TCP网络实验报告

TCP实验报告实验目的1.深入理解TCP原理，掌握连接状态控制、可靠传输等重要机制；2.为应用层提供网络编程接口，即socket接口。实验要求理解TCP的主要原理，针对客户端角色的、“停-等”模式的TCP，设计接收和发送流程。编程实现TCP段的接收流程，重点是段接收的有限状态机编程实现TCP段的发送流程，完成TCP段的封装处理。编程实现客户端Socket接口函数编程实现停-等协议的实现停-等协议主要体现在stud_tcp_send()函数和stud_tcp_recv()和函数中。实现的主要思路是：调用stud_tcp_send()发送一个数据包时，直到收到ack包并把ack交给stud_tcp_input()处理才退出调用stud_tcp_recv()接收一个数据包成功后，紧接着发送一个相应的ack包才退出上述两个设计保证了发送和接收窗口大小为1接收流程的有限状态机首先检查校验和与序号是否正确，只有当这两者都无误之后才进入状态机部分。状态机基于switch结构实现，根据当前TCB的状态分情形讨论状态的变化。处理流程如下发送时的封装和有限状态机查看当前的TCB是否为空，为空则创建当前的TCB封装数据拷贝数据设置源端口和目的端口设置包序列和ack序号设置包头长度设置flag设置windowsize和urgentPointer改变状态变换字节序将字节序从本地序变成网络序各接口函数的实现stud_tcp_socket()stud_tcp_connect()stud_tcp_send()stud_tcp_recv()stud_tcp_close()校验和的计算与IP包的校验类似，但是要求对伪首部进行校验伪首部由以下部分组成：32位IP源地址32位IP目的地址8位填充位（全0）8位协议号16位TCP头部长度实验遇到的问题校验和的计算问题难点在于理解伪首部的结构和作用。停等协议的理解实现接收一个数据包和返回ACK包的绑定；实现发送一个数据包和等待ACK包的绑定源代码#include"sysInclude.h"externvoidtcp_DiscardPkt(char*pBuffer,inttype);//TCP¶ªÆú¶Îº¯Êýexternvoidtcp_sendIpPkt(unsignedchar*pData,UINT16len,unsignedintsrcAddr,unsignedintdstAddr,UINT8 ttl);//IP·Ö×é·¢Ëͺ¯ÊýexternintwaitIpPacket(char*pBuffer,inttimeout);//IPÊý¾Ý·Ö×éÖ÷¶¯½ÓÊÕº¯ÊýexternunsignedintgetIpv4Address();externunsignedintgetServerIpv4Address();typedefstructtcphead{UINT16srcPort;UINT16destPort;UINT32seqNo;UINT32ackNo;UINT8headLen;UINT8flag;UINT16windowsize;UINT16checksum;UINT16urgentPointer;chardata[100];};typedefstructTCB{unsignedintsrcAddr;unsignedintdstAddr;unsignedshortsrcPort;unsignedshortdstPort;unsignedintseq;unsignedintack;intsockfd;BYTEstate;unsignedchar*data;};typedefstructtcb_node{TCB*current;structtcb_node*next;};structtcb_node*tcb_table;structTCB*current_tcb;enumstatus{CLOSED,SYN_SENT,ESTABLISHED,FIN_WAIT1,FIN_WAIT2,TIME_WAIT};intgSrcPort=2008;intgDstPort=2009;intgSeqNum=1234;intgAckNum=0;intsocknum=5;externunsignedintgetchecksum2(tcphead*thead,unsignedintsrcAddr,unsignedintdstAddr,unsignedshortlen,char*data);unsignedintgetchecksum(tcphead*header,unsignedintsrcAddr,unsignedintdstAddr,unsignedshortlen,char*data){unsignedintchecksum=0;checksum+=(srcAddr>>16)+srcAddr&0xffff;checksum+=(dstAddr>>16)+dstAddr&0xffff;checksum+=IPPROTO_TCP;checksum+=0x14;checksum+=ntohs(header->srcPort)+ntohs(header->destPort);checksum+=((header->seqNo)>>16)+(header->seqNo)&0xffff;checksum+=((header->ackNo)>>16)+(header->ackNo)&0xffff;checksum+=((header->headLen)<<8)+header->flag;if(header->flag==PACKET_TYPE_DATA){checksum+=len-0x14;intlength=len;char*p=data;while(length>0){checksum+=(*p)<<8;p++;checksum+=(*p);p++;length=length-2;}}checksum+=ntohs(header->windowsize);checksum+=ntohs(header->urgentPointer); checksum=(checksum>>16)+checksum&0xffff;checksum=(checksum>>16)+checksum&0xffff;checksum=(~checksum)&0xffff; returnchecksum;}intstud_tcp_input(char*pBuffer,unsignedshortlen,unsignedintsrcAddr,unsignedintdstAddr){tcphead*header=(tcphead*)pBuffer;header->seqNo=ntohl(header->seqNo);header->ackNo=ntohl(header->ackNo);if(getchecksum(header,ntohl(srcAddr),ntohl(dstAddr),len,NULL)!