## Pydantic models

<a href="https://docs.pydantic.dev/" class="external-link" target="_blank">Pydantic</a> is a Python library to perform data validation.

You declare the "shape" of the data as classes with attributes.

And each attribute has a type.

* Add a **JSON Schema** for the response, in the OpenAPI *path operation*.
    * This will be used by the **automatic docs**.
    * It will also be used by automatic client code generation tools.

    These Pydantic models define more or less a "schema" (a valid data shape).

    So this will help us avoiding confusion while using both.

### Create initial Pydantic *models* / schemas

    this because it only occurs if you have proxy configured and you share a connection pool among
    multiple `OkHttpClient` instances.

    This particularly-subtle bug was caused by us assigning each `OkHttpClient` instance its own
    `NullProxySelector` when an explicit proxy is configured. But we don't share connections when
    the proxy selectors are different. Ugh!


## Version 4.2.0

    assertThat(a.dispatcher).isNotNull()
    assertThat(a.connectionPool).isNotNull()
    assertThat(a.sslSocketFactory).isNotNull()
    assertThat(a.x509TrustManager).isNotNull()

    // Multiple clients share the instances.
    val b = client.newBuilder().build()
    assertThat(b.dispatcher).isSameAs(a.dispatcher)
    assertThat(b.connectionPool).isSameAs(a.connectionPool)

   *
   * Once true this is always true. Guarded by this.
   */
  var noNewExchanges = false

  /**
   * If true, this connection may not be used for coalesced requests. These are requests that could
   * share the same connection without sharing the same hostname.
   */
  private var noCoalescedConnections = false

  /**
   * The number of times there was a problem establishing a stream that could be due to route

        network stack is offline.

  [[3]] "Remote" repositories referenced using the file:// protocol may
        be available. However, if that file:// url references a
        file-share, as in the case of an NFS or SMB mount, that will
        be unavailable.

  So, offline mode has several implications, some of which may not be
  altogether obvious:

            if (relocatedArtifact != null) {
                if (withinSameGav(relocatedArtifact, a)) {
                    result.setArtifact(relocatedArtifact);
                    return model; // they share same model
                } else {
                    result.addRelocation(a);
                    a = relocatedArtifact;
                    result.setArtifact(a);
                }
            } else {

 *
 * The task runner is also responsible for releasing held threads when the library is unloaded.
 * This is for the benefit of container environments that implement code unloading.
 *
 * Most applications should share a process-wide [TaskRunner] and use queues for per-client work.
 */
class TaskRunner(
  val backend: Backend,
  internal val logger: Logger = TaskRunner.logger,
) {
  val lock: ReentrantLock = ReentrantLock()

            } else {
                repoMetadata.setMetadata(metadata);
                setRepository = true;
            }
        }
        return setRepository;
    }

    /*
     * TODO share with DefaultPluginMappingManager.
     */
    protected Metadata readMetadata(File mappingFile) throws RepositoryMetadataReadException {

        try (InputStream in = Files.newInputStream(mappingFile.toPath())) {