How can i create a istream from a uint8_t vector?

Question

I am in the process of adding the ability to get data over the network to code that used to only read local files. The network library I am using sends and receives data in the form of a vector<uint8_t>. I'd like to be able to reuse the code that processes the data after reading the file, but that code expects a std::istream, is there a way to have an istream read the vector data? It's the same data so I feel like there should be a way, but i haven't been able to find or figure out code for how to do it.

current code:

    std::ifstream stream("data.img", std::ios::in | std::ios::binary | std::ios::ate);

    if (!stream.is_open())
    {
        throw std::invalid_argument("Could not open file.");
    }
    // the arg for processData is std::istream
    processData(stream);

network framework:

    vector<uint8_t> data = networkMessage.data;

    // need some way to create istream from data
    std::istream stream = ?

    processData(stream);
    stream.close();

Is there a way to do this, or am I barking up the wrong tree?

Answer 1

Well C++ does actually have a class for this - istrstream, and you could use it like this:

    vector<uint8_t> data = ...;

    // need some way to create istream from data
    std::istrstream stream(reinterpret_cast<const char*>(data.data()), data.size());

    processData(stream);

As far as I can tell this doesn't copy the data, unlike the other answers. However it was also deprecated in C++98 because it's hard to know who is responsible for freeing the buffer, so you may want to write your own equivalent.

Answer 2

std::basic_istream gets its data from an associated std::basic_streambuf derived class. The STL provides such classes for file I/O and string I/O, but not for memory I/O or network I/O.

You could easily write (or find a 3rd party) memory-based streambuf class that uses the std::vector as its underlying buffer, and then you can construct an std::istream that uses that memory streambuf. For example (using the imemstream class from this answer):

std::vector<uint8_t> &data = networkMessage.data;
imemstream stream(reinterpret_cast<const char*>(data.data()), data.size());
processData(stream);