beats-server/src/websockets.h

#include <iostream>
#include <string>
#include <memory>
#include <functional>
#include <stdexcept>

#include <syslog.h>
#include <getopt.h>
#include <signal.h>
#include <string.h>

#include <lib/libwebsockets.h>

namespace websockets {
	// Will be caught in the callback and program will continue to run (but connection will be closed)
	struct runtime_error : public std::runtime_error {
		int return_value;

		runtime_error(const char * message, int return_value = -1)
		: std::runtime_error(message)
		, return_value(return_value)
		{}
	};

	// Will never be caught (by us), and hence things will terminate
	struct fatal_error : public std::runtime_error {
		fatal_error(const char * message)
		: std::runtime_error(message)
		{}
	};

	struct Log {
		Log(std::string const & name, int syslog_options, int debug_level){
			setlogmask(LOG_UPTO (LOG_DEBUG));
			openlog(name.c_str(), syslog_options, LOG_DAEMON);
			lws_set_log_level(debug_level, lwsl_emit_syslog);
		}

		#define log_function(nice_name, lwsl_name)\
		template <typename... T>\
		void nice_name(std::string const & format, T... args){\
			lwsl_name(format.c_str(), args...);\
		}

		log_function(notice, lwsl_notice)
		log_function(error, lwsl_err)
		log_function(warning, lwsl_warn)
		log_function(debug, lwsl_debug)

		#undef log_function

		~Log(){
			closelog();
		}
	};

	// Basic wrapper for the context pointer
	struct Context {
		std::unique_ptr<libwebsocket_context, decltype(libwebsocket_context_destroy)*> context;

		Context(lws_context_creation_info& info)
		: context(libwebsocket_create_context(&info), &libwebsocket_context_destroy)
		{
			if(context == nullptr){
				lwsl_err("libwebsocket init failed\n");
				throw std::runtime_error("libwebsocket init failed");
			}
		}

		libwebsocket_context const * get_raw() const {
			return context.get();
		}

		libwebsocket_context * get_raw() {
			return context.get();
		}
	};

	// Basic protocol to extend, already casts the void* to the actual type
	template <typename T>
	struct Protocol	{
		typedef T user_type;
		int callback(libwebsocket_context *context, libwebsocket *wsi, libwebsocket_callback_reasons reason, void *user, void *in, size_t len){
			return call(*context, *wsi, reason, *static_cast<T*>(user), in, len);
		}
		virtual int call(libwebsocket_context& context, libwebsocket& wsi, libwebsocket_callback_reasons reason, T& user, void *in, size_t len){
			return 0;
		};
	};

	struct basic_websocket_info{
		libwebsocket_context* context{nullptr};
		libwebsocket* wsi{nullptr};
		basic_websocket_info(libwebsocket_context* context, libwebsocket* wsi)
		: context(context)
		, wsi(wsi)
		{}
	};

	// 4-function Protocol, provide functions to handle establishment, closing, receiving and writing (follows receiving)
	// To let the callback return something non-zero (in case of error), use websockets::runtime_error
	// Only types with no-arg ctor are allowed (uses placement new, because libwebsockets allocates for us)
	template <typename T>
	struct TestProtocol {
		typedef T user_type;

		std::function<void(user_type&, basic_websocket_info)> establish_func;
		std::function<void(user_type&, basic_websocket_info)> close_func;
		std::function<std::string(user_type&, basic_websocket_info)> write_func;
		std::function<void(user_type&, std::string, basic_websocket_info)> receive_func;

		bool verbose{false};

		TestProtocol(decltype(establish_func) establish_func, decltype(close_func) close_func, decltype(write_func) write_func, decltype(receive_func) receive_func)
		: establish_func(establish_func)
		, close_func(close_func)
		, write_func(write_func)
		, receive_func(receive_func)
		{}

		int callback(libwebsocket_context* context, libwebsocket* wsi, libwebsocket_callback_reasons reason, void* user_ptr, void *in, size_t len){
			user_type& user = *static_cast<user_type*>(user_ptr);
			basic_websocket_info binfo{context, wsi};
			try{
				switch (reason) {
					case LWS_CALLBACK_ESTABLISHED:
						lwsl_notice("Connection established (%p, %p)\n", this, user_ptr);
						new (user_ptr) user_type();
						establish_func(user, binfo);
						break;
					case LWS_CALLBACK_CLOSED:
						lwsl_notice("Connection closed (%p, %p)\n", this, user_ptr);
						user.~user_type();
						close_func(user, binfo);
						break;
					case LWS_CALLBACK_SERVER_WRITEABLE:{
						std::string string_to_send = write_func(user, binfo);
						if(verbose) std::cout << string_to_send << std::endl;
						// we need the extra bytes padding on both sides :(
						unsigned char * buf = new unsigned char [LWS_SEND_BUFFER_PRE_PADDING + string_to_send.size() + LWS_SEND_BUFFER_POST_PADDING];
						memcpy(&buf[LWS_SEND_BUFFER_PRE_PADDING], string_to_send.c_str(), string_to_send.size());
						int n = libwebsocket_write(wsi, &buf[LWS_SEND_BUFFER_PRE_PADDING], string_to_send.size(), LWS_WRITE_TEXT);
						if (n < 0) throw runtime_error("Could not write", 1);
						if (n < string_to_send.size()) throw runtime_error("Partial write", -1);
						break;
					}
					case LWS_CALLBACK_RECEIVE:
						receive_func(user, std::string((char*)in, len), binfo);
						libwebsocket_callback_on_writable(context, wsi);
						break;
					default:
						break;
				}
			} catch(runtime_error& e){
				lwsl_err("Exception thrown: %s", e.what());
				return e.return_value;
			}
			return 0;
		}
	};


// Some wrappers to easily create the list of protocols from structs of above kind.
#define WSprotocol_callback(protocol)\
[](libwebsocket_context *context, libwebsocket *wsi, libwebsocket_callback_reasons reason, void *user, void *in, size_t len)\
{return protocol.callback(context, wsi, reason, user, in, len);}

#define WSstandard_protocol(name, protocol)\
{ name, WSprotocol_callback(protocol), sizeof(decltype(protocol)::user_type) }

	int default_main(int argc, char **argv, libwebsocket_protocols* protocols, std::function<void()> runloop_callback = nullptr);

} // namespace websockets