add support for json objects in the Message component

[willydouhard]

proposal to fix #291

[mpartel]

Might technically be a number or boolean too. Perhaps typeof content !== 'string' ?

[willydouhard]

just moved the logic to the server. it has to be a string because the message can be persisted and has to respect the DB schema

[ramnes]

LGTM

[mpartel]

Just occurred to me that LangChain's web scrapers produce Document. (They are Serializable and have methods json/to_json and dict). Not sure if they're dict'ified before they reach you, but worth checking I think.

[mpartel]

It gets a little fiddly.
If I add the following to #291 's code:

from langchain.schema.document import Document
...
                'structured': {
                    'doc': Document(page_content='...'),
                    ...

then I get

future: <Task finished name='Task-83' coro=<AsyncServer._emit_internal() done, defined at /home/martin/.cache/pypoetry/virtualenvs/chainlit-bug-6EGjyFTw-py3.10/lib/python3.10/site-packages/socketio/asyncio_server.py:427> exception=TypeError('Object of type Document is not JSON serializable')>
Traceback (most recent call last):
  File "/usr/lib/python3.10/asyncio/tasks.py", line 232, in __step
    result = coro.send(None)
  File "/home/martin/.cache/pypoetry/virtualenvs/chainlit-bug-6EGjyFTw-py3.10/lib/python3.10/site-packages/socketio/asyncio_server.py", line 437, in _emit_internal
    await self._send_packet(sid, self.packet_class(
  File "/home/martin/.cache/pypoetry/virtualenvs/chainlit-bug-6EGjyFTw-py3.10/lib/python3.10/site-packages/socketio/asyncio_server.py", line 442, in _send_packet
    encoded_packet = pkt.encode()
  File "/home/martin/.cache/pypoetry/virtualenvs/chainlit-bug-6EGjyFTw-py3.10/lib/python3.10/site-packages/socketio/packet.py", line 64, in encode
    encoded_packet += self.json.dumps(data, separators=(',', ':'))
  File "/usr/lib/python3.10/json/__init__.py", line 238, in dumps
    **kw).encode(obj)
  File "/usr/lib/python3.10/json/encoder.py", line 199, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "/usr/lib/python3.10/json/encoder.py", line 257, in iterencode
    return _iterencode(o, 0)
  File "/usr/lib/python3.10/json/encoder.py", line 179, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type Document is not JSON serializable

Looks like we'd need to give socketio.AsyncServer a json module (object?) that uses a JSONEncoder that supports LangChain's Serializable.

[ramnes]

This is another topic IMO. For this I'd say that we should let users pass whatever JSONEncoder they want to Chainlit rather than trying to handle all cases ourselves.

Edit: Actually no, I'll come back to what I just say: LangChain callback chain of thoughts should work out of the box indeed, so yes, we need something like this, at least when the LangChain callback handler is used.

[willydouhard]

I could even argue that a Langchain document should be a text element rather than a message content.

Should we keep the support for dicts in the message class and open another PR for Langchain edge cases or do you think everything should be handled in the Langchain specific solution and the message class should always accept a string?