ustreamer/src/http.c

/*****************************************************************************
#                                                                            #
#    uStreamer - Lightweight and fast MJPG-HTTP streamer.                    #
#                                                                            #
#    Copyright (C) 2018  Maxim Devaev <mdevaev@gmail.com>                    #
#                                                                            #
#    This program is free software: you can redistribute it and/or modify    #
#    it under the terms of the GNU General Public License as published by    #
#    the Free Software Foundation, either version 3 of the License, or       #
#    (at your option) any later version.                                     #
#                                                                            #
#    This program is distributed in the hope that it will be useful,         #
#    but WITHOUT ANY WARRANTY; without even the implied warranty of          #
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the           #
#    GNU General Public License for more details.                            #
#                                                                            #
#    You should have received a copy of the GNU General Public License       #
#    along with this program.  If not, see <https://www.gnu.org/licenses/>.  #
#                                                                            #
*****************************************************************************/


#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <strings.h>
#include <unistd.h>
#include <fcntl.h>
#include <assert.h>

#include <sys/socket.h>
#include <sys/un.h>
#include <sys/stat.h>

#include <event2/event.h>
#include <event2/thread.h>
#include <event2/http.h>
#include <event2/buffer.h>
#include <event2/bufferevent.h>
#include <event2/keyvalq_struct.h>

#include <uuid/uuid.h>

#ifndef EVTHREAD_USE_PTHREADS_IMPLEMENTED
#	error Required libevent-pthreads support
#endif

#include "tools.h"
#include "logging.h"
#include "encoder.h"
#include "stream.h"
#include "http.h"

#include "data/index_html.h"
#include "data/blank_jpeg.h"


static bool _http_get_param_true(struct evkeyvalq *params, const char *key);
static char *_http_get_param_uri(struct evkeyvalq *params, const char *key);

static void _http_callback_root(struct evhttp_request *request, void *arg);
static void _http_callback_state(struct evhttp_request *request, void *v_server);
static void _http_callback_snapshot(struct evhttp_request *request, void *v_server);

static void _http_callback_stream(struct evhttp_request *request, void *v_server);
static void _http_callback_stream_write(struct bufferevent *buf_event, void *v_ctx);
static void _http_callback_stream_error(struct bufferevent *buf_event, short what, void *v_ctx);

static void _http_exposed_refresh(int fd, short event, void *v_server);
static void _http_queue_send_stream(struct http_server_t *server, bool stream_updated, bool picture_updated);

static bool _expose_new_picture(struct http_server_t *server);
static bool _expose_blank_picture(struct http_server_t *server);


struct http_server_t *http_server_init(struct stream_t *stream) {
	struct http_server_runtime_t *run;
	struct http_server_t *server;
	struct exposed_t *exposed;

	A_CALLOC(exposed, 1);

	A_CALLOC(run, 1);
	run->stream = stream;
	run->exposed = exposed;
	run->drop_same_frames_blank = 10;

	A_CALLOC(server, 1);
	server->host = "127.0.0.1";
	server->port = 8080;
	server->timeout = 10;
	server->run = run;

	_expose_blank_picture(server);

	assert(!evthread_use_pthreads());
	assert((run->base = event_base_new()));
	assert((run->http = evhttp_new(run->base)));
	evhttp_set_allowed_methods(run->http, EVHTTP_REQ_GET|EVHTTP_REQ_HEAD);

	assert(!evhttp_set_cb(run->http, "/", _http_callback_root, NULL));
	assert(!evhttp_set_cb(run->http, "/state", _http_callback_state, (void *)server));
	assert(!evhttp_set_cb(run->http, "/snapshot", _http_callback_snapshot, (void *)server));
	assert(!evhttp_set_cb(run->http, "/stream", _http_callback_stream, (void *)server));

	return server;
}

void http_server_destroy(struct http_server_t *server) {
	if (server->run->refresh) {
		event_del(server->run->refresh);
		event_free(server->run->refresh);
	}