=ntohs(header->checksum)){ return-1;}intseqAdd=1;//SYN-SENTFINWAIT1if(current_tcb->state==FIN_WAIT2){seqAdd=0;}elseif(len>20){seqAdd=len-20;}if(header->ackNo!=(current_tcb->seq+seqAdd)){tcp_DiscardPkt(pBuffer,STUD_TCP_TEST_SEQNO_ERROR);return-1;}switch(current_tcb->state){caseSYN_SENT:if(header->flag==PACKET_TYPE_SYN_ACK){current_tcb->state=ESTABLISHED;current_tcb->ack=header->seqNo+1;current_tcb->seq=header->ackNo;stud_tcp_output(NULL,0,PACKET_TYPE_ACK,current_tcb->srcPort,current_tcb->dstPort,ntohl(srcAddr),ntohl(dstAddr));break;}else{return-1;}caseESTABLISHED:if(header->flag==PACKET_TYPE_ACK){if(len>20){current_tcb->ack=header->seqNo+len-20;current_tcb->seq=header->ackNo;break;}elseif(len==20){current_tcb->ack=header->seqNo+1;current_tcb->seq=header->ackNo;break;}elsereturn-1;}elsereturn-1;caseFIN_WAIT1:if(header->flag==PACKET_TYPE_ACK){current_tcb->ack=header->seqNo+1;current_tcb->seq=header->ackNo;current_tcb->state=FIN_WAIT2;break;}else{return-1;}caseFIN_WAIT2:if(header->flag==PACKET_TYPE_FIN_ACK){current_tcb->state=TIME_WAIT;stud_tcp_output(NULL,0,PACKET_TYPE_ACK,current_tcb->srcPort,current_tcb->dstPort,ntohl(srcAddr),ntohl(dstAddr));break;}else{return-1;}default:return-1;}return0;}voidstud_tcp_output(char*pData,unsignedshortlen,unsignedcharflag,unsignedshortsrcPort,unsignedshortdstPort,unsignedintsrcAddr,unsignedintdstAddr){if(current_tcb==NULL){current_tcb=newTCB;current_tcb->seq=gSeqNum;current_tcb->ack=gAckNum;current_tcb->srcPort=srcPort;current_tcb->dstPort=dstPort;current_tcb->srcAddr=srcAddr;current_tcb->dstAddr=dstAddr;current_tcb->state=CLOSED;}tcphead*thead=newtcphead;for(inti=0;i<len;i++){thead->data[i]=pData[i];}thead->srcPort=srcPort;thead->destPort=dstPort;thead->seqNo=current_tcb->seq;thead->ackNo=current_tcb->ack;thead->headLen=0x50;thead->flag=flag;thead->windowsize=1;thead->urgentPointer=0;switch(current_tcb->state){caseCLOSED:if(flag==PACKET_TYPE_SYN){current_tcb->state=SYN_SENT;}elsereturn;break;caseESTABLISHED:if(flag==PACKET_TYPE_FIN_ACK){current_tcb->state=FIN_WAIT1;break;}elseif(flag==PACKET_TYPE_DATA||flag==PACKET_TYPE_ACK){break;}elsereturn;break;defalut:return;}thead->checksum=ntohs(getchecksum2(thead,srcAddr,dstAddr,len,pData));thead->srcPort=ntohs(thead->srcPort);thead->destPort=ntohs(thead->destPort);thead->seqNo=ntohl(thead->seqNo);thead->ackNo=ntohl(thead->ackNo);thead->windowsize=ntohs(thead->windowsize);thead->urgentPointer=ntohs(thead->urgentPointer);tcp_sendIpPkt((unsignedchar*)thead,20+len,current_tcb->srcAddr,current_tcb->dstAddr,60);}intstud_tcp_socket(intdomain,inttype,intprotocol){if(domain!=AF_INET||type!=SOCK_STREAM||protocol!=IPPROTO_TCP)return-1;current_tcb=newTCB;if(tcb_table==NULL){tcb_table=newtcb_node;tcb_table->current=current_tcb;tcb_table->next=NULL;}else{tcb_node*head=tcb_table;while(head->next!