模擬telnet協議C語言客戶端程式-有解無憂

首先要了解telnet協議，一下兩篇blog給了我初步的思路
https://www.cnblogs.com/liang-ling/p/5833489.html 這篇有比較基礎的介紹以及IAC命令含義解釋
https://www.cnblogs.com/image-eye/archive/2012/03/28/2421726.html 這篇就很能抓住重點另外這位博主使用的是C# 寫的程式十分完整我這里關于IAC指令處理有部分是直接借鑒他的程式因此注釋都沒有修改仍然使用的是他的注釋

以上兩篇大致看過之后就可以了解本次po出來的程式了內容較為樸素

utils.h

#ifndef __UTILS__H
#define __UTILS__H

#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <errno.h>
#include <malloc.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/ioctl.h>
#include <stdarg.h>
#include <fcntl.h>
#include <fcntl.h>
#include <sys/poll.h>
#include <signal.h>
#include <sys/wait.h>

typedef signed long int ssize_t;
typedef unsigned long int size_t;

ssize_t readn(int fd, void *vptr,size_t n);
ssize_t writen(int fd, const void *vptr, size_t n);
ssize_t readline(int fd,void *vptr,size_t maxlen);

#endif

utils.c


#include"utils.h"


ssize_t readn(int fd, void *vptr,size_t n)
{
	size_t nleft;
	ssize_t nread;
	char *ptr;
	
	ptr = vptr;
	nleft = n;
	while(nleft >0)
	{
		if((nread = read(fd,ptr,nleft))<0)
		{
			if(errno == EINTR)//error：為EAGAIN，表示在非阻塞下，此時無資料到達，立即回傳，
                nread = 0;            //error：為EINTR，表示被信號中斷了，
			else
				return (-1);
		}
		else if(nread == 0)
			break;
		else 
			/* do nothing */
		nleft -= nread;
		ptr += nread;
	}
	return n-nleft;//實際讀了多少位元組
}

ssize_t writen(int fd, const void *vptr, size_t n)
{
	size_t nleft;
	ssize_t nwritten;
	const char *ptr;
	
	ptr = vptr;
	nleft = n;
	while(nleft > 0)
	{
		if((nwritten = write(fd,ptr,nleft)) < 0)
		{
			if(nwritten <0 &&  errno == EINTR)
			{
				nwritten = 0;
			}
			else
				return (-1);
		}
		else if(nwritten == 0)   
			break;
		else //nwritten > 0
		{
			/*do nothing*/
		}
		nleft = nleft - nwritten;
		ptr = ptr + nwritten;
	}
	return (n- nleft);//實際寫了多少位元組
}

ssize_t readline(int fd,void *vptr,size_t maxlen)
{
	ssize_t n =0,rc;
	char c,*ptr;
	
	ptr = vptr;
	while(1)
	{
		if((rc = read(fd,&c,1)) == 1)
		{
			*ptr++ = c;
			n++;
			if(c == '\n')
				break;
		}
		else if (rc == 0)
		{
			*ptr = '\0';
			return (n -1);
		}
		else
		{
			if(errno == EINTR)
				continue;
			else
				return (-1);
		}
	}
	*ptr = '\0';
	return n;
}

telnet.h


#ifndef __TELNET__H
#define __TELNET__H

//<IAC CMD OP >

#define IAC   255

//command word
#define NUL        0
#define BEL        7
#define BS         8
#define HT         9
#define LF         10
#define VT         11
#define FF         12
#define CR         13
#define SE         240
#define NOP        241
#define DM         242
#define BRK        243
#define IP         244
#define AO         245
#define AYT        246
#define EC         247
#define EL         248
#define GA         249
#define SB         250
#define WILL       251
#define WONT       252
#define DO         253
#define DONT       254

typedef unsigned char uint8;
typedef unsigned int  uint32;


//operation options

typedef enum tagOPERATION_OPTIONS
{
    TOPT_BIN = 0,
    TOPT_ECHO = 1,
    TOPT_RECN = 2,
    TOPT_SUPP = 3
	
}OPERATION_OPTIONS;


uint32 get_every_frame(uint8* recvbuf,uint32 len,uint8* sendbuf,uint32 sendlen);