	evhttp_free(server->run->http);
	if (server->run->unix_fd) {
		close(server->run->unix_fd);
	}
	event_base_free(server->run->base);
	libevent_global_shutdown();

	for (struct stream_client_t *client = server->run->stream_clients; client != NULL;) {
		struct stream_client_t *next = client->next;

		free(client->key);
		free(client);
		client = next;
	}

	free(server->run->exposed->picture.data);
	free(server->run->exposed);
	free(server->run);
	free(server);
}

int http_server_listen(struct http_server_t *server) {
	struct timeval refresh_interval;

	refresh_interval.tv_sec = 0;
	if (server->run->stream->dev->desired_fps > 0) {
		refresh_interval.tv_usec = 1000000 / (server->run->stream->dev->desired_fps * 2);
	} else {
		refresh_interval.tv_usec = 16000; // ~60fps
	}
	assert((server->run->refresh = event_new(server->run->base, -1, EV_PERSIST, _http_exposed_refresh, server)));
	assert(!event_add(server->run->refresh, &refresh_interval));

	server->run->drop_same_frames_blank = max_u(server->drop_same_frames, server->run->drop_same_frames_blank);

	evhttp_set_timeout(server->run->http, server->timeout);

	if (server->unix_path) {
		struct sockaddr_un unix_addr;
		int unix_fd_flags;

		LOG_DEBUG("Binding HTTP to UNIX socket '%s' ...", server->unix_path);

		assert((server->run->unix_fd = socket(AF_UNIX, SOCK_STREAM, 0)));
		assert((unix_fd_flags = fcntl(server->run->unix_fd, F_GETFL)) >= 0);
		unix_fd_flags |= O_NONBLOCK;
		assert(fcntl(server->run->unix_fd, F_SETFL, unix_fd_flags) >= 0);

		strncpy(unix_addr.sun_path, server->unix_path, 107);
		unix_addr.sun_path[107] = '\0';
		unix_addr.sun_family = AF_UNIX;

		if (server->unix_rm && unlink(server->unix_path) < 0) {
			if (errno != ENOENT) {
				LOG_PERROR("Can't remove old UNIX socket '%s'", server->unix_path);
				return -1;
			}
		}
		if (bind(server->run->unix_fd, (struct sockaddr *)&unix_addr, sizeof(struct sockaddr_un)) < 0) {
			LOG_PERROR("Can't bind HTTP to UNIX socket '%s'", server->unix_path);
			return -1;
		}
		if (server->unix_mode && chmod(server->unix_path, server->unix_mode) < 0) {
			LOG_PERROR("Can't set permissions %o to UNIX socket '%s'", server->unix_mode, server->unix_path);
			return -1;
		}
		if (listen(server->run->unix_fd, 128) < 0) {
			LOG_PERROR("Can't listen UNIX socket '%s'", server->unix_path);
			return -1;
		}
		if (evhttp_accept_socket(server->run->http, server->run->unix_fd) < 0) {
			LOG_PERROR("Can't evhttp_accept_socket() UNIX socket '%s'", server->unix_path);
			return -1;
		}

		LOG_INFO("Listening HTTP on UNIX socket '%s'", server->unix_path);

	} else {
		LOG_DEBUG("Binding HTTP to [%s]:%u ...", server->host, server->port);
		if (evhttp_bind_socket(server->run->http, server->host, server->port) < 0) {
			LOG_PERROR("Can't bind HTTP on [%s]:%u", server->host, server->port)
			return -1;
		}
		LOG_INFO("Listening HTTP on [%s]:%u", server->host, server->port);
	}

	return 0;
}

void http_server_loop(struct http_server_t *server) {
	LOG_INFO("Starting HTTP eventloop ...");
	event_base_dispatch(server->run->base);
	LOG_INFO("HTTP eventloop stopped");
}

void http_server_loop_break(struct http_server_t *server) {
	event_base_loopbreak(server->run->base);
}


