if (isClient) {
          "Server-sent frames must not be masked."
        } else {
          "Client-sent frames must be masked."
        },
      )
    }

    // Get frame length, optionally reading from follow-up bytes if indicated by special values.
    frameLength = (b1 and B1_MASK_LENGTH).toLong()
    if (frameLength == PAYLOAD_SHORT.toLong()) {

  val fileSystem: FileSystem = FileSystem.RESOURCES,
) {
  /** True after we've attempted to read the list for the first time. */
  private val listRead = AtomicBoolean(false)

  /** Used for concurrent threads reading the list for the first time. */
  private val readCompleteLatch = CountDownLatch(1)

  // The lists are held as a large array of UTF-8 bytes. This is to avoid allocating lots of strings

      return null // Another edit is in progress.
    }

    if (entry != null && entry.lockingSourceCount != 0) {
      return null // We can't write this file because a reader is still reading it.
    }

    if (mostRecentTrimFailed || mostRecentRebuildFailed) {
      // The OS has become our enemy! If the trim job failed, it means we are storing more data than

   * body. This was misleading for tracing because it was too early.
   */
  open fun responseBodyStart(call: Call) {
  }

  /**
   * Invoked immediately after receiving a response body and completing reading it.
   *
   * Will only be invoked for requests having a response body e.g. won't be invoked for a web socket
   * upgrade.
   *

      if (this.errorCode == null) {
        this.errorCode = errorCode
        condition.signalAll()
      }
    }
  }

  /**
   * Returns true if read timeouts should be enforced while reading response headers or body bytes.
   * We always do timeouts in the HTTP server role. For clients, we only do timeouts after the
   * request is transmitted. This is only interesting for duplex calls where the request and

    frame.writeInt(expectedStreamId and 0x7fffffff)
    frame.writeAll(headerBlock)

    // Check writer sends the same bytes.
    assertThat(sendHeaderFrames(false, sentHeaders)).isEqualTo(frame)

    // Reading the above frames should result in a concatenated headerBlock.
    reader.nextFrame(
      requireSettings = false,
      object : BaseTestHandler() {
        override fun headers(
          inFinished: Boolean,

### Asynchronous Get ([.kt][AsynchronousGetKotlin], [.java][AsynchronousGetJava])

Download a file on a worker thread, and get called back when the response is readable. The callback is made after the response headers are ready. Reading the response body may still block. OkHttp doesn't currently offer asynchronous APIs to receive a response body in parts.

=== ":material-language-kotlin: Kotlin"
    ```kotlin
      private val client = OkHttpClient()

  var complete = (upstream == null)

  /** The most recently read bytes from [upstream]. This is a suffix of [file]. Guarded by this. */
  val buffer = Buffer()

  /**
   * Reference count of the number of active sources reading this stream. When decremented to 0
   * resources are released and all following calls to [.newSource] return null. Guarded by this.
   */
  var sourceCount = 0

  val isClosed: Boolean
    get() = file == null

    check(state == STATE_OPEN_RESPONSE_BODY) { "state: $state" }
    state = STATE_READING_RESPONSE_BODY
    return FixedLengthSource(length)
  }

  private fun newChunkedSource(url: HttpUrl): Source {
    check(state == STATE_OPEN_RESPONSE_BODY) { "state: $state" }
    state = STATE_READING_RESPONSE_BODY
    return ChunkedSource(url)
  }

  private fun newUnknownLengthSource(): Source {

    // Give up because the cache cannot be written.
    try {
      editor?.abort()
    } catch (_: IOException) {
    }
  }

  /**
   * Initialize the cache. This will include reading the journal files from the storage and building
   * up the necessary in-memory cache information.
   *
   * The initialization time may vary depending on the journal file size and the current actual