CS144 Lab3
这里回顾CS 144 Lab 3: the TCP sender。
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
Lab 3: the TCP sender
准备工作
下载代码以及跑通流程
git checkout -b lab3-startercode
git fetch
git merge origin/lab3-startercode
make -j4 && make check_lab3说明
- 为了模块化，增加了Timer类。
- 整体思路是发送数据，然后判断是否要重传。
- SYN, FIN对应的负载长度为0。
- ack n表示序号n之前的都收到。
代码
Timer
实现 Timer类，方便后续使用：
class Timer {
private:
// 是否过期
bool _expired = false;
// RTO
unsigned int _rto = 0;
// 经历的时间
unsigned int _time = 0;
public:
Timer() {};
Timer(unsigned int rto) : _rto(rto) {};
// expired
bool is_expired() { return _expired; };
// rto
void update_rto(unsigned int rto) {
_rto = rto;
_expired = false;
};
unsigned int get_rto() { return _rto; };
void double_rto() {
_rto *= 2;
_expired = false;
};
// _time, 更新时间, 并判断是否过期
void update_time(unsigned int t) {
_time += t;
if (_time >= _rto) {
_expired = true;
}
}
};TCPSender
TCPSender需要添加一些成员变量和方法，具体作用见注释：
class TCPSender {
private:
//! our initial sequence number, the number for our SYN.
WrappingInt32 _isn;
//! outbound queue of segments that the TCPSender wants sent
std::queue<TCPSegment> _segments_out{};
//! retransmission timer for the connection
unsigned int _initial_retransmission_timeout;
//! outgoing stream of bytes that have not yet been sent
ByteStream _stream;
//! the (absolute) sequence number for the next byte to be sent
uint64_t _next_seqno{0};
// add begin
// 已发送, 未确认的segments
std::queue<TCPSegment> _segments{};
// 窗口大小, 初始化为1
unsigned int _window_size = 1;
// 已发送, 未确认的字节数
size_t _bytes_in_flight = 0;
// 连续重传次数
unsigned int _cnt = 0;
// 上一次ack的index
uint64_t _last_ack{0};
// Timer
// timer是否运行
bool _is_timer_running = false;
// 重传计时器
Timer _timer;
// RTO
unsigned int _rto = 0;
// SYN, FIN
// 下一个segment对应的syn
bool _syn = true;
// 下一个segment对应的fin
bool _fin = false;
// add end
public:
//! Initialize a TCPSender
TCPSender(const size_t capacity = TCPConfig::DEFAULT_CAPACITY,
const uint16_t retx_timeout = TCPConfig::TIMEOUT_DFLT,
const std::optional<WrappingInt32> fixed_isn = {});
//! \name "Input" interface for the writer
//!@{
ByteStream &stream_in() { return _stream; }
const ByteStream &stream_in() const { return _stream; }
//!@}
//! \name Methods that can cause the TCPSender to send a segment
//!@{
//! \brief A new acknowledgment was received
bool ack_received(const WrappingInt32 ackno, const uint16_t window_size);
//! \brief Generate an empty-payload segment (useful for creating empty ACK segments)
void send_empty_segment();
//! \brief create and send segments to fill as much of the window as possible
void fill_window();
//! \brief Notifies the TCPSender of the passage of time
void tick(const size_t ms_since_last_tick);
//!@}
//! \name Accessors
//!@{
//! \brief How many sequence numbers are occupied by segments sent but not yet acknowledged?
//! \note count is in "sequence space," i.e. SYN and FIN each count for one byte
//! (see TCPSegment::length_in_sequence_space())
size_t bytes_in_flight() const;
//! \brief Number of consecutive retransmissions that have occurred in a row
unsigned int consecutive_retransmissions() const;
//! \brief TCPSegments that the TCPSender has enqueued for transmission.
//! \note These must be dequeued and sent by the TCPConnection,
//! which will need to fill in the fields that are set by the TCPReceiver
//! (ackno and window size) before sending.
