Error details for stepwise long-running operations

[letmaik]

Services MUST perform as much synchronous validation as practical on stepwise requests. Services MUST prioritize returning errors in a synchronous way, with the goal of having only "Valid" operations processed using the long running operation wire protocol.

How should error details be exposed for operation failures? The guidelines are silent about that, whereas I would have expected that an OData-style "error" field should be included in the response.

I similarly can't see how real APIs deal with that which seems extremely odd: https://docs.microsoft.com/en-us/azure/cognitive-services/computer-vision/concept-recognizing-text

[letmaik]

While the general guidelines are silent about it, the Azure guidelines are more prescriptive: https://github.com/microsoft/api-guidelines/blob/vNext/azure/Guidelines.md#obtaining-status-and-results-of-long-running-operations. It may be worth recommending to use the "error" field in the general guidelines as well.

DO return a status monitor in the response body that conforms with the following structure:

OperationStatus : Object

Property	Type	Required	Description
id	string	true	The unique id of the operation
status	string	true	enum that includes values "NotStarted", "Running", "Succeeded", "Failed", and "Canceled"
error	ErrorDetail		Error object that describes the error when status is "Failed"
result	object		Only for POST action-type LRO, the results of the operation when completed successfully
additional properties			Additional named or dynamic properties of the operation