Checkpoint0: networking warmup
Networking by hand
在Web browser中访问网页。
接下来用命令手动完成浏览器所做的操作。
tinuvile@LAPTOP-7PVP3HH3:~$ telnet cs144.keithw.org http
Trying 104.196.238.229...
Connected to cs144.keithw.org.
Escape character is '^]'.
^]
telnet> close
Connection closed.这个命令指示telnet程序在我的电脑和cs144.keithw.org电脑间建立一个字节流连接，并访问该电脑上运行的特定服务http。
然后GET会告知服务器URL路径，Host输入主机部分，close以及句末回车再回车告知服务器已经完成HTTP请求。完整的如下：
tinuvile@LAPTOP-7PVP3HH3:~$ telnet cs144.keithw.org http
Trying 104.196.238.229...
Connected to cs144.keithw.org.
Escape character is '^]'.
GET /hello HTTP/1.1
Host: cs144.keithw.org
Connection: close
HTTP/1.1 200 OK
Date: Tue, 22 Apr 2025 10:04:29 GMT
Server: Apache
Last-Modified: Thu, 13 Dec 2018 15:45:29 GMT
ETag: "e-57ce93446cb64"
Accept-Ranges: bytes
Content-Length: 14
Connection: close
Content-Type: text/plain
Hello, CS144!
Connection closed by foreign host.Listening and connecting
这个是作为一个简单服务器的角色。在一个终端窗口中输入：
tinuvile@LAPTOP-7PVP3HH3:~$ netcat -v -l -p 9090
Listening on 0.0.0.0 9090
Connection received on localhost 54172然后在另一个终端中输入：
tinuvile@LAPTOP-7PVP3HH3:~$ telnet localhost 9090
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.这时候第一个终端窗口会出现：
Connection received on localhost 59892表明已经连接成功了。netcat是服务器端，telnet是客户端。
然后在netcat窗口ctrl+C退出程序，telnet也会立即退出。
Writing a network program using an OS stream socket
这个实验要用到Linux内核提供的stream socket功能，这个功能可以在两台计算机间创建可靠的双向字节流。
实验设计基于Unix套接字API，所以需要在Linux或者WSL环境下完成。我用的是Ubuntu 20.04.6 LTS。
tinuvile@LAPTOP-7PVP3HH3:~/CS144Lab$ cmake -S . -B build
-- The CXX compiler identification is GNU 13.1.0
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Setting build type to 'Debug'
-- Building in 'Debug' mode.
-- Configuring done (1.7s)
-- Generating done (0.1s)
-- Build files have been written to: /home/tinuvile/CS144Lab/build
tinuvile@LAPTOP-7PVP3HH3:~/CS144Lab$ cmake --build build
[ 26%] Building CXX object util/CMakeFiles/util_debug.dir/address.cc.o
[ 26%] Building CXX object src/CMakeFiles/minnow_debug.dir/byte_stream_helpers.cc.o
[ 26%] Building CXX object util/CMakeFiles/util_debug.dir/debug.cc.o
[ 26%] Building CXX object util/CMakeFiles/util_debug.dir/eventloop.cc.o
[ 26%] Building CXX object src/CMakeFiles/minnow_debug.dir/byte_stream.cc.o
[ 31%] Building CXX object apps/CMakeFiles/stream_copy.dir/bidirectional_stream_copy.cc.o
[ 36%] Building CXX object util/CMakeFiles/util_debug.dir/file_descriptor.cc.o
[ 42%] Building CXX object util/CMakeFiles/util_debug.dir/random.cc.o
[ 47%] Building CXX object tests/CMakeFiles/minnow_testing_debug.dir/common.cc.o
[ 52%] Building CXX object util/CMakeFiles/util_debug.dir/helpers.cc.o
[ 57%] Building CXX object util/CMakeFiles/util_debug.dir/socket.cc.o
[ 63%] Linking CXX static library libminnow_debug.a
[ 63%] Built target minnow_debug
[ 68%] Linking CXX static library libstream_copy.a
