Customizing InputAdapter

BentoML allows user to create customize InputAdapter to better suit for their system.

This guide demonstrate how to extending how to create a custom InputAdapter that check the incoming data and then uses the customized InputAdapter to create and test with BentoService

1. Create custom InputAdapter

The following code create a subclass from the StringInput and throw an AttributeError if the cohort_id is missing in the data. If the incoming data is invalid, the input adapter will discard the task with appropriate status code and message.


import json
from bentoml.adapters.string_input import StringInput

class MyCustomJsonInput(StringInput):
    # See more information about tasks at
    def extract_user_func_args(self, tasks):
        json_inputs = []
        for task in tasks:
                parsed_json = json.loads(
                if parsed_json.get('cohort_id', None) is None:
                    raise AttributeError('Missing cohort data')
            except json.JSONDecodeError:
                task.discard(http_status=400, err_msg="Not a valid JSON format")
            except AttributeError:
                task.discard(http_status=400, err_msg="Invalid request data")
            except Exception:  # pylint: disable=broad-except
                err = traceback.format_exc()
                task.discard(http_status=500, err_msg=f"Internal Server Error: {err}")
        return (json_inputs,)

2. Define and save BentoService with the customized InputAdapter


import bentoml
from bentoml.service.artifacts.common import PickleArtifact
from my_custom_input import MyCustomJsonInput

class MyService(bentoml.BentoService):
    @bentoml.api(input=MyCustomJsonInput(), batch=True)
    def predict(self, input_data):
        result = []
        for data in input_data:
            result.append(data.get('name') + data.get('cohort_id'))
        return result
from my_bento_service import MyService

svc = MyService()

3. Test with example data

$ bentoml serve MyService:latest

In another terminal to make a curl request

$ curl -i --header "Content-Type: application/json" \
  --request POST --data '{"name": "foo"}' \

# Output
X-Request-Id: cb63a61e-dc2a-4e12-a91c-8b15316a99df
Content-Type: text/html; charset=utf-8
Content-Length: 20
Server: Werkzeug/0.15.4 Python/3.7.3
Date: Wed, 10 Mar 2021 01:47:38 GMT

Invalid request data%

$ curl -i --header "Content-Type: application/json" \
  --request POST --data '{"name": "foo", "cohort_id": "1"}' \

# Output
HTTP/1.0 200 OK
Content-Type: application/json
X-Request-Id: 34ad9963-4be5-47a1-afcf-774b9d866e76
Content-Length: 6
Server: Werkzeug/0.15.4 Python/3.7.3
Date: Wed, 10 Mar 2021 01:48:37 GMT