Eclispe Milo handle missing Sever Nonce in ActivateSessionRequest

I use Eclipse Milo (0.2.3) in my prject for OPC UA communication. The OPC UA participants are a client (written using Eclipse Milo) and a server, which is running on a remote machine, and is not implemented using Milo).

I can connect the client to the server normally and if the remote server is shut down, I am able to reconnect the client automatically, as soon as the server is accessible again.

However, after updating the server software, the client can't reconnect any more and it floods the server with the following messages:

Create Session Request
- The server is able to create a session
Activate Session Request
- The server sends an Activate Session Response, in which the ServerNonce is missing and the service result is "bad"

This causes the client to send a new Create Session Request. This all happens multiple times within a second, which makes it impossible for the server to execute any other tasks then trying to create this session.

Are there any settings in Milo to specify the reconnection delay? Or is there any setting for sepcifying what should happen when receiving an empty ServerNonce?

The server's responses are as follows:

If the session can be activated:

OpcUa Binary Protocol
    Message Type: MSG
    Chunk Type: F
    Message Size: 96
    SecureChannelId: 1599759116
    Security Token Id: 1
    Security Sequence Number: 53
    Security RequestId: 3
    OpcUa Service : Encodeable Object
        TypeId : ExpandedNodeId
            NodeId EncodingMask: Four byte encoded Numeric (0x01)
            NodeId Namespace Index: 0
            NodeId Identifier Numeric: ActivateSessionResponse (470)
        ActivateSessionResponse
            ResponseHeader: ResponseHeader
                Timestamp: Nov 16, 2018 14:05:47.974000000
                RequestHandle: 1
                ServiceResult: 0x00000000 [Good]
                ServiceDiagnostics: DiagnosticInfo
                    EncodingMask: 0x00
                        .... ...0 = has symbolic id: False
                        .... ..0. = has namespace: False
                        .... .0.. = has localizedtext: False
                        .... 0... = has locale: False
                        ...0 .... = has additional info: False
                        ..0. .... = has inner statuscode: False
                        .0.. .... = has inner diagnostic info: False
                StringTable: Array of String
                    ArraySize: 0
                AdditionalHeader: ExtensionObject
                    TypeId: ExpandedNodeId
                    EncodingMask: 0x00
            ServerNonce: ab...
            Results: Array of StatusCode
                ArraySize: 0
            DiagnosticInfos: Array of DiagnosticInfo
                ArraySize: 0

If the session can't be activated (after updating the server's software):

OpcUa Binary Protocol
    Message Type: MSG
    Chunk Type: F
    Message Size: 64
    SecureChannelId: 1599759041
    Security Token Id: 1
    Security Sequence Number: 61
    Security RequestId: 11
    OpcUa Service : Encodeable Object
        TypeId : ExpandedNodeId
        ActivateSessionResponse
            ResponseHeader: ResponseHeader
                Timestamp: Nov 16, 2018 12:49:08.235000000 
                RequestHandle: 222
                ServiceResult: 0x80000000 [Bad]
                ServiceDiagnostics: DiagnosticInfo
                    EncodingMask: 0x00
                        .... ...0 = has symbolic id: False
                        .... ..0. = has namespace: False
                        .... .0.. = has localizedtext: False
                        .... 0... = has locale: False
                        ...0 .... = has additional info: False
                        ..0. .... = has inner statuscode: False
                        .0.. .... = has inner diagnostic info: False
                StringTable: Array of String
                    ArraySize: 0
                AdditionalHeader: ExtensionObject
                    TypeId: ExpandedNodeId
                    EncodingMask: 0x00
            ServerNonce: <MISSING>[OpcUa Null ByteString]
            Results: Array of StatusCode
                ArraySize: 0
            DiagnosticInfos: Array of DiagnosticInfo
                ArraySize: 0

Thank you in advance for your help.

Solution

This corner case you described where there's no delay between a failed re-activation and the subsequent re-creation is addressed on the dev/0.3 branch in this commit.

I might be able to back port it to 0.2.x next week if I have some spare time.

I don't think there are any workarounds you can use.