Chunked Retry

Failed chunks retry automatically with exponential backoff. Configure the retry count and initial delay.

What you should see: kill your network mid-upload and restore it. The failed chunk is retried up to 5 times with backoff, and only that chunk is resent — not the whole file.

Select a file to begin.

var uploader = CoreUpload.create('#retry-uploader', {
 uploadUrl: '/api/upload/upload',
 chunked: true,
 chunkSize: 2 * 1024 * 1024,
 retries: 5, // retry up to 5 times
 retryDelay: 1000, // initial delay: 1 second
 // exponential backoff is automatic
 autoUpload: true,
 maxFileSize: '200MB',
 onTaskProgress: function(file, percent) {
 console.log(file.name + ': ' + percent + '%');
 },
 onRetry: function(file, chunk, attempt) {
 console.log('Retry #' + attempt + ' for chunk ' + chunk);
 },
 onTaskComplete: function(file) {
 console.log('Upload complete:', file.name);
 }
});

Retrying one chunk, not the file

This is the practical reason chunked uploads win on unreliable networks. A failure costs one chunk and the retry re-sends only that chunk, where a single-request upload would start the whole file again — which on a bad connection often means never finishing at all.

The ceiling moves

With per-chunk retries, a multi-gigabyte upload over flaky mobile becomes a question of patience rather than luck. The limit stops being the length of the longest uninterrupted connection, and becomes whether the user stays on the page.