How to avoid CORS errors ("Failed to fetch" or "Server not found or an error occurred") when making requests from Swagger Editor?

Question

I have the following OpenAPI definition:

swagger: "2.0"

info:
  version: 1.0.0
  title: Simple API
  description: A simple API to learn how to write OpenAPI Specification

schemes:
  - https
host: now.httpbin.org
paths:
  /:
    get:
      summary: Get date in rfc2822 format
      responses:
        200:
          schema:
            type: object
            items:
              properties:
                now:
                  type: object
                    rfc2822:
                      type: string

I would like to retrieve rfc2822 from the response:

{"now": {"epoch": 1531932335.0632613, "slang_date": "today", "slang_time": "now", "iso8601": "2018-07-18T16:45:35.063261Z", "rfc2822": "Wed, 18 Jul 2018 16:45:35 GMT", "rfc3339": "2018-07-18T16:45:35.06Z"}, "urls": ["/", "/docs", "/when/:human-timestamp", "/parse/:machine-timestamp"]}  

But when I make a request from Swagger Editor, I get an error:

ERROR Server not found or an error occurred

What am I doing wrong?

Ventricle

What tool do you use to send the request? – Paisano

local swagger editor from the browser – Demagogue

What is the error message in the browser console? – Paisano

@Helen, No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:8081' is therefore not allowed access. Can I fix it somehow or play with swagger & now.httpbin.org from another place? – Demagogue

Answer 1

No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:8081' is therefore not allowed access.

This is a CORS issue. The server at https://now.httpbin.org does not support CORS, so the browsers won't let web pages served from other domains to make requests to now.httpbin.org from JavaScript.

You have a few options:

• Ask the owners of https://now.httpbin.org to support CORS.

  Note: The server must not require authentication for preflight OPTIONS requests. OPTIONS requests should return 200 with the proper CORS headers.

• If you are the owner - consider hosting Swagger UI on the same server and port (now.httpbin.org:443) to avoid CORS altogether.

• Disable CORS restrictions in your browser. This reduces browser security so only do this if you understand the risks.

  • Bypass CORS in Chrome
  • Bypass CORS in Firefox

• Use SwaggerHub instead of Swagger Editor to edit and test your API definitions. SwaggerHub proxies "try it out" requests through its servers so it's not subject to CORS restrictions. (Disclosure: I work for the company that makes SwaggerHub.)

By the way, your response definition is not valid. The response is missing a description and the schema is wrong (e.g. has an extra items keyword). It should be:

      responses:
        200:
          description: OK
          schema:
            type: object
            properties:
              now:
                type: object
                properties:
                  rfc2822:
                    type: string

Paisano

Answer 2

In my case, I sent an OAuth2 request to Keycloak and received this error message.

I resolved this issue by setting '*' in the "Web Origins" field in the Keycloak client options.

Baltoslavic