static bool _http_get_param_true(struct evkeyvalq *params, const char *key) {
	const char *value_str;

	if ((value_str = evhttp_find_header(params, key)) != NULL) {
		if (!strcasecmp(value_str, "true") || !strcasecmp(value_str, "yes") || value_str[0] == '1') {
			return true;
		}
	}
	return false;
}

static char *_http_get_param_uri(struct evkeyvalq *params, const char *key) {
	const char *value_str;

	if ((value_str = evhttp_find_header(params, key)) != NULL) {
		return evhttp_encode_uri(value_str);
	}
	return NULL;
}

#define ADD_HEADER(_key, _value) \
	assert(!evhttp_add_header(evhttp_request_get_output_headers(request), _key, _value))

#define PROCESS_HEAD_REQUEST { \
		if (evhttp_request_get_command(request) == EVHTTP_REQ_HEAD) { \
			evhttp_send_reply(request, HTTP_OK, "OK", NULL); \
			return; \
		} \
	}

static void _http_callback_root(struct evhttp_request *request, UNUSED void *arg) {
	struct evbuffer *buf;

	PROCESS_HEAD_REQUEST;

	assert((buf = evbuffer_new()));
	assert(evbuffer_add_printf(buf, "%s", HTML_INDEX_PAGE));
	ADD_HEADER("Content-Type", "text/html");
	evhttp_send_reply(request, HTTP_OK, "OK", buf);
	evbuffer_free(buf);
}

static void _http_callback_state(struct evhttp_request *request, void *v_server) {
	struct http_server_t *server = (struct http_server_t *)v_server;
	struct evbuffer *buf;
	enum encoder_type_t encoder_run_type;
	unsigned encoder_run_quality;

	PROCESS_HEAD_REQUEST;

#	define ENCODER(_next) server->run->stream->encoder->_next

	A_PTHREAD_M_LOCK(&ENCODER(run->mutex));
	encoder_run_type = ENCODER(run->type);
	encoder_run_quality = ENCODER(run->quality);
	A_PTHREAD_M_UNLOCK(&ENCODER(run->mutex));

	assert((buf = evbuffer_new()));

	assert(evbuffer_add_printf(buf,
		"{\"ok\": true, \"result\": {"
		" \"encoder\": {\"type\": \"%s\", \"quality\": %u},"
		" \"source\": {\"resolution\": {\"width\": %u, \"height\": %u},"
		" \"online\": %s, \"desired_fps\": %u, \"captured_fps\": %u},"
		" \"stream\": {\"queued_fps\": %u, \"clients\": %u, \"clients_stat\": {",
		encoder_type_to_string(encoder_run_type),
		encoder_run_quality,
		(server->fake_width ? server->fake_width : server->run->exposed->width),
		(server->fake_height ? server->fake_height : server->run->exposed->height),
		bool_to_string(server->run->exposed->online),
		server->run->stream->dev->desired_fps,
		server->run->exposed->captured_fps,
		server->run->exposed->queued_fps,
		server->run->stream_clients_count
	));

#	undef ENCODER

	for (struct stream_client_t * client = server->run->stream_clients; client != NULL; client = client->next) {
		assert(evbuffer_add_printf(buf,
			"\"%s\": {\"fps\": %u, \"extra_headers\": %s, \"advance_headers\": %s, \"dual_final_frames\": %s}%s",
			client->id,
			client->fps,
			bool_to_string(client->extra_headers),
			bool_to_string(client->advance_headers),
			bool_to_string(client->dual_final_frames),
			(client->next ? ", " : "")
		));
	}

	assert(evbuffer_add_printf(buf, "}}}}"));

	ADD_HEADER("Content-Type", "application/json");
	evhttp_send_reply(request, HTTP_OK, "OK", buf);
	evbuffer_free(buf);
}

static void _http_callback_snapshot(struct evhttp_request *request, void *v_server) {
	struct http_server_t *server = (struct http_server_t *)v_server;
	struct evbuffer *buf;
	char header_buf[64];

