libwebsocket: How to disconnect client if there is no server response for a while (with timeout)? - libwebsockets

Question

I have a client using libwebsocket to establish a connection to a server. Whenever the client sends a request, the server sends a response and after receiving the response the client closes the connection. Works fine.
But when the server does not answer to the request i have the problem that the client keeps waiting for a response forever. When nothing happens the callback is never called and its not possible to close connection with returning -1 from callback function.
Is there any way to enable a timeout for the connection to close? Or any possibility to close connection from outside the callback function?
Here is my code so far:
int callback_function(libwebsocket_context* context, libwebsocket* wsi, enum libwebsocket_callback_reasons reason, void* user, void* in, size_t len) {
switch (reason) {
case LWS_CALLBACK_CLIENT_ESTABLISHED: {
std::cout << "LWS_CALLBACK_CLIENT_ESTABLISHED" << std::endl;
libwebsocket_callback_on_writable(context, wsi);
}
break;
case LWS_CALLBACK_CLOSED:{
std::cout << "LWS_CALLBACK_CLOSED" << std::endl;
}
break;
case LWS_CALLBACK_CLIENT_RECEIVE_PONG:
case LWS_CALLBACK_CLIENT_RECEIVE:{
std::cout << "LWS_CALLBACK_CLIENT_RECEIVE" << endl;
((char *)in)[len] = '\0';
answers_[current_request] = answers_[current_request] + string((char *)in);
if (libwebsocket_is_final_fragment(wsi)){
std::cout << "request:" << requests_[current_request] << std::endl;
std::cout << "answer:" << answers_[current_request] << std::endl;
current_request++;
if(current_request >= answers_.size()) {
ready = true;
return -1;
}
libwebsocket_callback_on_writable(context, wsi);
}
}
break;
case LWS_CALLBACK_CLIENT_WRITEABLE:{
std::cout << "LWS_CALLBACK_CLIENT_WRITEABLE" << endl;
unsigned char buf[LWS_SEND_BUFFER_PRE_PADDING + 4096 + LWS_SEND_BUFFER_POST_PADDING];
const std::string message = std::string(requests_[current_request]);
std::copy(message.begin(), message.end(), &buf[LWS_SEND_BUFFER_PRE_PADDING]);
buf[LWS_SEND_BUFFER_PRE_PADDING+(int)message.size()]='\0';
int n = libwebsocket_write(wsi, &buf[LWS_SEND_BUFFER_PRE_PADDING], (size_t)message.size(), static_cast<libwebsocket_write_protocol>(LWS_WRITE_BINARY));
if (n < 0){
std::cout << kLogErr << "bad things are happening" << std::endl;
return -1;
}
if (n < (int)message.size()) {
std::cout << kLogErr << "Partial write LWS_CALLBACK_CLIENT_WRITEABLE" << std::endl;
return -1;
}
}
break;
default:
std::cout << "CALLBACK_DEFAULT: " << reason << endl;
break;
}
return 0;
}
vector<string> sendMessage(const string& server, int port, const string& path, const vector<string>& messages, bool& error) {
ready = error = false;
current_request = 0;
requests_ = vector<string>(messages);
answers_ = vector<string>(requests_.size(), "");
int ietf_version = -1; /* latest */
wsi_ = libwebsocket_client_connect(context_, server.c_str(), port, 2, path.c_str(), server.c_str(), "origin", NULL, ietf_version);
if (wsi_ == NULL) {
std::cout << kLogErr << "libwebsocket connect failed server:" << server << " port: " << port << " path: " << path << std::endl;
error = true;
return vector<string>();
}
bool first_time = true;
int n = 0;
while (n >= 0 && !force_exit && !ready) {
n = libwebsocket_service(context_, 0);
if(first_time) {
libwebsocket_callback_on_writable(context_, wsi_);
first_time = false;
}
if (n < 0){
continue;
}
if (wsi_ == NULL) {
break;
}
}
error = !ready;
wsi_ = NULL;
return vector<string>(answers_);
}

Answer 1

You could try using:
case LWS_CALLBACK_CLIENT_CONNECTION_ERROR:
return -1;
break;
Or
lws_set_timeout
But I'm not a 100% sure that will work, you could also try creating an issue/question on their GitHub, they tend to answer quite fast/clear.
I'm also not sure if you should implement

Answer 2

I solved the problem.
I programmed a timer in
vector<string> sendMessage(const string& server, int port, const string& path, const vector<string>& messages, bool& error)
and when the timeout is reaches, the timer sets a flag and triggers
libwebsocket_callback_on_writable(context_, wsi_);
again. Then in
int callback_function(libwebsocket_context* context, libwebsocket* wsi, enum libwebsocket_callback_reasons reason, void* user, void* in, size_t len)
in case
LWS_CALLBACK_CLIENT_WRITEABLE
i check the flag and if it is set the callback is aborted with
return -1;
Works fine!