I'm running into a weird CORS issue right now.

Here's the error message:

XMLHttpRequest cannot load http://localhost:8666/routeREST/select?q=[...] 
Origin http://localhost:8080 is not allowed by Access-Control-Allow-Origin

Two servers:

• localhost:8666/routeREST/ : this is a simple Python Bottle server.
• localhost:8080/ : Python simpleHTTPserver where I run y Javascript application. This app is executing Ajax requests on the server above.

Any thought on what could be the problem?

EDIT:

And... the port was the problem. Thanks for your answers :)

If anyone is using a Python bottle server as well, you can follow the answer given on this post to solve the CORS issue: Bottle Py: Enabling CORS for jQuery AJAX requests

It is only the same if the scheme, domain and port are identical. Same Origin Policy

Clarification

• http and https are not the same scheme. (By default they also use different ports)
• example.com and www.example.com are not the same domain.
• Port 80 and 443 are not the same port.

How to enable CORS

If you want to enable CORS you must follow Cross-Origin Resource Sharing (cors) by adding headers. Mozilla has examples.

In the incoming request you get an Origin header:

Origin: https://example.com

You need to add Access-Control-Allow-Origin as a header in your response. To allow everyone (you should probably NOT do that):

Access-Control-Allow-Origin: *

Multiple origins

If you need to support multiple origins (for example, both example.com and www.example.com), set the Access-Control-Allow-Origin header in your response to match the Origin header in the request (provided you have verified that the origin is on the whitelist).

WHY DO I GET REQUESTS WITH OPTIONS METHOD?

Note that some requests send a preflight-request, with an OPTIONS-method, so if you write your own code you must handle those requests too. See Mozilla for examples.