	PROCESS_HEAD_REQUEST;

#	define EXPOSED(_next) server->run->exposed->_next

	assert((buf = evbuffer_new()));
	assert(!evbuffer_add(buf, (const void *)EXPOSED(picture.data), EXPOSED(picture.size)));

	ADD_HEADER("Access-Control-Allow-Origin:", "*");
	ADD_HEADER("Cache-Control", "no-store, no-cache, must-revalidate, proxy-revalidate, pre-check=0, post-check=0, max-age=0");
	ADD_HEADER("Pragma", "no-cache");
	ADD_HEADER("Expires", "Mon, 3 Jan 2000 12:34:56 GMT");

#	define ADD_TIME_HEADER(_key, _value) \
		{ sprintf(header_buf, "%.06Lf", _value); ADD_HEADER(_key, header_buf); }

#	define ADD_UNSIGNED_HEADER(_key, _value) \
		{ sprintf(header_buf, "%u", _value); ADD_HEADER(_key, header_buf); }

	ADD_TIME_HEADER("X-Timestamp", get_now_real());

	ADD_HEADER("X-UStreamer-Online",					bool_to_string(EXPOSED(online)));
	ADD_UNSIGNED_HEADER("X-UStreamer-Dropped",			EXPOSED(dropped));
	ADD_UNSIGNED_HEADER("X-UStreamer-Width",			EXPOSED(width));
	ADD_UNSIGNED_HEADER("X-UStreamer-Height",			EXPOSED(height));
	ADD_TIME_HEADER("X-UStreamer-Grab-Time",			EXPOSED(picture.grab_time));
	ADD_TIME_HEADER("X-UStreamer-Encode-Begin-Time",	EXPOSED(picture.encode_begin_time));
	ADD_TIME_HEADER("X-UStreamer-Encode-End-Time",		EXPOSED(picture.encode_end_time));
	ADD_TIME_HEADER("X-UStreamer-Expose-Begin-Time",	EXPOSED(expose_begin_time));
	ADD_TIME_HEADER("X-UStreamer-Expose-Cmp-Time",		EXPOSED(expose_cmp_time));
	ADD_TIME_HEADER("X-UStreamer-Expose-End-Time",		EXPOSED(expose_end_time));
	ADD_TIME_HEADER("X-UStreamer-Send-Time",			get_now_monotonic());

#	undef ADD_UNSUGNED_HEADER
#	undef ADD_TIME_HEADER

	ADD_HEADER("Content-Type", "image/jpeg");

	evhttp_send_reply(request, HTTP_OK, "OK", buf);
	evbuffer_free(buf);

#	undef EXPOSED
}

#undef ADD_HEADER

static void _http_callback_stream(struct evhttp_request *request, void *v_server) {
	// https://github.com/libevent/libevent/blob/29cc8386a2f7911eaa9336692a2c5544d8b4734f/http.c#L2814
	// https://github.com/libevent/libevent/blob/29cc8386a2f7911eaa9336692a2c5544d8b4734f/http.c#L2789
	// https://github.com/libevent/libevent/blob/29cc8386a2f7911eaa9336692a2c5544d8b4734f/http.c#L362
	// https://github.com/libevent/libevent/blob/29cc8386a2f7911eaa9336692a2c5544d8b4734f/http.c#L791
	// https://github.com/libevent/libevent/blob/29cc8386a2f7911eaa9336692a2c5544d8b4734f/http.c#L1458

	struct http_server_t *server = (struct http_server_t *)v_server;
	struct evhttp_connection *conn;
	struct evkeyvalq params;
	struct bufferevent *buf_event;
	struct stream_client_t *client;
	char *client_addr;
	unsigned short client_port;
	uuid_t uuid;