std::queue<TCPSegment> &segments_out() { return _segments_out; }
//!@}
//! \name What is the next sequence number? (used for testing)
//!@{
//! \brief absolute seqno for the next byte to be sent
uint64_t next_seqno_absolute() const { return _next_seqno; }
//! \brief relative seqno for the next byte to be sent
WrappingInt32 next_seqno() const { return wrap(_next_seqno, _isn); }
//!@}
// add begin
// 将seqno和str封装为TCPSegment, 设置对应的syn, fin
TCPSegment get_segment(WrappingInt32 &seqno, std::string &str);
// add end
};构造函数TCPSender
添加_timer和_rto的初始化即可：
TCPSender::TCPSender(const size_t capacity, const uint16_t retx_timeout, const std::optional<WrappingInt32> fixed_isn)
: _isn(fixed_isn.value_or(WrappingInt32{random_device()()}))
, _initial_retransmission_timeout{retx_timeout}
, _stream(capacity)
, _timer()
, _rto(retx_timeout) {}bytes_in_flight
uint64_t TCPSender::bytes_in_flight() const {
return _bytes_in_flight;
}get_segment
// add
TCPSegment TCPSender::get_segment(WrappingInt32 &seqno, std::string &str) {
// 设置seqno和标志位
TCPHeader header;
header.syn = _syn;
header.fin = _fin;
header.seqno = seqno;
// 设置负载
Buffer payload(std::move(str));
// 设置TCPSegment
TCPSegment tcp_segment;
tcp_segment.header() = header;
tcp_segment.payload() = payload;
// 更新
size_t l = tcp_segment.length_in_sequence_space();
_bytes_in_flight += l;
_next_seqno += l;
// 4. 每次发送包含数据（在序列空间中长度非零）的段（不管是第一次还是重传），如果timer没有运行，就启动它，使它在RTO毫秒后失效（对于RTO的当前值）
if (!_is_timer_running) {
_timer = Timer(_rto);
_is_timer_running = true;
}
return tcp_segment;
}fill_window
void TCPSender::fill_window() {
// 根据FAQ, fill_window时候将窗口大小视为至少1
unsigned int window_size = _window_size ? _window_size : 1;
// send syn
if (_syn) {
std::string str = "";
WrappingInt32 seqno = next_seqno();
TCPSegment tcp_segment = get_segment(seqno, str);
// 更新已发送, 未确认的segments
_segments_out.push(tcp_segment);
// 发送segment
_segments.push(tcp_segment);
// 更新_syn
_syn = false;
return;
}
uint64_t free_size;
// [_last_ack, _next_seqno)部分已发送
// 当窗口未满, 并且还没收到fin
while (((free_size = window_size - (_next_seqno - _last_ack)) > 0) && (!_fin)) {
size_t l = free_size;
// 不能超过最大负载
l = min(l, TCPConfig::MAX_PAYLOAD_SIZE);
// 获得tcp_segment, 注意是read
std::string str = _stream.read(l);
WrappingInt32 seqno = next_seqno();
// 读取后再判断是否为fin
if (_stream.eof()) {
_fin = true;
}
TCPSegment tcp_segment = get_segment(seqno, str);
// 如果负载为空则返回
if (tcp_segment.length_in_sequence_space() == 0) {
break;
}
// 更新已发送, 未确认的segments
_segments_out.push(tcp_segment);
// 发送segment
_segments.push(tcp_segment);
}
}ack_received
bool TCPSender::ack_received(const WrappingInt32 ackno, const uint16_t window_size) {
// [_last_ack, _next_seqno)部分已发送未确认
// 绝对序列号
uint64_t abs_ackno = unwrap(ackno, _isn, _last_ack);
// 收到了未发送的确认, 直接返回false
if (abs_ackno > _next_seqno) {
return false;
}
// 更新窗口大小
_window_size = window_size;
// 确认已经收到, 直接返回true
if (abs_ackno < _last_ack) {
return true;
}
// 其余情况更新
_last_ack = abs_ackno;
// 7. 当接收方给发送方确认成功接收新数据的`ackno`时（该`ackno`反映了一个大于之前的任何`ackno`的绝对序列号）。
// 将RTO调回其“初始值”
_rto = _initial_retransmission_timeout;
// 如果发送方有任何未完成的数据，重新启动重传timer，使其在RTO毫秒后失效（对于RTO的当前值）
if (!_segments.empty()) {
_timer = Timer(_rto);
_is_timer_running = true;
}
// 将“连续重传”的计数重设为零
_cnt = 0;
// 删除已确认的部分
while (!_segments.empty()) {
TCPSegment seg = _segments.front();
TCPHeader header = seg.header();
// 序列范围是[start, end)
// 注意是seqno
WrappingInt32 start = header.seqno;
WrappingInt32 end = start + seg.length_in_sequence_space();
// 如果[start, end)都小于ackno, 则表示已确认; 否则退出循环
if (ackno - end >= 0) {
_segments.pop();
_bytes_in_flight -= seg.length_in_sequence_space();
} else {
break;
}
}
// 5. 当所有未完成的数据都被确认后，关闭重传计时器。
if (_segments.empty()) {
_is_timer_running = false;
}
// window
fill_window();
return true;
}tick
void TCPSender::tick(const size_t ms_since_last_tick) {
