src/Message/Stream/AbstractStream.php
public function isWritable()
    {
        if (! $this->stream) {
            return false;
        }
        $meta = stream_get_meta_data($this->stream);
        $mode = $meta['mode'];
        return (
            strstr($mode, 'x')
            || strstr($mode, 'w')
            || strstr($mode, 'c')
            || strstr($mode, 'a')
            || strstr($mode, '+')
        );
    }
public function isWritable()
    {
        if (! $this->stream) {
            return false;
        }
        $meta = stream_get_meta_data($this->stream);
        $mode = $meta['mode'];
        return (
            strstr($mode, 'x')
            || strstr($mode, 'w')
            || strstr($mode, 'c')
            || strstr($mode, 'a')
            || strstr($mode, '+')
        );
    }
Returns whether or not the stream is writable.

@return bool