Telnet 客户端服务器会话与协商

Question

我正在尝试为 Telnet 客户端服务器会话编写代码，该会话在它们之间发送协商。像会，不会，做，不要。我使用套接字编程编写了一个基本的客户端-服务器程序。 如果我能知道如何将客户端/服务器修改为带有协商的 telnet 客户端服务器，那将有很大帮助。以下是代码：

在此处输入代码

#include <stdio.h>
#include <stdlib.h>     
#include <string.h>
#include <cstring>
#include <sys/types.h> 
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <netdb.h>


char buf1[] = {0xff, 0xfb, 0x18, 0xff, 0xfb, 0x1f};
char buf2[] = {0xff, 0xfc, 0x20, 0xff, 0xfc, 0x23, 0xff, 0xfb, 0x27};
char buf3[] = {0xff, 0xfa, 0x1f, 0x00, 0x78, 0x00, 0x32, 0xff, 0xf0};
char buf4[] = {0xff, 0xfa, 0x27, 0x00, 0xff, 0xf0, 0xff, 0xfa, 0x18, 0x00, 0x41, 0x4e, 0x53, 0x49, 0xff, 0xf0};
char buf5[] = {0xff, 0xfd, 0x03};
char buf6[] = {0xff, 0xfb, 0x01, 0xff, 0xfe, 0x05, 0xff, 0xfc, 0x21};
char buf7[] = {0xff, 0xfc, 0x01};
char buf8[] = {0xff, 0xfd, 0x01};

void read (int sock)
{
    char buffer[256];

    /* Now read server response */
    memset(buffer, 0, sizeof(buffer));
    int n = recv( sock, buffer, 255, 0 );
    if (n < 0) 
    {
         perror("ERROR reading from socket");
         return;
    }
    printf("%d bytes received buffer is: %s\n", n, buffer);
    for (int i = 0; i < n; i++)
         printf("%2x ", buffer[i]);
    printf("\n");
}

void mwrite (int sock, char * buf, int size)
{
    int n = send( sock, buf, size, 0 );
    if (n < 0) 
    {
         perror("ERROR writing to socket");
         return;
    }
    printf("Bytes Sent: %d\n", n);
  }

int main(int argc, char *argv[])
{
    int sockfd, portno, n;
    struct sockaddr_in serv_addr;
    struct hostent *server;


    char buffer[256];

    if (argc < 3) {
        fprintf(stderr,"usage %s hostname port\n", argv[0]);
        return(0);
    }
    portno = atoi(argv[2]);
    /* Create a socket point */
    sockfd = socket(AF_INET, SOCK_STREAM, 0);

    if (sockfd < 0) 
    {
        perror("ERROR opening socket");
        return(1);
    }
    server = gethostbyname(argv[1]);
    if (server == NULL)
    {fprintf(stderr,"ERROR no such host \n");
     exit(0);}


    //printf("host %s, port %d\n", host.c_str(), portno);

    bzero((char *) &serv_addr , sizeof(serv_addr));

    serv_addr.sin_family = AF_INET;

    bcopy((char *)server->h_addr, (char*)&serv_addr.sin_addr.s_addr, server->h_length);


    //serv_addr.sin_addr.s_addr = inet_addr( host.c_str() ); // ( "127.0.0.1" );
    serv_addr.sin_port = htons( portno );

    /* Now connect to the server */
    if (connect( sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr) ) < 0) 
    {
         perror("ERROR connecting");
         return(1);
    }   

printf("Please enter the message=");
bzero(buffer,256);
fgets(buffer,255,stdin);

n= write(sockfd,buffer,strlen(buffer));
if(n<0)
printf("ERROR writing in socket %d  len %d", n, strlen(buffer));
bzero(buffer,256);

n = read(sockfd, buffer, 255);
if(n<0)
perror("ERROR reading from socket");

printf("%s\n",buffer);
close(sockfd);



return 0;