	PROCESS_HEAD_REQUEST;

	conn = evhttp_request_get_connection(request);
	if (conn != NULL) {
		A_CALLOC(client, 1);
		client->server = server;
		client->request = request;
		client->need_initial = true;
		client->need_first_frame = true;

		evhttp_parse_query(evhttp_request_get_uri(request), &params);
		client->key = _http_get_param_uri(&params, "key");
		client->extra_headers = _http_get_param_true(&params, "extra_headers");
		client->advance_headers = _http_get_param_true(&params, "advance_headers");
		client->dual_final_frames = _http_get_param_true(&params, "dual_final_frames");
		evhttp_clear_headers(&params);

		uuid_generate(uuid);
		uuid_unparse_lower(uuid, client->id);

		if (server->run->stream_clients == NULL) {
			server->run->stream_clients = client;
		} else {
			struct stream_client_t *last = server->run->stream_clients;

			for (; last->next != NULL; last = last->next);
			client->prev = last;
			last->next = client;
		}
		server->run->stream_clients_count += 1;

		evhttp_connection_get_peer(conn, &client_addr, &client_port);
		LOG_INFO("HTTP: Registered the new stream client: [%s]:%u; id=%s; advance_headers=%s; dual_final_frames=%s; clients now: %u",
			client_addr,
			client_port,
			client->id,
			bool_to_string(client->advance_headers),
			bool_to_string(client->dual_final_frames),
			server->run->stream_clients_count);

		buf_event = evhttp_connection_get_bufferevent(conn);
		bufferevent_setcb(buf_event, NULL, NULL, _http_callback_stream_error, (void *)client);
		bufferevent_enable(buf_event, EV_READ);
	} else {
		evhttp_request_free(request);
	}
}

#undef PROCESS_HEAD_REQUEST

static void _http_callback_stream_write(struct bufferevent *buf_event, void *v_client) {
#	define BOUNDARY "boundarydonotcross"
#	define RN "\r\n"

	struct stream_client_t *client = (struct stream_client_t *)v_client;
	struct evbuffer *buf;
	long double now = get_now_monotonic();
	long long now_second = floor_ms(now);

	if (now_second != client->fps_accum_second) {
		client->fps = client->fps_accum;
		client->fps_accum = 0;
		client->fps_accum_second = now_second;
	}
	client->fps_accum += 1;

	assert((buf = evbuffer_new()));

	// В хроме и его производных есть фундаментальный баг: он отрисовывает
	// фрейм с задержкой на один, как только ему придут заголовки следующего.
	// В сочетании с drop_same_frames это дает значительный лаг стрима
	// при большом количестве дропов (на статичном изображении, где внезапно
	// что-то изменилось.
	//
	// https://bugs.chromium.org/p/chromium/issues/detail?id=527446
	//
	// Включение advance_headers заставляет стример отсылать заголовки
	// будущего фрейма сразу после данных текущего, чтобы триггернуть отрисовку.
	// Естественным следствием этого является невозможность установки заголовка
	// Content-Length, так как предсказывать будущее мы еще не научились.
	// Его наличие не требуется RFC, однако никаких стандартов на MJPG over HTTP
	// в природе не существует, и никто не может гарантировать, что отсутствие
	// Content-Length не сломает вещание для каких-нибудь маргинальных браузеров.
	//
	// Кроме того, advance_headers форсит отключение заголовков X-UStreamer-*
	// по тем же причинам, по которым у нас нет Content-Length.

#	define ADD_ADVANCE_HEADERS \
		{ assert(evbuffer_add_printf(buf, \
		"Content-Type: image/jpeg" RN "X-Timestamp: %.06Lf" RN RN, get_now_real())); }

	if (client->need_initial) {
		assert(evbuffer_add_printf(buf,
			"HTTP/1.0 200 OK" RN
			"Access-Control-Allow-Origin: *" RN
			"Cache-Control: no-store, no-cache, must-revalidate, proxy-revalidate, pre-check=0, post-check=0, max-age=0" RN
			"Pragma: no-cache" RN
			"Expires: Mon, 3 Jan 2000 12:34:56 GMT" RN
			"Set-Cookie: stream_client=%s/%s; path=/; max-age=30" RN
			"Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY RN
			RN
			"--" BOUNDARY RN,
			(client->key != NULL ? client->key : "0"),
			client->id
		));

		if (client->advance_headers) {
			ADD_ADVANCE_HEADERS;
		}

		assert(!bufferevent_write_buffer(buf_event, buf));
		client->need_initial = false;
	}

