src/MemoryStream.php
public function unshift(string $data)
    {
        if (!strlen($data)) {
            return;
        }

        $this->buffer->unshift($data);

        if (null !== $this->delayed && !$this->buffer->isEmpty()) {
            $delayed = $this->delayed;
            $this->delayed = null;
            $delayed->resolve($this->remove());
        }
    }
public function unshift(string $data)
    {
        if (!strlen($data)) {
            return;
        }

        $this->buffer->unshift($data);

        if (null !== $this->delayed && !$this->buffer->isEmpty()) {
            $delayed = $this->delayed;
            $this->delayed = null;
            $delayed->resolve($this->remove());
        }
    }
Shifts the given data back to the front of the stream and will be the first bytes returned from any pending or
subsequent read.

@param string $data