[[Message-History]]
= Message History

Camel supports the
https://www.enterpriseintegrationpatterns.com/patterns/messaging/MessageHistory.html[Message History]
from the xref:enterprise-integration-patterns.adoc[EIP patterns] book.

The Message History from the EIP patterns allows for analyzing and debugging the flow of messages in a loosely coupled system.

image::eip/MessageHistory.gif[image]

Attaching a Message History to the message will provide a list of all applications that the message passed through since its origination.

IMPORTANT: The message history is disabled by default (to optimize for lower footprint out of the box). You should only enable message history
if needed, such as during development, where Camel can report route stack-traces when a message failed with an exception.
But for production usage, then message history should only be enabled if you have monitoring systems that rely on gathering these
fine grained details. When message history is enabled then there is a slight performance overhead as the history data is stored
in a `java.util.concurrent.CopyOnWriteArrayList` due to the need of being thread safe.

== Enabling or disabling Message History

The Message History can be enabled or disabled per CamelContext or per route (disabled by default).
For example you can turn it on with

[source,java]
----
camelContext.setMessageHistory(true);
----

Or in XML

[source,xml]
----
<camelContext messageHistory="true">

</camelContext>
----

You can also do this per route. Then a route level configuration overrides the CamelContext level configuration.

== Route stack-trace in exceptions logged by error handler

If Message History is enabled, then Camel will leverage this information,
when the Error Handler logs exhausted exceptions. Then in addition to the caused exception with its stacktrace,
you can see the message history; you may think this as a "route stacktrace".

And example is provided below:

[source,text]
----
2020-01-15 11:58:34,834 [read #3 - Delay] ERROR DefaultErrorHandler            - Failed delivery for (MessageId: ID-davsclaus-pro-local-1579085914402-0-2 on ExchangeId: ID-davsclaus-pro-local-1579085914402-0-3). Exhausted after delivery attempt: 1 caught: java.lang.IllegalArgumentException: Forced to dump message history

Message History
---------------------------------------------------------------------------------------------------------------------------------------
RouteId              ProcessorId          Processor                                                                        Elapsed (ms)
[route1            ] [route1            ] [from[seda://start]                                                            ] [       432]
[route1            ] [to1               ] [log:foo                                                                       ] [         5]
[route1            ] [to2               ] [direct:bar                                                                    ] [       111]
[route2            ] [to5               ] [log:bar                                                                       ] [         0]
[route2            ] [delay2            ] [delay[100]                                                                    ] [       110]
[route2            ] [to6               ] [mock:bar                                                                      ] [         0]
[route1            ] [delay1            ] [delay[300]                                                                    ] [       305]
[route1            ] [to3               ] [log:baz                                                                       ] [         2]
[route1            ] [process1          ] [Processor@0x5e600dd5                                                          ] [         0]

Stacktrace
---------------------------------------------------------------------------------------------------------------------------------------
java.lang.IllegalArgumentException: Forced to dump message history
	at org.apache.camel.processor.MessageHistoryDumpRoutingTest$1$1.process(MessageHistoryDumpRoutingTest.java:52) ~[test-classes/:?]
	at org.apache.camel.support.processor.DelegateSyncProcessor.process(DelegateSyncProcessor.java:64) ~[classes/:?]
	at org.apache.camel.processor.errorhandler.RedeliveryErrorHandler$RedeliveryState.run(RedeliveryErrorHandler.java:477) ~[classes/:?]
	at org.apache.camel.impl.engine.DefaultReactiveExecutor$Worker.schedule(DefaultReactiveExecutor.java:186) ~[classes/:?]
	at org.apache.camel.impl.engine.DefaultReactiveExecutor.schedule(DefaultReactiveExecutor.java:56) ~[classes/:?]
	at org.apache.camel.processor.errorhandler.RedeliveryErrorHandler$RedeliveryState.lambda$run$1(RedeliveryErrorHandler.java:481) ~[classes/:?]
	at org.apache.camel.processor.DelayProcessorSupport$ProcessCall$1.done(DelayProcessorSupport.java:77) [classes/:?]
	at org.apache.camel.support.AsyncProcessorConverterHelper$ProcessorToAsyncProcessorBridge.process(AsyncProcessorConverterHelper.java:63) [classes/:?]
	at org.apache.camel.processor.DelayProcessorSupport$ProcessCall.run(DelayProcessorSupport.java:70) [classes/:?]
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_201]
	at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_201]
	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180) [?:1.8.0_201]
	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) [?:1.8.0_201]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:1.8.0_201]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:1.8.0_201]
	at java.lang.Thread.run(Thread.java:748) [?:1.8.0_201]
----

When message history is enabled then the full history is logged as shown above. Here we can see the full path
the message has been routed, where it started from route1, called route2 and returned to route1 again, and so on.

