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    204 No Content

for nothing found is both not an error (because 2xx code) but also indicates there was nothing found to match the request.

If it's an API, a 200 with an empty JSON object or array in the body is legitimate as well, but a 204 is explicit.

by Sander_Marechal13 hours ago|

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There is no reason you can return that "no items matched your selection" with a 404 HTTP response code instead of a 200.

by evanspa31 minutes ago|

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Another reason not to return a 404 in that case is that chances there will be monitor tooling in place that will treat a 404 as an "error" that will show up in your alerting, but would not be ideal; it will just be noise.

by onion2k5 hours ago|

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You can return whatever HTTP response code you want, but if you care about knowing whether your site is working being about to look at the logs and see "That user requested a page that doesn't exist" being different to "That user requested a page that exists but had no results" is quite useful. In coding terms it's the difference between a null and an empty array.

by ah15084 hours ago|

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In this case I don't think the status should depend on the number of results. Here are you results, [] is a valid response body when there are no result. Returning 404 if there are no result (GET /books?title=a for instance) is misleading, the caller may think that /books is a non existent route and may conclude that books are reachable via another URI. To me, the querystring has no influence on the response status.

/books/1 could return 200 or 404 depending on the existence of the book#1, here it make sense because if /books/1 does not exist the API must tell it explicitly. However 404 belongs to the 4XX family which means "client error", is it an error to ask for a non existing book ? If you enter in a bookshop and ask for a book they don't have you did not "make a mistake". It's not like if you asked for a chainsaw. But in an API, especially with hypermedia, you are not supposed to request a resource that does not exist (unless the API provides a link to an existing resource that is was deleted before the caller try to reach it).

by kilburn2 hours ago|

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If you enter a bookshop and you ask for a book that does not exist then it's definitely your mistake.

If you ask for a book they don't have it's a different matter.

In any case, when you ask for a book in a library you are using their "search" endpoint. The equivalent to opening a books/1 url would be asking for a specific instance of a book by serial number or so. Then it's clear that you made a mistake uf you do that for an unexistent serial number...

by threatofrain12 hours ago|

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A response code of 204 seems more appropriate but the problem is you're not allowed to send further information, which would make that descriptive response... not descriptive enough.

by Xirdus6 hours ago|

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Code 204 is just code 200 with the "yes the body really is zero bytes this is not an error it's supposed to be like this" bit set.

by IgorPartola8 hours ago|

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I think of it like this:

/users/ returns a 404 in an API means that this resource does not exist. As in, this is not a part of the API.

/users/123 returns a 404 means this user record does not exist.

Yes this means that a 404 is context dependent but in a way that makes it easier for a human to think of and reason about.

by onion2k5 hours ago|

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Yes, and this is obvious if /users/ exists and returns a 400 if the ID is required. That way you can tell the difference between /users/ being there and expecting and ID, and it not being there.

by stouset13 hours ago|

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The point was that returning a 404 for unexpected query strings doesn’t just happen to okay per the specs, but that there is significant historical precedent for doing so based on application design that was common in the past.

by brightball13 hours ago|

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Yea, empty response at a valid path. Isn’t 204 the code for it?

Lots of REST libraries that I’ve used treat any 400 response as an error so generating a 404 when for an empty list would just create more headaches.

by HumanOstrich10 hours ago|

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Libraries that automatically throw errors for status codes in the 400 and 500 ranges are pretty obnoxious (looking at you, axios). It adds unnecessary overhead, complexity, and bad ergonomics by hijacking control flow from the app.

Responses with status codes in the 400 range are client errors, so the client shouldn't retry the same request. So a 404 is appropriate despite how annoying a library might be at handling it. Depending on which language/ecosystem you are using, there are likely more sane alternatives.

by mnahkies4 hours ago|

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Completely agree on the axios part - one implication of that is you can't statically type the error response shapes (since exceptions can't be typed). Where as with fetch you can have a discriminated union based on the status code (eg: https://github.com/mnahkies/openapi-code-generator/blob/main...)

Although I do feel like I've seen too many instances of a 404 being used for an empty collection where it would make more sense to return `[]` and treat it as an expected (successful) state.

by vlovich1239 hours ago|

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Generally true although 429 is often used for rate limiting so a back off and retry is appropriate. 409, 412, 428 may also be retriable depending on the specific semantics of the given situation. 421 apparently shows up commonly in HTTP/2 connection reuse and is retriable. 423 and 425 too potentially.

It would have been nice if there was an actually grouping of retriable and not retriable but in reality it’s a complete mess.

But at a minimum beware of 429. That’s not a permanent outage and is a frequent one you might get that needs a careful retry.

by sk5t12 hours ago|

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204 might be acceptable if you aren’t returning an entity body to describe what is missing, but do wish to indicate the request was successful.

by burnished11 hours ago|

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I think the author is comfortable creating headaches for people tacking query strings onto URLs