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32 lines
2.1 KiB
Markdown
32 lines
2.1 KiB
Markdown
---
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set: 3
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code: 304
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title: Not Modified
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references:
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"Rails HTTP Status Symbol": ":not_modified"
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"Go HTTP Status Constant": "http.StatusNotModified"
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"Symfony HTTP Status Constant": "Response::HTTP_NOT_MODIFIED"
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"Python2 HTTP Status Constant": "httplib.NOT_MODIFIED"
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"Python3+ HTTP Status Constant": "http.client.NOT_MODIFIED"
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"Python3.5+ HTTP Status Constant": "http.HTTPStatus.NOT_MODIFIED"
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---
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A conditional GET or HEAD request has been received and would have resulted in a [200 OK](/200) response if it were not for the fact that the condition evaluated to false.
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In other words, there is no need for the server to transfer a representation of the target resource because the request indicates that the client, which made the request conditional, already has a valid representation; the server is therefore redirecting the client to make use of that stored representation as if it were the payload of a [200 OK](/200) response.
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The server generating a 304 response MUST generate any of the following header fields that would have been sent in a [200 OK](/200) response to the same request: Cache-Control, Content-Location, Date, ETag, Expires, and Vary.
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Since the goal of a 304 response is to minimize information transfer when the recipient already has one or more cached representations, a sender SHOULD NOT generate representation metadata other than the above listed fields unless said metadata exists for the purpose of guiding cache updates (e.g., Last-Modified might be useful if the response does not have an ETag field).
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Requirements on a cache that receives a 304 response are defined in [Section 4.3.4 of RFC7234][2]. If the conditional request originated with an outbound client, such as a user agent with its own cache sending a conditional GET to a shared proxy, then the proxy SHOULD forward the 304 response to that client.
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A 304 response cannot contain a message-body; it is always terminated by the first empty line after the header fields.
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---
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* Source: [RFC7232 Section 4.1][1]
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[1]: <http://tools.ietf.org/html/rfc7232#section-4.1>
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[2]: <http://tools.ietf.org/html/rfc7234#section-4.3.4>
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