C++/WinRT Server-sent Events Implementation

winrt-sse.cpp

// These should be in pch.h
#include <winrt/Windows.Foundation.h>
#include <winrt/Windows.Foundation.Collections.h>
#include <winrt/Windows.Web.Http.h>
#include <winrt/Windows.Web.Http.Headers.h>
#include <winrt/Windows.Web.Http.Filters.h>
#include <winrt/Windows.Storage.Streams.h>
#include <iostream>

#include <Windows.h>
#include <synchapi.h>
#include <consoleapi.h>
#include <handleapi.h>
#include <processthreadsapi.h>

using namespace std;
using namespace winrt;
using namespace winrt::Windows::Web::Http;
using namespace winrt::Windows::Storage::Streams;
using namespace Windows::Foundation;

// Useful Readings:
// https://learn.microsoft.com/en-us/windows/uwp/cpp-and-winrt-apis/concurrency
// https://html.spec.whatwg.org/multipage/server-sent-events.html#event-stream-interpretation
// https://learn.microsoft.com/en-us/archive/msdn-magazine/2018/june/c-effective-async-with-coroutines-and-c-winrt

winrt::handle g_CtrlCHandle;

IAsyncAction ProcessEventStream(DataReader dataReader)
{
    // offload work onto the Windows thread pool
    // https://learn.microsoft.com/en-us/windows/uwp/cpp-and-winrt-apis/concurrency-2#offloading-work-onto-the-windows-thread-pool
    co_await resume_background();
    
    // nested cancellation pattern described in:
    // https://learn.microsoft.com/en-us/windows/uwp/cpp-and-winrt-apis/concurrency-2#register-a-cancellation-callback
    auto ct { co_await winrt::get_cancellation_token() };

    while (!ct())
    {
        DataReaderLoadOperation task = dataReader.LoadAsync(1024);

        ct.callback([=]() {
            task.Cancel();
        });

        co_await task;
        auto status = task.Status();
        if (status == AsyncStatus::Completed) {
            auto bytesRead = task.GetResults();
            hstring data = dataReader.ReadString(bytesRead);
            wcout << data.c_str();
        }
    }
}

IAsyncAction MainAsync()
{
    HttpClient httpClient{};
    Uri uri{ L"https://localhost:7238/sse" };

    // Set up the request per
    // https://html.spec.whatwg.org/multipage/server-sent-events.html
    HttpRequestMessage request{ HttpMethod::Get(), uri };
    request.Headers().Accept().ParseAdd(L"text/event-stream");
    request.Headers().CacheControl().ParseAdd(L"none");

    auto response{ co_await httpClient.SendRequestAsync(request, HttpCompletionOption::ResponseHeadersRead) };
    response.EnsureSuccessStatusCode();

    auto stream = co_await response.Content().ReadAsInputStreamAsync();

    DataReader dataReader{ stream };
    dataReader.UnicodeEncoding(UnicodeEncoding::Utf8);
    dataReader.InputStreamOptions(InputStreamOptions::Partial);

    auto task = ProcessEventStream(dataReader);

    // Run until ctrl-c is pressed
    co_await resume_on_signal(g_CtrlCHandle.get());
    task.Cancel();
}

int main()
{
    init_apartment();

    g_CtrlCHandle = winrt::handle{ ::CreateEvent(nullptr, true, false, nullptr) };

    winrt::check_bool(SetConsoleCtrlHandler([](DWORD ctrlType) -> BOOL {
        if (ctrlType == CTRL_C_EVENT)
        {
            cout << "Ctrl-C Received" << endl;
            ::SetEvent(g_CtrlCHandle.get());
            return TRUE;
        }
        return FALSE;
    }, true));

    MainAsync().get();
    return 0;
}