Numeric data or audio/video are most efficiently transmitted as bytes. Other representations such as JSON or base64 encoding lose precision, add significant parsing overhead and increase message sizes (e.g. ~33% increase for base64 encoding). Chains extends the JSON-centred pydantic ecosystem with two ways how you can include binary data: numpy array support and raw bytes.

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Numpy ndarray support

Once you have your data represented as a numpy array, you can easily (and often without copying) convert it to torch, tensorflow or other common numeric library’s objects.
To include numpy arrays in a pydantic model, chains has a special field type implementation NumpyArrayField. For example: 
import numpy as np
import pydantic

from truss_chains import pydantic_numpy


class DataModel(pydantic.BaseModel):
    some_numbers: pydantic_numpy.NumpyArrayField
    other_field: str
    ...


numbers = np.random.random((3, 2))
data = DataModel(some_numbers=numbers, other_field="Example")
print(data)
# some_numbers=NumpyArrayField(shape=(3, 2), dtype=float64, data=[
#   [0.39595027 0.23837526]
#   [0.56714894 0.61244946]
#   [0.45821942 0.42464844]])
# other_field='Example'
NumpyArrayField is a wrapper around the actual numpy array. Inside your python code, you can work with its array attribute: 
data.some_numbers.array += 10
# some_numbers=NumpyArrayField(shape=(3, 2), dtype=float64, data=[
#   [10.39595027 10.23837526]
#   [10.56714894 10.61244946]
#   [10.45821942 10.42464844]])
# other_field='Example'
The interesting part is, how it serializes when making communicating between Chainlets or with a client. It can work in two modes: JSON and binary.

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Binary

As a JSON alternative that supports byte data, Chains uses msgpack (with msgpack_numpy) to serialize the dict representation. For Chainlet-Chainlet RPCs this is done automatically for you by enabling binary mode of the dependency Chainlets, see all options: 
import truss_chains as chains


class Worker(chains.ChainletBase):
    async def run_remote(self, data: DataModel) -> DataModel:
        data.some_numbers.array += 10
        return data


class Consumer(chains.ChainletBase):

    def __init__(self, worker=chains.depends(Worker, use_binary=True)):
        self._worker = worker

    async def run_remote(self):
        numbers = np.random.random((3, 2))
        data = DataModel(some_numbers=numbers, other_field="Example")
        result = await self._worker.run_remote(data)
Now the data is transmitted in a fast and compact way between Chainlets which often gives performance increases.

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Binary client

If you want to send such data as input to a chain or parse binary output from a chain, you have to add the msgpack serialization client-side: 
import requests
import msgpack
import msgpack_numpy

msgpack_numpy.patch()  # Register hook for numpy.

# Dump to "python" dict and then to binary.
data_dict = data.model_dump(mode="python")
data_bytes = msgpack.dumps(data_dict)

# Set binary content type in request header.
headers = {
    "Content-Type": "application/octet-stream", "Authorization": ...
}

response = requests.post(url, data=data_bytes, headers=headers)
response_dict = msgpack.loads(response.content)
response_model = ResponseModel.model_validate(response_dict)
The steps of dumping from a pydantic model and validating the response dict into a pydantic model can be skipped, if you prefer working with raw dicts on the client.
The implementation of NumpyArrayField only needs pydantic, no other Chains dependencies. So you can take that implementation code in isolation and integrate it in your client code.
Some version combinations of msgpack and msgpack_numpy give errors, we know that msgpack = ">=1.0.2" and msgpack-numpy = ">=0.4.8" work.

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JSON

The JSON-schema to represent the array is a dict of shape (tuple[int]), dtype (str), data_b64 (str). E.g. 
print(data.model_dump_json())
'{"some_numbers":{"shape":[3,2],"dtype":"float64", "data_b64":"30d4/rnKJEAsvm...'
The base64 data corresponds to np.ndarray.tobytes(). To get back to the array from the JSON string, use the model’s model_validate_json method. As discussed in the beginning, this schema is not performant for numeric data and only offered as a compatibility layer (JSON does not allow bytes) - generally prefer the binary format.

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Simple bytes fields

It is possible to add a bytes field to a pydantic model used in a chain, or as a plain argument to run_remote. This can be useful to include non-numpy data formats such as images or audio/video snippets. In this case, the “normal” JSON representation does not work and all involved requests or Chainlet-Chainlet-invocations must use binary mode. The same steps as for arrays above apply: construct dicts with bytes values and keys corresponding to the run_remote argument names or the field names in the pydantic model. Then use msgpack to serialize and deserialize those dicts. Don’t forget to add Content-type headers and that response.json() will not work.