=NULL){head=head->next;}head->next=newtcb_node;head->next->current=current_tcb;head->next->next=NULL;}current_tcb->sockfd=socknum++;current_tcb->srcPort=gSrcPort++;current_tcb->seq=gSeqNum++;current_tcb->ack=gAckNum;current_tcb->state=CLOSED;returncurrent_tcb->sockfd;}intgetSockfd(intsockfd){tcb_node*current_p=tcb_table;while(current_tcb!=NULL&¤t_p->current!=NULL){if(current_p->current->sockfd==sockfd){current_tcb=current_p->current;return0;break;}current_p=current_p->next;}if(current_p==NULL)return-1;}intstud_tcp_connect(intsockfd,structsockaddr_in*addr,intaddrlen){if(getSockfd(sockfd)==-1)return-1; UINT32srcAddr=getIpv4Address();UINT32dstAddr=htonl(addr->sin_addr.s_addr);current_tcb->srcAddr=srcAddr;current_tcb->dstAddr=dstAddr;current_tcb->dstPort=ntohs(addr->sin_port);current_tcb->state=SYN_SENT;stud_tcp_output(NULL,0,PACKET_TYPE_SYN,current_tcb->srcPort,current_tcb->dstPort,srcAddr,dstAddr);tcphead*receive=newtcphead;intres=-1;while(res==-1){res=waitIpPacket((char*)receive,5000);}stud_tcp_input((char*)receive,20,ntohl(current_tcb->srcAddr),ntohl(current_tcb->dstAddr));return0;}intstud_tcp_send(intsockfd,constunsignedchar*pData,unsignedshortdatalen,intflags){if(getSockfd(sockfd)==-1)return-1;if(current_tcb->state!=ESTABLISHED)return-1;else{UINT32srcAddr=getIpv4Address();UINT32dstAddr=current_tcb->dstAddr;current_tcb->data=newunsignedchar(datalen);strcpy((char*)current_tcb->data,(char*)pData);stud_tcp_output((char*)current_tcb->data,datalen,PACKET_TYPE_DATA,current_tcb->srcPort,current_tcb->dstPort,srcAddr,dstAddr);tcphead*receive=newtcphead;intres=-1;while(res==-1){res=waitIpPacket((char*)receive,5000);}stud_tcp_input((char*)receive,datalen+20,ntohl(current_tcb->srcAddr),ntohl(current_tcb->dstAddr));} return0;}intstud_tcp_recv(intsockfd,unsignedchar*pData,unsignedshortdatalen,intflags){if(getSockfd(sockfd)==-1)return-1;if(current_tcb->state!=ESTABLISHED)return-1;else{UINT32srcAddr=getIpv4Address();UINT32dstAddr=current_tcb->dstAddr;tcphead*receive=newtcphead;intres=-1;while(res==-1) {res=waitIpPacket((char*)receive,5000);}strcpy((char*)pData,(char*)receive->data);datalen=sizeof(pData);stud_tcp_output(NULL,0,PACKET_TYPE_ACK,current_tcb->srcPort,current_tcb->dstPort,srcAddr,dstAddr);}}intstud_tcp_close(intsockfd){tcb_node*current_p=tcb_table;tcb_node*preCurrent=current_p;while(current_p!=NULL&¤t_p->current!=NULL){if(current_p->current->sockfd==sockfd){current_tcb=current_p->current;break;}preCurrent=current_p;current_p=current_p->next;}if(current_p==NULL)return-1;UINT32srcAddr=getIpv4Address();UINT32dstAddr=current_tcb->dstAddr;if(current_tcb->state!=ESTABLISHED){if(current_p!=preCurrent){preCurrent->next=current_p->next;deletecurrent_p;}elsedeletecurrent_tcb;current_tcb=NULL; return-1;}else{stud_tcp_output(NULL,0,PACKET_TYPE_FIN_ACK,current_tcb->srcPort,current_tcb->dstPort,srcAddr,dstAddr);current_tcb->state=FIN_WAIT1; tcphead*receive=newtcphead;intres=-1;while(res==-1){res=waitIpPacket((char*)receive,5000);}stud_tcp_input((char*)receive,20,ntohl(current_tcb->srcAddr),ntohl(current_tcb->dstAddr));//ackres=-1;while(res==-1){