#endif

telnet.c





#include"telnet.h"
#include<string.h>
#include<stdio.h>
#include <stdlib.h>

#define MAXLINE 1024
#define SEND    1
#define IS      0



static uint32 handle_telnetcmd_from_server(uint8* buf,uint32 len,uint8* resp,uint32 n);
static uint32 process_every_frame(uint8* startByte,uint8* endByte,uint8* sendbuf,uint32 startSendByte);

/* 2020-01-13 begin */
extern uint32 SOCKFD ;
extern void telnet_client_send_msg(int fd, const void *vptr, size_t n);
/* 2020-01-13 end*/

uint32 get_every_frame(uint8* recvbuf,uint32 len,uint8* sendbuf,uint32 sendlen)
{
	uint32 i =0,n=0,sum =0;
	//uint8* p = sendbuf;
	uint8* pRear = &recvbuf[len];
	uint8* startByte = recvbuf;
	uint8* endByte = recvbuf;
	uint8* strSendToMQTT = NULL;
	
	strSendToMQTT = (uint8*)malloc(MAXLINE);
	if(strSendToMQTT == NULL)
	{
		printf("==========strSendToMQTT malloc failed==============\n");
		return 0;
	}
	
#if 1	
	printf("-sum-receivelen----%d-------\n",len);
	printf("receive :<*");
	
	for(i =0 ;i<len;i++)
	{
		printf("%x*",recvbuf[i]);
	}
	printf("*>\n");
	
#endif	
	
	
	while(startByte != pRear)
	{
		if(*startByte == IAC)
		{
			sum = sum + n;
			switch(*(++endByte))
			{
	    /*fa 250 */case SB:while(*(++endByte) != SE){};n = process_every_frame(startByte,endByte,sendbuf,sum);break;
		/*fb 251 */case WILL:endByte +=2;n = process_every_frame(startByte,endByte,sendbuf,sum);break;
		/*fc 252 */case WONT:endByte +=2;n = process_every_frame(startByte,endByte,sendbuf,sum);break;
        /*fd 253 */case DO:endByte +=2;n = process_every_frame(startByte,endByte,sendbuf,sum);break;
        /*fe 254 */case DONT:endByte +=2;n = process_every_frame(startByte,endByte,sendbuf,sum);break;	
		/* 240 */case SE:break;
		/* sss */default : break;
			}
                        startByte = endByte;
		}
		else
		{
                        /* 2020-01-13 begin ：按照原來的寫法 else分支會造成死回圈，這里修改 */
			i = 0;
			memset(strSendToMQTT,0,MAXLINE);
			while((startByte != pRear)&&(*startByte != IAC ))
			{
				strSendToMQTT[i++] = *startByte ;
				++startByte;
			}
			strSendToMQTT[i] = '\0';
			/* 2020-01-13 strSendToMQTT的字串應當也要發送出去 */
			telnet_client_send_msg(SOCKFD,strSendToMQTT,i+1);
                       /* 2020-01-13 end ：按照原來的寫法 else分支會造成死回圈，這里修改 */
		}
	}
	if(sum > sendlen)
	{
		printf("--error3---sum > MAXLINE-----\n");
	}
	printf("--------------sum is %d ----\n",sum);
	return sum;
}



static uint32 process_every_frame(uint8* startByte,uint8* endByte,uint8* sendbuf,uint32 startSendByte)
{
	uint8 n = 0 ;
	uint8* pstartByte = startByte;
	
	while(pstartByte != endByte)
	{
		n++;
		pstartByte++;
	}
	return handle_telnetcmd_from_server(startByte,n,&sendbuf[startSendByte],MAXLINE);
}

static uint32 handle_telnetcmd_from_server(uint8* buf,uint32 len,uint8* resp,uint32 n)
{
	uint32 i =0;
	uint8 *p = resp;
	OPERATION_OPTIONS optionCode;
	uint8 cmdCode,ch;
	uint32 resplen =0;
	memset(resp,0,len);
	//first display cmd from server in string
	
#if 1
	printf("--receivelen----%d-------\n",len);
	printf("receive :<*");
	for(i =0 ;i<len;i++)
	{
		printf("%x*",buf[i]);
	}
	printf("*>\n");
	
