Check if a Raspberry Pi is connected to internet

Question

I'd like my Python script to check if it's online of not. Found pretty many answers here on Stack Overflow, but all failed for some weird reasons.

The scenario: a Raspberry Pi 3b+ connected to my router through Wifi. That said router is connected to internet through its cable

I wish to determine if the Raspberry has internet connection or not in order to change it's data source if needed. After searching here for the day, I found that the majority of the solutions use, for the better one, sockets, and for the worst ones (still tried to see if it changes anything, but no) urllib.urlopen .

Here's what I try:

def checkOnlineState(self, addr='http://www.google.com'):
    try:
        urllib2.urlopen(addr, timeout=2)

        if not self._onlineMode:
            print('Internet connection is back!')

        self._onlineMode = True
        return
    except:
        pass

    if self._onlineMode:
        print('I lost internet connection')

    self._onlineMode = False

I also tried with sockets, so instead of urllib2.urlopen I used

socket.create_connection((addr, 80), timeout=2)

or

socket.create_connection(('8.8.8.8', 0), timeout=2)

Whatever I do, except for entering a malformed ip or url, says I'm online. How do I know it? Well, the checkOnlineState runs in a loop, and if I take the internet cable off, the Raspberry still states it's online!

Answer 1

Do you know how android device checks if connected wifi is connected to internet? Yes, it just keeps sending message to Google and hope there is an expected response.

So you have to do the same thing.

Answer 2

So, after the answer from @Sraw, this is what I finally did:

req = requests.get('http://clients3.google.com/generate_204')
if req.status_code != 204:
    raise Exception

Yes, no exception, this is a heartbeat, I want to periodically check if I have access to internet, so whatever the error is, I want it signaled as offline

This won't fail because we check the request status. I found this way of doing here on Stackoverflow, on different questions