// 更新时间
_timer.update_time(ms_since_last_tick);
// 6. 如果tick被调用，并且重传计时器已经过期
// 有可以重传的部分
if (_timer.is_expired() && (!_segments.empty())) {
// 重传TCP接收方尚未完全确认的最早段
_segments_out.push(_segments.front());
// 如果窗口大小为非零
if (_window_size) {
_cnt++;
_rto *= 2;
}
// 启动重传timer，使其在RTO毫秒后过期
_timer = Timer(_rto);
_is_timer_running = true;
}
}consecutive_retransmissions
直接返回即可：
unsigned int TCPSender::consecutive_retransmissions() const {
return _cnt;
}send_empty_segment
void TCPSender::send_empty_segment() {
// 设置负载为空
std::string str = "";
WrappingInt32 seqno = next_seqno();
TCPSegment tcp_segment = get_segment(seqno, str);
// 注意空段不需要存储到未确认的部分
_segments_out.push(tcp_segment);
}测试
make -j4 && make check_lab3
Test project /cs144/sponge/build
Start 1: t_wrapping_ints_cmp
1/31 Test #1: t_wrapping_ints_cmp .............. Passed 0.00 sec
Start 2: t_wrapping_ints_unwrap
2/31 Test #2: t_wrapping_ints_unwrap ........... Passed 0.00 sec
Start 3: t_wrapping_ints_wrap
3/31 Test #3: t_wrapping_ints_wrap ............. Passed 0.00 sec
Start 4: t_recv_connect
4/31 Test #4: t_recv_connect ................... Passed 0.00 sec
Start 5: t_recv_transmit
5/31 Test #5: t_recv_transmit .................. Passed 0.05 sec
Start 6: t_recv_window
6/31 Test #6: t_recv_window .................... Passed 0.00 sec
Start 7: t_recv_reorder
7/31 Test #7: t_recv_reorder ................... Passed 0.00 sec
Start 8: t_recv_close
8/31 Test #8: t_recv_close ..................... Passed 0.00 sec
Start 9: t_send_connect
9/31 Test #9: t_send_connect ................... Passed 0.00 sec
Start 10: t_send_transmit
10/31 Test #10: t_send_transmit .................. Passed 0.05 sec
Start 11: t_send_retx
11/31 Test #11: t_send_retx ...................... Passed 0.00 sec
Start 12: t_send_window
12/31 Test #12: t_send_window .................... Passed 0.11 sec
Start 13: t_send_ack
13/31 Test #13: t_send_ack ....................... Passed 0.00 sec
Start 14: t_send_close
14/31 Test #14: t_send_close ..................... Passed 0.00 sec
Start 15: t_strm_reassem_cap
15/31 Test #15: t_strm_reassem_cap ............... Passed 0.00 sec
Start 16: t_strm_reassem_single
16/31 Test #16: t_strm_reassem_single ............ Passed 0.00 sec
Start 17: t_strm_reassem_seq
17/31 Test #17: t_strm_reassem_seq ............... Passed 0.00 sec
Start 18: t_strm_reassem_dup
18/31 Test #18: t_strm_reassem_dup ............... Passed 0.00 sec
Start 19: t_strm_reassem_holes
19/31 Test #19: t_strm_reassem_holes ............. Passed 0.00 sec
Start 20: t_strm_reassem_many
20/31 Test #20: t_strm_reassem_many .............. Passed 0.40 sec
Start 21: t_strm_reassem_overlapping
21/31 Test #21: t_strm_reassem_overlapping ....... Passed 0.00 sec
Start 22: t_strm_reassem_win
22/31 Test #22: t_strm_reassem_win ............... Passed 0.36 sec
Start 23: t_byte_stream_construction
23/31 Test #23: t_byte_stream_construction ....... Passed 0.00 sec
Start 24: t_byte_stream_one_write
24/31 Test #24: t_byte_stream_one_write .......... Passed 0.00 sec
Start 25: t_byte_stream_two_writes
25/31 Test #25: t_byte_stream_two_writes ......... Passed 0.00 sec
Start 26: t_byte_stream_capacity
26/31 Test #26: t_byte_stream_capacity ........... Passed 0.00 sec
Start 27: t_byte_stream_many_writes
27/31 Test #27: t_byte_stream_many_writes ........ Passed 0.01 sec
Start 28: t_webget
28/31 Test #28: t_webget ......................... Passed 1.05 sec
Start 48: t_address_dt
29/31 Test #48: t_address_dt ..................... Passed 0.00 sec
Start 49: t_parser_dt
30/31 Test #49: t_parser_dt ...................... Passed 0.00 sec
Start 50: t_socket_dt
31/31 Test #50: t_socket_dt ...................... Passed 0.01 sec
100% tests passed, 0 tests failed out of 31
Total Test time (real) = 2.15 sec
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