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/*
* 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 \
}
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