Fix CORS Blocked Error in Go

What Is the CORS Blocked Error?

Running into CORS Blocked while working with Go? This guide walks you through the root cause and a clean solution.

Why It Happens

This occurs when the server doesn't include the correct Access-Control-Allow-Origin headers, blocking cross-origin requests from the browser.

The Fix

func corsMiddleware(next http.Handler) http.Handler {
  return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Access-Control-Allow-Origin", "*")
    w.Header().Set("Access-Control-Allow-Methods", "GET, POST, OPTIONS")
    w.Header().Set("Access-Control-Allow-Headers", "Content-Type")
    if r.Method == "OPTIONS" { w.WriteHeader(200); return }
    next.ServeHTTP(w, r)
  })
}

Related Errors

This error is often accompanied by other issues in your Go application. Check for related warnings in your console output that might provide additional context. Sometimes what appears to be a CORS Blocked error is actually a symptom of a deeper configuration problem. Review your application's dependency versions to ensure compatibility, and check that all required environment variables are properly set in your deployment configuration.

Prevention

Set up [Bugsly](https://bugsly.dev) to catch this and similar errors in production with detailed stack traces and environment info.

If this error persists after applying the fix, try clearing all caches, restarting your development server, and verifying your Go version matches what's specified in your project configuration.

Remember that CORS Blocked might manifest differently across browsers or runtime environments. Test your fix across multiple environments to ensure consistent behavior in your Go app.

Key Takeaways

• Always handle this error gracefully with proper error handling
• Check your environment configuration
• Test thoroughly before deploying to production