Libwebsockets w C++ i połączenie z Cordovą

Biblioteka Websockets działa dobrze w C++ udostępniając mechanizm komunikacji za pomocą websockets (protokół na www do obustronnej komunikacji klient-serwer).

Ten przykład pokazuje połączenie dwóch przykładowych aplikacji będących załącznikami do bibliotek.
Pierwszy przykład pochodzi z biblioteki LIBWEBSOCKETS, aby ją uruchomić należy najpierw zainstalować i skompilować poleceniami

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sudo apt-get install libssl-dev
cmake .
make
sudo make install

Jeśli programy nie chcą się uruchomić trzeba dodać ścieżkę do biblioteki do ścieżek systemowych bibliotek

1	export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/local/lib

Programy kompilujemy z biblioteką -lwebsockets

1	g++ minimal-ws-server.c -o minimalserv -fpermissive -lwebsockets

Potem uruchamiamy nowy plik

1	./minimalserv

W katalogu libwebsockets/minimal-examples/ws-server/ jest przykład z którego pochodzi ten kod:

minimal-ws-server.c

/*
* lws-minimal-ws-server
*
* Written in 2010-2019 by Andy Green <andy@warmcat.com>
*
* This file is made available under the Creative Commons CC0 1.0
* Universal Public Domain Dedication.
*
* This demonstrates the most minimal http server you can make with lws,
* with an added websocket chat server.
*
* To keep it simple, it serves stuff in the subdirectory "./mount-origin" of
* the directory it was started in.
* You can change that by changing mount.origin.
*/

#include <libwebsockets.h>
#include <string.h>
#include <signal.h>
#include <iostream>
using namespace std;

#define LWS_PLUGIN_STATIC
#include "protocol_lws_minimal.c"

static struct lws_protocols protocols[] = {
{ "http", lws_callback_http_dummy, 0, 0 },
LWS_PLUGIN_PROTOCOL_MINIMAL,
{ NULL, NULL, 0, 0 } /* terminator */
};

static int interrupted;

static const struct lws_http_mount mount = {
/* .mount_next */ NULL, /* linked-list "next" */
/* .mountpoint */ "/", /* mountpoint URL */
/* .origin */ "./mount-origin", /* serve from dir */
/* .def */ "index.html", /* default filename */
/* .protocol */ NULL,
/* .cgienv */ NULL,
/* .extra_mimetypes */ NULL,
/* .interpret */ NULL,
/* .cgi_timeout */ 0,
/* .cache_max_age */ 0,
/* .auth_mask */ 0,
/* .cache_reusable */ 0,
/* .cache_revalidate */ 0,
/* .cache_intermediaries */ 0,
/* .origin_protocol */ LWSMPRO_FILE, /* files in a dir */
/* .mountpoint_len */ 1, /* char count */
/* .basic_auth_login_file */ NULL,
};

void sigint_handler(int sig)
{
interrupted = 1;
}
int main(int argc, const char **argv)
{
struct lws_context_creation_info info;
struct lws_context *context;
const char *p;
int n = 0, logs = LLL_USER | LLL_ERR | LLL_WARN | LLL_NOTICE
/* for LLL_ verbosity above NOTICE to be built into lws,
* lws must have been configured and built with
* -DCMAKE_BUILD_TYPE=DEBUG instead of =RELEASE */
/* | LLL_INFO */ /* | LLL_PARSER */ /* | LLL_HEADER */
/* | LLL_EXT */ /* | LLL_CLIENT */ /* | LLL_LATENCY */
/* | LLL_DEBUG */;

cout << "start!\n";
signal(SIGINT, sigint_handler);

if ((p = lws_cmdline_option(argc, argv, "-d")))
logs = atoi(p);

lws_set_log_level(logs, NULL);
lwsl_user("LWS minimal ws server | visit http://localhost:7681 (-s = use TLS / https)\n");

memset(&info, 0, sizeof info); /* otherwise uninitialized garbage */
info.port = 7681;
info.mounts = &mount;
info.protocols = protocols;
info.vhost_name = "localhost";
info.ws_ping_pong_interval = 10;
info.options =
LWS_SERVER_OPTION_HTTP_HEADERS_SECURITY_BEST_PRACTICES_ENFORCE;

