if (\strlen($this->buffer) < $this->content_length) {
                        // We know the number of remaining bytes to read - try to read them all at once.
                        $buf = \fread($this->input, $this->content_length - \strlen($this->buffer));
                        if (\is_string($buf) && \strlen($buf) > 0) {
                            $this->buffer .= $buf;