#endif

	if(len < 3)
	{
		printf("IAC command length is %d less then 3\n",len);
		return -1;
	}
	
	//獲得命令碼
	cmdCode = buf[1];
	//獲得選項碼
	optionCode = buf[2];
	
	
	//response requests from server
	
	*p = IAC;
	resplen++;
	if( optionCode == TOPT_SUPP)//if(optionCode == TOPT_ECHO || optionCode == TOPT_SUPP)
	{
		if (cmdCode == DO)
		{
			//我設定我應答的命令碼為 251(WILL) 即為支持 回顯或抑制繼續進行
			ch = WILL;
			*(++p) = ch;
			*(++p)= optionCode;
			resplen += 2;

		}
		//如果命令碼為 254(DONT)
		else if (cmdCode == DONT)
		{
			//我設定我應答的命令碼為 252(WONT) 即為我也會"拒絕啟動" 回顯或抑制繼續進行
			ch = WONT;
			*(++p)= ch;
			*(++p)= optionCode;
			resplen += 2;

		}
		//如果命令碼為251(WILL)
		else if (cmdCode == WILL)
		{
			//我設定我應答的命令碼為 253(DO) 即為我認可你使用回顯或抑制繼續進行
			ch = DO;
			*(++p)= ch;
			*(++p)= optionCode;
			resplen += 2;
			//break;
		}
		//如果接受到的命令碼為251(WONT) 
		else if (cmdCode == WONT)
		{
			//應答  我也拒絕選項請求回顯或抑制繼續進行
			ch = DONT;
			*(++p)= ch;
			*(++p)= optionCode;
			resplen += 2;
			//    break;
		}
		//如果接受到250(sb,標志子選項開始)
		else if (cmdCode == SB)
		{
			/*
			 * 因為啟動了子標志位,命令長度擴展到了4位元組,
			 * 取最后一個標志位元組為選項碼
			 * 如果這個選項碼位元組為1(send)
			 * 則回發為 250(SB子選項開始) + 獲取的第二個位元組 + 0(is) + 255(標志位IAC) + 240(SE子選項結束)
			*/
			ch = buf[3];
			if (ch == SEND)
			{
				ch = SB;
				*(++p)= ch;
				*(++p)= optionCode;
				*(++p)= IS;
				*(++p)= IAC;
				*(++p)= SE;
				resplen += 5;
			}
			else
			{
				printf("ch != SEND\n");
			}
		}
		else
		{
			/* do nothing */
		}
	}
	else/* 如果選項碼不是1 或者3  */
	{
		// 底下一系列代表,無論你發那種請求,我都不干
		if (cmdCode == DO)
		{
			ch = WONT;
			*(++p)= ch;
			*(++p)= optionCode;
			resplen += 2;
		}
		else if (cmdCode == DONT)
		{
			ch = WONT;
			*(++p)= ch;
			*(++p)= optionCode;
			resplen += 2;
		}
		else if (cmdCode == WILL)
		{
			ch = DONT;
			*(++p)= ch;
			*(++p)= optionCode;
			resplen += 2;
		}
		else if (cmdCode == WONT)
		{
			ch = DONT;
			*(++p)= ch;
			*(++p)= optionCode;
			resplen += 2;
		}
		else
		{
			/* do nothing */
		}
			
	}
	
#if 1
	printf("--resplen---%d-------\n",resplen);
	printf("response :<*");
	for(i =0 ;i<resplen;i++)
	{
		printf("%x*",resp[i]);
	}
	printf("*>\n");
#endif	
	
	
	if(n < resplen )
	{
		printf("error n < resplen !!! \n");
	}
	if(resplen < 3 )
	{
		printf("resplen < 3 \n");
	}
	return resplen;
}

client.c


//gcc client.c -o client


#include"utils.h"
#include"telnet.h"


