testing everything. You can even copy & paste HTTP responses from your real web
server to create representative test cases. Or test that your code survives in
awkward-to-reproduce situations like 500 errors or slow-loading responses.


### Example

Use MockWebServer the same way that you use mocking frameworks like
[Mockito](https://github.com/mockito/mockito):

1. Script the mocks.
2. Run application code.

        } else if (requestBody.isDuplex()) {
          logger.log("--> END ${request.method} (duplex request body omitted)")
        } else if (requestBody.isOneShot()) {
          logger.log("--> END ${request.method} (one-shot body omitted)")
        } else {
          var buffer = Buffer()
          requestBody.writeTo(buffer)

          var gzippedLength: Long? = null

import org.junit.jupiter.api.extension.RegisterExtension
import org.junit.jupiter.api.io.TempDir
import org.opentest4j.TestAbortedException

/** Android's URLConnectionTest, ported to exercise OkHttp's Call API.  */
@Tag("Slow")
class URLConnectionTest {
  @RegisterExtension
  val platform = PlatformRule()

  @RegisterExtension
  val clientTestRule = OkHttpClientTestRule()

  @TempDir
  lateinit var tempDir: File

@SuppressSignatureCheck
class YubikeyClientAuth {
  fun run() {
    // The typical PKCS11 slot, may vary with different hardware.
    val slot = 0

    val config = "--name=OpenSC\nlibrary=/Library/OpenSC/lib/opensc-pkcs11.so\nslot=$slot\n"

    // May fail with ProviderException with root cause like
    // sun.security.pkcs11.wrapper.PKCS11Exception: CKR_SLOT_ID_INVALID
    val pkcs11 = Security.getProvider("SunPKCS11").configure(config)

      codePoint.toChar() in encodeSet ||
      codePoint == '%'.code &&
      (!alreadyEncoded || strict && !isPercentEncoded(i, limit)) ||
      codePoint == '+'.code && plusIsSpace
    ) {
      // Slow path: the character at i requires encoding!
      val out = Buffer()
      out.writeUtf8(this, pos, i)
      out.writeCanonicalized(
        input = this,
        pos = i,
        limit = limit,

import java.io.File
import okio.FileSystem
import okio.Path
import okio.Path.Companion.toPath
import org.junit.jupiter.api.BeforeEach
import org.junit.jupiter.api.Tag
import org.junit.jupiter.api.Test

@Tag("Slow")
class OsgiTest {
  private lateinit var testResourceDir: Path
  private lateinit var workspaceDir: Path

  @BeforeEach
  fun setUp() {
    testResourceDir = "./build/resources/test/okhttp3/osgi".toPath()

   * corresponding response body stream. This is necessary if we want servers to be able to stop
   * inbound data and send an early 400 before the request body completes.
   *
   * This test sends a slow request that is canceled by the server. It expects the response to still
   * be readable after the request stream is canceled.
   */
  @Disabled
  @Test
  fun serverCancelsRequestBodyAndSendsResponseBody() {

import okio.use
import org.junit.jupiter.api.AfterEach
import org.junit.jupiter.api.BeforeEach
import org.junit.jupiter.api.Tag
import org.junit.jupiter.api.Test
import org.junit.jupiter.api.extension.RegisterExtension

@Tag("Slow")
class CacheTest {
  val fileSystem = FakeFileSystem()

  @RegisterExtension
  val clientTestRule = OkHttpClientTestRule()

  @RegisterExtension
  val platform = PlatformRule()

<component name="ProjectRunConfigurationManager">
  <configuration default="false" name="Not Slow" type="JUnit" factoryName="JUnit" singleton="false">
    <useClassPathOnly />
    <option name="MAIN_CLASS_NAME" value="" />
    <option name="METHOD_NAME" value="" />
    <option name="TEST_OBJECT" value="tags" />
    <option name="VM_PARAMETERS" value="-ea -Djunit.jupiter.extensions.autodetection.enabled=true" />
    <option name="PARAMETERS" value="" />

=====================

OkHttp 4.x upgrades our implementation language from Java to Kotlin and keeps everything else the
same. We’ve chosen Kotlin because it gives us powerful new capabilities while integrating closely
with Java.

We spent a lot of time and energy on retaining strict compatibility with OkHttp 3.x. We’re even
keeping the package name the same: `okhttp3`!

There are three kinds of compatibility we’re tracking: