Question

I’m trying to split up data into little packets. I’m not exactly sure how this read method is suppose to work but I’ve given a buffer size of 512 to read from the file.
But instead of getting 512 i just get 5 in my first packet. Others vary from 0 to above 512 ( which shouldn’t happen).

It’s a zip file I’m trying to split up:
In text the first few bytes look like this

(de bucket like characters are actually 2 characters)

It seems to grab the first 5 bytes as it should but afterwards just stops and goes to the next read block.

Since it’s a buffer of 512 everything after the first 5 bytes is garbage.
I’m using an ifstream. And the mode is set to Binary.

Any suggestions?

void FileProcessor::send()
{
    //If no file is opened return
    if(!_file.is_open()) return;
    //Reset position to beginning
    _file.seekg(0, ios::beg);

    //Result buffer
    char * buffer;
    char * partBytes = new char[_bufferSize];

    //Read the file and send it over the network
    while (_file.read(partBytes, _bufferSize))
    {

        buffer = Packet::create(Packet::FILE,partBytes);
        Packet *p = Packet::create(buffer);
        //cout <<  strlen(partBytes);
        //p->PrintHex(buffer,_bufferSize+Packet::HeaderSize);

        //break;
        cout << "Normal size : \t" << strlen(partBytes)<< "\tPacketSize: \t" << p->getLength()<<"\n";
        //cout << strcmp(p->getData().c_str(),partBytes) << "\n";
        writeToFile(p->getData().c_str(),p->getData().length());
        delete p;
    }
    //Write final bytes if any
    if(_file.gcount())
    {
        //writeToFile(partBytes, _file.gcount());


        buffer = Packet::create(Packet::FILE,partBytes);
        Packet *p = Packet::create(buffer);

        writeToFile(p->getData().c_str(),p->getData().length());
        //cout << p->getLength() << "\n";
        delete p;

    }   

    //cout<< *p << "\n";
    delete [] partBytes;
}

Im just testing a direct read write right now.

Answer 1

Inside your loop, instead of assuming it always reads a full buffer of data, use gcount() to find how many it actually read, and transmit that many.

I feel obliged to add that this:

    buffer = Packet::create(Packet::FILE,partBytes);
    Packet *p = Packet::create(buffer);

looks quite strange to me. Not sure it’s wrong, but it’s not immediately obvious that it’s right either (and if it is right, the design seems a bit odd).

I’d also skip the dynamic allocation and deletion:

char * partBytes = new char[_bufferSize];
// ...
delete [] partBytes;

and use a std::vector<char> instead.