模拟telnet协议C语言客户端程序

King

首先要了解telnet协议，一下两篇blog给了我初步的思路
https://www.cnblogs.com/liang-ling/p/5833489.html 这篇有比较基础的介绍以及IAC命令含义解释
https://www.cnblogs.com/image-eye/archive/2012/03/28/2421726.html 这篇就很能抓住重点另外这位博主使用的是C# 写的程序十分完整我这里关于IAC指令处理有部分是直接借鉴他的程序因此注释都没有修改仍然使用的是他的注释

以上两篇大致看过之后就可以了解本次po出来的程序了内容较为朴素

utils.h
‘’‘C

ifndef UTILSH

define UTILSH

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 <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
'''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：为EAGAIN，表示在非阻塞下，此时无数据到达，立即返回。
            nread = 0;            //error：为EINTR，表示被信号中断了。
        else
            return (-1);
    }
    else if(nread == 0)
        break;
    else 
        /* do nothing */
    nleft -= nread;
    ptr += nread;
}
return n-nleft;//实际读了多少字节

知识兔

}

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);//实际写了多少字节

知识兔

}

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;

知识兔

}

'''

telnet.h
'''C

ifndef TELNETH

define TELNETH

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
'''C

include"telnet.h"

include<string.h>

include<stdio.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);

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;

printf("-sum-receivelen----%d-------\n",len);
printf("receive :<*");

for(i =0 ;i<len;i++)
{
    printf("%x*",recvbuf[i]);
}
printf("*>\n");



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;
}
if(sum > sendlen)
{
    printf("--error3---sum > MAXLINE-----\n");
}
printf("--------------sum is %d ----\n",sum);
return sum;

知识兔

}

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);

知识兔

}

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

printf("--receivelen----%d-------\n",len);
printf("receive :<*");
for(i =0 ;i<len;i++)
{
    printf("%x*",buf[i]);
}
printf("*>\n");

if(len < 3)
{
    printf("IAC command length is %d less then 3\n",len);
    return -1;
}

//获得命令码
cmdCode = buf[1];
//获得选项码
optionCode = buf[2];


//response requests from server

*p = IAC;
resplen++;
if(optionCode == TOPT_ECHO || optionCode == TOPT_SUPP)
{
    if (cmdCode == DO)
    {
        //我设置我应答的命令码为 251(WILL) 即为支持 回显或抑制继续进行
        ch = WILL;
        *(++p) = ch;
        *(++p)= optionCode;
        resplen += 2;

    }
    //如果命令码为 254(DONT)
    else if (cmdCode == DONT)
    {
        //我设置我应答的命令码为 252(WONT) 即为我也会"拒绝启动" 回显或抑制继续进行
        ch = WONT;
        *(++p)= ch;
        *(++p)= optionCode;
        resplen += 2;

    }
    //如果命令码为251(WILL)
    else if (cmdCode == WILL)
    {
        //我设置我应答的命令码为 253(DO) 即为我认可你使用回显或抑制继续进行
        ch = DO;
        *(++p)= ch;
        *(++p)= optionCode;
        resplen += 2;
        //break;
    }
    //如果接受到的命令码为251(WONT) 
    else if (cmdCode == WONT)
    {
        //应答  我也拒绝选项请求回显或抑制继续进行
        ch = DONT;
        *(++p)= ch;
        *(++p)= optionCode;
        resplen += 2;
        //    break;
    }
    //如果接受到250(sb,标志子选项开始)
    else if (cmdCode == SB)
    {
        /*
         * 因为启动了子标志位,命令长度扩展到了4字节,
         * 取最后一个标志字节为选项码
         * 如果这个选项码字节为1(send)
         * 则回发为 250(SB子选项开始) + 获取的第二个字节 + 0(is) + 255(标志位IAC) + 240(SE子选项结束)
        */
        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/* 如果选项码不是1 或者3  */
{
    // 底下一系列代表,无论你发那种请求,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 */
    }
        
}

printf("--resplen---%d-------\n",resplen);
printf("response :<*");
for(i =0 ;i<resplen;i++)
{
    printf("%x*",resp[i]);
}
printf("*>\n");



if(n < resplen )
{
    printf("error n < resplen !!! \n");
}
if(resplen < 3 )
{
    printf("resplen < 3 \n");
}
return resplen;

知识兔

}

'''

client.c
'''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;

知识兔

}
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
        {
            writen(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;//此时碰到EOF 并且马上要发生FIN序列 所以标准输入不可读了
            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);
        writen(sockfd,(char *)buf,n);
    }
}

知识兔

}

'''

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
'''

以上为本次程序使用的源码程序在Linux系统上运行方式为 ./Client_telnet

以上

计算机

2022年2月04日

模拟telnet协议C语言客户端程序

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>

endif

include"utils.h"

ifndef __TELNET__H

define __TELNET__H

define IAC 255

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

endif

include"telnet.h"

include<string.h>

include<stdio.h>

define MAXLINE 1024

define SEND 1

define IS 0

include"utils.h"

include"telnet.h"

define IP_ADDRESS "127.0.0.1"

define IP_PORT 23

define SERV_PORT 3333

define MAXLINE 1024

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ifndef UTILSH

define UTILSH

ifndef TELNETH

define TELNETH