{* ../../docs_src/header_param_models/tutorial001_an_py310.py hl[9:14,18] *}

**FastAPI** will **extract** the data for **each field** from the **headers** in the request and give you the Pydantic model you defined.

## Check the Docs { #check-the-docs }

You can see the required headers in the docs UI at `/docs`:

<div class="screenshot">

  var bodyLimit: Long by delegate::bodyLimit

  var serverSocketFactory: ServerSocketFactory? by delegate::serverSocketFactory

  var dispatcher: Dispatcher = QueueDispatcher()
    set(value) {
      field = value
      delegate.dispatcher = value.wrap()
    }

  val port: Int
    get() {
      before() // This implicitly starts the delegate.
      return delegate.port
    }

  val hostName: String

    }

    if (userRequest.header("Connection") == null) {
      requestBuilder.header("Connection", "Keep-Alive")
    }

    // If we add an "Accept-Encoding: gzip" header field we're responsible for also decompressing
    // the transfer stream.
    var transparentGzip = false
    if (userRequest.header("Accept-Encoding") == null && userRequest.header("Range") == null) {
      transparentGzip = true

     * The media-type multipart/form-data follows the rules of all multipart MIME data streams as
     * outlined in RFC 2046. In forms, there are a series of fields to be supplied by the user who
     * fills out the form. Each field has a name. Within a given form, the names are unique.
     */
    @JvmField
    val FORM = "multipart/form-data".toMediaType()

    private val COLONSPACE = byteArrayOf(':'.code.toByte(), ' '.code.toByte())

        if (value != null && filePathMap.containsKey(value)) {
            return filePathMap.get(value);
        }
        return value;
    }

    /**
     * Updates the thumbnail field in the search index.
     * @param thumbnailId The thumbnail ID.
     * @param value The thumbnail value to update.
     */
    protected void updateThumbnailField(final String thumbnailId, final String value) {

        // Constructor should initialize the object without throwing exceptions
        assertNotNull(querySecurityDesc);

        // Test toString contains the expected values to verify field initialization
        String str = querySecurityDesc.toString();
        assertTrue(str.contains("fid=0x" + Hexdump.toHexString(fid, 4)));

// Only changing meaning of fields requires a version bump.
// bucketMetadataFormat refers to the format.
// bucketMetadataVersion can be used to track a rolling upgrade of a field.
type BucketMetadata struct {
	Name                        string
	Created                     time.Time
	LockEnabled                 bool // legacy not used anymore.
	PolicyConfigJSON            []byte

- **I/O Operations** (`org.codelibs.core.io`) - File handling, resource management, stream utilities, and traversal utilities for efficient resource processing
- **Reflection** (`org.codelibs.core.lang`) - Class loading, method/field access, type introspection utilities, and generics support
- **Exception Handling** (`org.codelibs.core.exception`) - Runtime exception wrappers for common checked exceptions with consistent error handling

### Modern Java 21 Support

  @Throws(IOException::class)
  fun createRequestBody(
    request: Request,
    contentLength: Long,
  ): Sink

  /** This should update the HTTP engine's sentRequestMillis field. */
  @Throws(IOException::class)
  fun writeRequestHeaders(request: Request)

  /** Flush the request to the underlying socket. */
  @Throws(IOException::class)
  fun flushRequest()

    }

    private void setValueToObject(Object obj, String name, Object value) {
        Field field = ClassUtil.getDeclaredField(obj.getClass(), name);
        field.setAccessible(true);
        FieldUtil.set(field, obj, value);
    }

    public void test_pruneNode() throws Exception {