Why is my Cross-Origin Request Blocked, and How Can I Fix It in Go and Firefox OS?

Cross-Origin Request Blocked: Understanding the Cause

HTTP requests that span different domains can face a security restriction known as the Same Origin Policy (SOP), causing the "Cross-Origin Request Blocked" error. This policy prevents scripts from making requests to other origins, such as servers or web pages, without explicit permission.

Solution for Go Handler

To resolve the issue in your Go handler, you need to explicitly allow cross-origin requests by setting the appropriate Access-Control-Allow-Origin header:

func handleMessageQueue(w http.ResponseWriter, r *http.Request) {
    // Allow cross-origin requests
    w.Header().Set("Access-Control-Allow-Origin", "*")
    ...
}

Solution for Firefox OS App

In your JavaScript code, a privileged XMLHttpRequest can be used to bypass the SOP restrictions. To do this, use the following syntax:

var xhr = new XMLHttpRequest({mozSystem: true});

Additional Manifest Configuration

For the privileged XMLHttpRequest to work in Firefox OS apps, you need to add the appropriate permission to your manifest file:

"permissions": {
       "systemXHR": {},
}

Reason for the Error

By default, browser requests to other origins are blocked as a security measure. When you made a POST request from your Firefox OS app to your Go handler, the handler's response was blocked due to the SOP. Setting the Access-Control-Allow-Origin header in your Go handler and using the privileged XMLHttpRequest in your app allows cross-origin requests, resolving the issue.

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