telnet客户端程序

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

#define DO 0xfd
#define WONT 0xfc
#define WILL 0xfb
#define DONT 0xfe
#define CMD 0xff
#define CMD_ECHO 1
#define CMD_WINDOW_SIZE 31
#define IAC 255
#define SB 250
#define SE 240
#define BUFLEN 200
#define ESCAPE 27

#define SA struct sockaddr

static struct termios tin;
static void terminal_set(void);
static void terminal_reset(void);
void negotiate(int sock, unsigned char *buf, int len);
void connect_to_server(int sock, int port, char *address);

int main(int argc, char *argv[]) {
    int sock;
    unsigned char buf[BUFLEN + ];
    int len;
    int i;
    int port = ;

    if (argc <  || argc > ) {
        printf("Usage: %s address [port]\n", argv[]);
        return ;
    }

    if (argc == )
        port = atoi(argv[]);

    // Create socket
    sock = socket(AF_INET, SOCK_STREAM, );
    if (sock == -) {
        perror("Could not create socket. Error");
        return ;
    }
    printf("Trying %s...\n", argv[]);

    connect_to_server(sock, port, argv[]);

    printf("Connected to %s\n", argv[]);
    puts("Escape character is '^]'.");

    // set terminal
    terminal_set();
    atexit(terminal_reset);

    // 1 second
    struct timeval ts;
    ts.tv_sec = ;
    ts.tv_usec = ;

    while () {
        // select setup
        fd_set fds;
        FD_ZERO(&fds);
        if (sock != )
            FD_SET(sock, &fds);
        FD_SET(, &fds);

        // wait for data
        int nready = select(sock + , &fds, (fd_set *) , (fd_set *) , &ts);
        if (nready < ) {
            perror("select. Error");
            return ;
        } else if (nready == ) {
            ts.tv_sec = ;
            ts.tv_usec = ;
        } else if (sock !=  && FD_ISSET(sock, &fds)) {
            // start by reading a single byte
            int rv;
            if ((rv = recv(sock, buf, , )) < )
                return ;
            else if (rv == ) {
                printf("Connection closed by the remote end\n\r");
                return ;
            }

            if (buf[] == CMD) {
                // read 2 more bytes
                len = recv(sock, buf + , , );
                if (len < )
                    return ;
                else if (len == ) {
                    printf("Connection closed by the remote end\n\r");
                    return ;
                }
                negotiate(sock, buf, );
            } else {
                len = ;
                buf[len] = '\0';
                printf("%s", buf);
                fflush(stdout);
            }
        }

        else if (FD_ISSET(, &fds)) {
            static char crlf[] = { '\r', '\n' };
            buf[] = getc(stdin); //fgets(buf, 1, stdin);
            if (buf[] == '\n') { // with the terminal in raw mode we need to force a LF
                if (send(sock, crlf, , ) < ) {
                    return ;
                }
            } else if (buf[] == ESCAPE) {
                printf("Connection closed by the client end\n\r");
                return ;
            } else {
                if (send(sock, buf, , ) < )
                    return ;
            }
        }
    }
    close(sock);
    return ;
}

void negotiate(int sock, unsigned char *buf, int len) {
    int i;
    const char* option_code[];
    option_code[] = "TRANSMIT-BINARY";
    option_code[] = "ECHO";
    option_code[] = "SUPPRESS-GO-AHEAD";
    option_code[] = "STATUS";
    option_code[] = "TIMING-MARK";
    option_code[] = "NAOCRD";
    option_code[] = "NAOHTS";
    option_code[] = "NAOHTD";
    option_code[] = "NAOFFD";
    option_code[] = "NAOVTS";
    option_code[] = "NAOVTD";
    option_code[] = "NAOLFD";
    option_code[] = "EXTEND-ASCII";
    option_code[] = "LOGOUT";
    option_code[] = "BM";
    option_code[] = "DET";
    option_code[] = "SEND-LOCATION";
    option_code[] = "TERMINAL-TYPE";
    option_code[] = "END-OF-RECORD";
    option_code[] = "TUID";
    option_code[] = "OUTMRK";
    option_code[] = "TTYLOC";
    option_code[] = "3270-REGIME";
    option_code[] = "X.3-PAD";
    option_code[] = "NAWS";
    option_code[] = "TERMINAL-SPEED";
    option_code[] = "TOGGLE-FLOW-CONTROL";
    option_code[] = "LINEMODE";
    option_code[] = "X-DISPLAY-LOCATION";
    option_code[] = "ENVIRON";
    option_code[] = "AUTHENTICATION";
    option_code[] = "ENCRYPT";
    option_code[] = "NEW-ENVIRON";
    option_code[] = "TN3270E";
    option_code[] = "CHARSET";
    option_code[] = "COM-PORT-OPTION";
    option_code[] = "KERMIT";
    option_code[] = "SB";
    option_code[] = "SE";
    option_code[] = "WILL";
    option_code[] = "WONT";
    option_code[] = "DO";
    option_code[] = "DONT";
    option_code[] = "IAC";
    if (buf[] == DO && buf[] == CMD_WINDOW_SIZE) {
        unsigned char tmp1[] = { IAC, WILL, CMD_WINDOW_SIZE };
        if (send(sock, tmp1, , ) < )
            exit();

        unsigned char tmp2[] = { IAC, SB, CMD_WINDOW_SIZE, , , , , IAC,
        SE };
        if (send(sock, tmp2, , ) < )
            exit();
        return;
    }

    for (i = ; i < len; i++) {
        if (buf[i] == DO) {
            buf[i] = WONT;
        } else if (buf[i] == WILL) {
            buf[i] = DO;
        }
    }

    if (send(sock, buf, len, ) < )
        exit();
}

static void terminal_set(void) {
    // save terminal configuration
    tcgetattr(STDIN_FILENO, &tin);

    static struct termios tlocal;
    memcpy(&tlocal, &tin, sizeof(tin));
    // The file descriptor which has to be turned to raw mode is the standard
    // input of the parent process
    cfmakeraw(&tlocal);
    tcsetattr(STDIN_FILENO, TCSANOW, &tlocal);
}

static void terminal_reset(void) {
    // restore terminal upon exit
    tcsetattr(STDIN_FILENO, TCSANOW, &tin);
}

void connect_to_server(int sock, int port, char* address) {
    struct sockaddr_in server;
    server.sin_addr.s_addr = inet_addr(address);
    server.sin_family = AF_INET;
    server.sin_port = htons(port);

    //Connect to remote server
    if (connect(sock, (SA *) &server, sizeof(server)) < ) {
        perror("connect failed. Error\n");
        exit();
    }
}