Bug 63710

Summary: HTTP 304 NOT MODIFIED should not set Content-Length
Product: Tomcat 9 Reporter: Boris Petrov <boris_petrov>
Component: CatalinaAssignee: Tomcat Developers Mailing List <dev>
Status: RESOLVED FIXED    
Severity: normal    
Priority: P2    
Version: 9.0.24   
Target Milestone: -----   
Hardware: PC   
OS: Linux   

Description Boris Petrov 2019-08-30 12:15:22 UTC
Tomcat seems to set the `Content-Length` header to 0 when the HTTP response code is 304 (Not Modified). This should not be done. Some references:

https://trac.nginx.org/nginx/ticket/459
https://github.com/playframework/playframework/issues/3899
Comment 1 Mark Thomas 2019-08-30 17:58:58 UTC
The default servlet does not do this.

Tomcat does not do this if a Servlet returns a 304 response.

An application may well do this but that would be an application issue.
Comment 2 Boris Petrov 2019-08-30 18:53:03 UTC
Is it possible that the default Tomcat configuration adds this header?

When I run our integration tests (which use the embedded Tomcat), this header is not present in these responses. However, in production the header is there.

How do I debug who adds it?
Comment 3 Mark Thomas 2019-08-30 18:55:22 UTC
That is a question for the users mailing list.
Comment 4 Boris Petrov 2019-09-12 16:54:49 UTC
As noted in a mailing list message:

https://mail-archives.apache.org/mod_mbox/tomcat-users/201909.mbox/%3C0be01580-54c6-c5c4-16b7-000a577c4ebb%40profuzdigital.com%3E

This happens only on HTTP/2 and is indeed a Tomcat bug.
Comment 5 Mark Thomas 2019-09-12 20:06:40 UTC
Fixed in:
- master for 9.0.25 onwards
- 8.5.x for 8.5.46 onwards