSITE:
 if format != PG_FORMAT_BINARY:
-raiseNotImplementedError(
+raiseexceptions.UnsupportedClientFeatureError(
 'cannot decode type "{}"."{}": text encoding of '
 'composite types is not supported'.format(schema, name))
 self.encoder =<codec_encode_func>&self.encode_composite
@@ -675,9 +675,8 @@ cdef class DataCodecConfig:
 # added builtin types, for which this version of
 # asyncpg is lacking support.
 #
-raiseNotImplementedError(
-'unhandled standard data type{!r} (OID{})'.format(
- name, oid))
+raise exceptions.UnsupportedClientFeatureError(
+ f'unhandled standard data type{name!r} (OID{oid})')
 else:
 # This is a non-BKI type, and as such, has no
 # stable OID, so no possibility of a builtin codec.

tests/test_codecs.py

@@ -1091,7 +1091,7 @@ async def test_extra_codec_alias(self):
 # This should fail, as there is no binary codec for
 # my_dec_t and text decoding of composites is not
 # implemented.
-withself.assertRaises(NotImplementedError):
+withself.assertRaises(asyncpg.UnsupportedClientFeatureError):
 res=awaitself.con.fetchval('''
  SELECT ($1::my_dec_t, 'a=>1'::hstore)::rec_t AS result
  ''', 44)
@@ -1148,7 +1148,7 @@ def hstore_encoder(obj):
 self.assertEqual(at[0].type, pt[0])
 
 err='cannot use custom codec on non-scalar type public._hstore'
-withself.assertRaisesRegex(ValueError, err):
+withself.assertRaisesRegex(asyncpg.InterfaceError, err):
 awaitself.con.set_type_codec('_hstore',
 encoder=hstore_encoder,
 decoder=hstore_decoder)
@@ -1160,7 +1160,7 @@ def hstore_encoder(obj):
 try:
 err='cannot use custom codec on non-scalar type '+ \
 'public.mytype'
-withself.assertRaisesRegex(ValueError, err):
+withself.assertRaisesRegex(asyncpg.InterfaceError, err):
 awaitself.con.set_type_codec(
 'mytype', encoder=hstore_encoder,
 decoder=hstore_decoder)
@@ -1261,13 +1261,14 @@ async def test_custom_codec_on_domain(self):
  ''')
 
 try:
-awaitself.con.set_type_codec(
-'custom_codec_t',
-encoder=lambdav: str(v),
-decoder=lambdav: int(v))
-
-v=awaitself.con.fetchval('SELECT $1::custom_codec_t', 10)
-self.assertEqual(v, 10)
+withself.assertRaisesRegex(
+asyncpg.UnsupportedClientFeatureError,
+'custom codecs on domain types are not supported'
+ ):
+awaitself.con.set_type_codec(
+'custom_codec_t',
+encoder=lambdav: str(v),
+decoder=lambdav: int(v))
 finally:
 awaitself.con.execute('DROP DOMAIN custom_codec_t')
 
@@ -1666,7 +1667,7 @@ async def test_unknown_type_text_fallback(self):
 # Text encoding of ranges and composite types
 # is not supported yet.
 withself.assertRaisesRegex(
-RuntimeError,
+asyncpg.UnsupportedClientFeatureError,
 'text encoding of range types is not supported'):
 
 awaitself.con.fetchval('''
@@ -1675,7 +1676,7 @@ async def test_unknown_type_text_fallback(self):
  ''', ['a', 'z'])
 
 withself.assertRaisesRegex(
-RuntimeError,
+asyncpg.UnsupportedClientFeatureError,
 'text encoding of composite types is not supported'):
 
 awaitself.con.fetchval('''
@@ -1847,7 +1848,7 @@ async def test_custom_codec_large_oid(self):
 
 expected_oid=self.LARGE_OID
 ifself.server_version>= (11, 0):
-# PostgreSQL 11 automatically create a domain array type
+# PostgreSQL 11 automatically creates a domain array type
 # _before_ the domain type, so the expected OID is
 # off by one.
 expected_oid+=1
@@ -1858,14 +1859,5 @@ async def test_custom_codec_large_oid(self):
 v=awaitself.con.fetchval('SELECT $1::test_domain_t', 10)
 self.assertEqual(v, 10)
 
-# Test that custom codec logic handles large OIDs
-awaitself.con.set_type_codec(
-'test_domain_t',
-encoder=lambdav: str(v),
-decoder=lambdav: int(v))
-
-v=awaitself.con.fetchval('SELECT $1::test_domain_t', 10)
-self.assertEqual(v, 10)
-
 finally:
 awaitself.con.execute('DROP DOMAIN test_domain_t')