Supporting ETag and if-none-match

[RobertGardner]

My server supports ETag and if-none-match on some requests with large payloads, but SWR doesn't seem to pay attention to these out-of-the-box. What is the suggested technique for supporting these?

[pip8786]

@RobertGardner Have you found any solution to this? I'm struggling to figure out how to use refreshInterval without sending all of the data back each time if I know the client has the latest. Does anyone have a suggestion for that?

[RobertGardner]

I ended up implementing a custom fetcher that implemented the ETag logic. Not the greatest but it worked and wasn’t very hard. Unfortunately, I no longer work at that company so I can’t access the code to provide more details.

[LiFaytheGoblin]

My server sends etags and can process if-none-match headers. My react frontend makes GET requests with an SWR fetcher.

The issue: When I checked the network requests in the browser, I saw etags coming back but no if-none-match header was ever sent on subsequent requests, even though browsers should handle etags automatically.
I tried to make my swr fetcher handle etags (using an etag store), but it was buggy.

Solution: In the end, it turned out the issue was that in my fetcher a content-type header was being set even for GET requests. This prevents the browser from automatically handling etags it appears.

After removing the unnecessary content-type header for the GET requests, etag was handled automatically by the browser. In my swr fetcher I only returned undefined when receiving a 304 code to be sure (but it seems to never land there anyway). No need to implement custom etag handling with swr 🥳