


How Can We Reliably Detect Browser File Download Completion Without Browser Events?
Dec 23, 2024 pm 09:11 PMDetecting Browser File Download Completion
Problem Statement
A page featuring a dynamic file download mechanism requires a visual indicator to signal when the download completes. However, browsers do not always trigger events to indicate file reception when a "Save" dialog appears.
Server Response Limitations
The provision of a "Content-Disposition: attachment" header instructs browsers to display the "Save" dialog, but it suppresses the loading of the iframe used for event monitoring.
Proposed Solution
Implement a client-based solution leveraging JavaScript and server-side cookies:
Client Algorithm
- Generate a unique token.
- Submit the download request with the token.
- Display the "waiting" indicator.
- Poll the server at regular intervals for a cookie named "fileDownloadToken" that matches the token.
- If the cookie is found, remove the "waiting" indicator.
Server Algorithm
- Extract the token from the request.
- Create a cookie with the name "fileDownloadToken" and set its value to the received token.
Example Implementation
- Client-Side JavaScript (simplified)
- Server-Side PHP (simplified)
Benefits
- Does not require temporary file creation.
- Detects file download readiness without relying on event listeners.
- Can be customized to specific token names and cookie settings.
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