[ 68%] Built target stream_copy
[ 73%] Linking CXX static library libminnow_testing_debug.a
[ 78%] Linking CXX static library libutil_debug.a
[ 78%] Built target minnow_testing_debug
[ 78%] Built target util_debug
[ 84%] Building CXX object apps/CMakeFiles/webget.dir/webget.cc.o
[ 89%] Building CXX object apps/CMakeFiles/tcp_native.dir/tcp_native.cc.o
[ 94%] Linking CXX executable tcp_native
[100%] Linking CXX executable webget
[100%] Built target tcp_native
[100%] Built target webget编译源代码。
课程给我们提供了一些编码建议，希望充分利用新特性实现最大程度的安全编程，可查阅C++ Core Guidelines。核心理念是确保每个对象的设计具备尽可能小的公开接口，包含大量内部安全检查机制，难以被误用，并能自主清理资源。具体来说：
避免成对操作，如
malloc/free,new/delete，因为这些操作的后者可能因为函数提前返回或抛出异常而无法执行。建议采用Resource acquisition is initialization的模式（RAII），操作应在对象构造函数中完成，逆向操作则应在析构函数中自动执行。尽量不要使用原始指针，必要时使用智能指针
unique_ptr或shared_ptr。避免使用模板、线程、锁和虚函数。
避免使用C风格字符串
char *str或字符串函数，改用std::string。切勿使用C风格类型转换，必要时使用C++的
static_cast。函数参数传递优先使用常量引用方式，如
const Address & address。所有不需要修改的变量和方法都声明为
const。避免使用全局变量，尽可能为每个变量赋予最小的作用域。
提交作业前运行
cmake --build build --target tidy获取改进建议，并运行cmake --build build --target format保持代码格式一致。
Reading the Minnow support code
公共接口部分阅读util/socket.hh和util/file_descriptor.hh。继承关系为TCPSocket → Socket → FileDescriptor，关键部分列在下面：
file_descriptor.hh
这个类是一个引用计数的文件描述符句柄，用shared_ptr管理FDWrapper，FDWrapper封装了底层的文件描述符。然后这个类将 POSIX 系统调用封装成了 C++ 方法。
class FileDescriptor {
public:
// 核心操作
void read( std::string& buffer ); // 读取数据到字符串
size_t write( std::string_view buffer ); // 写入字符串数据
void close(); // 显式关闭描述符
// 状态查询
int fd_num() const; // 获取底层文件描述符编号
bool eof() const; // 检查是否到达文件末尾
bool closed() const; // 检查是否已关闭
// 高级功能
void set_blocking( bool blocking ); // 设置阻塞/非阻塞模式
FileDescriptor duplicate() const; // 复制描述符（共享底层 FDWrapper）
};socket.hh
Socket继承自FileDescriptor，增加了网络相关的方法，子类TCPSocket、UDPSocket进一步特化。
class Socket : public FileDescriptor {
public:
// 基础操作
void bind( const Address& address ); // 绑定本地地址
void connect( const Address& address ); // 连接到远程地址
void shutdown( int how ); // 关闭连接方向（SHUT_RD/SHUT_WR）
// 地址信息
Address local_address() const; // 获取本地绑定地址
Address peer_address() const; // 获取对端地址
// 高级选项
void set_reuseaddr(); // 允许地址重用（SO_REUSEADDR）
};
class TCPSocket : public Socket {
public:
void listen( int backlog = 16 ); // 开始监听连接
TCPSocket accept(); // 接受新连接
};
class UDPSocket : public DatagramSocket {
public:
void sendto( const Address& dest, std::string_view payload ); // 发送数据报
void recv( Address& src, std::string& payload ); // 接收数据报
};Writing webget
void get_URL( const string& host, const string& path )
{
// cerr << "Function called: get_URL(" << host << ", " << path << ")\n";
// cerr << "Warning: get_URL() has not been implemented yet.\n";
// 创建 TCP 套接字并连接目标地址
TCPSocket socket;
socket.connect( Address( host, "http" ) );
// 构建 HTTP 请求头
