libwebsockets/minimal-examples-lowlevel/ws-server/minimal-ws-broker/protocol_lws_minimal.c

/*
 * ws protocol handler plugin for "lws-minimal-broker"
 *
 * 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 implements a minimal "broker", for systems that look like this
 *
 * [ publisher  ws client ] <-> [ ws server  broker ws server ] <-> [ ws client subscriber ]
 *
 * The "publisher" role is to add data to the broker.
 *
 * The "subscriber" role is to hear about all data added to the system.
 *
 * The "broker" role is to manage incoming data from publishers and pass it out
 * to subscribers.
 *
 * Any number of publishers and subscribers are supported.
 *
 * This example implements a single ws server, using one ws protocol, that treats ws
 * connections as being in publisher or subscriber mode according to the URL the ws
 * connection was made to.  ws connections to "/publisher" URL are understood to be
 * publishing data and to any other URL, subscribing.
 */

#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;
	uint32_t tail;
	char publishing; /* nonzero: peer is publishing to us */
};

/* 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 lws_ring *ring; /* ringbuffer holding unsent messages */
};

/* 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));
	const struct msg *pmsg;
	struct msg amsg;
	char buf[32];
	int n, m;

	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);

		vhd->ring = lws_ring_create(sizeof(struct msg), 8,
					    __minimal_destroy_message);
		if (!vhd->ring)
			return 1;
		break;

	case LWS_CALLBACK_PROTOCOL_DESTROY:
		lws_ring_destroy(vhd->ring);
		break;

	case LWS_CALLBACK_ESTABLISHED:
		pss->tail = lws_ring_get_oldest_tail(vhd->ring);
		pss->wsi = wsi;
		if (lws_hdr_copy(wsi, buf, sizeof(buf), WSI_TOKEN_GET_URI) > 0)
			pss->publishing = !strcmp(buf, "/publisher");
		if (!pss->publishing)
			/* add subscribers to the list of live pss held in the vhd */
			lws_ll_fwd_insert(pss, pss_list, vhd->pss_list);
		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);
		break;

	case LWS_CALLBACK_SERVER_WRITEABLE:

		if (pss->publishing)
			break;

		pmsg = lws_ring_get_element(vhd->ring, &pss->tail);
		if (!pmsg)
			break;

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

		lws_ring_consume_and_update_oldest_tail(
			vhd->ring,	/* lws_ring object */
			struct per_session_data__minimal, /* type of objects with tails */
			&pss->tail,	/* tail of guy doing the consuming */
			1,		/* number of payload objects being consumed */
			vhd->pss_list,	/* head of list of objects with tails */
			tail,		/* member name of tail in objects with tails */
			pss_list	/* member name of next object in objects with tails */
		);

		/* more to do? */
		if (lws_ring_get_element(vhd->ring, &pss->tail))
			/* come back as soon as we can write more */
			lws_callback_on_writable(pss->wsi);
		break;

	case LWS_CALLBACK_RECEIVE:

		if (!pss->publishing)
			break;

		/*
		 * For test, our policy is ignore publishing when there are
		 * no subscribers connected.
		 */
		if (!vhd->pss_list)
			break;

		n = (int)lws_ring_get_count_free_elements(vhd->ring);
		if (!n) {
			lwsl_user("dropping!\n");
			break;
		}

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

		memcpy((char *)amsg.payload + LWS_PRE, in, len);
		if (!lws_ring_insert(vhd->ring, &amsg, 1)) {
			__minimal_destroy_message(&amsg);
			lwsl_user("dropping 2!\n");
			break;
		}

		/*
		 * let every subscriber 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) {
			if (!(*ppss)->publishing)
				lws_callback_on_writable((*ppss)->wsi);
		} lws_end_foreach_llp(ppss, pss_list);
		break;

	default:
		break;
	}

	return 0;
}

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