OkHttpClient
        .Builder()
        .protocols(listOf(Protocol.H2_PRIOR_KNOWLEDGE, Protocol.H2_PRIOR_KNOWLEDGE))
    }.also { expected ->
      assertThat(expected.message).isEqualTo(
        "protocols containing h2_prior_knowledge cannot use other protocols: " +
          "[h2_prior_knowledge, h2_prior_knowledge]",
      )
    }
  }

   *
   * See also [Starting HTTP/2 with Prior Knowledge][rfc_7540_34].
   *
   * [rfc_7540_34]: https://datatracker.ietf.org/doc/html/rfc7540#autoid-10
   */
  H2_PRIOR_KNOWLEDGE("h2_prior_knowledge"),

  /**
   * QUIC (Quick UDP Internet Connection) is a new multiplexed and secure transport atop UDP,
   * designed from the ground up and optimized for HTTP/2 semantics. HTTP/1.1 semantics are layered

    assertThat(get("http/1.1")).isEqualTo(Protocol.HTTP_1_1)
    assertThat(get("spdy/3.1")).isEqualTo(Protocol.SPDY_3)
    assertThat(get("h2")).isEqualTo(Protocol.HTTP_2)
    assertThat(get("h2_prior_knowledge")).isEqualTo(Protocol.H2_PRIOR_KNOWLEDGE)
    assertThat(get("quic")).isEqualTo(Protocol.QUIC)
    assertThat(get("h3")).isEqualTo(Protocol.HTTP_3)
    assertThat(get("h3-29")).isEqualTo(Protocol.HTTP_3)
  }

  @Test

      server.protocols = listOf(Protocol.H2_PRIOR_KNOWLEDGE, Protocol.H2_PRIOR_KNOWLEDGE)
      fail<Any>()
    } catch (expected: IllegalArgumentException) {
      assertThat(expected.message).isEqualTo(
        "protocols containing h2_prior_knowledge cannot use other protocols: " +
          "[h2_prior_knowledge, h2_prior_knowledge]",
      )
    }
  }

  @Test

      server.protocols = listOf(Protocol.H2_PRIOR_KNOWLEDGE, Protocol.H2_PRIOR_KNOWLEDGE)
      fail<Unit>()
    } catch (expected: IllegalArgumentException) {
      assertThat(expected.message).isEqualTo(
        "protocols containing h2_prior_knowledge cannot use other protocols: " +
          "[h2_prior_knowledge, h2_prior_knowledge]",
      )
    }
  }

  @Test

/**
 * Used when we were unsuccessful in the planning phase of a connection:
 *
 *  * A DNS lookup failed
 *  * The configuration is incapable of carrying the request, such as when the client is configured
 *    to use `H2_PRIOR_KNOWLEDGE` but the URL's scheme is `https:`.
 *  * Preemptive proxy authentication failed.
 *
 * Planning failures are not necessarily fatal. For example, even if we can't DNS lookup the first

          "CLEARTEXT communication to $host not permitted by network security policy",
        )
      }
    } else {
      if (Protocol.H2_PRIOR_KNOWLEDGE in route.address.protocols) {
        throw UnknownServiceException("H2_PRIOR_KNOWLEDGE cannot be used with HTTPS")
      }
    }

    val tunnelRequest =
      when {
        route.requiresTunnel() -> createTunnelRequest(route)

    set(value) {
      val protocolList = value.toImmutableList()
      require(Protocol.H2_PRIOR_KNOWLEDGE !in protocolList || protocolList.size == 1) {
        "protocols containing h2_prior_knowledge cannot use other protocols: $protocolList"
      }
      require(Protocol.HTTP_1_1 in protocolList || Protocol.H2_PRIOR_KNOWLEDGE in protocolList) {
        "protocols doesn't contain http/1.1: $protocolList"
      }

        require(Protocol.H2_PRIOR_KNOWLEDGE in protocolsCopy || HTTP_1_1 in protocolsCopy) {
          "protocols must contain h2_prior_knowledge or http/1.1: $protocolsCopy"
        }
        require(Protocol.H2_PRIOR_KNOWLEDGE !in protocolsCopy || protocolsCopy.size <= 1) {
          "protocols containing h2_prior_knowledge cannot use other protocols: $protocolsCopy"
        }

    server.setProtocols(Collections.singletonList(Protocol.H2_PRIOR_KNOWLEDGE));
    server.enqueue(new MockResponse().setBody("hello"));
    server.start();

    OkHttpClient client = new OkHttpClient.Builder()
        .socketFactory(new UnixDomainSocketFactory(socketFile))
        .protocols(Collections.singletonList(Protocol.H2_PRIOR_KNOWLEDGE))
        .build();

    Request request = new Request.Builder()