#	define EXPOSED(_next) client->server->run->exposed->_next

	if (!client->advance_headers) {
		assert(evbuffer_add_printf(buf,
			"Content-Type: image/jpeg" RN
			"Content-Length: %zu" RN
			"X-Timestamp: %.06Lf" RN
			"%s",
			EXPOSED(picture.size) * sizeof(*EXPOSED(picture.data)),
			get_now_real(), (client->extra_headers ? "" : RN)
		));
		if (client->extra_headers) {
			assert(evbuffer_add_printf(buf,
				"X-UStreamer-Online: %s" RN
				"X-UStreamer-Dropped: %u" RN
				"X-UStreamer-Width: %u" RN
				"X-UStreamer-Height: %u" RN
				"X-UStreamer-Client-FPS: %u" RN
				"X-UStreamer-Grab-Time: %.06Lf" RN
				"X-UStreamer-Encode-Begin-Time: %.06Lf" RN
				"X-UStreamer-Encode-End-Time: %.06Lf" RN
				"X-UStreamer-Expose-Begin-Time: %.06Lf" RN
				"X-UStreamer-Expose-Cmp-Time: %.06Lf" RN
				"X-UStreamer-Expose-End-Time: %.06Lf" RN
				"X-UStreamer-Send-Time: %.06Lf" RN
				RN,
				bool_to_string(EXPOSED(online)),
				EXPOSED(dropped),
				EXPOSED(width),
				EXPOSED(height),
				client->fps,
				EXPOSED(picture.grab_time),
				EXPOSED(picture.encode_begin_time),
				EXPOSED(picture.encode_end_time),
				EXPOSED(expose_begin_time),
				EXPOSED(expose_cmp_time),
				EXPOSED(expose_end_time),
				now
			));
		}
	}

	assert(!evbuffer_add(buf,
		(void *)EXPOSED(picture.data),
		EXPOSED(picture.size) * sizeof(*EXPOSED(picture.data))
	));
	assert(evbuffer_add_printf(buf, RN "--" BOUNDARY RN));

	if (client->advance_headers) {
		ADD_ADVANCE_HEADERS;
	}

	assert(!bufferevent_write_buffer(buf_event, buf));
	evbuffer_free(buf);

	bufferevent_setcb(buf_event, NULL, NULL, _http_callback_stream_error, (void *)client);
	bufferevent_enable(buf_event, EV_READ);

#	undef EXPOSED
#	undef ADD_ADVANCE_HEADERS
#	undef RN
#	undef BOUNDARY
}

static void _http_callback_stream_error(UNUSED struct bufferevent *buf_event, UNUSED short what, void *v_client) {
	struct stream_client_t *client = (struct stream_client_t *)v_client;
	struct evhttp_connection *conn;
	char *client_addr = "???";
	unsigned short client_port = 0;

	client->server->run->stream_clients_count -= 1;

	conn = evhttp_request_get_connection(client->request);
	if (conn != NULL) {
		evhttp_connection_get_peer(conn, &client_addr, &client_port);
	}
	LOG_INFO("HTTP: Disconnected the stream client: [%s]:%u; clients now: %u",
		client_addr, client_port, client->server->run->stream_clients_count);
	if (conn != NULL) {
		evhttp_connection_free(conn);
	}

	if (client->prev == NULL) {
		client->server->run->stream_clients = client->next;
	} else {
		client->prev->next = client->next;
	}
	if (client->next != NULL) {
		client->next->prev = client->prev;
	}
	free(client->key);
	free(client);
}

