byte-stream/lib/OutputStream.php

<?php

namespace Amp\ByteStream;

use Amp\Promise;

/**
 * An `OutputStream` allows writing data in chunks. Writers can wait on the returned promises to feel the backpressure.
 */
interface OutputStream {
    /**
     * Writes data to the stream.
     *
     * @param string $data Bytes to write.
     *
     * @return Promise Succeeds once the data has been successfully written to the stream.
     *
     * @throws ClosedException If the stream has already been closed.
     */
    public function write(string $data): Promise;

    /**
     * Marks the stream as no longer writable. Optionally writes a final data chunk before. Note that this is not the
     * same as forcefully closing the stream. This method waits for all pending writes to complete before closing the
     * stream. Socket streams implementing this interface should only close the writable side of the stream.
     *
     * @param string $finalData Bytes to write.
     *
     * @return Promise Succeeds once the data has been successfully written to the stream.
     *
     * @throws ClosedException If the stream has already been closed.
     */
    public function end(string $finalData = ""): Promise;
}