could use new flow control capacity before acknowledging it, causing strict HTTP/2 servers to
    fail the call.


## Version 4.1.1

_2019-09-05_

 *  Fix: Don't drop repeated headers when validating cached responses. In our Kotlin upgrade we
    introduced a regression where we iterated the number of unique header names rather than then
    number of unique headers. If you're using OkHttp's response cache this may impact you.

=== ":material-language-kotlin: Kotlin"
    ```kotlin

   */
  @get:JvmName("handshake") val handshake: Handshake?,
  /** Returns the HTTP headers. */
  @get:JvmName("headers") val headers: Headers,
  /**
   * Returns a non-null value if this response was passed to [Callback.onResponse] or returned
   * from [Call.execute]. Response bodies must be [closed][ResponseBody] and may
   * be consumed only once.
   *

 * if (forceCacheResponse.code() != 504) {
 *   // The resource was cached! Show it.
 * } else {
 *   // The resource was not cached.
 * }
 * ```
 *
 * This technique works even better in situations where a stale response is better than no response.
 * To permit stale cached responses, use the `max-stale` directive with the maximum staleness in
 * seconds:
 *
 * ```java

 * This class currently pins a certificate's Subject Public Key Info as described on
 * [Adam Langley's Weblog][langley]. Pins are either base64 SHA-256 hashes as in
 * [HTTP Public Key Pinning (HPKP)][rfc_7469] or SHA-1 base64 hashes as in Chromium's
 * [static certificates][static_certificates].
 *
 * ## Setting up Certificate Pinning
 *

    }
  }

  // TODO GET preferred order - with tests to confirm this
  // 1. successful fresh cached GET response
  // 2. unsuccessful (404, 500) fresh cached GET response
  // 3. successful network response
  // 4. successful stale cached GET response
  // 5. unsuccessful response
  @Test
  fun usesCache() {
    val cache = Cache(cacheFs, "cache".toPath(), (100 * 1024).toLong())

  @get:JvmName("minFreshSeconds") val minFreshSeconds: Int,
  /**
   * This field's name "only-if-cached" is misleading. It actually means "do not use the network".
   * It is set by a client who only wants to make a request if it can be fully satisfied by the
   * cache. Cached responses that would require validation (ie. conditional gets) are not permitted
   * if this header is set.
   */

      return Response.Builder()
        .request(chain.request())
        .protocol(Protocol.HTTP_1_1)
        .code(HTTP_GATEWAY_TIMEOUT)
        .message("Unsatisfiable Request (only-if-cached)")
        .sentRequestAtMillis(-1L)
        .receivedResponseAtMillis(System.currentTimeMillis())
        .build().also {
          listener.satisfactionFailure(call, it)
        }
    }

 *
 * ### The response body must be closed.
 *
 * Each response body is backed by a limited resource like a socket (live network responses) or
 * an open file (for cached responses). Failing to close the response body will leak resources and
 * may ultimately cause the application to slow down or crash.
 *
 * Both this class and [Response] implement [Closeable]. Closing a response simply

     * transient query params, or has a canonical URL possibly for a CDN.
     *
     * Note that POST requests will not be sent to the server if this URL is set
     * and matches a cached response.
     */
    fun cacheUrlOverride(cacheUrlOverride: HttpUrl?) =
      apply {
        this.cacheUrlOverride = cacheUrlOverride
      }

    open fun build(): Request = Request(this)
  }