Compression streams

Compressing output and decompressing input streams including GZip, BZip2, Brotli, Snappy and ZStandard.

Examples

Reading a GZIP-compressed file:

use io\streams\FileInputStream;
use io\streams\compress\GzipInputStream;

$in= new GzipInputStream(new FileInputStream('message.txt.gz'));
while ($in->available()) {
  echo $in->read();
}
$in->close();

Writing a file, compressing the data on-the-fly with BZIP2:

use io\streams\FileOutputStream;
use io\streams\compress\Bzip2OutputStream;

$out= new Bzip2OutputStream(new FileOutputStream('message.txt.bz2'));
$out->write('Hello World!');
$out->write("\n");
$out->close();

Dependencies

Compression algorithms might require a specific PHP extension:

• GZip - requires PHP's "zlib" extension
• Bzip2 - requires PHP's "bzip2" extension
• Brotli - requires https://github.com/kjdev/php-ext-brotli
• Snappy - no dependencies, implemented in userland
• ZStandard - requires https://github.com/kjdev/php-ext-zstd

Accessing these algorithms can be done via the Compression API:

use io\streams\{Compression, FileInputStream, FileOutputStream};

// Returns an algorithm instance. Raises a lang.MethodNotImplementedException
// if the required "bzip2" extension is not loaded
$compressed= Compression::named('bzip2');

// Compress and decompress
$bytes= $compressed->compress('Test', Compression::STRONGEST);
$test= $compressed->decompress($bytes);

Continuing the above example using streams:

// Read from a file
$bytes= '';
$in= $compressed->open(new FileInputStream($file));
while ($in->available()) {
  $bytes.= $in->read();
}
$in->close();

// Write using strongest compression (other predefined values are FASTEST
// and DEFAULT; alternatively, the level can be passed directly).
$out= $compressed->create(new FileOutputStream($file), Compression::STRONGEST);
$out->write($bytes);
$out->close();

Discovering supported algorithms can be done using the Compression API:

use io\streams\Compression;

echo "Supported algorithms:\n";
foreach (Compression::algorithms()->supported() as $compression) {
  echo '✓ ', $compression->name(), "\n";
}

...or as a one-line shell command:

$ xp -w '\io\streams\Compression::algorithms()'
io.streams.compress.Algorithms@{
  io.streams.compress.Gzip(token: gzip, extension: .gz, supported: true, levels: 1..9)
  io.streams.compress.Bzip2(token: bzip2, extension: .bz2, supported: false, levels: 1..9)
  io.streams.compress.Brotli(token: br, extension: .br, supported: true, levels: 1..11)
  io.streams.compress.Snappy(token: snappy, extension: .sn, supported: true, levels: 0..0)
  io.streams.compress.ZStandard(token: zstd, extension: .zstd, supported: true, levels: 1..22)
}

Advanced example

Fetching a given URL using HTTP Accept-Encoding and Content-Encoding:

use io\streams\Compression;
use peer\http\HttpConnection;

// Compile list of supported compression algorithms, e.g. "gzip, br"
$accept= Compression::algorithms()->accept();
echo "== Sending {$accept} ==\n";

// Make request, sending supported content encodings via Accept-Encoding
$conn= new HttpConnection($argv[1]);
$res= $conn->get(null, ['Accept-Encoding' => $accept]);

// Handle Content-Encoding header
if ($encoding= $res->header('Content-Encoding')) {
  $compression= Compression::named($encoding[0]);

  echo "== Using ", $compression->name(), " ==\n";
  $in= $compression->open($res->in());
} else {
  echo "== Uncompressed ==\n";
  $in= $res->in();
}

// Write contents to output
while ($in->available()) {
  echo $in->read();
}
$in->close();

See also

• The PHP RFC Modern Compression suggests adding zstd and brotli into PHP.
• Snappy does not aim for maximum compression, or compatibility with any other compression library; instead, it aims for very high speeds and reasonable compression, quoting its Wikipedia page