gnodet-bot commented on code in PR #29113:
URL: https://github.com/apache/camel/pull/29113#discussion_r4457670874
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components/camel-web3j/src/main/docs/web3j-component.adoc:
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@@ -171,3 +171,39 @@ YAML::
atBlock: 10
----
====
+
+== UndeliverableException when a filter is removed
+
+The consumer operations `ETH_LOG_OBSERVABLE`, `ETH_BLOCK_HASH_OBSERVABLE`,
`ETH_PENDING_TRANSACTION_HASH_OBSERVABLE`,
+`BLOCK_OBSERVABLE`, `TRANSACTION_OBSERVABLE` and
`PENDING_TRANSACTION_OBSERVABLE` install a filter on the node and poll it.
+web3j removes the filter with `eth_uninstallFilter` when the consumer stops.
For `BLOCK_OBSERVABLE`,
+`TRANSACTION_OBSERVABLE` and `PENDING_TRANSACTION_OBSERVABLE`, web3j also
removes it when fetching a block or a
+transaction fails, before the consumer subscribes again.
+
+If `eth_uninstallFilter` fails, for example because the node is down or has
already dropped the filter, RxJava reports an
+`io.reactivex.exceptions.UndeliverableException` caused by web3j's
`org.web3j.protocol.core.filters.FilterException`.
+By default RxJava prints the stack trace and passes it to the uncaught
exception handler of the thread.
+This is only noise: the consumer keeps working. The cause is in web3j, see
+https://github.com/LFDT-web3j/web3j/issues/1937[web3j issue 1937].
+
+To log these errors at a lower level, an application can set a JVM-wide RxJava
2 error handler once at startup,
+before the routes start. The handler below logs the web3j filter errors at
DEBUG and handles all other errors as RxJava
+does by default:
+
+[source,java]
+----
+import io.reactivex.exceptions.UndeliverableException;
+import io.reactivex.plugins.RxJavaPlugins;
+import org.web3j.protocol.core.filters.FilterException;
+
+RxJavaPlugins.setErrorHandler(e -> {
Review Comment:
`LOG` is not defined in the snippet. Users who copy this verbatim will get a
compilation error. Consider either declaring the logger explicitly or using
`System.err.println`:
```suggestion
System.err.println("[web3j] Could not uninstall a filter: " +
e.getCause().getMessage());
```
Or, if the user is expected to have their own logger, add a comment making
it explicit:
```
// LOG is your application's logger (e.g.
LoggerFactory.getLogger(MyApp.class))
LOG.debug("web3j could not uninstall a filter: {}",
e.getCause().getMessage());
```
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