if (lws_cmdline_option(argc, argv, "-s")) {
lwsl_user("Server using TLS\n");
info.options |= LWS_SERVER_OPTION_DO_SSL_GLOBAL_INIT;
info.ssl_cert_filepath = "localhost-100y.cert";
info.ssl_private_key_filepath = "localhost-100y.key";
}

if (lws_cmdline_option(argc, argv, "-h"))
info.options |= LWS_SERVER_OPTION_VHOST_UPG_STRICT_HOST_CHECK;

context = lws_create_context(&info);
if (!context) {
lwsl_err("lws init failed\n");
return 1;
}

while (n >= 0 && !interrupted)
n = lws_service(context, 1000);

lws_context_destroy(context);

return 0;
}

i drugi plik z obsługą przerwania, protocol_lws_minimal.c:

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/*
* ws protocol handler plugin for "lws-minimal"
*
* Written in 2010-2019 by Andy Green <andy@warmcat.com>
*
* This file is made available under the Creative Commons CC0 1.0
* Universal Public Domain Dedication.
*
* This version holds a single message at a time, which may be lost if a new
* message comes. See the minimal-ws-server-ring sample for the same thing
* but using an lws_ring ringbuffer to hold up to 8 messages at a time.
*/

#if !defined (LWS_PLUGIN_STATIC)
#define LWS_DLL
#define LWS_INTERNAL
#include <libwebsockets.h>
#endif

#include <string.h>

/* one of these created for each message */

struct msg {
void *payload; /* is malloc'd */
size_t len;
};

/* one of these is created for each client connecting to us */

struct per_session_data__minimal {
struct per_session_data__minimal *pss_list;
struct lws *wsi;
int last; /* the last message number we sent */
};

/* one of these is created for each vhost our protocol is used with */

struct per_vhost_data__minimal {
struct lws_context *context;
struct lws_vhost *vhost;
const struct lws_protocols *protocol;

struct per_session_data__minimal *pss_list; /* linked-list of live pss*/

struct msg amsg; /* the one pending message... */
int current; /* the current message number we are caching */
};

/* destroys the message when everyone has had a copy of it */

static void
__minimal_destroy_message(void *_msg)
{
struct msg *msg = _msg;

free(msg->payload);
msg->payload = NULL;
msg->len = 0;
}

static int
callback_minimal(struct lws *wsi, enum lws_callback_reasons reason,
void *user, void *in, size_t len)
{
struct per_session_data__minimal *pss =
(struct per_session_data__minimal *)user;
struct per_vhost_data__minimal *vhd =
(struct per_vhost_data__minimal *)
lws_protocol_vh_priv_get(lws_get_vhost(wsi),
lws_get_protocol(wsi));

string *cordovaMessage;
char *cordovaTemp = new char[len+1]; //do konwersji void * > string *

int m;
cerr << "CALLBACK:"<<reason <<" \n";
switch (reason) {
case LWS_CALLBACK_PROTOCOL_INIT:
vhd = lws_protocol_vh_priv_zalloc(lws_get_vhost(wsi),
lws_get_protocol(wsi),
sizeof(struct per_vhost_data__minimal));
vhd->context = lws_get_context(wsi);
vhd->protocol = lws_get_protocol(wsi);
vhd->vhost = lws_get_vhost(wsi);
cerr<< "----INIT\n";
break;

case LWS_CALLBACK_ESTABLISHED:
/* add ourselves to the list of live pss held in the vhd */
lws_ll_fwd_insert(pss, pss_list, vhd->pss_list);
pss->wsi = wsi;
pss->last = vhd->current;
cerr<< "----ESTABLISHED\n";
break;

case LWS_CALLBACK_CLOSED:
/* remove our closing pss from the list of live pss */
lws_ll_fwd_remove(struct per_session_data__minimal, pss_list,
pss, vhd->pss_list);
cerr<< "----CLOSED\n";
break;

case LWS_CALLBACK_SERVER_WRITEABLE:
if (!vhd->amsg.payload)
break;

if (pss->last == vhd->current)
break;

