poc.php

<?php

use function Clue\React\Block\await;
use React\EventLoop\Factory;
use React\Promise\Deferred;
use function React\Promise\Stream\buffer;
use React\Stream\ThroughStream;
use WyriHaximus\React\Stream\Base64\WritableStreamBase64Encode;
use WyriHaximus\React\Stream\Hash\WritableStreamHash;

require 'vendor/autoload.php';

$loop = Factory::create();

$destination = new ThroughStream();
$fileStream = new ThroughStream();
$hashStream = $fileStream;

$loop->futureTick(function () use ($destination, $fileStream) {
    $deferred = new Deferred();
    $decoratedFileStream = new WritableStreamHash(new WritableStreamBase64Encode($fileStream), 'sha1');
    $destination->write('{');
    $destination->write('"message":"filename",');
    $destination->write('"comitter": {');
    $destination->write('"name":"Cees-Jan Kiewiet",');
    $destination->write('"email":"hi@ceesjankiewiet.nl');
    $destination->write('},');
    $destination->write('"content": "');
    $fileStream->on('data', function ($data) use ($destination) {
        $destination->write($data);
    });
    $fileStream->on('close', function () use ($destination, $deferred) {
        $deferred->promise()->then(function ($hash) use ($destination) {
            $destination->write('",');
            $destination->write('"sha": "' . $hash . '"');
            $destination->end('}');
        });
    });
    $decoratedFileStream->on('hash', function ($hash) use ($deferred) {
        $deferred->resolve($hash);
    });

    $decoratedFileStream->end('foo.bar');
});

var_export(await(buffer($destination), $loop));