Support for 304 Not Modified

[ranger-ross]

Hello, I have a query in my application that is fetching a large json object from an api (that I do not own).

I have a the staleTime set fairly low because I want this data to be updated frequently.
Everything is working fine, but looking in the DevTools Network tab I'm using a lot of bandwidth for the revalidation.

The API I am using supports If-Modified-Since header, but I am not exactly sure to go able implementing it with React Query.

I see 2 problems:

1. How do I get the previous fetch timestamp and how do I get that to my fetch function? 🤔
2. When the api responds with a 304 status, it will not return a response body, so what should my fetch function return?

I guess I could implement this using external state, but if React Query has a first class way to do this that would be great.

[TkDodo]

This is not something react-query can or will support out of the box because it is not something that react-query is concerned with. React-Query is an async state manager - it is not tied to data fetching, and thus cannot know about http headers.

Isn't that something that browser would do automatically?

For example:

• if the server responds with an ETag, browsers will send the ETag back as an if-none-match header.
• if the server responds with a Last-Modified header, browsers will send that timestamp back as If-Modified-since

at least that's what I though so far. Would be weird if clients had to manage those dates by themselves 🤔

[ranger-ross]

I see, I think you are correct. (although the Chrome DevTools is a bit misleading, since it reports the original request's status code)

I think my mistake was including 'cache-control': 'no-cache' in my request headers by mistake.
Thanks for the quick reply 💯