PHP implementation code for downloading large files and resuming breakpoint downloads

$sourceFile = "jbxue.tmp"; //The name of the temporary file to be downloaded
$outFile = "User Order.xls"; //The name of the file to be downloaded and saved to the client
$file_extension = strtolower(substr(strrchr($sourceFile, "."), 1)); //Get the file extension
//echo $sourceFile;
if (!ereg("[tmp|txt|rar|pdf|doc] ", $file_extension))exit ("Illegal resource download");
//Check whether the file exists
if (!is_file($sourceFile)) {
die("404 File not found!}
$len = filesize($sourceFile); //Get the file size
$filename = basename($sourceFile); //Get the file name
$outFile_extension = strtolower(substr(strrchr($outFile, " ."), 1)); //Get the file extension
//Indicate the output browser format according to the extension
switch ($outFile_extension) {
case "exe" :
$ctype = "application/octet-stream";
break;
case "zip" :
$ctype = "application/zip";
break;
case "mp3" :
$ctype = "audio/mpeg";
break;
case "mpg" :
$ctype = "video/mpeg";
break;
case "avi" :
$ctype = "video/x-msvideo";
break;
default :
$ctype = "application/force-download";
}
/ /Begin writing headers
header("Cache-Control:");
header("Cache-Control: public");
//Set the output browser format
header("Content-Type: $ctype");
header ("Content-Disposition: attachment; filename=" . $outFile);
header("Accept-Ranges: bytes");
$size = filesize($sourceFile);
//If there is $_SERVER['HTTP_RANGE'] Parameters
if (isset ($_SERVER['HTTP_RANGE'])) {
/*Range header field The Range header field can request one or more sub-ranges of the entity.
For example,
 represents the first 500 bytes: bytes=0-499
 represents the second 500 bytes: bytes=500-999
 represents the last 500 bytes: bytes=-500
 represents the range after 500 bytes :bytes=500-
First and last bytes: bytes=0-0,-1
Specify several ranges at the same time: bytes=500-600,601-999
But the server can ignore this request header if the unconditional GET contains Range request header, the response will be returned with status code 206 (PartialContent) instead of 200 (OK).
*/
// Connect again after the breakpoint. The value of $_SERVER['HTTP_RANGE'] is bytes=4390912-
list ($a, $range) = explode("=", $_SERVER['HTTP_RANGE']);
 //if yes, download missing part
str_replace($range, "-", $range); //What is this sentence for? . . .
$size2 = $size -1; //The total number of bytes in the file
$new_length = $size2 - $range; //Get the length of the next download
header("HTTP/1.1 206 Partial Content");
header( "Content-Length: $new_length"); //Enter the total length
header("Content-Range: bytes $range$size2/$size"); //Content-Range: bytes 4908618-4988927/4988928 95% of the time
 } else {
//First connection
$size2 = $size -1;
header("Content-Range: bytes 0-$size2/$size"); //Content-Range: bytes 0-4988927/4988928
header("Content-Length: " . $size); //Output total length
}
//Open the file
//edit bbs.it-home.org
$fp = fopen("$sourceFile", "rb" );
//Set the pointer position
fseek($fp, $range);
//Unreal output
while (!feof($fp)) {
//Set the maximum file execution time
set_time_limit(0);
 print (fread($fp, 1024 * 8)); //Output file
flush(); //Output buffer
ob_flush();
}
fclose($fp);
exit ();
?>