assertThat(response.trailers()).isEqualTo(headersOf("t1", "v1"))
  }

  @Test
  fun peekTrailersHttp1() {
    peekTrailers(Protocol.HTTP_1_1)
  }

  @Test
  fun peekTrailersHttp2() {
    peekTrailers(Protocol.HTTP_2)
  }

  private fun peekTrailers(protocol: Protocol) {
    val responseBody = "a".repeat(OKHTTP_CLIENT_WINDOW_SIZE)
    enableProtocol(protocol)

    server.enqueue(

      !response.promisesBody() -> 0L
      else -> response.headersContentLength()
    }

  override fun openResponseBodySource(response: Response): Source = stream!!.source

  override fun peekTrailers(): Headers? = stream!!.peekTrailers()

  override fun cancel() {
    canceled = true
    stream?.closeLater(ErrorCode.CANCEL)
  }

  companion object {
    private const val CONNECTION = "connection"

    } catch (e: IOException) {
      eventListener.responseFailed(call, e)
      trackFailure(e)
      throw e
    }
  }

  @Throws(IOException::class)
  fun peekTrailers(): Headers? = codec.peekTrailers()

  fun upgradeToSocket(): Socket {
    call.timeoutEarlyExit()
    (codec.carrier as RealConnection).useAsSocket()

    eventListener.requestBodyStart(call)

  @Throws(IOException::class)
  fun openResponseBodySource(response: Response): Source

  /** Returns the trailers after the HTTP response if they're ready. May be empty. */
  @Throws(IOException::class)
  fun peekTrailers(): Headers?

  /**
   * Cancel this stream. Resources held by this stream will be cleaned up, though not synchronously.
   * That may happen later by the connection pool thread.
   */
  fun cancel()

  /**

            response
              .newBuilder()
              .body(responseBody)
              .trailers(
                object : TrailersSource {
                  override fun peek() = exchange.peekTrailers()

                  override fun get(): Headers {
                    val source = responseBody.source()
                    if (source.isOpen) {
                      source.skipAll()
                    }

    val stream = connection.newStream(headerEntries("a", "artichaut"), false)
    connection.writePingAndAwaitPong()
    assertThat(stream.takeHeaders()).isEqualTo(headersOf("headers", "bam"))
    assertThat(stream.peekTrailers()).isEqualTo(Headers.EMPTY)
    assertThat(connection.openStreamCount()).isEqualTo(0)

    // Verify the peer received what was expected.
    val synStream = peer.takeFrame()

          newFixedLengthSource(response.request.url, contentLength)
        } else {
          newUnknownLengthSource(response.request.url)
        }
      }
    }

  override fun peekTrailers(): Headers? {
    if (trailers === TRAILERS_RESPONSE_BODY_TRUNCATED) {
      throw IOException("Trailers cannot be read because the response body was truncated")
    }

   *
   * @throws IOException if the trailers cannot be loaded, such as if the network connection is
   *     dropped.
   */
  @Throws(IOException::class)
  fun peekTrailers(): Headers? = trailersSource.peek()

  /**
   * Peeks up to [byteCount] bytes from the response body and returns them as a new response

      }
      throw errorException ?: StreamResetException(errorCode!!)
    }
  }

  /**
   * Returns the trailers if they're immediately available.
   */
  @Throws(IOException::class)
  fun peekTrailers(): Headers? {
    withLock {
      if (source.finished && source.receiveBuffer.exhausted() && source.readBuffer.exhausted()) {
        return source.trailers ?: Headers.EMPTY
      }
      if (errorCode != null) {

Change Log
==========

## Version 4.x

See [4.x Change log](https://square.github.io/okhttp/changelogs/changelog_4x/) for the stable version changelogs.

## Version 5.1.0

_2025-07-07_

 *  New: `Response.peekTrailers()`. When we changed `Response.trailers()` to block instead of
    throwing in 5.0.0, we inadvertently removed the ability for callers to peek the trailers