Publishing interval of 0 (max rate) together with non-zero HeartbeatInterval causes DivideByZero exception

[derSchtefan]

Describe the bug

When we configure a OpcPublishingInterval of 0 via publishednodes.json, and a non-zero HeartbeatInterval , a DivideByZeroException is triggered in /src/components/opc-ua/src/Microsoft.Azure.IIoT.OpcUa.Protocol/src/Services/SubscriptionServices.cs:line 573

A publishing interval of 0 means max sampling rate / event based sampling, and is supported by the OPC UA server. (And the OPC UA standard ( https://reference.opcfoundation.org/v104/Core/docs/Part4/5.12.1/ ))

The bug appears only in conjunction with a HeartbeatInterval, and is triggered by this code:

/// /src/components/opc-ua/src/Microsoft.Azure.IIoT.OpcUa.Protocol/src/Services/SubscriptionServices.cs:line 573
 if (m.HeartbeatInterval != null && m.HeartbeatInterval != TimeSpan.Zero) {
                        var itemKeepAliveCount = (uint)m.HeartbeatInterval.Value.TotalMilliseconds /
                            (uint)_subscription.Configuration.PublishingInterval.Value.TotalMilliseconds;
                        revisedKeepAliveCount = GreatCommonDivisor(revisedKeepAliveCount, itemKeepAliveCount);
                    }

Happens both when configured via the IIoT Stack and stand-alone via publishednodes.json .

To Reproduce

Setup a subscription (IIoT stack or standalone via publishednodes.json) that has a non-zero HeartbeatInterval and a 0 OpcPublishingInterval.

Screenshots

    [2021-06-10 13:30:30Z ERR Microsoft.Azure.IIoT.OpcUa.Protocol.Services.SubscriptionServices+SubscriptionWrapper] Failed to activate subscription
System.DivideByZeroException: Attempted to divide by zero.
   at Microsoft.Azure.IIoT.OpcUa.Protocol.Services.SubscriptionServices.SubscriptionWrapper.<>c__DisplayClass32_0.<GetSubscription>b__0(MonitoredItemModel m) in /src/components/opc-ua/src/Microsoft.Azure.IIoT.OpcUa.Protocol/src/Services/SubscriptionServices.cs:line 573
   at System.Collections.Generic.List`1.ForEach(Action`1 action)
   at Microsoft.Azure.IIoT.OpcUa.Protocol.Services.SubscriptionServices.SubscriptionWrapper.GetSubscription(Session session, SubscriptionConfigurationModel configuration, Boolean activate) in /src/components/opc-ua/src/Microsoft.Azure.IIoT.OpcUa.Protocol/src/Services/SubscriptionServices.cs:line 571
   at Microsoft.Azure.IIoT.OpcUa.Protocol.Services.SubscriptionServices.SubscriptionWrapper.ReapplyAsync(Session session, Boolean activate) in /src/components/opc-ua/src/Microsoft.Azure.IIoT.OpcUa.Protocol/src/Services/SubscriptionServices.cs:line 259
   at Microsoft.Azure.IIoT.OpcUa.Protocol.Services.SubscriptionServices.SubscriptionWrapper.ActivateAsync(Session session) in /src/components/opc-ua/src/Microsoft.Azure.IIoT.OpcUa.Protocol/src/Services/SubscriptionServices.cs:line 229