/* notice we allowed for LWS_PRE in the payload already */
m = lws_write(wsi, ((unsigned char *)vhd->amsg.payload) +
LWS_PRE, vhd->amsg.len, LWS_WRITE_TEXT);
if (m < (int)vhd->amsg.len) {
lwsl_err("ERROR %d writing to ws\n", m);
return -1;
}
}

pss->last = vhd->current;
cerr<< "----WRITABLE\n";

break;

case LWS_CALLBACK_RECEIVE:
if (vhd->amsg.payload)
__minimal_destroy_message(&vhd->amsg);

vhd->amsg.len = len;
/* notice we over-allocate by LWS_PRE */
vhd->amsg.payload = malloc(LWS_PRE + len);
if (!vhd->amsg.payload) {
lwsl_user("OOM: dropping\n");
break;
}

memcpy((char *)vhd->amsg.payload + LWS_PRE, in, len);
//TU MOŻNA ODCZYTAĆ TRANSMISJĘ PRZYCHODZĄCĄ np. do zmiennej typu std::string *
memcpy(cordovaTemp, in, len); //kopiowanie z void * do char *
cordovaTemp[len] = '\0'; //dodanie znaku konca stringu (brakowalo)

cordovaMessage = new string(cordovaTemp);
cerr << "Got cordova message: " << *cordovaMessage << "\n";
delete cordovaMessage; //jak niepotrzebne - usuwamy
//^ //////////////////////////////////////////////////////////////////////

vhd->current++;

/*
* let everybody know we want to write something on them
* as soon as they are ready
*/
lws_start_foreach_llp(struct per_session_data__minimal **,
ppss, vhd->pss_list) {
lws_callback_on_writable((*ppss)->wsi);
} lws_end_foreach_llp(ppss, pss_list);
cerr<< "----RECEIVE\n";

break;
case LWS_CALLBACK_ADD_HEADERS:
cerr << "---HEADERS\n";

break;
default:
break;
}

delete[] cordovaTemp;
return 0;
}

#define LWS_PLUGIN_PROTOCOL_MINIMAL \
{ \
"lws-minimal", \
callback_minimal, \
sizeof(struct per_session_data__minimal), \
128, \
0, NULL, 0 \
}

#if !defined (LWS_PLUGIN_STATIC)

/* boilerplate needed if we are built as a dynamic plugin */

static const struct lws_protocols protocols[] = {
LWS_PLUGIN_PROTOCOL_MINIMAL
};

LWS_EXTERN LWS_VISIBLE int
init_protocol_minimal(struct lws_context *context,
struct lws_plugin_capability *c)
{
if (c->api_magic != LWS_PLUGIN_API_MAGIC) {
lwsl_err("Plugin API %d, library API %d", LWS_PLUGIN_API_MAGIC,
c->api_magic);
return 1;
}

c->protocols = protocols;
c->count_protocols = LWS_ARRAY_SIZE(protocols);
c->extensions = NULL;
c->count_extensions = 0;

return 0;
}

LWS_EXTERN LWS_VISIBLE int
destroy_protocol_minimal(struct lws_context *context)
{
return 0;
}
#endif

Po drugiej stronie mamy klienta w Javascripcie (np. w Cordovie) z prostym kodem pochodzącym ze strony echo.websocket.org:

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//Tu wpisz adres IP serwera i port taki sam jak ustawiony w plikach wyżej:
var wsUri = "ws://192.168.1.102:7681/";// "wss://echo.websocket.org/";
var output;

function testWebSocket()
{
websocket = new WebSocket(wsUri, "lws-minimal"); //BARDZO WAŻNE: lws-minimal oznacza naszą bibliotekę z C++ i jej protokół
websocket.onopen = function(evt) { onOpen(evt) };
websocket.onclose = function(evt) { onClose(evt) };
websocket.onmessage = function(evt) { onMessage(evt) };
websocket.onerror = function(evt) { onError(evt) };
}

function onOpen(evt)
{
console.log("CONNECTED");
doSend("Hello");
}

function onClose(evt)
{
console.log("DISCONNECTED");
}

function onMessage(evt)
{
console.log('RESPONSE: ' + evt.data+'');
websocket.close();
}

function onError(evt)
{
console.log('<span style="color: red;">ERROR:</span> ' + evt.data);
}

function doSend(message)
{
console.log("SENT: " + message);
websocket.send(message);
}

wywołujemy po załadowaniu strony (onload) funkcję

1	testWebSockets();

po załadowaniu strony przejrzyjcie konsolę JAVASCRIPT, powinna wyglądać tak:

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CONNECTED
(index):326 SENT: Hello
(index):326 RESPONSE: Hello
(index):326 DISCONNECTED

C, Cordova (phonegap), JavaScript

Libwebsockets w C++ i połączenie z Cordovą

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