Raise an error when a binary COPY FROM is attempted w/o appropriate codec.

COPY .. FROM .. (FORMAT binary) currently requires that all data is
encoded in binary format.  Hence, we need to check if we have
appropriate codecs for all columns before initiating CopyIn.

Issue: #157.

Author: elprans

asyncpg/protocol/protocol.pyx

@@ -376,9 +376,11 @@ cdef class BaseProtocol(CoreProtocol):
                 settings = self.settings
 
                 for codec in codecs:
-                    if not codec.has_encoder():
+                    if (not codec.has_encoder() or
+                            codec.format != PG_FORMAT_BINARY):
                         raise RuntimeError(
-                            'no encoder for OID {}'.format(codec.oid))
+                            'no binary format encoder for '
+                            'type {} (OID {})'.format(codec.name, codec.oid))
 
                 for row in records:
                     # Tuple header

tests/test_copy.py

@@ -574,7 +574,7 @@ async def __anext__(self):
         finally:
             await self.con.execute('DROP TABLE copytab')
 
-    async def test_copy_records_to_table(self):
+    async def test_copy_records_to_table_1(self):
         await self.con.execute('''
             CREATE TABLE copytab(a text, b int, c timestamptz);
         ''')
@@ -597,3 +597,19 @@ async def test_copy_records_to_table(self):
 
         finally:
             await self.con.execute('DROP TABLE copytab')
+
+    async def test_copy_records_to_table_no_binary_codec(self):
+        await self.con.execute('''
+            CREATE TABLE copytab(a numeric);
+        ''')
+
+        try:
+            records = [(123.123,)]
+
+            with self.assertRaisesRegex(
+                    RuntimeError, 'no binary format encoder'):
+                await self.con.copy_records_to_table(
+                    'copytab', records=records)
+
+        finally:
+            await self.con.execute('DROP TABLE copytab')