Quick Checking of Listening Socket Using Boost ASIO
This morning a user wanted to be able to see if a Broker was alive and listening on the machine and port it was supposed to be on. This came up because Unix Admin decided to do a kernel update on all the staging machines last night, and we didn't have everything set to auto-restart. Therefore, we had no processes for people to look to. Not good. Thankfully, we have backups, but how does a user know when to hit the backup? After a failed call, sure, but with retries built into the code, that can take upwards of 10 sec. What about something a little faster?
Seems like a reasonable request, and to this morning I added a little isAlive() method to the main Broker client. It's very simple - just tries to connect to the specific host and port that it's supposed to use, and if something is there listening, it returns 'true', otherwise, it returns 'false'. Really easy.
Boost ASIO makes it a little un-easy, but still, it's not too bad:
bool MMDClient::isAlive() { bool success = false; // only try if they have set the URL to something useful... if (!mHostname.empty() && (mPort > 0)) { using namespace boost::system; using namespace boost::asio; using namespace boost::asio::ip; // getting the connection in boost is a painful process… tcp::resolver resolver(mIOService); std::ostringstream port; port << mPort; error_code err = error::host_not_found; tcp::resolver::query query(mHostname, port.str()); tcp::resolver::iterator it = resolver.resolve(query, err); tcp::socket sock(mIOService); if (err != error::host_not_found) { err = error::host_not_found; tcp::resolver::iterator end; while (err && (it != end)) { sock.close(); sock.connect(*it++, err); } } // if we got a connection, then something is there… success = !err; // …and close the socket regardless of anything else sock.close(); } return success; }
While using boost isn't trivial, I've found that the pros outweigh the cons, and it's better to have something like this that can handle multi-DNS entries and find what you're looking for, than to have to implement it all yourself.
This guy tested out and works great. Another happy customer!