Re: throttle output streamed from a file?

D. Dante Lorenso wrote:

All, I have a file which I want to stream from PHP:

it's not that relevant, but, I don't thinking streaming is the correct term. your merely dumping a files' content to std output.

readfile($file_name);

the trick you need to employ involves opening the file and reading/dumping it in suitably sized chunks.

However, this function has the problem that it reads the whole file into memory and then tries to write it to output. Sometimes, you can hit the memory limit in PHP before the file contents are completely output resulting in 2M or 8M truncation of output. I have seen code posted to the readfile user comments which hints at trying a userspace 'readfile_chunked' function to break the file into smaller parts, but this is still not entirely what I want: http://us2.php.net/manual/en/function.readfile.php My specific case is this. I have a queue of very large files that I'd like to output in series. I want to do something equivalent to this: readfile($big_file1); // 20 MB readfile($big_file2); // 20 MB readfile($big_file3); // 20 MB readfile($big_file4); // 20 MB

doing that would mean the client ends up with garbage - I think - because the client justs see one big stream of data with no way of knowing that it constitutes multiple files. using something like exec() to call the systems tar & gzip commands on the files in question and then dumping out the resulting 'tarball' in chunks as described above would be a way to achieve this.

but I really don't want to start writing $big_file2 until $big_file1 has been written and I don't want PHP to consume 20 MB at a time either. Ideally I'd like to have an output buffer size of NN bytes and only let PHP fill that buffer until the client has read enough of the bytes to warrant another refill. That way, I might only consume about 1MB sliding window of output. To do this, I would think I need a function in PHP which will output a buffered stream with blocking enabled. Can anybody point me in the right direction?

http://php.net/streams - only I doubt that this would give you what you want given that the client is a webbrowser and the connection is not directly under the control of php (it's the webservers responsibility). this is conjecture - I'm still breaking my head on streams concepts on a regular basis!

Dante