CS144 Lab4

这里回顾CS 144 Lab 4: the summit (TCP in full)，这次的实验对我难度还是太大了，只能通过85%左右的测试，所以这里只给出一点实验经验。

实验资料：

• https://www.cnblogs.com/kangyupl/p/stanford_cs144_labs.html
• https://kangyupl.gitee.io/cs144.github.io/
• https://gitee.com/kangyupl/sponge
• https://segmentfault.com/a/1190000039220243
• https://kiprey.github.io/2021/11/cs144-lab4/#%E5%85%AD%E3%80%81%E5%85%B7%E4%BD%93%E5%AE%9E%E7%8E%B0
• https://www.cnblogs.com/kangyupl/p/stanford_cs144_labs.html
• http://yuzijun.life/2021-02/CS144

Lab 4: the summit (TCP in full)

准备工作

下载代码以及跑通流程

git checkout -b lab4-startercode
git fetch
git merge origin/lab4-startercode
cd build
make -j4 && make check_lab4

说明

比较重要的3张图：

出处：

• https://cs144.github.io/assignments/lab2.pdf
• https://cs144.github.io/assignments/lab3.pdf
• https://en.wikipedia.org/wiki/File:Tcp_state_diagram_fixed.svg

这里比较重要的就是建立receiver, sender和TCP状态的对应关系，这部分在tcp_state.hh和tcp_state.cc中：

namespace TCPReceiverStateSummary {
const std::string ERROR = "error (connection was reset)";
const std::string LISTEN = "waiting for stream to begin (listening for SYN)";
const std::string SYN_RECV = "stream started";
const std::string FIN_RECV = "stream finished";
}  // namespace TCPReceiverStateSummary

namespace TCPSenderStateSummary {
const std::string ERROR = "error (connection was reset)";
const std::string CLOSED = "waiting for stream to begin (no SYN sent)";
const std::string SYN_SENT = "stream started but nothing acknowledged";
const std::string SYN_ACKED = "stream ongoing";
const std::string FIN_SENT = "stream finished (FIN sent) but not fully acknowledged";
const std::string FIN_ACKED = "stream finished and fully acknowledged";
}  // namespace TCPSenderStateSummary

TCPState::TCPState(const TCPState::State state) {
    switch (state) {
        case TCPState::State::LISTEN:
            _receiver = TCPReceiverStateSummary::LISTEN;
            _sender = TCPSenderStateSummary::CLOSED;
            break;
        case TCPState::State::SYN_RCVD:
            _receiver = TCPReceiverStateSummary::SYN_RECV;
            _sender = TCPSenderStateSummary::SYN_SENT;
            break;
        case TCPState::State::SYN_SENT:
            _receiver = TCPReceiverStateSummary::LISTEN;
            _sender = TCPSenderStateSummary::SYN_SENT;
            break;
        case TCPState::State::ESTABLISHED:
            _receiver = TCPReceiverStateSummary::SYN_RECV;
            _sender = TCPSenderStateSummary::SYN_ACKED;
            break;
        case TCPState::State::CLOSE_WAIT:
            _receiver = TCPReceiverStateSummary::FIN_RECV;
            _sender = TCPSenderStateSummary::SYN_ACKED;
            _linger_after_streams_finish = false;
            break;
        case TCPState::State::LAST_ACK:
            _receiver = TCPReceiverStateSummary::FIN_RECV;
            _sender = TCPSenderStateSummary::FIN_SENT;
            _linger_after_streams_finish = false;
            break;
        case TCPState::State::CLOSING:
            _receiver = TCPReceiverStateSummary::FIN_RECV;
            _sender = TCPSenderStateSummary::FIN_SENT;
            break;
        case TCPState::State::FIN_WAIT_1:
            _receiver = TCPReceiverStateSummary::SYN_RECV;
            _sender = TCPSenderStateSummary::FIN_SENT;
            break;
        case TCPState::State::FIN_WAIT_2:
            _receiver = TCPReceiverStateSummary::SYN_RECV;
            _sender = TCPSenderStateSummary::FIN_ACKED;
            break;
        case TCPState::State::TIME_WAIT:
            _receiver = TCPReceiverStateSummary::FIN_RECV;
            _sender = TCPSenderStateSummary::FIN_ACKED;
            break;
        case TCPState::State::RESET:
            _receiver = TCPReceiverStateSummary::ERROR;
            _sender = TCPSenderStateSummary::ERROR;
            _linger_after_streams_finish = false;
            _active = false;
            break;
        case TCPState::State::CLOSED:
            _receiver = TCPReceiverStateSummary::FIN_RECV;
            _sender = TCPSenderStateSummary::FIN_ACKED;
            _linger_after_streams_finish = false;
            _active = false;
            break;
    }
}

最严谨的思路应该是根据不同的TCPState做出不同的动作，但是这部分一直没有调通，只能通过单元测试，无法通过实际的测试，希望之后有机会可以完成这部分。

一些坑

• 这部分实验很依赖于前两次的实验实现，许多问题在前两次中无法体现，导致这次实验很困难；
• 网友表示webget在wsl中似乎无法跑通；