How can I set a user custom pointer in libwebsockets callback? - c

Question

How can I set a user custom pointer in libwebsockets callback?
I added a pointer variable into a lws_protocol.
When callback function is called, user pointer is always NULL.
I use libwebsockets v3.0.
static int interrupted, rx_seen, test;
int ws_callback(struct lws *ws, enum lws_callback_reasons reason, void *user, void *in, size_t len) {
// user is NULL
return lws_callback_http_dummy(ws, reason, user, in, len);
}
int main() {
struct lws *ws;
struct lws_context_creation_info context_info;
struct lws_client_connect_info client_info;
struct lws_context *context;
struct lws_protocols protocols[] = {
{ "ws_callback", ws_callback, 0, 0, 0, POINTER_VARIABLE /* HERE */, 0 }
};
int n = 0;
// context creation info
memset(&context_info, 0, sizeof(context_info));
context_info.options = LWS_SERVER_OPTION_DO_SSL_GLOBAL_INIT;
context_info.port = CONTEXT_PORT_NO_LISTEN;
context_info.protocols = protocols;
context = lws_create_context(&context_info);
if (!context) {
return;
}
memset(&client_info, 0, sizeof(client_info));
client_info.context = context;
client_info.port = 8080;
client_info.address = "192.168.1.1";
client_info.path = "/";
client_info.host = client_info.address;
client_info.origin = client_info.address;
client_info.protocol = protocols[0].name;
client_info.pwsi = &ws;
lws_client_connect_via_info(&client_info);
while (n >= 0 && ws && !interrupted) {
n = lws_service(context, 1000);
}
lws_context_destroy(context);
return 0;
}

Answer 1

You must specify the size of per session data structure, but not the pointer itself. Per session data will be different for each connection.
typedef struct per_session_data {
void *user_space;
} per_session_data;
int ws_callback(struct lws *ws, enum lws_callback_reasons reason, void *user, void *in, size_t len)
{
/* This will be different for every connected peer */
per_session_data *data = (per_session_data*)user;
}
struct lws_protocols protocols[] = {
{ "ws_callback", ws_callback, sizeof(per_session_data), 0 }
{ NULL, NULL, 0, 0 } /* terminator */
};
You can also set optional user pointer that will be associated with the context. lws_context_creation_info has user variable for userspace. You must set it before creating the context
typedef struct per_session_data {
void *user_space;
/*
Same other variables
*/
} per_session_data;
int ws_callback(struct lws *ws, enum lws_callback_reasons reason, void *user, void *in, size_t len)
{
/* This will be different for every connected peer */
per_session_data *data = (per_session_data*)user;
/* This will be same for every connected peer */
void *userdata = lws_context_user(lws_get_context(ws));
/* userdata is POINTER_VARIABLE specified before context creating */
switch (reason)
{
case LWS_CALLBACK_ESTABLISHED:
/* Initialize per session data here */
break;
case LWS_CALLBACK_CLOSED:
/* Destroy per session data here */;
break;
default:
break;
}
}
struct lws_protocols protocols[] = {
{ "ws_callback", ws_callback, sizeof(per_session_data), 0 }
{ NULL, NULL, 0, 0 } /* terminator */
};
int main()
{
/*
your code here
*/
// context creation info
memset(&context_info, 0, sizeof(context_info));
context_info.options = LWS_SERVER_OPTION_DO_SSL_GLOBAL_INIT;
context_info.port = CONTEXT_PORT_NO_LISTEN;
context_info.protocols = protocols;
context_info.user = POINTER_VARIABLE; /* HERE */
context = lws_create_context(&context_info);
if (!context) {
return;
}
/*
your code here
*/
}