Sending files over TCP using C++, recving wrong size

问题

I am very new to socket programming, and i am trying to send over TCP connection but getting few errors.

here is my code

        FILE* File;
        char* Buffer;
        unsigned long Size;

        File = fopen("C:\\test.zip", "rb");
        if (!File)
        {
            printf("Error while readaing the file\n");
            return;
        }
        // file size 1
        fseek(File, 0, SEEK_END);
        Size = ftell(File);
        fseek(File, 0, SEEK_SET);


        Buffer = new char[Size]; 

        fread(Buffer, Size, 1, File);
        char cSize[MAX_PATH];
        sprintf(cSize, "%i", Size);

        cout << "MAX PATH " << MAX_PATH<<endl;
        cout << "cSize: " << cSize << endl;
        fclose(File);

` So this to find the size of my file. most of the code i am trying it out from other questions in here but it didnt solve my problem. ' my send and recv:

unsigned long filechunk = 1025;

unsigned long byteSent = 0;
unsigned long bytesToSend = 0;

send(Sub, cSize, MAX_PATH, 0); // File size to client

while (byteSent < Size) {

    if ((Size - byteSent) >= filechunk) {
        bytesToSend = filechunk;
    }
    else {
        bytesToSend = Size - byteSent;
    }
    if (send(Sub, Buffer + byteSent, bytesToSend, 0)) {
        std::cout << "Sent: ";
    }
    byteSent += bytesToSend;
    std::cout << "Size : "<<Size<<"    BytesSent : "<<byteSent<<"   Bytes to send: " << bytesToSend << std::endl;
    system("pause");

on the client side:

int Size;
char* Filesize = new char[5000000]; // is there a better way? my sfiles size are unknown but at least 50mb

if (recv(Socket, Filesize, 5000000, 0)) // File size
{
    Size = atoi((const char*)Filesize);
    printf("File size: %d\n", Size);
}

char* Buffer = new char[Size];
FILE* File;
File = fopen("test.zip", "wb"); //start copying from the server, creating the file first.
std::string convert;
long conv;

std::cout << "Size: " << Size << std::endl;

int total=Size;
int byteRecv = 0;
int recvCheck;
int bytes = 1025;

//getting the file
while (byteRecv < Size ) {

    recvCheck = recv(Socket, Buffer, bytes, 0);
    if (recvCheck >0) // File
    {
        fwrite(Buffer, 1, byteRecv, File);

        std::cout << "Recieved:" << byteRecv << std::endl;

        Size -= byteRecv;
        byteRecv += byteRecv;
        std::cout << "Error: " << WSAGetLastError();
    }
    else {
        std::cout << "Error: " << WSAGetLastError();
        total += 1; // the loop often get into infinit loop so i force it in case of this error.
        if (total > 3) {
            break;
        }
    }
}
fclose(File);

So, i know it is not very efficient and i am not sure if there are similar questions as i have been digging in here for a few weeks now.

-is there a better way i can make a char*[]? as i dont know the size of the files i want to send yet. - does ftell() and sifeof() work the same way? -when i check for the size i recved from the server it is alays wrong. Ex: server file: 32633513, recv size: 3263 -most of the code i have taken from other problems and combined it. if you see anything that is not needed do tell me so i take notes of that.

回答1:

There is a lot of wrong things but that may correct your problem at first:

On the client side replace (your are both decrementing the total count of bytes and the received ones with the wrong value):

Size -= byteRecv;
byteRecv += byteRecv;

with:

byteRecv += recvCheck; // actualizes the count of received bytes

The other problem is your buffer size. Never try to get an entire file in memory, this is nonsense in general; files are usually managed chunks by chunks. As you are reading at most 1025 bytes in each loop, then only use a buffer of size 1025, you don't need more. Same for reading and writing...

来源：https://stackoverflow.com/questions/61246287/sending-files-over-tcp-using-c-recving-wrong-size

标签

c++

file

websocket

tcp

transfer