* body on another thread.
   *
   * Note that transport-layer success (receiving a HTTP response code, headers and body) does not
   * necessarily indicate application-layer success: `response` may still indicate an unhappy HTTP
   * response code like 404 or 500.
   */
  @Throws(IOException::class)
  fun onResponse(
    call: Call,
    response: Response,
  )

   *
   * Note that transport-layer success (receiving a HTTP response code, headers and body) does not
   * necessarily indicate application-layer success: `response` may still indicate an unhappy HTTP
   * response code like 404 or 500.
   *
   * @throws IOException if the request could not be executed due to cancellation, a connectivity

### [Fast Fallback](https://square.github.io/okhttp/4.x/okhttp/okhttp3/-ok-http-client/-builder/fast-fallback/)

Since version 5.0, `OkHttpClient` supports fast fallback, which is our implementation of Happy Eyeballs [RFC 6555](https://datatracker.ietf.org/doc/html/rfc6555).

  dependencies:
    ansi-styles "^4.0.0"
    string-width "^4.1.0"
    strip-ansi "^6.0.0"

wrappy@1:
  version "1.0.2"
  resolved "https://registry.yarnpkg.com/wrappy/-/wrappy-1.0.2.tgz#b5243d8f3ec1aa35f1364605bc0d1036e30ab69f"
  integrity sha1-tSQ9jz7BqjXxNkYFvA0QNuMKtp8=

ws@~8.2.3:
  version "8.2.3"

```kotlin
implementation("com.squareup.okhttp3:okhttp:4.12.0")
```

Snapshot builds are [available][snap]. [R8 and ProGuard][r8_proguard] rules are available.

Also, we have a [bill of materials (BOM)][bom] available to help you keep OkHttp artifacts up to date and be sure about version compatibility.

```kotlin

    libraries. Do not use them if you aren't willing to track changes to them.

 *  Breaking: Drop support for Kotlin Multiplatform.

    We planned to support multiplatform in OkHttp 5.0, but after building it, we weren't happy with
    the implementation trade-offs. We can't use our HTTP client engine on Kotlin/JS, and we weren't
    prepared to build a TLS API for Kotlin/Native.

      }

    /**
     * Configure this client to perform fast fallbacks by attempting multiple connections
     * concurrently, returning once any connection connects successfully.
     *
     * This implements Happy Eyeballs ([RFC 6555][rfc_6555]), balancing connect latency vs.
     * wasted resources.
     *
     * Defaults to enabled, call with [fastFallback] = false to revert to 4.x behaviour.
     *

   * be received. The default implementation returns an empty response. Mischievous implementations
   * can return other values to test HTTP edge cases, such as unhappy socket policies or throttled
   * request bodies.
   */
  open fun peek(): MockResponse {
    return MockResponse(socketPolicy = KeepOpen)
  }

  /**

   * Implementations must support such concurrent calls.
   *
   * Note that cancellation is best-effort and that a call may proceed normally after it has been
   * canceled. For example, happy-path events like [requestHeadersStart] and [requestHeadersEnd] may
   * occur after a call is canceled. Typically cancellation takes effect when an expensive I/O
   * operation is required.
   *