# Description The purpose of this ticket is to implement the server diagnostics in S2OPC. S2OPC provides partial support for the OPC UA Server Diagnostics feature. ## Detailed description The following variables will be implemented : * `serverViewCount` * `currentSessionCount` * `cumulatedSessionCountType` * `securityRejectedSessionCount` * `rejectedSessionCount` * `sessionTimeoutCount` * `sessionAbortCount` * `currentSubscriptionCount` * `cumulatedSubscriptionCount` * `publishingIntervalCount` * `securityRejectedRequestsCount` * `rejectedRequestsCount` Detailed diagnostics are currently not supported. In particular, the following diagnostics are not exposed: * `SubscriptionDiagnosticsArray` * `SessionsDiagnosticsSummary`, including `SessionDiagnosticsArray` and `SessionSecurityDiagnosticsArray` * `SamplingIntervalDiagnosticsArray` # Code version identification current master : bad930a6f63cb23cde9666b3e46384c5b9f4352f # Security impact No security impact # Implementation For the session variables, we should intercept the session event callback and update the runtime variable. For the subscription variables, we should create a new base machine subscription_diagnostics_bs.mch The `ServerDiagnostics.EnabledFlag` node controls whether the supported diagnostic values are exposed in the AddressSpace. At server configuration: * If `EnabledFlag` is `TRUE`, diagnostics are supported and enabled. * If `EnabledFlag` is `FALSE` but writable (in AccessLevel), diagnostics are supported but initially disabled. They can later be enabled by writing `TRUE` to `EnabledFlag`. * If `EnabledFlag` is `FALSE` and not writable, diagnostics are considered unsupported for the whole server lifecycle. * If the `EnabledFlag` node is not present in the configured AddressSpace, diagnostics are inhibited. When diagnostics are supported but `EnabledFlag` is `FALSE`, S2OPC continues to maintain the supported diagnostic counters internally, but their values are not exposed as valid diagnostic information in the AddressSpace. When `EnabledFlag` is changed to `TRUE`, the AddressSpace is updated with the current internally maintained diagnostic values. Subsequent changes to the diagnostic counters are then reflected in the AddressSpace. When `EnabledFlag` is changed back to `FALSE`, diagnostic values are made unavailable in the AddressSpace while the counters continue to be maintained internally. Concerning `securityRejectedRequestsCount` and `rejectedRequestsCount`, given the lack of specification details, we propose to exclude SecureChannel requests/responses and messages rejected at the SecureChannel protocol layer. `rejectedRequestsCount`: all requests for which a ServiceFault is returned due to service treatment `securityRejectedRequestsCount`: same as `securityRejectedRequestsCount` but only for ServiceFault with a security related status. OpenSecureChannel and CloseSecureChannel are also excluded, since the specification wording appears to target OPC UA Service requests, explicitly mentioning Session requests but not SecureChannel requests. # Known limitations S2OPC supports `ServerDiagnosticsSummary` and the diagnostic variables written in 'Detailed description'. However, detailed diagnostics are not supported, see 'Detailed description'. Local services bypass the AccessLevel check: when diagnostics are not supported, a local write of EnabledFlag remains possible but has no effect on diagnistics.