TCP服务器崩溃

Question

我只是想知道为什么当客户端连接时会崩溃？？它应该是一个简单的TCP服务器，当客户端连接并发送一个字符串时，服务器用字符串中的A的数量进行响应。一旦客户端输入一个字母，服务器就会崩溃。

#include<io.h>
#include<stdio.h>
#include<winsock2.h>

#pragma comment(lib,"ws2_32.lib") //Winsock Library

int main(int argc , char *argv[])
{
WSADATA wsa;
SOCKET s , new_socket, master;
struct sockaddr_in server , address;
int c, valread;
char *message = "Welcome to Marshall's TCP Server!!";
int MAXRECV = 1024;
char *buffer;
char AmmtA = 'a';
char AmmtB = 'A';
int count = 0, x;
fd_set readfds;
buffer =  (char*) malloc((MAXRECV + 1) * sizeof(char));

printf("\nInitialising Winsock...");
if (WSAStartup(MAKEWORD(2,2),&wsa) != 0)
{
    printf("Failed. Error Code : %d",WSAGetLastError());
    return 1;
}

printf("Initialised.\n");

//Create a socket
if((s = socket(AF_INET , SOCK_STREAM , 0 )) == INVALID_SOCKET)
{
    printf("Could not create socket : %d" , WSAGetLastError());
}

printf("Socket created.\n");

//Prepare the sockaddr_in structure
server.sin_family = AF_INET;
server.sin_addr.s_addr = INADDR_ANY;
server.sin_port = htons( 9000 );

//Bind
if( bind(s ,(struct sockaddr *)&server , sizeof(server)) == SOCKET_ERROR)
{
    printf("Bind failed with error code : %d" , WSAGetLastError());
    exit(EXIT_FAILURE);
}

puts("Bind done");

//Listen to incoming connections
listen(s , 3);
//Accept and incoming connection
puts("Waiting for incoming connections...");

c = sizeof(struct sockaddr_in);

while( (new_socket = accept(s , (struct sockaddr *)&address, &c)) != INVALID_SOCKET )
{
    puts("Connection accepted");

send(new_socket , message , strlen(message) , 0);   

valread = recv( new_socket , buffer, MAXRECV, 0);

            if( valread == SOCKET_ERROR)
            {
                int error_code = WSAGetLastError();
                if(error_code == WSAECONNRESET)
                {
                    //Somebody disconnected , get his details and print
                    printf("Host disconnected unexpectedly , ip %s , port %d \n" , inet_ntoa(address.sin_addr) , ntohs(address.sin_port));

                    //Close the socket and mark as 0 in list for reuse
                    closesocket( s );
                }
                else
                {
                    printf("recv failed with error code : %d" , error_code);
                }
            }
            if ( valread == 0)
            {
                //Somebody disconnected , get his details and print
                printf("Host disconnected , ip %s , port %d \n" , inet_ntoa(address.sin_addr) , ntohs(address.sin_port));

                //Close the socket and mark as 0 in list for reuse
                closesocket( s );
            }

            else
            {
       for (x = 0; buffer[x] != '\0'; x++) {
                if (buffer[x] == AmmtA || buffer[x] == AmmtB)
                count++;
    }

        char feedback[150];
        sprintf(feedback, "There is %d A's in your string", count);
                feedback[MAXRECV] = '\0';
                printf("%s:%d - %s \n" , inet_ntoa(address.sin_addr) , ntohs(address.sin_port), buffer);
                send( s , feedback , MAXRECV , 0 );
            }
free(buffer);
}

if (new_socket == INVALID_SOCKET)
{
    printf("accept failed with error code : %d" , WSAGetLastError());
    return 1;
}

closesocket(s);
WSACleanup();

return 0;

}

Answer 1

10057 - WSAENOTCONN -套接字未连接。

发送调用是正确的，并且它使用了new_socket。但是recv调用使用socket/sd "s“。recv调用也应该使用new_socket。

返回错误10057是因为s仅绑定到本地端点，而不与远程端连接，而由accept返回的新套接字连接到远程端。

Answer 2

   for (x = 0; buffer[x] != '\0'; x++) {
            if (buffer[x] == AmmtA || buffer[x] == AmmtB)
            count++;
}

为什么要将buffer[x]与0进行比较。缓冲区中的任何特定条目都应该为零没有特殊原因，这很容易从缓冲区的末尾读取。也许您认为buffer包含一个字符串。但它没有，它包含你从套接字读取的任何东西，并且它没有特殊的格式或终止符。

幸运的是，您确实知道读取的字节数。您将其存储在valread中，因此您需要：

   for (x = 0; x < valread; x++) {