The Service Mail Handler drops emails containing attachments with less than 3 characters

Summary

When using the Service Desk Mail Handler, if the customer replies to a notification and includes an attachment with a filename shorter than 3 characters, the email is discarded and no comment is added to the ticket.

Steps to reproduce

• Configure an SMTP server in ⚙ > System > Outgoing Mail
• Create a Service Desk project
• Configure a SD Mail Handler in Project Settings > Email Requests
• Log into the Customer Portal as a customer, and create a Request
• Log into the customer's mailbox and wait for the "Issue Created" Customer Notification to be received
• Reply to this customer notification and include a file that has less than 2 characters in the filename. For example: 0

Expected behavior

A comment is added to the Service Desk ticket and the file is attached to it.

Observed behavior

• The email is discarded by Service Desk and no comment is added to the ticket
• The customer does not receive any notification about this failure
• The following FAILURE is shown in the UI in the SD logs:
  

• The following exception is found in the incoming email logs:

  2018-09-17 14:33:31,419 ERROR [] Caesium-1-2 anonymous     Exception when MailHandlerWorker handles message: 
  java.lang.RuntimeException: Unexpected error while running action as user 'julienreyjiratestcustomer2@gmail.com'
  	at com.atlassian.pocketknife.internal.util.runner.AuthenticationContextUtilImpl.runAs(AuthenticationContextUtilImpl.java:60) [?:?]
  	at com.atlassian.servicedesk.internal.feature.emailchannel.IncomingEmailServiceImpl.inEmailContext(IncomingEmailServiceImpl.java:473) [?:?]
  	at com.atlassian.servicedesk.internal.feature.emailchannel.IncomingEmailServiceImpl.lambda$doCreateNewOrCommentOnIssueWithMailChannel$15(IncomingEmailServiceImpl.java:172) [?:?]
  	at io.atlassian.fugue.Either$Right.fold(Either.java:620) [fugue-4.5.0.jar:?]
  	at com.atlassian.servicedesk.internal.feature.emailchannel.IncomingEmailServiceImpl.doCreateNewOrCommentOnIssueWithMailChannel(IncomingEmailServiceImpl.java:170) [?:?]
  	at com.atlassian.servicedesk.internal.feature.emailchannel.IncomingEmailServiceImpl.lambda$createNewOrCommentOnIssueWithMailChannel$6(IncomingEmailServiceImpl.java:145) [?:?]
  ...
  Caused by: java.lang.IllegalArgumentException: Prefix string too short
  	at java.io.File.createTempFile(File.java:2001) [?:1.8.0_121]
  	at java.io.File.createTempFile(File.java:2070) [?:1.8.0_121]
  	at com.atlassian.servicedesk.internal.comment.InternalServiceDeskCommentServiceScala.com$atlassian$servicedesk$internal$comment$InternalServiceDeskCommentServiceScala$$createTempFile(InternalServiceDeskCommentServiceScala.scala:521) [?:?]
  	at com.atlassian.servicedesk.internal.comment.InternalServiceDeskCommentServiceScala$$anonfun$14.apply(InternalServiceDeskCommentServiceScala.scala:502) [?:?]
  

Workaround

There is no ideal workaround for this issue besides ensuring that customers never attach files that have less than 3 characters when replying to notifications. This can be a problem when customers use mail clients which convert images into thumbnails, since these thumbnails often have names of only 1 character.

Notes

This issuse only occurs with the Service Desk Mail Handler, and only when replying to a notification to comment in a ticket. It does not occur when creating an issue via email.

Also, this issue does not occur with the JIRA Core Mail Handler which is configured in ⚙ > System > Incoming Mail (the bug was fixed for this Mail Handler in JRASERVER-1229).