Need a way to change the CHUNK_SIZE value at runtime.

Or am I using cpprest in the wrong way?

Our application normally transfers data (using HTTP GET) of several hundred megabytes, the default 64 Kb chunk size seems too small for optimal download rate. Changing the value to 5 Mb can reduce download time of 2 Gb data from 2minutes to 28 seconds.

The demo code, which just allocates the requested data in-memory and send them:

#include <Windows.h>
#include <cpprest/http_listener.h>
#include <cpprest/json.h>
#include <cpprest/streams.h>
#include <cpprest/filestream.h>
#include <cpprest/producerconsumerstream.h>
#include <algorithm>
#include <chrono>
#include <iostream>
#include <string>

using namespace concurrency::streams;
using namespace web;
using namespace http;
using namespace http::experimental::listener;

int main(int argc, char *argv[]) {

    http_listener listener(L"http://*:8080/bytes");

    listener.support(methods::GET, [](http_request &request) {

        auto q = web::uri::split_query(request.request_uri().query());

        // default: 100 MB of data
        std::size_t bytes_to_write = 100 * 1048576;

        if (q.find(L"b") != std::end(q)) {
            bytes_to_write = std::stoul(q[L"b"]);
        }
        if (q.find(L"kb") != std::end(q)) {
            bytes_to_write = std::stoul(q[L"kb"]) * 1024;
        }
        if (q.find(L"mb") != std::end(q)) {
            bytes_to_write = std::stoul(q[L"mb"]) * 1024 * 1024;
        }

        request.reply(status_codes::OK, std::string(bytes_to_write, '+'));
        std::cout << "Sent " << bytes_to_write << "bytes\n";
    });

    listener.open().wait();

    std::wcout << "Listening on " << listener.uri().port() << std::endl;

    while (true) {
        try {
            Sleep(1);
        }
        catch (...) {
            break;
        }
    }

    listener.close().wait();

    return 0;
}

And using curl for testing:

curl -o NUL http://localhost:8080/bytes?mb=2000

Using 64Kb chunk size:

[root@localhost ~]# curl -o NUL 10.50.10.51:8080/bytes?mb=2000
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 2000M  100 2000M    0     0  15.7M      0  0:02:06  0:02:06 --:--:-- 14.8M

Using 5Mb chunck size:

  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 2000M  100 2000M    0     0  69.2M      0  0:00:28  0:00:28 --:--:-- 77.1M