@yzy613 This code snippet handles the setting of the Access-Control-Allow-Origin response header for CORS (Cross-Origin Resource Sharing). Let me explain in detail:

1. First, check for the Origin header:

if origin := r.Request.Header.Get("Origin"); origin != "" {
    options.AllowOrigin = origin
}

• If the request contains an Origin header, use its value directly as AllowOrigin
• The Origin header is typically automatically added by browsers in cross-origin requests

2. If no Origin header is present, try using the Referer:

else if referer := r.Request.Referer(); referer != "" {
    if p := gstr.PosR(referer, "/", 6); p != -1 {
        options.AllowOrigin = referer[:p]
    } else {
        options.AllowOrigin = referer
    }
}

• If a Referer header exists, attempt to extract the domain portion
• gstr.PosR(referer, "/", 6) searches for the 6th "/" from right to left
• If the 6th "/" is found, take the substring before it as AllowOrigin
• If not found, use the entire Referer value

Example:

1. With Origin header:

Origin: https://example.com
-> AllowOrigin = "https://example.com"

2. With only Referer:

Referer: https://example.com/path/to/page.html
-> AllowOrigin = "https://example.com"

The purpose of this logic is to:

1. Prioritize the standard Origin header
2. Fall back to extracting domain from Referer if Origin is not available
3. Ensure proper setting of the CORS Access-Control-Allow-Origin response header
4. Enable cross-origin requests to work correctly

This is a flexible approach that:

• Supports standard cross-origin requests
• Handles special cases where only Referer is available
• Maintains security by properly setting CORS headers
• Follows web standards while providing fallback options

This implementation helps in managing cross-origin requests effectively while maintaining security and compatibility across different browsers and scenarios.

Example 2 has a problem.

referer := "https://example.com/path/to/page.html"
if p := gstr.PosR(referer, "/", 6); p != -1 {
	fmt.Println(referer[:p]) //https://example.com/path/to
} else {
	fmt.Println(referer)
}