Google App Engine

Exceptions and HTTP

In many situations, you may want to use common HTTP status codes to indicate the success or failure of a user's API request. For example, if a user is attempting to retrieve an entity which does not exist, you may want to send an HTTP 404 status code saying No entity with the ID entity_id exists.

You can send such common HTTP status codes by raising an exception provided by the endpoints library as follows:

message = 'No entity with the id "%s" exists.' % entity_id
raise endpoints.NotFoundException(message)

Exceptions Provided by Endpoints

The endpoints library provides the following exceptions, corresponding to specific HTTP status codes:

Exception Corresponding HTTP Status Code
endpoints.BadRequestException HTTP 400
endpoints.UnauthorizedException HTTP 401
endpoints.ForbiddenException HTTP 403
endpoints.NotFoundException HTTP 404
endpoints.InternalServerErrorException HTTP 500

Supported HTTP Status Codes

Endpoints supports a subset of HTTP status codes in API responses. The following table describes the supported codes.

HTTP Status Codes Support
HTTP 2xx HTTP 200 is typically assumed by Endpoints if the API method returns successfully.
If the API method response type is VoidMessage or the return value of the API method is None , HTTP 204 will be set instead.
HTTP 2xx codes should not be used in custom exception classes.
HTTP 3xx HTTP 3xx codes are not supported. Use of any HTTP 3xx codes will result in an HTTP 404 response.
HTTP 4xx Only the HTTP 4xx codes listed below are supported:
  • 400
  • 401
  • 403
  • 404
  • 405
  • 408
  • 409
  • 410
  • 412
  • 413
Use of other HTTP 4xx codes will result in an HTTP 404 response.
HTTP 5xx All HTTP 5xx status codes are converted to be HTTP 503 in the client response.

Creating Your Own Exception Classes

If you want to create other exception classes for other HTTP status codes, you can do so by subclassing endpoints.ServiceException. The following snippet shows how to create an exception class that represents an HTTP 409 status code:

import endpoints
import httplib

class ConflictException(endpoints.ServiceException):
    """Conflict exception that is mapped to a 409 response."""
    http_status = httplib.CONFLICT

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