supports both synchronous blocking calls and async calls with callbacks.


Get a URL
---------

This program downloads a URL and prints its contents as a string. [Full source][get_example].

```java
OkHttpClient client = new OkHttpClient();

String run(String url) throws IOException {
  Request request = new Request.Builder()
      .url(url)

    EventListener.Factory { call -> ClientRuleEventListener(eventListenerFactory.create(call), ::addEvent) }

  /**
   * Returns an OkHttpClient for tests to use as a starting point.
   *
   * The returned client installs a default event listener that gathers debug information. This will
   * be logged if the test fails.
   *

      Headers.Builder()
        .add("foo: bar")
        .add(" foo: baz") // Name leading whitespace is trimmed.
        .add("foo : bak") // Name trailing whitespace is trimmed.
        .add("\tkey\t:\tvalue\t") // '\t' also counts as whitespace
        .add("ping:  pong  ") // Value whitespace is trimmed.
        .add("kit:kat") // Space after colon is not required.
        .build()
    assertThat(headers.values("foo")).containsExactly("bar", "baz", "bak")

 *  New: Switch our Internationalized Domain Name (IDN) implementation to [UTS #46 Nontransitional
    Processing][uts46]. With this fix, the `ß` code point no longer maps to `ss`. OkHttp now embeds
    its own IDN mapping table in the library.

 *  New: Prefer the client's configured precedence order for TLS cipher suites. (OkHttp used to

     *
     * The default value of 0 disables client-initiated pings.
     */
    fun pingInterval(
      interval: Long,
      unit: TimeUnit,
    ) = apply {
      pingInterval = checkDuration("interval", interval, unit)
    }

    /**
     * Sets the interval between HTTP/2 and web socket pings initiated by this client. Use this to

    assertThat(stringPrep("\u2029")).isNull()
    assertThat(stringPrep("\ud834\udd7a")).isNull() // Note that this is one code point.
  }

  @Test fun prohibitionPrivateUse() {
    assertThat(stringPrep("\uf8ff")).isNull()
    assertThat(stringPrep("\udbff\udffd")).isNull() // Note that this is one code point.
  }

  @Test fun prohibitionNonCharacter() {
    assertThat(stringPrep("\ufdd0")).isNull()

    ) {
    }
  }

  companion object {
    /** Arbitrary code point that's 2 bytes in UTF-8 and valid in IdnaMappingTable.txt. */
    private const val UNICODE_2 = 0x1a5

    /** Arbitrary code point that's 3 bytes in UTF-8 and valid in IdnaMappingTable.txt. */
    private const val UNICODE_3 = 0x2202

    /** Arbitrary code point that's 4 bytes in UTF-8 and valid in IdnaMappingTable.txt. */

  }

  @Test fun outOfBounds() {
    assertFailsWith<IllegalArgumentException> {
      table.map(-1, Buffer())
    }
    table.map(0, Buffer()) // Lowest legal code point.
    table.map(0x10ffff, Buffer()) // Highest legal code point.
    assertFailsWith<IllegalArgumentException> {
      table.map(0x110000, Buffer())
    }
  }

  @Test fun binarySearchEvenSizedRange() {

    // 0 - 63 bytes
    var length = source.readByte().toInt()

    if (length < 0) {
      // compressed name pointer, first two bits are 1
      // drop second byte of compression offset
      source.skip(1)
    } else {
      while (length > 0) {
        // skip each part of the domain name
        source.skip(length.toLong())
        length = source.readByte().toInt()
      }
    }
  }

   * operation is required.
   *
   * This is invoked at most once, even if [Call.cancel] is invoked multiple times. It may be
   * invoked at any point in a call's life, including before [callStart] and after [callEnd].
   */
  open fun canceled(call: Call) {
  }

  /**
   * Invoked when a call fails due to cache rules.