John Davidson

Message:

My original code does this:

    $data = file_get_contents($source);

    $compressed_data = gzencode($data);

    file_put_contents($destination, $compressed_data);

This works fine, and it seemingly supports a lot of different values for $source and $destination - including in-memory file systems, stdin/stdout streams, etc.

However, large files have to be fully loaded into memory, so I'd like to switch this over to a chunked approach.

I've tried the following:

    $in = fopen($source, 'rb');

    $out = gzopen($destination, 'wb');

    while (!feof($in)) {

        gzwrite($out, fread($in, 4096));

    }

But this gives me an error with stream wrappers (such as https://packagist.org/packages/mikey179/vfsstream): gzopen(): cannot represent a stream of type user-space as a File Descriptor.

Also tried the following:

    $in = fopen($source, 'rb');

    $out = fopen($destination, 'wb');

    stream_filter_append($out, 'zlib.deflate', STREAM_FILTER_WRITE, -1);

    while (!feof($in)) {

        fwrite($out, fread($in, 4096));

    }

But the resulting output doesn't appear to be valid GZIP (missing header maybe?)

Finally I tried this:

    $in = fopen($source, 'rb');

    $out = fopen('compress.zlib://' . $destination, 'wb');

    while (!feof($in)) {

        fwrite($out, fread($in, 4096));

    }

But (unsurprisingly) this failed if $destination already had a wrapper (such as php://stdin or the vfs:// mentioned above).

There has to be a way to do this, but searching hasn't turned up any examples for it.

---

My Answer:
One way to achieve writing a chunked gzip file to an arbitrary output stream in PHP is to use the `Zlib` extension. Here's an example code snippet that demonstrates how to do this:

php
$source = 'path/to/source/file';
$destination = 'path/to/destination/file';

$in = fopen($source, 'rb');
$out = fopen($destination, 'wb');

stream_filter_append($out, 'zlib.deflate', STREAM_FILTER_WRITE, ['window' => 15]);

while (!feof($in)) {
$chunk = fread($in, 4096);
fwrite($out, $chunk);
}

fclose($in);
fclose($out);


In this code snippet:
- We open the source file in read mode and the destination file in write mode.
- We append the `zlib.deflate` filter to the output stream, which will compress the data using gzip compression.
- We read the source file in chunks of 4096 bytes and write each chunk to the output stream.
- Finally, we close both input and output streams.

This approach should work for writing chunked gzip files to various types of output streams, including file streams, memory streams, and others.