Question

I’m writing a small networking program in C++. Among other things it has to download twitter profile pictures. I have a list (stl::vector) of URLs. And I think that my next step is to create for-loop and send GET messages through the socket and save the pictures to different png-files. The problem is when I send the very first message, receive the answer segments and save png-data all things seems to be fine. But right at the next iteration the same message, sent through the same socket, produces 0 received bytes by recv() function. I solved the problem by adding a socket creation code to the cycle body, but I’m a bit confused with the socket concepts. It looks like when I send the message, the socket should be closed and recreated again to send next message to the same server (in order to get next image). Is this a right way of socket’s networking programming or it is possible to receive several HTTP response messages through the same socket?

Thanks in advance.

UPD: Here is the code with the loop where I create a socket.

    // Get links from xml.
    ...
    // Load images in cycle.
    int i=0;
    for (i=0; i<imageLinks.size(); i++)
    {
        // New socket is returned from serverConnect. Why do we need to create new at each iteration?
        string srvAddr = "207.123.60.126";
        int socketImg = serverConnect(srvAddr);
        // Create a message.
        ...
        string message = "GET " + relativePart;
                message += " HTTP/1.1\r\n";
        message += "Host: " + hostPart + "\r\n";
        message += "\r\n";
        // Send a message.
        BufferArray tempImgBuffer = sendMessage(sockImg, message, false);
        fstream pFile;
        string name;
        // Form the name.
        ...
        pFile.open(name.c_str(), ios::app | ios::out | ios::in | ios::binary);
        // Write the file contents.
        ...
        pFile.close();
        // Close the socket.
        close(sockImg);
    }

Answer 1

The other side is closing the connection. That’s how HTTP/1.0 works. You can:

• Make a different connection for each HTTP GET
• Use HTTP/1.0 with the unofficial Connection: Keep-Alive
• Use HTTP/1.1. In HTTP 1.1 all connections are considered persistent unless declared otherwise.

Obligatory xkcd link Server Attention Span

Wiki HTTP

The original version of HTTP
(HTTP/1.0) was revised in HTTP/1.1.
HTTP/1.0 uses a separate connection to
the same server for every
request-response transaction, while
HTTP/1.1 can reuse a connection
multiple times