getIamPolicy for KMS KeyManagementServiceClient is erroring with Syntax Error: Unexpected token < in JSON at position 0 , when using fallback REST

[sirohiwebdev]

1. Is this a client library issue or a product issue?
   Yes it is a client library issue, the definition for getIamPolicy method in iam_services.json mentions POST call whether the actual call is GET

2. Did someone already solve this?
   Could not find any solution or issues created for the same.

3. Do you have a support contract?
   No

Environment details

• OS: WSL 2Ubuntu 20.04.4 LTS
• Node.js version: 18.14.2
• npm version: 9.5.0
• google-gax version: 3.6.0

Steps to reproduce

1. Call the following method for KMS

import * as kms from "@google-cloud/kms";
import { google } from "@google-cloud/iap/build/protos/protos";
import GetIamPolicyRequest = google.iam.v1.GetIamPolicyRequest;

const keyManagementServiceClient = new kms.KeyManagementServiceClient({
  credentials: {
    client_email: "user@project-id.iam.gserviceaccount.com",
    private_key:"very-long-private-key",
  },
  projectId: "project-id",
  fallback: "rest",
});

const req = new GetIamPolicyRequest({
  resource: "projects/project-id/locations/global/keyRings/qflow",
});
keyManagementServiceClient
  .getIamPolicy(req)
  .then(console.log)
  .catch(console.error);

2. It is using the POST method to hit the API
   Output (Before)
   

3. After making a change to the following [file ](https://github.com/googleapis/gax-
   nodejs/blob/main/protos/iam_service.json#L43,L49)and replacing post with get issue seems to be resolved.

Changes

Output (After)

Making sure to follow these steps will guarantee the quickest resolution possible.

Thanks!

[sirohiwebdev]

Hi @alexander-fenster
Eagerly waiting for your response.