选择重传协议 C语言实现

代码如下：

#include <stdio.h>#include <string.h>#include "protocol.h"#include "datalink.h"#define MAX_SEQ 31#define DATA_TIMER 3800//calculagraph timer#define ACK_TIMER 1100#define NR_BUFS 16   //windows number#define inc(k)if(k<MAX_SEQ)k++;else k=0typedef enum{false,true}bool;typedef unsigned char seq_nr;//sequence or ack numbertypedef struct{unsigned char info[PKT_LEN];}packet;//packet definitionstatic int phl_ready = 0;bool no_nak=true;typedef struct FRAME {     unsigned char kind; // FRAME_DATA     seq_nr ack;//acknowledgement number    seq_nr  seq;//sequence number    packet data; //the network layer packet    unsigned int  padding;}Frame;static int between(seq_nr a,seq_nr b,seq_nr c){      if((a <= b && b < c) || (c < a && a <= b) || (b < c && c < a))          return true;      else          return false; }//add crcstatic void put_frame(unsigned char *frame, int len){    *(unsigned int *)(frame + len) = crc32(frame, len);    send_frame(frame, len + 4);    phl_ready = 0;}//send data to physical layerstatic void send_data(unsigned char fk,seq_nr frame_nr,seq_nr frame_expected,packet buffer[]){    Frame s;    s.kind = fk;    s.seq = frame_nr;//insert sequence number into frame    s.ack = (frame_expected+ MAX_SEQ)%(MAX_SEQ+1);//piggyback ackif(fk == FRAME_DATA)memcpy(s.data.info, buffer[frame_nr%NR_BUFS].info, PKT_LEN);//insert packet into frameif(fk == FRAME_NAK)no_nak = false;  //one nak per frame,please    dbg_frame("Send DATA %d %d, ID %d\n", s.seq, s.ack, *(short *)s.data.info);if (fk == FRAME_DATA)     put_frame((unsigned char *)&s, 3 + PKT_LEN);//put CRC following the frameif(fk == FRAME_NAK||fk==FRAME_ACK)put_frame((unsigned char *)&s, 2);//put CRC following the frame    if(fk == FRAME_DATA)start_timer(frame_nr%NR_BUFS, DATA_TIMER);stop_ack_timer();//no need for separate ack frame}int main(int argc, char **argv){    int event,arg,len=0;    int i;//contol the number of circle of arrived    Frame r;//scratch variable    seq_nr next_frame_to_send;//the upper of the send's window    seq_nr ack_expected;//the lower of the send's window    seq_nr frame_expected;//the lower of the reciver's window    seq_nr too_far;//the upper of the reciver's window    seq_nr nbuffered;//currently window    packet out_buf[NR_BUFS];//buffer for the outbound stream    packet in_buf[NR_BUFS];//buffer for the in stream    bool arrived[NR_BUFS];        enable_network_layer();    //disable_network_layer();//allow netword_layer_ready events    ack_expected = 0;    next_frame_to_send = 0;    frame_expected = 0;    too_far = NR_BUFS;    nbuffered = 0;      for(i = 0;i < NR_BUFS;i++)        arrived[i] = false;protocol_init(argc, argv);     lprintf("Designed by chenchen_07415_071419, build: " __DATE__"  "__TIME__"\n\n");    while(true){        event = wait_for_event(&arg);        switch(event){            case NETWORK_LAYER_READY:   nbuffered++;//expand the sender's window                   get_packet(out_buf[next_frame_to_send%NR_BUFS].info);//fetch new packet                   send_data(FRAME_DATA,next_frame_to_send,frame_expected,out_buf);//transmit the packet       inc(next_frame_to_send);//advance the upper edge of sender's window                   break;            case PHYSICAL_LAYER_READY:                 phl_ready = 1;                 break;            case FRAME_RECEIVED:                 len = recv_frame((unsigned char *)&r, sizeof r);//from physical frame's len                 if (len < 5 || crc32((unsigned char *)&r, len) !=0){//CRC error                     dbg_event("**** Receiver Error, Bad CRC Checksum\n");                     if(no_nak)                         send_data(FRAME_NAK,0,frame_expected,out_buf);                     break;                 }                 if(r.kind == FRAME_DATA){                    if((r .seq != frame_expected)&&no_nak)//not arrival in the right order                         send_data(FRAME_NAK,0,frame_expected,out_buf);//send nac and send again                    else                         start_ack_timer(ACK_TIMER);                    if(between(frame_expected,r.seq,too_far)&&(arrived[r.seq%NR_BUFS]==false)){                         arrived[r.seq%NR_BUFS] = true;//the frame arrival     //for(j=0;j<NR_BUFS;j++)                          in_buf[r.seq%NR_BUFS] = r.data;//keep in the in_buf                          while(arrived[frame_expected%NR_BUFS]){                             put_packet(in_buf[frame_expected%NR_BUFS].info, len-7);                             no_nak = true;                             arrived[frame_expected%NR_BUFS]=false;                             inc(frame_expected);//advance upper edge of ceiver's windowsge                             inc(too_far);                             start_ack_timer(ACK_TIMER);                         }                      }                 }                 if((r.kind == FRAME_NAK)&&between(ack_expected,(r.ack+1)%(MAX_SEQ+1),next_frame_to_send))                 //receive nak &&between the windows                      send_data(FRAME_DATA,(r.ack+1)%(MAX_SEQ+1),frame_expected,out_buf);                 while(between(ack_expected,r.ack,next_frame_to_send)){                       nbuffered--;                       stop_timer(ack_expected%NR_BUFS);                       inc(ack_expected);                 }                 break;            case ACK_TIMEOUT: dbg_event("---- DATA %d timeout\n", arg);                 send_data(FRAME_ACK,0,frame_expected,out_buf);                 break;            case DATA_TIMEOUT:                 dbg_event("---- DATA %d timeout\n", arg);          if(! between(ack_expected,arg,next_frame_to_send))                    arg = arg + NR_BUFS;                 send_data(FRAME_DATA,arg,frame_expected,out_buf);//select the bad frame and resend it                  break;        }        if (nbuffered <NR_BUFS&& phl_ready)            enable_network_layer();        else            disable_network_layer();    }}