cs144_lab0

准备工作

Writing webget

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

    // 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).
    TCPSocket ss;
    ss.connect(Address(host, "http"));

    // 模拟http请求头部
    string str = "GET "+ path + " HTTP/1.1\r\nHost: " + host + "\r\nConnection: close\r\n\r\n";
    string recv_str;
    // 向服务器发送
    ss.write(str);
    // eof保证接受完
    while(ss.eof() == false) {
        ss.read(recv_str);
        cout<<recv_str;
    }
    ss.close();
}

An in-memory reliable byte stream

数据结构

std::string _buffer = ""; //缓存区
size_t _capacity = 0;
bool _input_ended_flag = false;
size_t _write_count = 0;
size_t _read_count = 0;

功能实现

write

size_t ByteStream::write(const string &data) {
    size_t len = data.length();
    if(len > _capacity - _buffer.length()) {
        len = _capacity - _buffer.length();
    }
    _write_count = _write_count + len;
    std::string msg = data.substr(0, len);
    _buffer += msg;
    return len;
}

peek_output

string ByteStream::peek_output(const size_t len) const {
    size_t lenght = len;
    std::string msg;
    if(len > _buffer.size())
        lenght = _buffer.size();
    msg = _buffer.substr(0, lenght);
    return msg;
}

pop_output

void ByteStream::pop_output(const size_t len) { 
    size_t lenght = len;
    if(len > _buffer.size())
        lenght = _buffer.size();
    _read_count += lenght;
    _buffer.erase(0, lenght);
}

read

std::string ByteStream::read(const size_t len) {
    string s = peek_output(len);
    pop_output(len);
    return s;
}

其他

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

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

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

bool ByteStream::buffer_empty() const { return _buffer.length() == 0; }

bool ByteStream::eof() const { return buffer_empty() && input_ended(); }

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

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

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

问题

当程序逻辑完全正确的情况。执行make check_lab0, 可能会出现以下问题

[100%] Testing Lab 0...
Test project /home/ubuntu/CS144_2021/lab0/sponge/build
    Start 26: t_byte_stream_construction
1/9 Test #26: t_byte_stream_construction .......***Failed    0.00 sec
Test Failure on expectation:
        Expectation: buffer_empty: 1

Failure message:
        The ByteStream should have had buffer_empty equal to 1 but instead it was 0

List of steps that executed successfully:
        Initialized with (capacity=15)
        Expectation: input_ended: 0

Exception: The test "construction" failed
.........
5/9 Test #30: t_byte_stream_many_writes ........***Failed    0.00 sec
Test Failure on expectation:
             Action: write "xrvebsengdwiqtkslspvlftaqaadlafzowwevyeqmyokuxdmgnbfjiilhczumsxolkvdcpficcgnigauadmpnlgalffifjhgnzydbzrjtcpwsmhujsbjzcptbifgiynnodjbbbjnpwrmffcctvcwx" to the stream

Failure message:
        The ByteStream should have had bytes_written equal to 149 but instead it was 0

List of steps that executed successfully:
        Initialized with (capacity=200000)

Exception: The test "many writes" failed
.....

这时需要重新对整个项目make一下，之后再执行make check_lab0