c - 当用户键入其中一个箭头键时，从服务器端阻止客户端连接

Question

我需要根据在客户端键入 up/down/left/right arrow 的用户从服务器端阻止连接。

我尝试了以下方法之一，但它不起作用:

strcmp( userName, "^[[A" ) == 0

我创建了一个套接字服务器，用于检查连接的有效昵称，但是当客户端键入其中一个箭头时:

up arrow    = ^[[A
down arrow  = ^[[B
left arrow  = ^[[D
right arrow = ^[[C

在服务器端只是被忽略，它不会关闭客户端。这是一个说明问题的程序:

#include <errno.h>
#include <string.h>
#include <stdio.h>
#include <netinet/in.h>
#include <net/if.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <string.h>

#define PORT 8888
#define MSGLEN 256
#define MAXNAMELENGTH 25

int server_socket = 0;
int client_socket = 0;
struct sockaddr_in address;

void create_sckt  ( void );
void bind_sckt    ( const size_t server_len );
void listen_sckt  ( void );
void accept_sckt  ( size_t server_len );
ssize_t recv_sckt ( char *const userName );
void send_msg ( const int userID, const char *const userName );


int main( void )
{
    size_t server_len              = sizeof( address );
    char userName[ MSGLEN + 1 ]    = { 0 };
    const char *const wrong_name   = "[+]Please type a Valide Name and come back.\n";

    create_sckt ();
    bind_sckt   ( server_len );
    listen_sckt ();

    printf( "Starting Server...\n" );
    while ( 1 )
    {
        accept_sckt( server_len );
        memset( userName, '\0', sizeof(userName ) );
        recv_sckt( userName );
        userName[ strcspn( userName, "\n" ) ] = 0;
        if ( strcmp( userName, "^[[A" ) == 0 && strlen( userName ) > MAXNAMELENGTH )
        {
            send_msg ( client_socket, wrong_name );
            close( client_socket );
            break;
        }else
        {
            char welcome_msg[1024] = { 0 };
            sprintf( welcome_msg, " Welcome %s\n", userName );
            send_msg ( client_socket, welcome_msg );
        }
    }
    close( server_socket );
}

void create_sckt ( void )
{
    server_socket = socket( AF_INET, SOCK_STREAM, 0 );
    if ( server_socket == -1 )
    {
        printf("socket() failed\n");
        fprintf(stderr, "%s %d\n", strerror(errno), errno);
        exit ( EXIT_FAILURE );
    }

    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons( PORT );
}

void listen_sckt ( void )
{
    int ret = listen( server_socket, 3 );
    if ( ret == -1 )
    {
        printf ( "listen() failed\n" );
        fprintf( stderr, "%s %d\n", strerror( errno ), errno );
        exit   ( EXIT_FAILURE );
    }
}
void bind_sckt ( const size_t server_len )
{
    int ret = bind( server_socket, ( struct sockaddr* )&address, ( socklen_t )server_len );
    if (  ret == -1 )
    {
        printf ( "bind() failed\n" );
        fprintf( stderr, "%s %d\n", strerror( errno ), errno);
        exit   ( EXIT_FAILURE );
    }
}

void accept_sckt ( size_t server_len )
{
    client_socket = accept( server_socket, (struct sockaddr *)&address, (socklen_t*)&server_len );
    if ( client_socket == -1 )
    {
        printf ( "accept() failed\n" );
        fprintf( stderr, "%s %d\n", strerror(errno), errno );
        exit   ( EXIT_FAILURE );
    }
}

void send_msg ( const int userID, const char *const userName )
{
    ssize_t ret = send( userID , userName , strlen( userName ) , 0 );
    if ( ret == -1 )
    {
        printf ( "recv() failed\n" );
        fprintf( stderr, "%s %d\n", strerror( errno ), errno );
        exit   ( EXIT_FAILURE );
    }else
    {
        printf( "Hello message sent\n" );
    }
}

ssize_t recv_sckt ( char *const userName )
{
    ssize_t ret = recv( client_socket, userName, MSGLEN, 0);
    if ( ret == -1 )
    {
        printf ( "recv() failed\n" );
        fprintf( stderr, "%s %d\n", strerror( errno ), errno );
        exit   ( EXIT_FAILURE );
    }
    return ret;
}

当在客户端使用 arrow 键之一时，我应该如何阻止连接？在客户端打印(欢迎):

Please enter your name: ^[[A
Connect to Server: 192.168.0.103:8888
You are: 192.168.0.103:42074
 Welcome

Answer 1

在我尝试了上面的答案和一条评论中提供的示例之后，但没有用。我找到了解决问题的方法。

GCC 似乎允许 \e 但它不是标准的:

error: non-ISO-standard escape sequence, '\e'|

也尝试了 "\x27[A" 但仍然没有工作。

在这种情况下唯一有效的是0x1B:

if ( userName[0] == 0x1B )