在winsock中接收奇怪的字符/符号

Question

我正在学习Winsock和我在发送和接收一个简单的字符串时遇到一个奇怪的问题.这是我的代码(纯C):

客户:

//...
//Declarations and stuff

//----------- SEND SOME DATA -------------------------------------------------

    char string1[] = "string-1";
    int bytes_sent = 0;

    bytes_sent = send(client_socket, string1, strlen(string1), 0);  

    printf("BYTES SENT: %i\n", bytes_sent);
    printf("\n-----------------------------------------------\n\n");

    system("pause");

//...

服务器:

//...
//Declarations and stuff

//----------- START LISTENING FOR REQUESTS ------------------------------------

    SOCKET ClientSocket;

    #define BUFFER_SIZE 256

    int size;
    struct sockaddr_in client_info;
    char client_ip[16];
    char data_received[BUFFER_SIZE];    
    int bytes_received = 0; 

    listen(ListenSocket, SOMAXCONN);

    while(1){           

        ClientSocket = accept(ListenSocket, (struct sockaddr *)&client_info, &size);        
        strcpy(client_ip, inet_ntoa(client_info.sin_addr));     

        do{

            bytes_received = recv(ClientSocket, data_received, BUFFER_SIZE, 0);

            if(bytes_received > 0){
                printf("DATA RECEIVED FROM %s: %s (%i bytes)\n", client_ip, data_received, bytes_received);
            }


        }while(bytes_received > 0);

        printf("\n-----------------------------------------------\n\n");


    }

//...

问题是服务器打印我的字符串+一些奇怪的符号(见图).

奇怪的符号

我正在使用流套接字.这个例子非常简单,所以我不知道什么是错的.如果我随机修改字符串或服务器的缓冲区大小,或两者兼而有之,问题就会消失(服务器打印OK字符串).问题修复如果在send()调用中我使用sizeof()而不是strlen().我有点迷失在这里.如果我错过了什么,请善待,这是我在这里的第一篇文章.我可以提供整个代码(它基本上是winsock start和socket定义).

Answer 1

您发送的数据不包含终止空字符:

bytes_sent = send(client_socket, string1, strlen(string1), 0);

...因为strlen不计算终止空值.这本身并不是问题,而是与接收方的事实相结合:

char data_received[BUFFER_SIZE];
// ...
bytes_received = recv(ClientSocket, data_received, BUFFER_SIZE, 0);

data_received未初始化,您可以接收最多BUFFER_SIZE字节.这意味着,因为您发送的数据不是以空值终止的:

• 如果bytes_received < BUFFER_SIZE,其余部分data_received 可能未初始化,因此访问/打印将是未定义的行为.它实际上并非100%明确,因为文档说:

  [...]调用recv将返回当前可用的数据 - 达到指定缓冲区的大小[...]

  ...所以这可能意味着缓冲区的其余部分保持不变.

• 如果bytes_received == BUFFER_SIZE没有null-terminator,那么printf将通过尝试打印它来调用未定义的行为,因为它不知道字符串停止的位置并将超出数组.

解决这些问题的最简单方法是发送空终止符:

bytes_sent = send(client_socket, string1, strlen(string1)+1, 0); // +1 here
bytes_sent = send(client_socket, string1, sizeof(string1), 0);   // same as above

...或者接收较少的字节并将null终止符放在接收大小上:

bytes_received = recv(ClientSocket, data_received, BUFFER_SIZE-1, 0); // -1 here
data_received[bytes_received] = 0;

我亲自去第一个.