NetRiver - 滑动窗口协议实验

本文的滑动窗口协议实验是NetRiver实验系统下的一个子实验，由清华大学开发，目前很多大学都在采用该系统作为计算机网络课程的Lab教学系统。（虽然bug很多而且说明指导书没什么用）

滑动窗口实验的三个函数代码实际上异曲同工，区别只在于窗口大小以及对TIMEOUT和NAK的处理上。

思路是利用数组把等待缓冲区和窗口都做成循环队列。当然链表也No problem。我也看过用C++的deque库实现的版本，优点是代码简洁，同样很有参考价值。然而个人测试发现网上流传的版本基本都无法通过NetRiver第二个子实验，经过个人调试发现是系统本身的bug。如果有兴趣读者可以自己尝试一下，找到第二个实验的问题所在。

话不多说，具体代码见下，附详细注释，以飨后人。

/** MIT license* Copyright © 2016 Maristie* * Permission is hereby granted, free of charge, to any person obtaining a copy of this software* and associated documentation files (the "Software"), to deal in the Software without restriction,* including without limitation the rights to use, copy, modify, merge, publish, distribute, * sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, * subject to the following conditions:* The above copyright notice and this permission notice shall be * included in all copies or substantial portions of the Software.* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED* TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE* OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.*/#include "sysinclude.h"  extern void SendFRAMEPacket(unsigned char* pdata, unsigned int len);#define WINDOW_SIZE_STOP_WAIT 1  #define WINDOW_SIZE_BACK_N_FRAME 4#define max_wait_num 1000/** The following definitions are just as NetRiver instructions.*/typedef enum { data, ack, nak } frame_kind;typedef struct frame_head{    frame_kind kind;    unsigned int seq;    unsigned int ack;    unsigned char data[100];};typedef struct frame{    frame_head head;    unsigned int size;};/** stop and wait*/int stud_slide_window_stop_and_wait(char *pBuffer, int bufferSize, UINT8 messageType){    // two queues for window and waiting    static frame *window[WINDOW_SIZE_STOP_WAIT] = { 0 };    static frame *waiting[max_wait_num] = { 0 };    static int win_begin = 0, win_end = 0, wait_begin = 0, wait_end = 0;    static int win_num = 0, wait_num = 0;    // when send    if (messageType == MSG_TYPE_SEND)    {        // push pBuffer into waiting queue        // allocate space for frame        waiting[wait_end] = (frame*)malloc(sizeof(frame));        // copy pBuffer to waiting queue        memcpy(waiting[wait_end], (frame*)pBuffer, sizeof(frame));        waiting[wait_end]->size = (unsigned int)bufferSize;        wait_end = (wait_end + 1) % max_wait_num;        wait_num++;        // when window is not full        if (win_num < WINDOW_SIZE_STOP_WAIT)        {            // pop one frame from waiting queue            frame *temp = waiting[wait_begin];            wait_begin = (wait_begin + 1) % max_wait_num;            wait_num--;            // push the frame into window            window[win_end] = temp;            win_end = (win_end + 1) % WINDOW_SIZE_STOP_WAIT;            win_num++;            // try to send            SendFRAMEPacket((unsigned char*)temp, temp->size);        }        // when window is full, no more needs to be done    }    // when receive      else if (messageType == MSG_TYPE_RECEIVE)    {        frame *temp = (frame*)pBuffer;        frame_kind kind = (frame_kind)ntohl((unsigned long)temp->head.kind);        // check kind        if (kind == nak)        {            // when nak, first find which frame needs to be resent            int cursor = win_begin;            unsigned int seq = ntohl(temp->head.ack);            while (seq != ntohl(window[cursor]->head.seq))                cursor = (cursor + 1) % WINDOW_SIZE_STOP_WAIT;            // then resend it            SendFRAMEPacket((unsigned char*)window[cursor], window[cursor]->size);        }        else if (kind == ack)        {            // when ack, close windows before or equal it            unsigned int ack = ntohl(temp->head.ack);            while (ntohl(window[win_begin]->head.seq) <= ack)            {                // close a window                free(window[win_begin]);                win_begin = (win_begin + 1) % WINDOW_SIZE_STOP_WAIT;                win_num--;                // when waiting queue is not empty, then pop one and push into window                if (wait_num > 0)                {                    window[win_end] = waiting[wait_begin];                    // try to send it                    SendFRAMEPacket((unsigned char*)window[win_end], window[win_end]->size);                    wait_begin = (wait_begin + 1) % max_wait_num;                    wait_num--;                    win_end = (win_end + 1) % WINDOW_SIZE_STOP_WAIT;                    win_num++;                }            }        }    }    // when time out     else if (messageType == MSG_TYPE_TIMEOUT)    {        UINT32 temp = ntohl(*((UINT32*)pBuffer));        int cursor = win_begin;        // resend all frames after MSG_TYPE_TIMEOUT        if (temp <= window[cursor]->head.seq)            SendFRAMEPacket((unsigned char*)window[cursor], window[cursor]->size);        cursor = (cursor + 1) % WINDOW_SIZE_STOP_WAIT;        while (cursor != win_end)        {            if (temp <= window[cursor]->head.seq)                SendFRAMEPacket((unsigned char*)window[cursor], window[cursor]->size);            cursor = (cursor + 1) % WINDOW_SIZE_STOP_WAIT;        }    }    return 0;}/** Almost same as stop-wait except WINDOW_SIZE_BACK_N_FRAME.*//** back n frame*/int stud_slide_window_back_n_frame(char *pBuffer, int bufferSize, UINT8 messageType){    // two queues for window and waiting    static frame *window[WINDOW_SIZE_BACK_N_FRAME] = { 0 };    static frame *waiting[max_wait_num] = { 0 };    static int win_begin = 0, win_end = 0, wait_begin = 0, wait_end = 0;    static int win_num = 0, wait_num = 0;    // when send    if (messageType == MSG_TYPE_SEND)    {        // push pBuffer into waiting queue        // allocate space for frame        waiting[wait_end] = (frame*)malloc(sizeof(frame));        // copy pBuffer to waiting queue        memcpy(waiting[wait_end], (frame*)pBuffer, sizeof(frame));        waiting[wait_end]->size = (unsigned int)bufferSize;        wait_end = (wait_end + 1) % max_wait_num;        wait_num++;        // when window is not full        if (win_num < WINDOW_SIZE_BACK_N_FRAME)        {            // pop one frame from waiting queue            frame *temp = waiting[wait_begin];            wait_begin = (wait_begin + 1) % max_wait_num;            wait_num--;            // push the frame into window            window[win_end] = temp;            win_end = (win_end + 1) % WINDOW_SIZE_BACK_N_FRAME;            win_num++;            // try to send            SendFRAMEPacket((unsigned char*)temp, temp->size);        }        // when window is full, no more needs to be done    }    // when receive      else if (messageType == MSG_TYPE_RECEIVE)    {        frame *temp = (frame*)pBuffer;        frame_kind kind = (frame_kind)ntohl((unsigned long)temp->head.kind);        // check kind        if (kind == nak)        {            // when nak, first find which frame needs to be resent            int cursor = win_begin;            unsigned int seq = ntohl(temp->head.ack);            while (seq != ntohl(window[cursor]->head.seq))                cursor = (cursor + 1) % WINDOW_SIZE_BACK_N_FRAME;            // then resend it            SendFRAMEPacket((unsigned char*)window[cursor], window[cursor]->size);        }        else if (kind == ack)        {            // when ack, close windows before or equal it            unsigned int ack = ntohl(temp->head.ack);            while (ntohl(window[win_begin]->head.seq) <= ack)            {                // close a window                free(window[win_begin]);                win_begin = (win_begin + 1) % WINDOW_SIZE_BACK_N_FRAME;                win_num--;                // when waiting queue is not empty, then pop one and push into window                if (wait_num > 0)                {                    window[win_end] = waiting[wait_begin];                    // try to send it                    SendFRAMEPacket((unsigned char*)window[win_end], window[win_end]->size);                    wait_begin = (wait_begin + 1) % max_wait_num;                    wait_num--;                    win_end = (win_end + 1) % WINDOW_SIZE_BACK_N_FRAME;                    win_num++;                }            }        }    }    // when time out     else if (messageType == MSG_TYPE_TIMEOUT)    {        UINT32 temp = ntohl(*((UINT32*)pBuffer));        int cursor = win_begin;        // resend all frames after MSG_TYPE_TIMEOUT        // here is where I found the bug of lab system        SendFRAMEPacket((unsigned char*)window[cursor], window[cursor]->size);        cursor = (cursor + 1) % WINDOW_SIZE_BACK_N_FRAME;        while (cursor != win_end)        {               SendFRAMEPacket((unsigned char*)window[cursor], window[cursor]->size);            cursor = (cursor + 1) % WINDOW_SIZE_BACK_N_FRAME;        }    }    return 0;}/** Almost same as back-n-frame.