const string request = "GET " + path + " HTTP/1.0\r\n"
+ "Host: " + host + "\r\n"
+ "Connection: close\r\n\r\n";
// 发送 HTTP 请求
socket.write( request );
// 读取直到连接关闭
string buffer;
while ( !socket.eof() ) {
socket.read(buffer);
cout << buffer;
}
// 关闭套接字
socket.close();
}HTTP 请求是通过 TCP 连接发送的纯文本字节流，write方法将字节流写入文件描述符。
运行测试：
tinuvile@LAPTOP-7PVP3HH3:~/CS144Lab$ cd build
tinuvile@LAPTOP-7PVP3HH3:~/CS144Lab/build$ ./apps/webget cs144.keithw.org /hello
HTTP/1.1 200 OK
Date: Fri, 09 May 2025 06:27:15 GMT
Server: Apache
Last-Modified: Thu, 13 Dec 2018 15:45:29 GMT
ETag: "e-57ce93446cb64"
Accept-Ranges: bytes
Content-Length: 14
Connection: close
Content-Type: text/plain
Hello, CS144!运行cmake --build build --target check_webget通过。
tinuvile@LAPTOP-7PVP3HH3:~/CS144Lab$ cmake --build build --target check_webget
Test project /home/tinuvile/CS144Lab/build
Start 1: compile with bug-checkers
1/2 Test #1: compile with bug-checkers ........ Passed 0.09 sec
Start 2: t_webget
2/2 Test #2: t_webget ......................... Passed 1.14 sec
100% tests passed, 0 tests failed out of 2
Total Test time (real) = 1.24 sec
Built target check_webgetAn in-memory reliable byte stream
这个任务需要我们实现字节流功能。这个字节流是有限容量的，写入的数据不能超过当前可用容量。当写入者写入数据时，如果缓冲区已满，只能写入部分数据。读取者可以读取数据，并从缓冲区中移除已读取的部分，这样释放空间，让写入者可以继续写入。同时，写入者可以关闭流，读取者在读取完所有数据后会到达EOF。
class Writer : public ByteStream
{
public:
void push( std::string data ); // Push data to stream, but only as much as available capacity allows.
void close(); // Signal that the stream has reached its ending. Nothing more will be written.
bool is_closed() const; // Has the stream been closed?
uint64_t available_capacity() const; // How many bytes can be pushed to the stream right now?
uint64_t bytes_pushed() const; // Total number of bytes cumulatively pushed to the stream
};
class Reader : public ByteStream
{
public:
std::string_view peek() const; // Peek at the next bytes in the buffer
void pop( uint64_t len ); // Remove `len` bytes from the buffer
bool is_finished() const; // Is the stream finished (closed and fully popped)?
uint64_t bytes_buffered() const; // Number of bytes currently buffered (pushed and not popped)
uint64_t bytes_popped() const; // Total number of bytes cumulatively popped from stream
};首先ByteStream需要维护一个缓冲区，我选用的是std::string。
class ByteStream
{
public:
explicit ByteStream( uint64_t capacity );
// Helper functions (provided) to access the ByteStream's Reader and Writer interfaces
Reader& reader();
const Reader& reader() const;
Writer& writer();
const Writer& writer() const;
void set_error() { error_ = true; }; // Signal that the stream suffered an error.
bool has_error() const { return error_; }; // Has the stream had an error?
protected:
// Please add any additional state to the ByteStream here, and not to the Writer and Reader interfaces.
