基于前面两篇及B站上大牛小方的解析视频：

 【1】【Filezilla】 dispatch函数重载的例子-CSDN博客

【2】【C++】【FileZilla】事件调用机制代码解析-CSDN博客

当线程entry()调用process_event()时，通过语句 (*std::get<0>(ev0))(*std::get<1>(ev0))调用operator 方法，当元组 ev0 的第零个元素 event_handler 类型匹配 CSftpControlSocket 时，语句调用重载的 CSftpControlSocket::operator() ，元组 ev0 的第一个元素 event_base 作为形参 ev传入operator（参考【2】），而当 ev 的实际类型匹配 CSftpEvent 时，实际调用下面重载的分发方法中的CSftpControlSocket::OnSftpEvent（参考【1】）。元组 ev 第零个元素的实际类型还有可能是 process_event, CCommandEvent等。

// In event_loop.hpp
typedef std::deque<std::tuple<event_handler*, event_base*, bool>> Events;
    // Events::value_type ev{};


// In sftpcontrolsocket.cpp
void CSftpControlSocket::operator()(fz::event_base const& ev)
{
	if (fz::dispatch<fz::process_event, CSftpEvent, CSftpListEvent, SftpRateAvailableEvent>(ev, this,
		&CSftpControlSocket::OnProcessEvent,
		&CSftpControlSocket::OnSftpEvent,
		&CSftpControlSocket::OnSftpListEvent,
		&CSftpControlSocket::OnQuotaRequest)) {
		return;
	}

	CControlSocket::operator()(ev);
}

关注CSftpControlSocket::OnSftpEvent()方法：

void CSftpControlSocket::OnSftpEvent(sftp_message const& message)
{
    ......
    switch (message.type)
    {
        ......
        case sftpEvent::Recv:......break;
        case sftpEvent::Send:......break;
        case sftpEvent::Transfer:......break;
        case sftpEvent::io_nextbuf:
	        if (!operations_.empty() && operations_.back()->opId == Command::transfer) {
		        auto & data = static_cast<CSftpFileTransferOpData&>(*operations_.back());
		        data.OnNextBufferRequested(fz::to_integral<uint64_t>(message.text[0]));
	        }
	        break;
        case sftpEvent::io_open:
	        if (!operations_.empty() && operations_.back()->opId == Command::transfer) {
		        auto & data = static_cast<CSftpFileTransferOpData&>(*operations_.back());
		        data.OnOpenRequested(fz::to_integral<uint64_t>(message.text[0]));
	        }
	        break;
        case sftpEvent::io_size:
	        if (!operations_.empty() && operations_.back()->opId == Command::transfer) {
		        auto & data = static_cast<CSftpFileTransferOpData&>(*operations_.back());
		        data.OnSizeRequested();
	        }
	        break;
        case sftpEvent::io_finalize:
	        if (!operations_.empty() && operations_.back()->opId == Command::transfer) {
		        auto & data = static_cast<CSftpFileTransferOpData&>(*operations_.back());
		        data.OnFinalizeRequested(fz::to_integral<uint64_t>(message.text[0]));
	        }
	        break;
        default:......
    }
    ......
}

可以注意到其中 case sftpEvent::io_nextbuf 处理了数据的传输。

• 上传：std::tie(r, buffer_) = reader_->get_buffer(*this);
• 下载：auto r = writer_->add_buffer(std::move(buffer_), *this);

void CSftpFileTransferOpData::OnNextBufferRequested(uint64_t processed)
{
	if (reader_) {
		fz::aio_result r;
		std::tie(r, buffer_) = reader_->get_buffer(*this);
		if (r == fz::aio_result::wait) {
			return;
		}
		if (r == fz::aio_result::error) {
			controlSocket_.AddToSendBuffer("--1\n");
			return;
		}
		if (buffer_->size()) {
			controlSocket_.AddToSendBuffer(fz::sprintf("-%d %d\n", buffer_->get() - base_address_, buffer_->size()));
		}
		else {
			controlSocket_.AddToSendBuffer(fz::sprintf("-0\n"));
		}
	}
	else if (writer_) {
		buffer_->resize(processed);
		auto r = writer_->add_buffer(std::move(buffer_), *this);
		if (r == fz::aio_result::ok) {
			buffer_ = controlSocket_.buffer_pool_->get_buffer(*this);
			if (!buffer_) {
				r = fz::aio_result::wait;
			}
		}
		if (r == fz::aio_result::wait) {
			return;
		}
		if (r == fz::aio_result::error) {
			controlSocket_.AddToSendBuffer("--1\n");
			return;
		}
		controlSocket_.AddToSendBuffer(fz::sprintf("-%d %d\n", buffer_->get() - base_address_, buffer_->capacity()));
	}
	else {
		controlSocket_.AddToSendBuffer("--1\n");
		return;
	}
}