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41 lines
1.8 KiB
Markdown
41 lines
1.8 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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---
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The 304 Not Modified status code indicates that a conditional GET or HEAD
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request has been received and would have resulted in a [200 (OK)](/200) response
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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
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the target resource because the request indicates that the client, which made
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the request conditional, already has a valid representation; the server is
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therefore redirecting the client to make use of that stored representation as if
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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
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fields that would have been sent in a [200 (OK)](/200) response to the same
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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
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recipient already has one or more cached representations, a sender SHOULD NOT
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generate representation metadata other than the above listed fields unless said
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metadata exists for the purpose of guiding cache updates (e.g., Last-Modified
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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
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[Section 4.3.4 of RFC7234][2]. If the conditional request originated with an
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outbound client, such as a user agent with its own cache sending a conditional
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GET to a shared proxy, then the proxy SHOULD forward the 304 response to that
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client.
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A 304 response cannot contain a message-body; it is always terminated by the
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first empty line after the header fields.
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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> |