davsclaus commented on code in PR #28128:
URL: https://github.com/apache/camel/pull/28128#discussion_r4324149816
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docs/user-manual/modules/ROOT/pages/camel-4x-upgrade-guide-4_24.adoc:
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@@ -1806,6 +1806,28 @@ the server does not have, with the status code
`Bad_NodeIdUnknown`, and the othe
affected. Previously an awaited write or read completed without an error and
with a `null` body, and a browse failed
with a `NullPointerException`.
+=== camel-milo - the consumer reports a lost connection and refreshes its
values after it
+
+The OPC UA client consumer delivers `Bad_NoCommunication` with a null value
for every monitored node when
+communication with the server is lost, and the current value of every node
once communication is restored. Before,
+the consumer delivered nothing during an outage, and values that did not
change were not delivered again after it.
+
+A consumer that starts while the server cannot be reached, or whose client
cannot connect at all, for example because
+of wrong credentials or an untrusted server certificate, delivers the status
for its nodes too; the cause is in the
+log. A connection that Camel rebuilds after a failed request delivers it for
every node of the connection. Each loss and
+each recovery delivers one exchange per node.
+
+A route that uses only the value of the `DataValue` body receives a null for
these exchanges, which the type converters
+turn into `0` or `false`; a route that stores values checks the status code of
the body first, for example with
+`${body.statusCode.bad}`. A value can now arrive again after an outage, so a
route that counts values, computes
+differences or detects changes must tolerate repeats. The consumer's route
also runs during an outage: an OPC UA write
+that it makes while the client reconnects waits for the next reconnect attempt
and can take effect after communication
+is restored, and a request that fails rebuilds the connection.
+
+To keep the previous behaviour, filter the exchanges with a bad status out
right after the consumer, for example with
+`filter(simple("${body.statusCode.good}"))`. This also drops the other bad
statuses, such as the refusal of a node, and
Review Comment:
Nit (my suggestion, sorry): `${body.statusCode.good}` also drops Uncertain
values, which were delivered before this change. `${body.statusCode.bad} ==
false` would be closer to the previous behaviour: it drops only the Bad
statuses. Either is fine if you prefer to keep it as is.
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