애플리케이션에서의 ETag — 개념, 목적 및 원리

class EtagClient {
    private val etagCache =
        mutableMapOf<String, String>()

    private val client = OkHttpClient.Builder().build()

    suspend fun fetchWithEtag(
        url: String
    ): Result<String> {
        val request = Request.Builder()
            .url(url)
            .header("If-None-Match",
                etagCache[url] ?: "")
            .build()

        val response = client.newCall(request).await()

        return when (response.code) {
            304 -> Result.success(
                "not_modified")
            200 -> {
                response.header("ETag")?.let {
                    etagCache[url] = it
                }
                Result.success(response.body?.string()
                    ?: "")
            }
            else -> Result.failure(
                Exception("HTTP ${response.code}"))
        }
    }
}