DscConfigurationClient.GetContent is broken since `2020-01-13-preview/automation` API version

[dz-sourced]

Bug Report

Summary:
When trying to read back a DSC Configuration content using func (client DscConfigurationClient) GetContent an error happens in the version of the API 2020-01-13-preview/automation and later while trying to unmarshall DSC Configuration content from JSON. DSC Configurations are not valid JSON objects and thus unmarshalling fails. This issue was not happening in 2018-06-30-preview/automation and earlier, where DSC Configuration content was treated as a plain string value. I have confirmed the issue on the main branch.

Details:
In the 2020-01-13-preview/automation the actual failure seems to happen when trying to unmarshall DSC Configuration content from JSON:

azure-sdk-for-go/services/preview/automation/mgmt/2020-01-13-preview/automation/dscconfiguration.go

Line 384 in 94316ba

autorest.ByUnmarshallingJSON(&result.Value),

The error that I get when trying to read back a sample DSC Configuration like Configuration test {} is:

automation.DscConfigurationClient#GetContent: Failure responding to request: StatusCode=200 -- Original Error: Error occurred unmarshalling JSON - Error = 'invalid character 'C' looking for beginning of value' JSON = 'Configuration test{}'

This was not happening in the previous version of the API 2018-06-30-preview/automation and the content value was just passed as is:

azure-sdk-for-go/services/preview/automation/mgmt/2018-06-30-preview/automation/dscconfiguration.go

Line 383 in 94316ba

resp,

Finally, the root cause can be traced to the change in the Swagger API definitions. The latest version of the GetContent API defines the output as a string type, which I assume is tried to be de-serialized from JSON by default:
https://github.com/Azure/azure-rest-api-specs/blob/3034ada77d465b317cda51250a92454824cca06b/specification/automation/resource-manager/Microsoft.Automation/stable/2019-06-01/dscConfiguration.json#L309

In the earlier version of the API spec the output type is set to file:
https://github.com/Azure/azure-rest-api-specs/blob/3026119ab41bbce77275cfa3a1afbabf43af5aea/specification/automation/resource-manager/Microsoft.Automation/stable/2015-10-31/dscConfiguration.json#L309

I don't know whether this was intentional API spec change, or whether there is a need to provide further type modifiers in the Swagger API or whether it's an issue with the SDK codegen tool.

Here is a small script that demostrates the problem https://gist.github.com/dz-sourced/11654206078fcc159c54564de6758659
It creates a resource group, an automation account, a sample empty DSC Configuration and the tries to read it using older and new API versions. You should be able to see that read is succesful in 2018-06-30-preview/automation and fails in the 2020-01-13-preview/ version.

[ArcturusZhang]

Hi @dz-sourced thank you for this issue!

By looking at the error message, it is very likely to be an issue that the service is returning something uncompatible with its swagger. But could you please paste the request log here so that we could confirm where does this issue come from?
You could get the request logs by exporting an env var AZURE_GO_SDK_LOG_FILE=DEBUG

[dz-sourced]

Hey @ArcturusZhang, do I need to initialize the logger in any way? I set then env variable as you asked, but I don't see any debug logs. You can see the code I'm using here https://gist.github.com/dz-sourced/11654206078fcc159c54564de6758659