#define IP_ADDRESS   "127.0.0.1"
#define IP_PORT      23
#define SERV_PORT    3333
#define MAXLINE      1024

typedef struct sockaddr SA;


void str_cli(FILE *fp,uint32 sockfd);
uint32 max(uint32 a,uint32 b);
void ERR_EXIT(char* s);

uint32 main(uint32 argc,uint32 **argv)
{
	uint32 sockfd,isReady=0;
	struct sockaddr_in servaddr;
	uint32 hname[128];

	sockfd = socket(AF_INET,SOCK_STREAM,0);
	bzero(&servaddr,sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_port = htons(IP_PORT);
	servaddr.sin_addr.s_addr = inet_addr(IP_ADDRESS);
	printf("servaddr: IP is %s, Port is %d\n",inet_ntoa(servaddr.sin_addr), ntohs(servaddr.sin_port));

	while(connect(sockfd,(SA*)&servaddr,sizeof(servaddr))){};
	printf("connect has been ready\n");
	
	str_cli(stdin,sockfd);
	exit(0);
	return 0;
}
void ERR_EXIT(char* s)
{
	perror(s);
	exit(EXIT_FAILURE);
}
void INFO_PRINT(char* s)
{
	printf("%s",s);
}
uint32 max(uint32 a,uint32 b)
{
	return (a>b?a:b);
}

void str_cli(FILE *fp,uint32 sockfd)
{
	uint32 maxfdp1,nready;//stdineof;
	fd_set rset;
	uint8 buf[MAXLINE];
	uint8 respbuff[MAXLINE] = {0};;
	uint32 resplen;
	uint32 n;
	uint8 echo_cmd[] = {0xff,0xfb,0x01};
	//stdineof = 0;
	FD_ZERO(&rset);
	writen(sockfd,echo_cmd,3);
	
	for(;;)
	{
		//if(stdineof == 0)
		FD_SET(fileno(fp),&rset);
		FD_SET(sockfd,&rset);
		maxfdp1 = max(fileno(fp),sockfd)+1;
		nready = select(maxfdp1,&rset,NULL,NULL,NULL);
		
		if(nready < 0)
		{
			ERR_EXIT("ERROR!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!");
		}
		
		if(FD_ISSET(sockfd,&rset))
		{
			memset(buf,0,MAXLINE);
			if((n = read(sockfd,buf,MAXLINE))==0)
			{
				ERR_EXIT("str_cli:server termination prematurely");
			}
			buf[n] = '\0';
			//printf("FD_ISSET(sockfd,&rset)-------------%s\n",buf);
			
			if(buf[0] == IAC)
			{
				memset(respbuff,0,MAXLINE);
				resplen = get_every_frame(buf,n,respbuff,MAXLINE);
				writen(sockfd,respbuff,resplen);
			}
			else
			{
				telnet_client_send_msg(fileno(stdout),(char *)buf,n);
			}
			
			//writen(fileno(stdout),buf,n);
		}
		if(FD_ISSET(fileno(fp),&rset))
		{
			memset(buf,0,MAXLINE);
			if((n = readline(fileno(fp),(char *)buf,MAXLINE)) == 0)
			{
				//stdineof = 1;//此時碰到EOF 并且馬上要發生FIN序列 所以標準輸入不可讀了
				shutdown(sockfd,SHUT_WR);
				FD_CLR(fileno(fp),&rset);
				INFO_PRINT("nothing input!");
				continue;
			}
			else if(n >0)
			{
				/* do nothing */
			}
			else
			{
				ERR_EXIT("some error occurred ");
			}
			//printf("FD_ISSET(fileno(fp),&rset)----%d--\n",n);
			//memset(buf,0,MAXLINE);
			telnet_client_send_msg(sockfd,(char *)buf,n);
		}
	}
}

makefile

all:Client_telnet
	@echo ""
	@echo "This is telnet Client compile......."
	@echo ""
	
Client_telnet:client.o utils.o telnet.o
	gcc -g -o Client_telnet client.o utils.o telnet.o
	
client.o:client.c utils.h telnet.h
	gcc -g -c client.c
	
utils.o:utils.c utils.h
	gcc -g -c utils.c 
	
telnet.o:telnet.c telnet.h
	gcc -g -c telnet.c
	
clean :
	-rm client.o utils.o telnet.o Client_telnet

以上為本次程式使用的原始碼程式在Linux系統上運行方式為 ./Client_telnet

然后是運行截圖如此下：

以上

轉載請註明出處，本文鏈接：https://www.uj5u.com/houduan/67325.html

標籤：C

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