static void _http_queue_send_stream(struct http_server_t *server, bool stream_updated, bool picture_updated) {
	struct evhttp_connection *conn;
	struct bufferevent *buf_event;
	long long now;
	bool queued = false;
	static unsigned queued_fps_accum = 0;
	static long long queued_fps_second = 0;

	for (struct stream_client_t *client = server->run->stream_clients; client != NULL; client = client->next) {
		conn = evhttp_request_get_connection(client->request);
		if (conn != NULL) {
			// Фикс для бага WebKit. При включенной опции дропа одинаковых фреймов,
			// WebKit отрисовывает последний фрейм в серии с некоторой задержкой,
			// и нужно послать два фрейма, чтобы серия была вовремя завершена.
			// Это похоже на баг Blink (см. _http_callback_stream_write() и advance_headers),
			// но фикс для него не лечит проблему вебкита. Такие дела.

			bool dual_update = (
				server->drop_same_frames
				&& client->dual_final_frames
				&& stream_updated
				&& client->updated_prev
				&& !picture_updated
			);

			if (dual_update || picture_updated || client->need_first_frame) {
				buf_event = evhttp_connection_get_bufferevent(conn);
				bufferevent_setcb(buf_event, NULL, _http_callback_stream_write, _http_callback_stream_error, (void *)client);
				bufferevent_enable(buf_event, EV_READ|EV_WRITE);

				client->need_first_frame = false;
				client->updated_prev = (picture_updated || client->need_first_frame); // Игнорировать dual
				queued = true;
			} else if (stream_updated) { // Для dual
				client->updated_prev = false;
			}
		}
	}

	if (queued) {
		if ((now = floor_ms(get_now_monotonic())) != queued_fps_second) {
			server->run->exposed->queued_fps = queued_fps_accum;
			queued_fps_accum = 0;
			queued_fps_second = now;
		}
		queued_fps_accum += 1;
	}
}

static void _http_exposed_refresh(UNUSED int fd, UNUSED short what, void *v_server) {
	struct http_server_t *server = (struct http_server_t *)v_server;
	bool stream_updated = false;
	bool picture_updated = false;

#	define UNLOCK_STREAM \
		{ server->run->stream->updated = false; A_PTHREAD_M_UNLOCK(&server->run->stream->mutex); }

	if (server->run->stream->updated) {
		LOG_DEBUG("Refreshing HTTP exposed ...");
		A_PTHREAD_M_LOCK(&server->run->stream->mutex);
		if (server->run->stream->picture.size > 0) { // If online
			picture_updated = _expose_new_picture(server);
			UNLOCK_STREAM;
		} else {
			UNLOCK_STREAM;
			picture_updated = _expose_blank_picture(server);
		}
		stream_updated = true;
	} else if (!server->run->exposed->online) {
		LOG_DEBUG("Refreshing HTTP exposed (BLANK) ...");
		picture_updated = _expose_blank_picture(server);
		stream_updated = true;
	}

#	undef UNLOCK_STREAM

	_http_queue_send_stream(server, stream_updated, picture_updated);
}

static bool _expose_new_picture(struct http_server_t *server) {
#	define STREAM(_next) server->run->stream->_next
#	define EXPOSED(_next) server->run->exposed->_next

	assert(STREAM(picture.size) > 0);
	EXPOSED(captured_fps) = STREAM(captured_fps);
	EXPOSED(expose_begin_time) = get_now_monotonic();

