From: psurmano at ucalgary dot ca
Operating system: Redhat 8.0
PHP version: 4.3.3
PHP Bug Type: Output Control
Bug description: fread() reads entire file to memory

When the following code is run in a browser on a very large file php will
first read in the entire file into memory and only afterwards will it
display a download dialog in the browser. This is even though I'm reading
in 8192 bytes at a time.

On a large file this results in a delay of several seconds.

Using readfile() doesn't have this problem but it is unacceptable since I
will need to add code to throttle download speed.

Reproduce code:
header("Content-type: application/octet-stream");
header("Content-Disposition: attachment; filename=largeFile");
header("Content-Length: " . filesize("largeFile"));

$handle = fopen ("largeFile", "rb");
do {
$data = fread($handle, 8192);
if (strlen($data) == 0) {
echo $data;
} while(true);
fclose ($handle);

Expected result:
PHP should first show the download dialog and then start reading the file.
This is what happens with readfile()

Actual result:
The file will first get read entirely into memory resulting in a large
delay. Only then is the user prompted with a download dialog.

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