Caching note - sending both ETag and If-Modified .. #26108
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| > During cache revalidation, if both `If-Modified-Since` and `If-None-Match` are present, then `If-None-Match` takes precedence for the validator. | ||
| > If you are only considering caching, you may think that `Last-Modified` is unnecessary. | ||
| > However, `Last-Modified` is not just useful for caching; it is a standard HTTP header that is also used by content-management (CMS) systems to display the last-modified time, by crawlers to adjust crawl frequency, and for other various purposes. | ||
| > So considering the overall HTTP ecosystem, it is better to provide both `ETag` and `Last-Modified`. | ||
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This just rearranges the original suggestion by Jxck (below is a subedited version of that)
Note: When evaluating how to use
ETagandLast-Modified, consider the following:
during cache revalidation, if bothIf-Modified-SinceandIf-None-Matchare present, thenIf-None-Matchtakes precedence for the validator.
If you are only considering caching, you may think thatLast-Modifiedis unnecessary.
However,Last-Modifiedis not just useful for caching; it is a standard HTTP header that is also used by content-management (CMS) systems to display the last-modified time, by crawlers to adjust crawl frequency, and for other various purposes.
So considering the overall HTTP ecosystem, it is better to provide bothETagandLast-Modified.
This is why RFC9110 prefers that server should send bothETagandLast-Modifiedfor a200response if possible.
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Preview URLs (comment last updated: 2023-04-14 01:28:29) |
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LGTM, thanks ! |
Co-authored-by: Jean-Yves Perrier <jypenator@gmail.com>
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Thanks. Accepted your change @teoli2003 - ready for re-review |
* Caching note - sending both ETag and If-Modified .. * Update files/en-us/web/http/caching/index.md Co-authored-by: Jean-Yves Perrier <jypenator@gmail.com> --------- Co-authored-by: Jean-Yves Perrier <jypenator@gmail.com>
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In the process of discussing retrospectives, a "fresh" PR (Pull Request) is also included as one of the changes. |
Fixes #26064 using a slightly modified form of the comment provided by @Jxck .
The difference is that the note starts with direction for the user "send both headers", and then explains why. Generally this is a better way to write because people scanning the material get the point first.