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

## Recap

You have been reading here some of the main concepts that you would probably need to keep in mind when deciding how to deploy your application:

* Security - HTTPS
* Running on startup
* Restarts

### Create Pydantic *models* / schemas for reading / returning

Now create Pydantic *models* (schemas) that will be used when reading data, when returning it from the API.

For example, before creating an item, we don't know what will be the ID assigned to it, but when reading it (when returning it from the API) we will already know its ID.

### Creating the `Settings` only once with `lru_cache`

Reading a file from disk is normally a costly (slow) operation, so you probably want to do it only once and then re-use the same settings object, instead of reading it for each request.

But every time we do:

```Python
Settings()
```

    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()