Hi. Did anybody successfully implemented http cache-control on Ktor client? If yes, then I'll much a...

# ktor

[rsetkus]

Hi. Did anybody successfully implemented http cache-control on Ktor client? If yes, then I'll much appreciate if you could point me to any source (articles, documentation, code samples etc.) of implementation.

[Marc Knaup]

What do you mean by implementing? What needs to be implemented?

You can enable an in-memory cache using install(HttpCache).

[rsetkus]

It seems it is disabled for some of HttpEngines https://youtrack.jetbrains.com/issue/KTOR-660

[Marc Knaup]

The issue means that the HTTP requests ignore iOS’ own cache. You can still use HttpCache which is Ktor’s own implementation, but in-memory only.

[Marc Knaup]

NSURLRequestReloadIgnoringCacheData may break revalidation calls though. I’m not sure about that. It should not.

[rsetkus]

Okay. So by default, only in memory cache is supported by Ktor.

Since we'll be using Ktor in context of mobile applications (Kotlin Multiplatform), we're looking for more persistent cache (disk storage etc.) option. I'd guess we'd need to write our own Ktor feature for it.

[Marc Knaup]

Yes, when using HttpCache you can configure it to use your own HttpCacheStorage implementation. That implementation needs to load & save requests as told by HttpCache. So you build on top of HttpCache instead of re-inventing it 🙂

[Marc Knaup]

Here’s the in-memory version. You’d have to provide an on-disk version:
https://github.com/ktorio/ktor/blob/master/ktor-client/ktor-client-core/common/src/io/ktor/client/features/cache/storage/UnlimitedCacheStorage.kt

[rsetkus]

Thanks @Marc Knaup. For now, I think I know where to start. 🙂

[Marc Knaup]

I just saw that there’s an issue with implementing your own cache.
https://youtrack.jetbrains.com/issue/KTOR-501

You’ll have to create HttpCacheEntry instances when loading data from disk but its constructor is internal for some reason.
As a workaround you could force the usage of the internal constructor (@Suppress("INVISIBLE_MEMBER") - it may break in future Ktor updates) and engage in the ticket to get this improved.

[Marc Knaup]

I’ve also added https://youtrack.jetbrains.com/issue/KTOR-1135
There may be ways around that but the implementation is less clean then 😕

[Marc Knaup]

When in doubt, just copy & paste HttpCache for now and use the official version again once it was improved.