* The only difference is that back-n-frame has TIMEOUT, but choice-frame-resend has nak.*//** choice frame resend*/int stud_slide_window_choice_frame_resend(char *pBuffer, int bufferSize, UINT8 messageType){    // two queues for window and waiting    static frame *window[WINDOW_SIZE_BACK_N_FRAME] = { 0 };    static frame *waiting[max_wait_num] = { 0 };    static int win_begin = 0, win_end = 0, wait_begin = 0, wait_end = 0;    static int win_num = 0, wait_num = 0;    // when send    if (messageType == MSG_TYPE_SEND)    {        // push pBuffer into waiting queue        // allocate space for frame        waiting[wait_end] = (frame*)malloc(sizeof(frame));        // copy pBuffer to waiting queue        memcpy(waiting[wait_end], (frame*)pBuffer, sizeof(frame));        waiting[wait_end]->size = (unsigned int)bufferSize;        wait_end = (wait_end + 1) % max_wait_num;        wait_num++;        // when window is not full        if (win_num < WINDOW_SIZE_BACK_N_FRAME)        {            // pop one frame from waiting queue            frame *temp = waiting[wait_begin];            wait_begin = (wait_begin + 1) % max_wait_num;            wait_num--;            // push the frame into window            window[win_end] = temp;            win_end = (win_end + 1) % WINDOW_SIZE_BACK_N_FRAME;            win_num++;            // try to send            SendFRAMEPacket((unsigned char*)temp, temp->size);        }        // when window is full, no more needs to be done    }    // when receive      else if (messageType == MSG_TYPE_RECEIVE)    {        frame *temp = (frame*)pBuffer;        frame_kind kind = (frame_kind)ntohl((unsigned long)temp->head.kind);        // check kind        if (kind == nak)        {            // when nak, first find which frame needs to be resent            int cursor = win_begin;            unsigned int seq = ntohl(temp->head.ack);            while (seq != ntohl(window[cursor]->head.seq))                cursor = (cursor + 1) % WINDOW_SIZE_BACK_N_FRAME;            // then resend it            SendFRAMEPacket((unsigned char*)window[cursor], window[cursor]->size);        }        else if (kind == ack)        {            // when ack, close windows before or equal it            unsigned int ack = ntohl(temp->head.ack);            while (ntohl(window[win_begin]->head.seq) <= ack)            {                // close a window                free(window[win_begin]);                win_begin = (win_begin + 1) % WINDOW_SIZE_BACK_N_FRAME;                win_num--;                // when waiting queue is not empty, then pop one and push into window                if (wait_num > 0)                {                    window[win_end] = waiting[wait_begin];                    // try to send it                    SendFRAMEPacket((unsigned char*)window[win_end], window[win_end]->size);                    wait_begin = (wait_begin + 1) % max_wait_num;                    wait_num--;                    win_end = (win_end + 1) % WINDOW_SIZE_BACK_N_FRAME;                    win_num++;                }            }        }    }    // when time out     else if (messageType == MSG_TYPE_TIMEOUT)    {        UINT32 temp = ntohl(*((UINT32*)pBuffer));        int cursor = win_begin;        // resend all frames after MSG_TYPE_TIMEOUT        SendFRAMEPacket((unsigned char*)window[cursor], window[cursor]->size);        cursor = (cursor + 1) % WINDOW_SIZE_BACK_N_FRAME;        while (cursor != win_end)        {            SendFRAMEPacket((unsigned char*)window[cursor], window[cursor]->size);            cursor = (cursor + 1) % WINDOW_SIZE_BACK_N_FRAME;        }    }    return 0;}