When message history is disabled (by default) then the error handler logs a brief history with the last node
where the exception occurred as shown below:

[source,text]
----
2020-01-15 11:59:33,238 [read #3 - Delay] ERROR DefaultErrorHandler            - Failed delivery for (MessageId: ID-davsclaus-pro-local-1579085972821-0-2 on ExchangeId: ID-davsclaus-pro-local-1579085972821-0-3). Exhausted after delivery attempt: 1 caught: java.lang.IllegalArgumentException: Forced to dump message history

Message History (complete message history is disabled)
---------------------------------------------------------------------------------------------------------------------------------------
RouteId              ProcessorId          Processor                                                                        Elapsed (ms)
[route1            ] [route1            ] [from[seda://start]                                                            ] [       419]
	...
[route1            ] [process1          ] [Processor@0x229c6181                                                          ] [         0]

Stacktrace
---------------------------------------------------------------------------------------------------------------------------------------
java.lang.IllegalArgumentException: Forced to dump message history
	at org.apache.camel.processor.MessageHistoryDumpRoutingTest$1$1.process(MessageHistoryDumpRoutingTest.java:52) ~[test-classes/:?]
	at org.apache.camel.support.processor.DelegateSyncProcessor.process(DelegateSyncProcessor.java:64) ~[classes/:?]
	at org.apache.camel.processor.errorhandler.RedeliveryErrorHandler$RedeliveryState.run(RedeliveryErrorHandler.java:477) ~[classes/:?]
	at org.apache.camel.impl.engine.DefaultReactiveExecutor$Worker.schedule(DefaultReactiveExecutor.java:186) ~[classes/:?]
	at org.apache.camel.impl.engine.DefaultReactiveExecutor.schedule(DefaultReactiveExecutor.java:56) ~[classes/:?]
	at org.apache.camel.processor.errorhandler.RedeliveryErrorHandler$RedeliveryState.lambda$run$1(RedeliveryErrorHandler.java:481) ~[classes/:?]
	at org.apache.camel.processor.DelayProcessorSupport$ProcessCall$1.done(DelayProcessorSupport.java:77) [classes/:?]
	at org.apache.camel.support.AsyncProcessorConverterHelper$ProcessorToAsyncProcessorBridge.process(AsyncProcessorConverterHelper.java:63) [classes/:?]
	at org.apache.camel.processor.DelayProcessorSupport$ProcessCall.run(DelayProcessorSupport.java:70) [classes/:?]
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_201]
	at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_201]
	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180) [?:1.8.0_201]
	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) [?:1.8.0_201]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:1.8.0_201]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:1.8.0_201]
	at java.lang.Thread.run(Thread.java:748) [?:1.8.0_201]
----


=== Configuring route stack-trace from error handler

You can turn off logging message history from the Error Handler using

[source,java]
----
errorHandler(defaultErrorHandler().logExhaustedMessageHistory(false));
----

The Error Handler does not log the message body/header details (to avoid logging sensitive message body details).
You can enable this on the error handler as shown:

[source,java]
----
errorHandler(defaultErrorHandler().logExhaustedMessageBody(true));
----

== MessageHistory API

When message history is enabled during routing Camel captures how the Exchange is routed, as a `org.apache.camel.MessageHistory` entity
that is stored on the Exchange. On the `org.apache.camel.MessageHistory` there is information about the
route id, processor id, timestamp, and elapsed time it took to process the Exchange by the processor.

You can access the message history from Java code:

[source,java]
----
List<MessageHistory> list = exchange.getProperty(Exchange.MESSAGE_HISTORY, List.class);
for (MessageHistory history : list) {
    System.out.println("Routed at id: " + history.getNode().getId());
}
----
