Caching

The Ktor client provides the HttpCache plugin that allows you to save previously fetched resources in an in-memory or persistent cache.

Add dependencies

HttpCache only requires the ktor-client-core artifact and doesn't need any specific dependencies.

In-memory cache

To install HttpCache, pass it to the install function inside a client configuration block:

import io.ktor.client.*
import io.ktor.client.engine.cio.*
import io.ktor.client.plugins.cache.*
//...
val client = HttpClient(CIO) {
    install(HttpCache)
}

This is enough to enable the client to save previously fetched resources in an in-memory cache. For example, if you make two consequent requests to a resource with the configured Cache-Control header, the client executes only the first request and skips the second one since data is already saved in a cache.

Persistent cache

Ktor allows you to create a persistent cache by implementing the CacheStorage interface. On JVM, you can create a file storage by calling the FileStorage function.

To create a file cache storage, pass the File instance to the FileStorage function. Then, pass the created storage to the publicStorage or privateStorage function depending on whether this storage is used as a shared or private cache.

        val client = HttpClient(CIO) {
            install(HttpCache) {
                val cacheFile = Files.createDirectories(Paths.get("build/cache")).toFile()
                publicStorage(FileStorage(cacheFile))
            }
        }

Last modified: 02 April 2024