Add StaticHeadersWriter.setIgnoreIfContainsHeader(boolean)

[rwinch]

Summary

We should add a property to StaticHeadersWriter that indicates it should skip adding a header if the header already exists.

[ankurpathak]

@rwinch I would like to take this one.

[ankurpathak]

@rwinch With this issue:
#6454
and corresponding pull request:
#6456
now be will be aready checking for header already exists
before writing any header in any HeaderWriter.
So does we need this Issue?

[mickaeltr]

Hi @ankurpathak,

I think the changes you've made in #6456 forStaticHeadersWriter, won't be enough for my use case (described at #6476):

if (!response.containsHeader(header.getName())) {
    response.setHeader(header.getName(), value);
} else {
    response.addHeader(header.getName(), value);
}

I would like the static header to be skipped if it already exists in the response. But with this code, it would be added, not skipped.

Thanks for helping.

[ankurpathak]

@mickaeltr We can modify method something like this to acheive:

		for (Header header : headers) {
			for (String value : header.getValues()) {
				if(!hasHeader(response, header.getName(), value)){
					response.addHeader(header.getName(), value);
				}
			}
		}
	

	private boolean hasHeader(HttpServletResponse response, String headerName, String headerValue) {
		return response.containsHeader(headerName) && response.getHeaders(headerName).contains(headerValue);
	}

Changed in #6456 as well.

[mickaeltr]

@ankurpathak In my case, I think that still would not work

I would like my static Cache-Control to be: max-age=0, no-cache, must-revalidate

I would like to override it, for example with: max-age=3600

With your implementation, I understand that I would get max-age=3600, no-cache, must-revalidate instead of only max-age=3600.

So I am more in favor of an ignoreIfContainsHeader flag, as suggested by @rwinch. Besides that would avoid breaking backward compatibility.

[ankurpathak]

@mickaeltr This will cover your case I think.

                for (Header header : headers) {
			if (!response.containsHeader(header.getName())) {
				for (String value : header.getValues()) {
					response.addHeader(header.getName(), value);
				}
			}
		}

Changed in #6456 as well.

[mickaeltr]

Yes that would work for me. 👍
However that would break backward compatibility… I am not sure what is the policy about that.

[ankurpathak]

Yes that would work for me.
However that would break backward compatibility… I am not sure what is the policy about that.

Issue for which I have submitted PR yet to be reviewed. The issue itself is about checking header existence before writing them. I will be able to comment on backward compatabilty only after that. But in current state its not breaking any existing tests.

[rwinch]

@ankurpathak Thanks for pointing that out. You are right this is a duplicate.

@mickaeltr You are right to worry about passivity. We will move that discussion to the existing tickets though