PHP file download empty - php

Question

Please help, this code downloads file but file is empty(0byte) but inside the folder its 1mb.
function dowloadbooks($id){
$allbooks ="SELECT * FROM books_table WHERE books_id = '$id' ";
$result=$this->conn->query($allbooks);
$row = array();
if($result->num_rows >0){
while($res = $result->fetch_assoc()){
$row = $res['book_upload'];
header('Content-Description: File Transfer');
header('Content-Type: application/octet-stream');
header('Content-Disposition: attachment; filename=' .$row.'');
header('Expires: 0');
header('Cache-Control: must-revalidate');
header('Pragma: public');
header('Content-Length: ' . filesize($row));
readfile($row);
}
}
return $row;
}

Answer 1

I suggest you break your problem into smaller chunks:
Your file does not exist most likely or you are using the wrong path relative to your script. When I modify your example to use an existing file and exclude DB functionality, the file downloads correctly with no errors:
dowloadbooks();
function dowloadbooks(){
$row = 'c:/ExistingFile.png';
header('Content-Description: File Transfer');
header('Content-Type: application/octet-stream');
header('Content-Disposition: attachment; filename=' .$row.'');
header('Expires: 0');
header('Cache-Control: must-revalidate');
header('Pragma: public');
header('Content-Length: ' . filesize($row));
readfile($row);
return $row;
}
Let's try the same example with non existing file:
//error_reporting(0);
dowloadbooks();
function dowloadbooks(){
$row = 'c:/NonExistingFile.png';
header('Content-Description: File Transfer');
header('Content-Type: application/octet-stream');
header('Content-Disposition: attachment; filename=' .$row.'');
header('Expires: 0');
header('Cache-Control: must-revalidate');
header('Pragma: public');
header('Content-Length: ' . filesize($row));
readfile($row);
return $row;
}
I get two errors:
PHP Warning: filesize(): stat failed for c:/NonExistingFile.png in test.php on line 13
PHP Warning: readfile(c:/NonExistingFile.png): failed to open stream: No such file or directory in test.php on line 14
But when I disable the error reporting with error_reporting(0), suddenly the file is downloading with zero size!!!
Conclusion:
Try displaying the file path first or/and enable errors with error_reporting(-1) - you should see where the problem is.