TCP协议实验

网络课第四次上机实验报告-TCP协议实验l 实验内容实验内容主要包括： 设计保存TCP 连接相关信息的数据结构（TCB）； TCP 协议的接收处理和封装发送； TCP 协议提供的Socket 函数接口。l 实验过程l 设计保存TCP 连接相关信息的数据结构（TCB）用数据结构TCB为每一个TCP连接维护socketfd，srcAddr，dstAddr,srcPort,dstPort,seq,ack,windowSize,state这些状态信息。以链表形式组织多个连接，nextTcb指向下一个连接的数据结构。l TCP 分组接收函数stud_tcp_input( )首先，检查校验和；然后通过字节序转换获取相应的信息，检查序列号。如果序列号不正确，则调用tcp_DiscardPkt；最后将报文交由输入有限状态机处理，有限状态机对报文进行处理，转换状态。根据当前的状态并调用stud_tcp_output 函数完成tcp 建连、数据传递时返回ACK、tcp 断连等工作l TCP 分组发送函数stud_tcp_output ( )判断需要发送的报文类型，根据报的类型对包中的相应字段进行设置，判断是否可以发送（发送窗口不为0）。构造TCP 数据报文并发送。填写TCP 报文各字段的内容和数据，转换字节序，计算校验和，然后调用发送流程的下层接口函数sendIpPkt( )发送。l stud_tcp_socket ( )函数分配相应的socketfd并且新建TCB表项，并对成员变量进行初始化l stud_tcp_connect ( )函数设定目的IPv4 地址和端口，源IPv4 地址和端口；初始化TCB 结构中的相关变量；设定TCB 中的输入状态为SYN-SENT，及其它相关变量，准备发送SYN 报文；调用发送流程的下层接口函数stud_tcp_output ( )发送SYN 报文（发送类型为PACKET_TYPE_SYN）；等待“三次握手”完成后返回，建立连接成功；或者出错返回。l stud_tcp_send ( )函数判断是否处于ESTABLISHED 状态；将应用层协议的数据拷贝到TCB 的输入缓冲区；调用stud_tcp_output ( )发送TCP 的数据报文（发送类型为PACKET_TYPE_DATA）；同时等待ACK以实现停等式协议l stud_tcp_recv ( )函数判断是否处于ESTABLISHED 状态；从TCB 的输入缓冲区读出数据；将数据交给应用层协议。l stud_tcp_close ( )函数在正常情况下（ESTABLISHED 状态），进行相应状态转换，非正常情况下（SYN-SENT 状态），直接删除TCB 结构后退出；调用发送流程下层接口函数stud_tcp_output ( )发送FIN 报文（发送类型为PACKET_TYPE_FIN）；等待回应的ACK 报文，收到后成功返回，或者出错返回；删除相应的TCB表项。l 实验总结通过本次实验，加深了对TCP 协议的原理和设计实现的机制的了解，对TCP协议有了更具体的认识，对概论课的学习有很大的帮助！附：上机代码（注释）#include sysInclude.hextern void tcp_DiscardPkt(char *pBuffer, int type);extern void tcp_sendReport(int type);extern void tcp_sendIpPkt(unsigned char *pData, UINT16 len, unsigned int srcAddr, unsigned int dstAddr, UINT8ttl);extern int waitIpPacket(char *pBuffer, int timeout);extern unsigned int getIpv4Address();extern unsigned int getServerIpv4Address();#define BUFFER_SIZE 1024#define TIMEOUT 5enum statusCLOSED,SYN_SENT,ESTABLISHED,FIN_WAIT_1,FIN_WAIT_2,TIME_WAIT; /状态int gSrcPort = 2007;int gDstPort = 2006;int gSeqNum = 1;int gAckNum = 0;struct TCB int socketfd;UINT32 srcAddr;UINT32 dstAddr;UINT16 srcPort;UINT16 dstPort;UINT32 seq;UINT32 ack;UINT16 windowSize;UINT8 state;TCB *nextTcb;TCB() / 用于TCP报文接收发送流程socketfd = 0;srcAddr = getIpv4Address();dstAddr = getServerIpv4Address();srcPort = gSrcPort;dstPort = gDstPort;seq = gSeqNum;ack = gAckNum;windowSize = 1;state = CLOSED;nextTcb = NULL;TCB(int fd) / 用于客户端socket函数的构建函数socketfd = fd;seq = gSeqNum;ack = gAckNum;windowSize = 1;state = CLOSED;nextTcb = NULL;UINT16 CalcChecksum(char *pBuffer, int len, UINT32 srcAddr, UINT32 dstAddr)int tcp_len = len + 12;UINT32 checkSum = 0;if(tcp_len & 0x1 = 1) tcp_len += 1; char *buffer = new chartcp_len;memset(buffer, 0, tcp_len);memcpy(buffer + 12, pBuffer, len);*(UINT32 *)buffer) = htonl(srcAddr);*(UINT32 *)(buffer + 4) = htonl(dstAddr);buffer9 = 6;/ 传输层协议号*(UINT16 *)(buffer + 10) = htons(len);for (int i = 0; i 16);checkSum = checkSum;return checkSum;TCB *tcbLinkTable = NULL; / TCB链表/* 通过两端的IP地址和端口号寻找TCB表项 */TCB* findTCB(UINT32 srcAddr, UINT16 srcPort, UINT32 dstAddr, UINT16 dstPort)TCB* tcb = tcbLinkTable;while(tcb != NULL) if(tcb-srcAddr = srcAddr) & (tcb-srcPort = srcPort) & (tcb-dstAddr = dstAddr) & (tcb-dstPort = dstPort) return tcb;tcb = tcb-nextTcb;return NULL;int stud_tcp_input(char *pBuffer, unsigned short len, unsigned int srcAddr, unsigned int dstAddr)/* 检查校验和 */if (CalcChecksum(pBuffer, len, ntohl(srcAddr), ntohl(dstAddr) != 0) return -1;UINT16 srcPort = ntohs(*(UINT16 *)pBuffer);UINT16 dstPort = ntohs(*(UINT16 *)(pBuffer + 2);UINT32 seq = ntohl(*(UINT32 *)(pBuffer + 4);UINT32 ack = ntohl(*(UINT32 *)(pBuffer + 8);UINT8 flags = (pBuffer13 & 0x13); TCB *tcb = findTCB(ntohl(dstAddr), dstPort, ntohl(srcAddr), srcPort);if(tcb = NULL) return -1;if(ack != tcb-seq + 1) tcp_DiscardPkt(pBuffer, STUD_TCP_TEST_SEQNO_ERROR); return -1;/* 有限状态机转换 */if(tcb-state = SYN_SENT) & (flags = 0x12) tcb-seq = ack; tcb-ack = seq + 1; stud_tcp_output(NULL, 0, PACKET_TYPE_ACK, tcb-srcPort, tcb-dstPort, tcb-srcAddr, tcb-dstAddr); tcb-state = ESTABLISHED; else if(tcb-state = FIN_WAIT_1) & (flags = 0x10) tcb-state = FIN_WAIT_2; else if(tcb-state = FIN_WAIT_2) & (flags = 0x11) tcb-ack = seq + 1;tcb-seq = ack;tcb-state = TIME_WAIT;stud_tcp_output(NULL, 0, PACKET_TYPE_ACK, tcb-srcPort, tcb-dstPort, tcb-srcAddr, tcb-dstAddr);tcb-state = CLOSED;return 0;void stud_tcp_output(char *pData, unsigned short len, unsigned char flag, unsigned short srcPort, unsigned short dstPort, unsigned int srcAddr, unsigned int dstAddr)TCB *tcb = findTCB(srcAddr, srcPort, dstAddr, dstPort); / 寻找TCB项if(tcbLinkTable = NULL) / 用于TCP报文接收发送流程 tcb = new TCB();tcbLinkTable = tcb;if(tcb = NULL | tcb-windowSize = 0) return;/* 构造新的发送报文 */unsigned char *packet = new unsigned charlen + 20;memset(packet, 0, len + 20);memcpy(packet + 20, pData, len);*(UINT16 *)(packet) = htons(tcb-srcPort);*(UINT16 *)(packet + 2) = htons(tcb-dstPort);*(UINT32 *)(packet + 4) = htonl(tcb-seq);*(UINT32 *)(packet + 8) = htonl(tcb-ack);packet12=20state = SYN_SENT;/ 发送SYN报文，状态转移为SYN_SENT break;case PACKET_TYPE_ACK: packet13=0x10; break;case PACKET_TYPE_SYN_ACK: packet13=0x12; break;case PACKET_TYPE_FIN: packet13=0x01; break;case PACKET_TYPE_FIN_ACK: packet13=0x11; tcb-state = FIN_WAIT_1; break;case PACKET_TYPE_DATA: break;*(UINT16 *)(packet+14)=htons(tcb-windowSize);*(UINT16 *)(packet+16)=CalcChecksum(char *)packet, len + 20, srcAddr, dstAddr);tcp_sendIpPkt(packet, len + 20, tcb-srcAddr, tcb-dstAddr, 255);return;int stud_tcp_socket(int domain, int type, int protocol)static int socketfd = 1;TCB *tcb = new TCB(socketfd+);tcb-nextTcb = tcbLinkTable;tcbLinkTable = tcb;return tcb-socketfd;int stud_tcp_connect(int sockfd, struct sockaddr_in *addr, int addrlen)char bufferBUFFER_SIZE;TCB* tcbPointer = tcbLinkTable;while(tcbPointer != NULL) & (tcbPointer-socketfd != sockfd) tcbPointer = tcbPointer-nextTcb;TCB *tcb = tcbPointer; / 找到TCB相应表项if(tcb = NULL) return -1;/* 初始化源和目的的地址及端口号 */tcb-srcAddr = getIpv4Address();tcb-srcPort = gSrcPort;tcb-dstAddr = ntohl(addr-sin_addr.s_addr);tcb-dstPort = ntohs(addr-sin_port);/* 建立连接：发送SYN报文 */stud_tcp_output(NULL, 0, PACKET_TYPE_SYN, tcb-srcPort, tcb-dstPort, tcb-srcAddr, tcb-dstAddr);/* 接收SYN_ACK报文 */if(waitIpPacket(buffer, TIMEOUT) = -1 | (buffer13 & 0x13) != 0x12) return -1;tcb-seq = ntohl(*(UINT32 *)(buffer + 8);tcb-ack = ntohl(*(UINT32 *)(buffer + 4) + 1;/* 发送ACK报文，建立连接完成 */stud_tcp_output(NULL, 0, PACKET_TYPE_ACK, tcb-srcPort, tcb-dstPort, tcb-srcAddr, tcb-dstAddr);tcb-state = ESTABLISHED;return 0;int stud_tcp_send(int sockfd, const unsigned char *pData, unsigned short datalen, int flags)char bufferBUFFER_SIZE;TCB* tcbPointer = tcbLinkTable;while(tcbPointer != NULL) & (tcbPointer-socketfd != sockfd) tcbPointer = tcbPointer-nextTcb;TCB *tcb = tcbPointer; / 找到TCB相应表项if(tcb = NULL | tcb-state != ESTABLISHED) return -1;/* 发送DATA报文 */stud_tcp_output(char *)pData, datalen, PACKET_TYPE_DATA, tcb-srcPort, tcb-dstPort, tcb-srcAddr, tcb-dstAddr);/* 等待接收ACK */if(waitIpPacket(buffer, TIMEOUT) = -1) return -1;if(buffer13 & 0x13) != 0x10) return -1;tcb-seq = ntohl(*(UINT32 *)(buffer + 8);tcb-ack = ntohl(*(UINT32 *)(buffer + 4) + 1;return 0;int stud_tcp_recv(int sockfd, unsigned char *pData, unsigned short datalen, int flags)char bufferBUFFER_SIZE;int len = 0;TCB* tcbPointer = tcbLinkTable;while(tcbPointer != NULL) & (tcbPointer-socketfd != sockfd) tcbPointer = tcbPointer-nextTcb;TCB *tcb = tcbPointer; if(tcb = NULL | tcb-state != ESTABLISHED) return -1;/* 等待接收数据 */if(len = waitIpPacket(buffer, TIMEOUT) = -1) return -1;int header_length = (buffer12 2) & 0x3C; memcpy(pData, buffer + header_length, len - header_length);tcb-seq = ntohl(*(UINT32 *)(buffer + 8);tcb-ack = ntohl(*(UINT32 *)(buffer + 4) + (len - header_length);stud_tcp_output(NULL, 0, PACKET_TYPE_ACK, tcb-srcPort, tcb-dstPort, tcb-srcAddr, tcb-dstAddr);return 0;int stud_tcp_close(int sockfd)char bufferBUFFER_SIZE;TCB *pre = NULL; TCB *tcb = tcbLinkTable;while(tcb != NULL) & (tcb-socketfd != sockfd) pre = tcb;tcb = tcb-nextTcb;if(tcb = NULL) return -1;if(t