Exceptions

All nanopie exceptions are based on the nanopie.misc.errors.ServiceError class. This class has four subclasses:

• nanopie.misc.errors.AuthenticationError: The class for all authentication related exceptions.
• nanopie.misc.errors.SerializationError: The class for all serialization related exceptions.
• nanopie.misc.errors.ValidatorError: The class for all data validation related exceptions.
• nanopie.misc.errors.FoundationError: The class for exceptions in internal handlers.

ValidatorError has its own subclasses, which you can catch when validating data:

Exceptions	Field-related Error	Description
ModelTypeNotMatchedError	No	The input data is not of the data model type used for validation.
RequiredFieldMissingError	Yes	A required field is missing (not assigned a value or assigned the value of None).
FieldTypeNotMatchedError	Yes	The input data is not of the data type specified in the field.
ListItemTypeNotMatchedError	Yes	One or more items in the input array (list) is not of the data type specified in the ArrayField.
StringMaxLengthExceededError	Yes	The input string is too long.
StringMinLengthBelowError	Yes	The input string is too short.
StringPatternNotMatchedError	Yes	The input string does not match the specified pattern.
NumberMaxExceededError	Yes	The input integer or float is too large.
NumberMinBelowError	Yes	The input integer or float is too small.
ListTooManyItemsError	Yes	The input array (list) has too many items.
ListTooLitteItemsError	Yes	The input array (list) has too little items.

These validation exceptions include additional information that details the error; the following attributes are available:

• source: The field or data model used for data validation.
• data: The input data.
• assigned_field_name: The name of the field assigned in the data model. This attribute is only available for field-related errors.
• message: The error message.

Exceptions and responses

All nanopie exceptions have an attribute, response, defined in the ServiceError base class, which accepts a RPCResponse object. When an exception is raised in a nanopie service during the processing of requests, the service checks if the response attribute is set. If so, nanopie will return the specified response to the user (when applicable). This is helpful when you would like to report user errors, such as invalid input data, or unauthenticated requests, to users automatically.

The code snippet below specifies an endpoint in a nanopie HTTP service which makes use of the response field in exceptions to return 400 Bad Request responses to users when the request data is invalid:

from flask import Flask
from nanopie import (
    FlaskService,
    Model,
    StringField,
    IntField,
    parsed_request,
    # HTTPResponse is a subclass of RPCResponse
    HTTPResponse
)
from nanopie.misc.errors import ValidationError

app = Flask(__name__)
svc = FlaskService(app=app)

class User(Model):
    name = StringField(max_length=20, min_length=1, required=True)
    age = IntField(maximum=120, minimum=0, required=True)

@svc.create(name="create_user",
            rule="/users",
            data_cls=User)
def create_user():
    user = parsed_request.data
    try:
        user.validate()
    except ValidationError as ex:
        # Set the response field and re-raise the exception
        # nanopie will return the HTTP response as specified
        ex.response = HTTPResponse(status_code=400,
                                   data="Bad request: Invalid user data.")
        raise ex