Question

I have a file transfer code written in C using windows sockets which seems to work but keeps transferring fewer than the desired number of bytes of the file.

Any ideas?

Send code:

while(!feof(fp))
{
   bzero(bufferin,256);
   fread(bufferin,sizeof(char),255,fp);
   send(remsock,bufferin,255,0);

   if(n < 0)
      error("ERROR writing to socket");
}
send(remsock,"done",255,0);

Accept code:

while(1)
{
    recv(sockfd,buffer,255,0);
    if(compare(buffer,"done") == 0)
        break;  
    fwrite(buffer,1,255,fplog);
}
printf("File Transfer complete\n\n");

Answer 1

As others have stated, you MUST look at the return values of all the functions you are calling, eg:

Sending:

while (!feof(fp))
{
    int nRead = fread(bufferin, sizeof(char), 256, fp);
    if (nRead <= 0)
        error("ERROR reading file");

    char *pBuf = bufferin;
    while (nRead > 0)
    {
        int nSent = send(remsock, pBuf, nRead, 0);
        if (nSent == SOCKET_ERROR)
        {
            if (WSAGetLastError() != WSAEWOULDBLOCK)
                error("ERROR writing to socket");

            fd_set writefd;
            FD_ZERO(&writefd);
            FD_SET(remsock, &writefd);

            if (select(0, NULL, &writefd, NULL, NULL) != 1)
                error("ERROR waiting to write to socket");

            continue;
        }

        if (nSent == 0)
            error("DISCONNECTED writing to socket");

        pBuf += nSent;
        nRead -= nSent;
    }
}

closesocket(remsock);

Receiving:

while(1)
{
    int nRecv = recv(sockfd, buffer, 256, 0);
    if (nRecv == SOCKET_ERROR)
    {
        if (WSAGetLastError() != WSAEWOULDBLOCK)
            error("ERROR reading from socket");

        fd_set readfd;
        FD_ZERO(&readfd);
        FD_SET(sockfd, &readfd);

        if (select(0, &readfd, NULL, NULL, NULL) != 1)
            error("ERROR waiting for data from socket");

        continue;
    }

    if (nRecv == 0)
        break;

    char *pBuf = buffer;
    while (nRecv > 0)
    {
        int nWritten = fwrite(pBuf, sizeof(char), nRecv, fplog);
        if (nWritten <= 0)
            error("ERROR writing to file");

        pBuf += nWritten;
        nRecv -= nWritten;
    }
}

printf("File Transfer complete\n\n");