How do I encode/decode my type with conn.set_type_codec?

[tamis-laan]

I have the following type:

CREATE TYPE REC_CONTENT AS (
	id               TEXT,
	filename         TEXT,
	mimetype         TEXT,
	extract          JSONB
);

This is my current attempt:

await conn.set_type_codec(
    'rec_content',
    encoder=lambda x: (x['id'], x['filename'], x['mimetype'], json.dumps(x['extract'])),
    decoder=lambda t: {'id': t[0], 'filename': t[1], 'mimetype': t[2], 'extract': json.loads(t[3])},
    format='tuple'
)

But I get back the error:

asyncpg.exceptions._base.UnsupportedClientFeatureError: cannot decode type "public"."rec_content": text encoding of composite types is not supported