NoSuchFlowExecutionException multiple log lines

[Francesco Malvezzi]

Dear shibboleth users,

since upgrading from shibboleth-identity-provider-3.3.2 [1] to
shibboleth-identity-provider-3.4.1, my $IDP_HOME/logs/idp-warn.log is
filled with:

ERROR
[org.springframework.webflow.execution.repository.NoSuchFlowExecutionException:76]

I used to have around 150 such messages per hour, but now it's about
twice as much.

I also noticed the message before was:

2018-11-07 10:59:44,458 - ERROR
[org.springframework.webflow.execution.repository.NoSuchFlowExecutionException:76]
-
org.springframework.webflow.execution.repository.NoSuchFlowExecutionException:
No flow execution could be found with key 'e1s1' -- perhaps this
executing flow has ended or expired? This could happen if your users are
relying on browser history (typically via the back button) that
references ended flows.
	at
org.springframework.webflow.execution.repository.support.AbstractFlowExecutionRepository.getConversation(AbstractFlowExecutionRepository.java:172)
Caused by:
org.springframework.webflow.conversation.NoSuchConversationException: No
conversation could be found with id '1' -- perhaps this conversation has
ended?
	at
org.springframework.webflow.conversation.impl.ConversationContainer.getConversation(ConversationContainer.java:126)

now it's longer: after the ERROR there is a WARN as well:

2018-11-07 11:03:56,952 - ERROR
[org.springframework.webflow.execution.repository.NoSuchFlowExecutionException:76]
-
org.springframework.webflow.execution.repository.NoSuchFlowExecutionException:
No flow execution could be found with key 'e1s1' -- perhaps this
executing flow has ended or expired? This could happen if your users are
relying on browser history (typically via the back button) that
references ended flows.
	at
org.springframework.webflow.execution.repository.support.AbstractFlowExecutionRepository.getConversation(AbstractFlowExecutionRepository.java:172)
Caused by:
org.springframework.webflow.conversation.NoSuchConversationException: No
conversation could be found with id '1' -- perhaps this conversation has
ended?
	at
org.springframework.webflow.conversation.impl.ConversationContainer.getConversation(ConversationContainer.java:126)
2018-11-07 11:03:56,952 - WARN
[net.shibboleth.ext.spring.error.ExtendedMappingExceptionResolver:136] -
Resolved
[org.springframework.webflow.execution.repository.NoSuchFlowExecutionException:
No flow execution could be found with key 'e1s1' -- perhaps this
executing flow has ended or expired? This could happen if your users are
relying on browser history (typically via the back button) that
references ended flows.] to ModelAndView: reference to view with name
'error'; model is
{exception=org.springframework.webflow.execution.repository.NoSuchFlowExecutionException:
No flow execution could be found with key 'e1s1' -- perhaps this
executing flow has ended or expired? This could happen if your users are
relying on browser history (typically via the back button) that
references ended flows., request=Request(GET
https://idp.unimore.it/idp/profile/SAML2/Redirect/SSO?execution=e1s1)@19707007,
encoder=class net.shibboleth.utilities.java.support.codec.HTMLEncoder,
springContext=Root WebApplicationContext: startup date [Wed Nov 07
08:12:21 CET 2018]; root of context hierarchy}

I don't understand: do I miss a view so the WARN is triggered or is it a
mistake in the logger configuration?

I think I did two mistakes:
1) one that adds a WARN line after the ERROR;
2) one that lets a single back button action to trigger two ERRORs (so I
could explain why the amount of these ERROR is more or less doubled).

Can you help me find a way out from this (small) nuisance?

thank you,

franz



[1] I believ I already did what required here:
https://wiki.shibboleth.net/confluence/display/IDP30/ReleaseNotes#ReleaseNotes-ImportantNotesforUpgraders.3