https://bz.apache.org/bugzilla/show_bug.cgi?id=64226
Bug ID: 64226
Summary: Tomcat 9 can return HTTP date headers in timzone other
than GMT
Product: Tomcat 9
Version: 9.0.27
Hardware: PC
Status: NEW
Severity: regression
Priority: P2
Component: Util
Assignee: dev@tomcat.apache.org
Reporter: gaz...@live.co.uk
Target Milestone: -----
We have an existing web application deployed within Tomcat. Recently we
upgraded Tomcat from 8.0.32 to 9.0.27. The application sets an Expires HTTP
header ultimately via Response.setDateHeader. Initially the application
correctly returns the Expires header in the GMT timezone but over time (since
the last restart) these headers begin to be returned in CET timezone. Different
nodes in the cluster will flip to CET at different times.
We can flip a node to CET by sending a request with a CET date in a header e.g.
$ curl -H "If-Modified-Since: Thu, 12 Mar 2020 14:40:22 CET" --verbose
localhost:18000/some/url/within/our/application -o /dev/null
After investigation the issue appears to be with the new ConcurrentDateFormat
class which uses a ConcurrentLinkedQueue to hold a reusable collection of
SimpleDateFormats. The collection is shared between the format and parse
methods. When parse is called with a date string containing a timezone that is
*not* GMT (e.g. "Thu, 12 Mar 2020 14:40:22 CET") then the timezone within the
SimpleDateFormat used is changed to the timezone in the string (e.g. CET). This
SimpleDateFormat is then placed back in the queue where it will be used by
calls to format which will then return date strings in the wrong timezone.
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