    buffer[0] = 0x0d;
    buffer[1] = 0x0a;
    mwrite ( sockfd, buffer, 2);
    printf("read 1 ");
    read(sockfd);

    mwrite( sockfd, buf1, sizeof(buf1));
    sleep(2);
    mwrite( sockfd, buf2, sizeof(buf2));
    printf("read 2 ");
    read(sockfd);

    mwrite( sockfd, buf3, sizeof(buf3));
    printf("read 3a ");
    read(sockfd);
    sleep(2);
    mwrite( sockfd, buf4, sizeof(buf4));
    printf("read 3b ");
    read(sockfd);

    mwrite( sockfd, buf5, sizeof(buf5));
    sleep(2);
    mwrite( sockfd, buf6, sizeof(buf6));
    printf("read 4 ");    
    read(sockfd);

    mwrite( sockfd, buf7, sizeof(buf7));
    sleep(2);
    mwrite( sockfd, buf8, sizeof(buf8));
    read(sockfd);

    mwrite ( sockfd, buffer, 2);
    read(sockfd);

    return 0;
}

服务器.cpp

enter code here : 

#include <stdio.h>
#include <stdlib.h>     
#include <string.h>
#include <string>
#include <sys/types.h> 
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>


void error(char *msg)
{
perror(msg);
exit(1);
}

int main(int argc, char *argv[])
{

int sockfd, newsockfd, portno;
//unsigned clilen;
socklen_t clilen;
char buffer[256];
struct sockaddr_in serv_addr, cli_addr;
int n;

if (argc < 2)
{
fprintf(stderr,"ERROR, no port provided\n");
exit(1);
}

sockfd = socket(AF_INET, SOCK_STREAM, 0);

if (sockfd < 0)
{
error("ERROR opening socket");
}

bzero((char *) &serv_addr, sizeof(serv_addr));

portno = atoi(argv[1]);

serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = INADDR_ANY;
serv_addr.sin_port = htons(portno);

if (bind(sockfd, (struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0)
{
error("ERROR on binding");
}

listen(sockfd,5);
clilen = sizeof(cli_addr);

newsockfd = accept(sockfd,(struct sockaddr *) &cli_addr, &clilen);

if (newsockfd < 0)
{
error("ERROR on accept");
}

bzero(buffer,256);

n = read(newsockfd,buffer,255);

if (n < 0)
{
error("ERROR reading from socket");
}

printf("Here is the message: %s\n",buffer);

n = write(newsockfd,"I got your message",18);

if (n < 0)
{
error("ERROR writing to socket");
}
return 0;
}

提前致谢。

Answer 1

[对于cmets来说开始太多了，所以我写作为答案。]

至于你的问题，它实际上不是一个单一的问题，而是两个混合的问题：缓冲和协商。您需要缓冲，因为 TCP 是一种流式协议，接收调用可能只接收 telnet 消息的一部分，而发送调用可能只发送 telnet 消息的一部分。第二个问题是协商，为此您需要一个所谓的状态机。每个选项都需要一个状态。

您还需要阅读和理解RFC854 和RFC855。有关 RFC 的完整列表，请参阅 Telnet Wikipedia article。

对于选项协商，WILL 和WONT 由DO 或DONT 响应。除非您已经收到 WILL 或 WONT，否则您通常不应发送 DO 或 DONT。对于初学者，在您正确处理选项之前，我建议您在收到WILL（当然还有WONT）消息时始终回答DONT。不要发送 WILL 或 WONT ，除非您确实需要协商选项。

---

在实现方面，我推荐四个状态表，您发送的WILL、WONT、DO 和DONT 各一张。这些表包含简单的布尔值，告诉您是否已向对等方发送了相应的消息。这四个表假设您收到的任何无法识别的选项都以DONT 或WONT 回复。

如果您发送WILL，那么您将其标记在相应的状态表中，这样当您收到选项的DO 或DONT 时，您就知道是您发起了协商。