#	define MEM_STREAM_TO_EXPOSED \
		EXPOSED(picture.data), STREAM(picture.data), \
		STREAM(picture.size) * sizeof(*STREAM(picture.data))

	if (server->drop_same_frames) {
		if (
			EXPOSED(online)
			&& EXPOSED(dropped) < server->drop_same_frames
			&& EXPOSED(picture.size) == STREAM(picture.size)
			&& !memcmp(MEM_STREAM_TO_EXPOSED)
		) {
			EXPOSED(expose_cmp_time) = get_now_monotonic();
			EXPOSED(expose_end_time) = EXPOSED(expose_cmp_time);
			LOG_VERBOSE("HTTP: dropped same frame number %u; comparsion time = %.06Lf",
				EXPOSED(dropped), EXPOSED(expose_cmp_time) - EXPOSED(expose_begin_time));
			EXPOSED(dropped) += 1;
			return false; // Not updated
		} else {
			EXPOSED(expose_cmp_time) = get_now_monotonic();
			LOG_VERBOSE("HTTP: passed same frame check (frames are differ); comparsion time = %.06Lf",
				EXPOSED(expose_cmp_time) - EXPOSED(expose_begin_time));
		}
	}

	if (EXPOSED(picture.allocated) < STREAM(picture.allocated)) {
		A_REALLOC(EXPOSED(picture.data), STREAM(picture.allocated));
		EXPOSED(picture.allocated) = STREAM(picture.allocated);
	}

	memcpy(MEM_STREAM_TO_EXPOSED);

#	undef MEM_STREAM_TO_EXPOSED

	EXPOSED(picture.size) = STREAM(picture.size);

	EXPOSED(picture.grab_time) = STREAM(picture.grab_time);
	EXPOSED(picture.encode_begin_time) = STREAM(picture.encode_begin_time);
	EXPOSED(picture.encode_end_time) = STREAM(picture.encode_end_time);

	EXPOSED(width) = STREAM(width);
	EXPOSED(height) = STREAM(height);
	EXPOSED(online) = true;
	EXPOSED(dropped) = 0;
	EXPOSED(expose_cmp_time) = EXPOSED(expose_begin_time);
	EXPOSED(expose_end_time) = get_now_monotonic();

	LOG_VERBOSE("HTTP: exposed new frame; full exposition time =  %.06Lf",
		 EXPOSED(expose_end_time) - EXPOSED(expose_begin_time));

#	undef EXPOSED
#	undef STREAM
	return true; // Updated
}

static bool _expose_blank_picture(struct http_server_t *server) {
#	define EXPOSED(_next)	server->run->exposed->_next
#	define BLANK_JPEG_LEN	ARRAY_LEN(BLANK_JPEG_DATA)

	EXPOSED(expose_begin_time) = get_now_monotonic();
	EXPOSED(expose_cmp_time) = EXPOSED(expose_begin_time);

	if (EXPOSED(online) || EXPOSED(picture.size) == 0) {
		if (EXPOSED(picture.allocated) < BLANK_JPEG_LEN) {
			A_REALLOC(EXPOSED(picture.data), BLANK_JPEG_LEN);
			EXPOSED(picture.allocated) = BLANK_JPEG_LEN;
		}

		memcpy(EXPOSED(picture.data), BLANK_JPEG_DATA, BLANK_JPEG_LEN * sizeof(*EXPOSED(picture.data)));

		EXPOSED(picture.size) = BLANK_JPEG_LEN;

		EXPOSED(picture.grab_time) = 0;
		EXPOSED(picture.encode_begin_time) = 0;
		EXPOSED(picture.encode_end_time) = 0;

		EXPOSED(width) = BLANK_JPEG_WIDTH;
		EXPOSED(height) = BLANK_JPEG_HEIGHT;
		EXPOSED(captured_fps) = 0;
		EXPOSED(online) = false;
		goto updated;
	}

	if (EXPOSED(dropped) < server->run->drop_same_frames_blank) {
		LOG_PERF("HTTP: dropped same frame (BLANK) number %u", EXPOSED(dropped));
		EXPOSED(dropped) += 1;
		EXPOSED(expose_end_time) = get_now_monotonic();
		return false; // Not updated
	}

	updated:
		EXPOSED(dropped) = 0;
		EXPOSED(expose_end_time) = get_now_monotonic();
		return true; // Updated

#	undef BLANK_JPEG_LEN
#	undef EXPOSED
}