std::string buffer_; // Buffer to store data
uint64_t start_position_; // Position of the start of the buffer
uint64_t bytes_pushed_; // Number of bytes pushed to the buffer
uint64_t bytes_popped_; // Number of bytes popped from the buffer
bool closed_; // Flag indicating whether the stream has been closed
bool eof_; // Flag indicating whether the stream has reached its ending
uint64_t capacity_; // Maximum capacity of the buffer
bool error_ {};
};然后实现Reader和Writer的具体函数，比较简单。
#include "byte_stream.hh"
using namespace std;
ByteStream::ByteStream( uint64_t capacity )
: buffer_()
, start_position_( 0 )
, bytes_pushed_( 0 )
, bytes_popped_( 0 )
, closed_( false )
, eof_( false )
, capacity_( capacity )
, error_( false )
{}
void Writer::push( string data )
{
if ( closed_ || error_ )
return;
const uint64_t available = available_capacity();
const uint64_t byte_to_push = min( data.size(), available );
if ( byte_to_push > 0 ) {
buffer_.append( data.substr( 0, byte_to_push ) );
bytes_pushed_ += byte_to_push;
}
}
void Writer::close()
{
closed_ = true;
}
bool Writer::is_closed() const
{
return closed_;
}
uint64_t Writer::available_capacity() const
{
return capacity_ - ( buffer_.size() - start_position_ );
}
uint64_t Writer::bytes_pushed() const
{
return bytes_pushed_;
}
string_view Reader::peek() const
{
return string_view( buffer_ ).substr( start_position_ );
}
void Reader::pop( uint64_t len )
{
len = min( len, buffer_.size() - start_position_ );
start_position_ += len;
bytes_popped_ += len;
// if data_read is greater than 4 KB and half of the buffer is used,
// remove the unused part of the buffer
if ( start_position_ > 4096 && start_position_ >= buffer_.size() / 2 ) {
buffer_ = buffer_.substr( start_position_ );
start_position_ = 0;
}
}
bool Reader::is_finished() const
{
return closed_ && ( start_position_ == buffer_.size() );
}
uint64_t Reader::bytes_buffered() const
{
return buffer_.size() - start_position_;
}
uint64_t Reader::bytes_popped() const
{
return bytes_popped_;
}运行测试。
tinuvile@LAPTOP-7PVP3HH3:~/CS144Lab$ cmake --build build --target check0
Test project /home/tinuvile/CS144Lab/build
Start 1: compile with bug-checkers
1/11 Test #1: compile with bug-checkers ........ Passed 6.11 sec
Start 2: t_webget
2/11 Test #2: t_webget ......................... Passed 1.16 sec
Start 3: byte_stream_basics
3/11 Test #3: byte_stream_basics ............... Passed 0.01 sec
Start 4: byte_stream_capacity
4/11 Test #4: byte_stream_capacity ............. Passed 0.01 sec
Start 5: byte_stream_one_write
5/11 Test #5: byte_stream_one_write ............ Passed 0.01 sec
Start 6: byte_stream_two_writes
6/11 Test #6: byte_stream_two_writes ........... Passed 0.01 sec
Start 7: byte_stream_many_writes
7/11 Test #7: byte_stream_many_writes .......... Passed 0.09 sec
Start 8: byte_stream_stress_test
8/11 Test #8: byte_stream_stress_test .......... Passed 0.02 sec
Start 37: no_skip
9/11 Test #37: no_skip .......................... Passed 0.01 sec
Start 38: compile with optimization
10/11 Test #38: compile with optimization ........ Passed 2.61 sec
Start 39: byte_stream_speed_test
ByteStream throughput (pop length 4096): 20.07 Gbit/s
ByteStream throughput (pop length 128): 14.28 Gbit/s
ByteStream throughput (pop length 32): 11.13 Gbit/s
11/11 Test #39: byte_stream_speed_test ........... Passed 0.14 sec
100% tests passed, 0 tests failed out of 11
Total Test time (real) = 10.16 sec
Built target check0提交前用clang-format统一代码风格。
tinuvile@LAPTOP-7PVP3HH3:~/CS144Lab$ cmake --build build --target format
[100%] Formatting source code...
[100%] Built target format这样就算完成了。
Last updated