lab0

个人实验留档：cs144-2021

仔细看指导书，很详细。

Networking by hand

这一部分是手动发送http请求、发送邮件。

Writing a network program using an OS stream socket

实验要求

实现apps/webget.c中的get_URL() 函数

基本就是按照注释以及上面手动发送http请求的流程来做。

代码实现

apps/webget.c

void get_URL(const string &host, const string &path) {
    // Your code here.

    // You will need to connect to the "http" service on
    // the computer whose name is in the "host" string,
    // then request the URL path given in the "path" string.
    Address addr(host, "http");
    TCPSocket http_socket;
    http_socket.connect(addr);
    http_socket.write("GET " + path + " HTTP/1.1\r\n");
    http_socket.write("Host: " + host + "\r\n");
    http_socket.write("Connection: close\r\n");
    http_socket.write("\r\n");

    // Then you'll need to print out everything the server sends back,
    // (not just one call to read() -- everything) until you reach
    // the "eof" (end of file).
    while (!http_socket.eof())
        cout << http_socket.read();
    http_socket.close();
    // cerr << "Function called: get_URL(" << host << ", " << path << ").\n";
    // cerr << "Warning: get_URL() has not been implemented yet.\n";
}

测试

• ./apps/webget [cs144.keithw.org](http://cs144.keithw.org/) /hello

• make check_webget

An in-memory reliable byte stream

实验要求

实现一个内存中的可靠字节流缓冲区，该缓冲区可以被写入数据以及读出数据(FIFO)。

使用STL中的双端队列来做。

代码实现

• 添加相对应的成员属性，libsponge/byte_stream.hh

class ByteStream {
  private:
    // Your code here -- add private members as necessary.

    // Hint: This doesn't need to be a sophisticated data structure at
    // all, but if any of your tests are taking longer than a second,
    // that's a sign that you probably want to keep exploring
    // different approaches.

    size_t _capacity;         //!< Maximum number of bytes that can be written.
    std::deque<char> _queue;  //!< Buffer of bytes.
    size_t _written_size;     //!<  Number of bytes written.
    size_t _read_size;        //!< Number of bytes read.
    bool _input_ended;        //!< Flag indicating that the input has ended.

    bool _error{};  //!< Flag indicating that the stream suffered an error.

...后面省略

• 实现相对应的成员函数，libsponge/byte_stream.cc

ByteStream::ByteStream(const size_t capacity)
    : _capacity(capacity), _queue(), _written_size(0), _read_size(0), _input_ended(false), _error(false) {}

size_t ByteStream::write(const string &data) {
    if (_input_ended)
        return 0;
    size_t size_to_write = min(data.size(), _capacity - _queue.size());
    for (size_t i = 0; i < size_to_write; i++) {
        _queue.push_back(data[i]);
    }
    _written_size += size_to_write;
    return size_to_write;
}

//! \param[in] len bytes will be copied from the output side of the buffer
string ByteStream::peek_output(const size_t len) const {
    size_t peek_size = min(len, _queue.size());
    return string(_queue.begin(), _queue.begin() + peek_size);
}

//! \param[in] len bytes will be removed from the output side of the buffer
void ByteStream::pop_output(const size_t len) {
    // Attention: according to the test case, _read_size is updata here!!!
    size_t pop_size = min(len, _queue.size());
    _queue.erase(_queue.begin(), _queue.begin() + pop_size);
    ;
    _read_size += len;
}

//! Read (i.e., copy and then pop) the next "len" bytes of the stream
//! \param[in] len bytes will be popped and returned
//! \returns a string
std::string ByteStream::read(const size_t len) {
    string read_data = peek_output(len);
    pop_output(len);
    return read_data;
}

void ByteStream::end_input() { _input_ended = true; }

bool ByteStream::input_ended() const { return _input_ended; }

size_t ByteStream::buffer_size() const { return _queue.size(); }

bool ByteStream::buffer_empty() const { return _queue.empty(); }

bool ByteStream::eof() const { return _queue.empty() && _input_ended; }

size_t ByteStream::bytes_written() const { return _written_size; }

size_t ByteStream::bytes_read() const { return _read_size; }

size_t ByteStream::remaining_capacity() const { return _capacity - _queue.size(); }

• 注意事项 实现的时候，一开始将更新_read_size放在了read函数里面，一直过不了测试。后来查看测试用例发现在pop_output的时候也需要更新_read_size。

测试

• make check_lab0

总结

这个实验还是挺简单的，不过我c++有些东西没用还是忘了点。其次就是关于第二部分的测试，一开始没看报错信息乱改花了不少时间，后来仔细看测试用例怎么写的才解决。