How client sends close signal to graphql subscription server?

I’m working on a graphql server and there is one subscription API. This is the starter code I found on gqlgen documentation:

// CurrentTime is the resolver for the currentTime field.
func (r *subscriptionResolver) CurrentTime(ctx context.Context) (<-chan *model.Time, error) {
    // First you'll need to `make()` your channel. Use your type here!
    ch := make(chan *model.Time)

    // You can (and probably should) handle your channels in a central place outside of `schema.resolvers.go`.
    // For this example we'll simply use a Goroutine with a simple loop.
    go func() {
        // Handle deregistration of the channel here. Note the `defer`
    defer close(ch)

        for {
            // In our example we'll send the current time every second.
            time.Sleep(1 * time.Second)
            fmt.Println("Tick")

            // Prepare your object.
            currentTime := time.Now()
            t := &model.Time{
                UnixTime:  int(currentTime.Unix()),
                TimeStamp: currentTime.Format(time.RFC3339),
            }

            // The subscription may have got closed due to the client disconnecting.
            // Hence we do send in a select block with a check for context cancellation.
            // This avoids goroutine getting blocked forever or panicking,
            select {
            case <-ctx.Done(): // This runs when context gets cancelled. Subscription closes.
                fmt.Println("Subscription Closed")
                // Handle deregistration of the channel here. `close(ch)`
                return // Remember to return to end the routine.
            
            case ch <- t: // This is the actual send.
                // Our message went through, do nothing 
            }
        }
    }()

    // We return the channel and no error.
    return ch, nil
}

I want to know what happens when I receive ctx.Done() signal. Is the client sending this signal by unsubscribing or closing subscription? Or it can happen automatically after some time?( I mean setting some timeout parameter for being idle.)
Also, I want to know can a timeout on my side(server side) trigers Done() signal?