~~- Lab5 NetWork Interface~~

~~- Lab6 Router~~

材料

schedule 2019

cs144视频 2013

Lab4 TCPConnection

2020/05/28 ~ 06/01


TCP协议的Lab告一段落,后面的是发送EthernetFrame和Router的lab

1. fsm是(finite state machine)的缩写,有限状态机

2. 重传列表的问题 , cpp的queue在空的时候也会返回一个默认值 , 需要判断空的情况 , 对语言的库不熟悉,排查了好久,之后都要当心为空返回默认值的情况 (虽然我觉得为空的时候peek front应该报错)

3. 主动关闭才需要linger , 被动关闭不需要 ,被动关闭的判断（inbound在outbound之前关闭)

4.每次tick timeout都需要重置, 但只有重传的时候才执行exponential backoff

5. 触发RST的场景

6.linger的判断

7.debug skill++ (ide断点, 还是没有打log好用)

关于连接关闭

由于"Two General's Problem' , clean shutdown是不可能实现的一个目标 , 但tcp使用了一个非常接近的实现 , 在送出最后一个ack之后等待10*rt_timeout,如果对端没有重传,则假设达成了clean shutdown

重要的图示

connection 和 receiver/sender对应的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;
    }

https://cs144.github.io/lab_faq.html

https://cs144.github.io/assignments/lab4.pdf

https://www.bilibili.com/video/BV137411Z7LR?p=28

https://blog.csdn.net/wuji0447/article/details/78356875

Lab3 TCPSender

2020/05/24 ~ 05/27

note/pesudo

TCPSender

guide

1.超时机制是 exponential backoff , 指数补偿

2.下一个 lab 还是多写点 helper 吧

3.fin 也占一个窗口位

4.只要收到 ack 就要更新窗口

5.cpp 的 list 遍历,erase 后返回下一个 iterator 的指针 

6.segfault 要怎么调试?

7.前闭后开区间的意义: unsigned int 不能为负值,前闭后开可以定义大小为 0 的区间

8.初始 windowSize 为 1 (发 syn)

Lab2 TCPReceiver

2020/05/20 ~ 05/23

1.实现对 syn,fin,和带data 的 tcp segment 的接收,处理和响应

2.看着 test case 写了第一版 pesudo code, 然后直接在 pesudo code 上重构了一版,以窗口为模型,截取在窗口内的字节流

3.最后精简完,就 100 多行代码...用了 2 天

4.测试用例很完善, 真的感谢课程作者

5.lab2 对 lab1的 reassembler 增加了容量限制的 test case , 又回去 debug 了一会 , 涉及容量的问题只取在窗口内的字节就行了

6.同时收到 fin 和数据的时候,要处理完数据再处理 fin

7.window size只更新连续字节流部分

8.还没找到这套测试框架打印数据的方法

9.写入 Reassembler 的时候要用absolute index, 从 0 开始的,不计算 syn 位的索引

Lab1 StreamReassembler

2020/05/18 ~ 05/20

notes/pesudo

Reassembler

guide

1.lab1用了5，6个小时的时间才做完，测试用例有点难度

2.实现的是`TCP`的一个组件，重新组装segment成为连续的字节流，提供给上层应用

3.本来想使用递归让代码看起来清楚一点，结果`segfault`了，还是改成循环了

4.在虚拟机里写的代码，没有输入法，写的英文注释看起来挺美观，蹩脚的英文

5.没有人肉走完`test case`就开始写代码，结果是想的模型不对，不能满足后面的`case`，基本是推翻重写 （第一次是用`segment`，字符串的角度进行重组，但遇到了增量更新，未重组字节级别的覆盖，重组字节级别覆盖的`case`，最后把思考的模型改成字节流，代码也清晰许多）,这点让我想到业务开发里也是一样，没有往后思考可能的需求（更完善的`test case` ） ，导致代码只能东拼西凑满足功能，完全不堪入目。

6.dian fan bao boom

7.pesudo code + test case is a powerful combo

8.maybe multiple eof , so need to store every eof state

9 imple an out of order , repeat, overlapping , increment update , reliable reassembler

Lab0 ByteStream

2020/05/17 ~ 05/18

ByteStream

webget.cc

guide

1.实现了一个`in-memory reliable ordered bystream`,做这个的目的是因为`tcp`实际上就是这样的一个可靠有序的字节流,不过是基于网络的,
实现这一个小`lab`可以更好地理解了`tc`p两端的一些交互,
比如说`http`的请求中,客户端发送完请求后会向服务端发送一个`SHUTDOWN_WRITE`的 信号,
就对应`byteSteam`类的`input_ended()`,
这时候服务端就知道,在这个`sequence number`之后没有新数据了,接收完前面的字节就可以开始处理请求,
这里的`seq number`就可以用作`eof`的判断

2.`webget`这个`task`用课程提供的虚拟镜像运行不了,折腾了好久,放到自己的`ubuntu16.04`里成功运行,越底层的语言开发环境越折磨人

.

For build prereqs, see the CS144 VM setup instructions.

Sponge quickstart

To set up your build directory:

$ mkdir -p <path/to/sponge>/build
$ cd <path/to/sponge>/build
$ cmake ..

Note: all further commands listed below should be run from the build dir.

To build:

$ make

You can use the -j switch to build in parallel, e.g.,

$ make -j$(nproc)

To test (after building; make sure you've got the build prereqs installed!)

$ make check

The first time you run make check, it will run sudo to configure two TUN devices for use during testing.

build options

You can specify a different compiler when you run cmake:

$ CC=clang CXX=clang++ cmake ..

You can also specify CLANG_TIDY= or CLANG_FORMAT= (see "other useful targets", below).

Sponge's build system supports several different build targets. By default, cmake chooses the Release target, which enables the usual optimizations. The Debug target enables debugging and reduces the level of optimization. To choose the Debug target:

$ cmake .. -DCMAKE_BUILD_TYPE=Debug

The following targets are supported:

Release - optimizations
Debug - debug symbols and -Og
RelASan - release build with ASan and UBSan
RelTSan - release build with ThreadSan
DebugASan - debug build with ASan and UBSan
DebugTSan - debug build with ThreadSan

Of course, you can combine all of the above, e.g.,

$ CLANG_TIDY=clang-tidy-6.0 CXX=clang++-6.0 .. -DCMAKE_BUILD_TYPE=Debug

Note: if you want to change CC, CXX, CLANG_TIDY, or CLANG_FORMAT, you need to remove build/CMakeCache.txt and re-run cmake. (This isn't necessary for CMAKE_BUILD_TYPE.)

other useful targets

To generate documentation (you'll need doxygen; output will be in build/doc/):

$ make doc

To lint (you'll need clang-tidy):

$ make -j$(nproc) tidy

To run cppcheck (you'll need cppcheck):

$ make cppcheck

To format (you'll need clang-format):

$ make format

To see all available targets,

$ make help

yfhwang / CS144

材料

Lab4 TCPConnection

关于连接关闭

重要的图示

Lab3 TCPSender

Lab2 TCPReceiver

Lab1 StreamReassembler

Lab0 ByteStream

.

Sponge quickstart

build options

other useful targets

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