Add write_more to support mjpeg streaming

Created by: dsmyth

This was based on code found at https://github.com/aanon4/RobotVision -- they just pulled in Simple-Web-Server and modified it locally rather than pushing it back as a pull request.

MJPEG resource: // mjpeg stream resource server.resource["^/stream"]["GET"] = [this](std::shared_ptr<SimpleWeb::ServerSimpleWeb::HTTP::Response> response, std::shared_ptr<SimpleWeb::ServerSimpleWeb::HTTP::Request> request) { response->set_nodelay(); std::thread streamThread([this, response] { class MJPEG { public: static void send_image(RestServer* server, const std::shared_ptr<SimpleWeb::ServerSimpleWeb::HTTP::Response> &response) { std::unique_lockstd::mutex lk(server->streamMutex); server->streamCv.wait(lk); int size = (int)server->vJPEG.size(); response->write_more("--mjpegstream\r\n"); response->write_more("Content-Type: image/jpeg\r\n"); response->write_more(str(boost::format("Content-Length: %1%\r\n\r\n") % size)); response->write((const char*)server->vJPEG.data(), size); lk.unlock(); response->write_more("\r\n"); response->send(server, response { if (!ec) { send_image(server, response); } else { // Done if (server->active > 0) { server->active--; } } }); } }; SimpleWeb::CaseInsensitiveMultimap headers; headers.emplace("Content-Type", "multipart/x-mixed-replace;boundary=mjpegstream"); headers.emplace("Connection", "close"); headers.emplace("Cache-Control", "no-cache, no-store, max-age=0, must-revalidate"); headers.emplace("Content-Length", "-1"); response->write(SimpleWeb::StatusCode::success_ok, headers); active++; MJPEG::send_image(this, response); }); streamThread.detach(); };

and image update for openCV: class MJPEGServer { SimpleWeb::ServerSimpleWeb::HTTP server; std::mutex streamMutex; std::condition_variable streamCv; std::vector vJPEG; unsigned int active = 0;

void setStreamJPEG(cv::Mat &streamMat) { // only do the work if we are actively streaming if (active > 0 && streamMutex.try_lock()) { cv::imencode(".jpg", streamMat, vJPEG, std::vector()); streamCv.notify_all(); streamMutex.unlock(); } } }