How can I detect a file change during a chunking upload? - php

Question

I am doing a chunk file upload to a server and I am interested in such a thing as determining whether this file has changed.
Suppose I send a file of size 5 mb. The size of one chunk is 1 mb. 4 chunks are sent to the server, and the last one did not go because of a broken connection.
After the document was changed at the beginning and the first chunk of this document no longer matches the first chunk on the server, the last chunk is loaded, but the contents are already different.
In order to determine that one of the chunks has been changed, you need to re-send all the chunks to the server to get the hash of the amount, but then the whole load loses its meaning.
How can I determine that a file has been modified without sending all the chunks to the server?
Additionally:
Uploading files is as follows:
First, the browser sends a request to create a new session for uploading files.
Request params:
part_size: 4767232
files: [
{
"file_size":4767232,
"file_type":"application/msword",
"file_name":"5 mb.doc"
}
]
Next:
New records about uploaded files are added to the database.
The server creates temporary folders for storing chunks.
(Folder name is the guids of the file record created by the database.)
The method returns file guids.
After receiving the guids, the browser divides the files into chunks using the JavaScript Blob.slice() method and sends each chunk as a separate request, attaching the file identifier to the request.
Chunks are saved and after the last chunk has been uploaded the file is collected.
Code:
/**
* #param $binary - The binary data.
* #param $directory - Current file with chunks directory path.
*/
private static function createChunk($binary, $directory)
{
//Create a unique id for the chunk.
$id = 'chunk_' . md5($binary);
// Save the chunk to dad with the rest of the chunks of the file.
Storage::put($directory . '/' . $id, $binary);
// We get a json file with information about uploading session.
$session = self::uploadSessionInfo($directory);
// Increase the number of loaded chunks by 1 and add a new element to the subarray chunks.
$session['chunks_info']['loaded_chunks'] = $session['chunks_info']['loaded_chunks'] + 1;
$session['chunks_info']['chunks'][] = [
'chunk_id' => $id
];
// Save the modified session file.
Storage::put($directory . '/session.json', json_encode($session));
// If the number of loaded chunks and the number of total chunks are the same, then we create the final file.
if ($session['chunks_info']['total_chunks'] === $session['chunks_info']['loaded_chunks']) {
Storage::put($directory . '/' . $session['file_name'], []);
foreach ($session['chunks_info']['chunks'] as $key => $value) {
$file = fopen(storage_path() . '/app/' . $directory . '/' . $value['chunk_id'], 'rb');
$buff = fread($file, 2097152);
fclose($file);
$final = fopen(storage_path() . '/app/'. $directory . '/' . $session['file_name'], 'ab');
$write = fwrite($final, $buff);
fclose($final);
}
}
}
Visually looks like this: