c++ - 是什么导致 fprintf 出现 C++ 缓冲区溢出错误？

Question

我正在尝试使用 GoBackN 窗口在 C++ 中使用套接字和 UDP 设置客户端、路由器、服务器。我不确定为什么我在 Client::write_log() 中的 fprintf() 行收到缓冲区溢出错误。

主run()函数

void Client::run()
{
    srand ( time(NULL) );

    //socket data types
    SOCKET client_socket;   // Client socket
    SOCKADDR_IN sa_out;      // fill with server info, IP, port

    char buffer[RAWBUF_SIZE]; // Buffer

    WSADATA wsadata;                                    // WSA connection
    char router[11];                                    // Host data
    char cusername[128], filename[128], direction[3];   // Other header data
    DWORD dwusername = sizeof(cusername);               // Retains the size of the username
    char trace_data[128];

    FILE* logfile = fopen("client.log", "w");

    try 
    {
        if (WSAStartup(0x0202,&wsadata)!=0)
        {  
            throw "Error in starting WSAStartup";
        } 
        else 
        {

            /* Display the wsadata structure */
            cout<< endl
                << "wsadata.wVersion "       << wsadata.wVersion       << endl
                << "wsadata.wHighVersion "   << wsadata.wHighVersion   << endl
                << "wsadata.szDescription "  << wsadata.szDescription  << endl
                << "wsadata.szSystemStatus " << wsadata.szSystemStatus << endl
                << "wsadata.iMaxSockets "    << wsadata.iMaxSockets    << endl
                << "wsadata.iMaxUdpDg "      << wsadata.iMaxUdpDg      << endl << endl;
        }  

        client_socket = open_port(PEER_PORT2);

        prompt("Enter the router hostname: ",router);
        sa_out = prepare_peer_connection(router, ROUTER_PORT2);

        prompt("Enter a filename: ",filename);                  // Retrieve a filename from the client
        prompt("Direction of transfer [get|put]: ", direction);  // Retrieve a transfer direction

        // Make sure the direction is one of get or put
        if(!strcmp(direction,GET) || !strcmp(direction,PUT))
        { 
            // Retrieve the local user name
            GetUserName(cusername, &dwusername);

            int selected = rand() % 256;
            int received, verify;

            int client_num = 0; // Client packet number
            int server_num = 0; // Server packet number

            int progress = 0;
            int rcv;

            cout << "Starting packet ID negotiation..." << endl;

            while(1)
            {

                // Send a random number to the server
                if(progress < 1)
                {
                    memset(buffer, 0, sizeof(buffer));
                    sprintf(buffer,"RAND %d",selected);
                    cout << "Sending " << buffer << endl;

                    if((rcv = send_safe(client_socket, sa_out, buffer, RAWBUF_SIZE, 200)) == 201)
                    {
                        progress = 1;
                    }
                    else if(rcv != 200)
                    {
                        continue;
                    }

                    // Finally wait for a response from the server with the number
                    if(recv_safe(client_socket, sa_out, buffer, RAWBUF_SIZE, 100) == 100)
                    {
                        cout << "Received " << buffer << endl;
                        sscanf(buffer,"RAND %d %d",&verify,&received);
                    }
                    else 
                        continue;

                    progress = 1;
                }

                // Send acknowledgement to the server along with our random number
                memset(buffer, 0, sizeof(buffer));
                sprintf(buffer, "RAND %d", received);
                cout << "Sending " << buffer << endl;

                if(send_safe(client_socket, sa_out, buffer, RAWBUF_SIZE, 201) != 201)
                {
                    progress = 0;
                    continue;
                }

                break;
            }

            client_num = selected % WINDOW_SIZE + 1;
            server_num = received % WINDOW_SIZE + 1;

            cout << "Negotiated server start " << server_num << " and client start " << client_num << endl;

            sprintf(trace_data, "Negotiated srv %d and cli %d", server_num, client_num);
            write_log(logfile, cusername, trace_data);

            // Send client headers
            sprintf(buffer, HEADER, cusername, direction, filename); 
            while((rcv = send_safe(client_socket,sa_out,buffer,RAWBUF_SIZE,777)) != 777)
            {
                if(rcv == 101) 
                    break;
            }

            // Perform a get request
            if(!strcmp(direction,GET))
            {
                get(client_socket, sa_out, cusername, filename, client_num, server_num, logfile);

            }
            else if(!strcmp(direction,PUT))
            {
                put(client_socket, sa_out, cusername, filename, client_num, server_num, logfile);
            }
        }
        else
        {
            throw "The method you requested does not exist, use get or put";
        }

    }
    catch (const char *str) 
    {
        cerr << str << WSAGetLastError() << endl;
    }

    //close the client socket and clean up
    fclose(logfile);
    closesocket(client_socket);

    WSACleanup();      
}

PUT() 代码

void Client::put(SOCKET s, SOCKADDR_IN sa, char * username, char* filename, int client_num, int server_num, FILE* logfile)
{
    char window[FRAME_SIZE * WINDOW_SIZE];  // data retention window
    char buffer[FRAME_SIZE];                // send buffer
    int filesize;
    int size = 0, sent = 0;                 // Trace variables
    char tracebuf[128];

    FILE* send_file;
    fopen_s(&send_file, filename, "rb");

    if(send_file != NULL)
    {    
        // open the file

        // Determines the file size
        fseek(send_file, 0L, SEEK_END);
        filesize = ftell(send_file);
        fseek(send_file, 0L, SEEK_SET);

        //write filesize to logfile
        sprintf(tracebuf, "Filesize %d", filesize);
        write_log(logfile, username, tracebuf);

        //add file size to buffer
        strncpy_s(buffer, "SIZ", 3);
        memcpy(buffer + (3 * sizeof(char)), &filesize, sizeof(int));

        //if filesize was sent to server successfully
        if(send_safe(s,sa,buffer,FRAME_SIZE,101) == 101)
        {
            cout << "Sent filesize, starting transfer..." << endl;

            //reset buffer
            memset(buffer, 0, sizeof(buffer));

            int count = 0;
            int offset = 0;
            int frames_outstanding = 0; //for frames not ACKED
            int next = 0;
            bool resend = false;
            int packet_id;
            int pid_max = WINDOW_SIZE + 1;

            // Start sending the file
            while (1)
            {
                // If the acks mismatch with the current send offset and there are frames not ACKED, this has to be a resend
                if(next != offset && frames_outstanding > 0) 
                    resend = true;

                // Send as many frames as available for the given window size
                while((!feof(send_file) && frames_outstanding < WINDOW_SIZE) || resend)
                {
                    if(next == offset) 
                        resend = false;

                    if(!resend)
                    {
                        if(feof(send_file)) 
                            break;
                        fread(buffer,1,FRAME_SIZE,send_file);                       // Read the next block of data
                        memcpy(window + (offset * FRAME_SIZE), buffer, FRAME_SIZE); // Store the data in the local window
                        //memcpy(window, buffer, FRAME_SIZE); // Store the data in the local window
                        send_packet(s, sa, buffer, FRAME_SIZE, offset);             // Send the packet to peer
                        offset = (offset + 1) % pid_max;                        // Update the offset
                        frames_outstanding++;
                    }
                    else
                    {
                        // Resend by copying the data from the window
                        memcpy(buffer, window + (next * FRAME_SIZE), FRAME_SIZE);
                        send_packet(s, sa, buffer, FRAME_SIZE, next);

                        //log

                        sprintf(tracebuf, "Resending packet %d", next);
                        write_log(logfile, username, tracebuf);

                        next = (next + 1) % pid_max;
                    }
                }

                // Receive ACKs before continuing sending
                //while the # of unacked frames are greater than 0
                while(frames_outstanding > 0)
                {
                    //if packet id < 0
                    if((packet_id = recv_packet(s,sa,buffer,FRAME_SIZE,next)) < 0)
                    {
                        if(count < filesize) 
                            resend = true;

                        break;
                    }

                    // Receive acknowledgment from the client
                    if(!strncmp(buffer,"NAK", 3))
                    {
                        if(packet_id >= 0) 
                            next = packet_id;    // Set the next packet to the packet id
                        break;
                    }
                    else if(!strncmp(buffer,"ALL", 3))
                    {
                        frames_outstanding = 0;
                        break;
                    }

                    //log   
                    sprintf(tracebuf, "Sent %d bytes", count);
                    write_log(logfile, username, tracebuf);

                    memset(buffer, 0, sizeof(buffer));      // Zero the buffer

                    next = (next + 1) % pid_max;            // Update the next frame tracker
                    frames_outstanding--;                  // Another frame has been acked
                }

                if(feof(send_file) && frames_outstanding == 0) 
                    break; // Break when done reading the file and all frames are acked
            }

            cout << "File transfer completed" << endl;
            fclose(send_file);
        }
        else
        {           
            fclose(send_file);
            return put(s,sa,username,filename, client_num, server_num, logfile);
        }
    }
}

WRITE_LOG() 代码

void Client::write_log(FILE* logfile, char* username, char* message)
{   
    fprintf(logfile, "%s > %s\n", username, message);

    memset(message, 0, sizeof(message));
}

Answer 1

完全不确定您在这里实际打算做什么:

memset(message, 0, sizeof(message));

但它可能没有按照您的预期进行。 sizeof(message) 在现代系统中要么是 4，要么更可能是 8。因此，您正在向 message 写入 8 个零。首先可能不是 8 个字节长。

可能你想要:

memset(message, 0, strlen(message));

或:

message[0] = 0; 

(这会将字符串设置为“空”，但不会用零填充整个字符串)。