How Can I Reliably Detect File Download Completion in a Browser?
Jan 05, 2025 pm 09:06 PM
Handle File Download Completion Detection
Problem:
Detecting when a browser fully receives a dynamically generated file download becomes crucial when displaying waiting indicators. Currently, using an iframe's "load" event fails to address this issue due to browser inconsistencies.
Solution 1: Browser-Based Token Verification
A client-side JavaScript solution involves:
- Generating a unique token for the download request.
- Submitting the request with the token.
- Displaying a "waiting" indicator.
- Setting a timer to periodically check for a corresponding cookie with the token value.
- Hiding the indicator upon finding the cookie.
On the server-side, the algorithm:
- Checks for the token in the request.
- Sets a cookie with the token value if found.
Code Snippet (JavaScript):
function setFormToken() {
var downloadToken = new Date().getTime();
document.getElementById("downloadToken").value = downloadToken;
return downloadToken;
}
Code Snippet (PHP):
// Set a cookie to unblock submit button when download begins. $TOKEN = "downloadToken"; $this->setCookieToken($TOKEN, $_GET[$TOKEN]);
Solution 2: Server Polling
Alternatively, a server-side approach involves:
- Initiating file creation.
- Polling the server until completion.
- Downloading the ready file.
This method avoids creating temporary server files. However, it requires client-server communication during the waiting period.
Pros and Cons:
Using a browser token allows for dynamic detection, but may have browser compatibility issues. Server polling is a more reliable but slower option.
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