You can declare a Pydantic model with `bytes` fields, and then use `val_json_bytes` in the model config to tell it to use base64 to *validate* input JSON data, as part of that validation it will decode the base64 string into bytes.

{* ../../docs_src/json_base64_bytes/tutorial001_py310.py ln[1:9,29:35] hl[9] *}

If you check the `/docs`, they will show that the field `data` expects base64 encoded bytes:

<div class="screenshot">

from fastapi.testclient import TestClient
from pydantic import BaseModel, ConfigDict
from pydantic.fields import FieldInfo


def test_model_field_default_required():
    from fastapi._compat import v2

    # For coverage
    field_info = FieldInfo(annotation=str)
    field = v2.ModelField(name="foo", field_info=field_info)
    assert field.default is Undefined


def test_complex():
    app = FastAPI()

    @app.post("/")

    return set(re.findall("{(.*?)}", path))


_invalid_args_message = (
    "Invalid args for response field! Hint: "
    "check that {type_} is a valid Pydantic field type. "
    "If you are using a return type annotation that is not a valid Pydantic "
    "field (e.g. Union[Response, dict, None]) you can disable generating the "
    "response model from the type annotation with the path operation decorator "

        final String[] fields = getParamValueArray(request, "facet.field");
        final String[] queries = getParamValueArray(request, "facet.query");
        if (fields.length == 0 && queries.length == 0) {
            return null;
        }
        final FacetInfo facetInfo = new FacetInfo();
        facetInfo.field = fields;
        facetInfo.query = queries;

        assertTrue(messages.hasMessageOf("doc.title"), "Required field 'title' should have error at 'doc.title' property");
        assertTrue(messages.hasMessageOf("doc.role"), "Required field 'role' should have error at 'doc.role' property");
        assertTrue(messages.hasMessageOf("doc.boost"), "Required field 'boost' should have error at 'doc.boost' property");

        });
    }

    @Test
    void testInheritedFields() throws Exception {
        // Verify inherited fields are properly set
        assertEquals(0x10, msrpcShareGetInfo.getOpnum());

        // Test that the info field is properly initialized
        Field infoField = msrpcShareGetInfo.getClass().getSuperclass().getDeclaredField("info");
        infoField.setAccessible(true);

    /** Mapping type for array fields. */
    public static final String MAPPING_TYPE_ARRAY = "array";

    /** Mapping type for string fields. */
    public static final String MAPPING_TYPE_STRING = "string";

    /** Mapping type for long fields. */
    public static final String MAPPING_TYPE_LONG = "long";

    /** Mapping type for double fields. */

     * Returns the field.
     *
     * @return the field
     */
    Field getField();

    /**
     * Returns the field name.
     *
     * @return the field name
     */
    String getFieldName();

    /**
     * Returns the type of the field.
     *
     * @param <T>
     *            the type of the field
     * @return the type of the field
     */
    <T> Class<T> getFieldType();

    /**

    /**
     * Field name for ID.
     */
    public static final String ID = "id";

    /**
     * Field name for transformer name.
     */
    public static final String TRANSFORMER_NAME = "transformerName";

    /**
     * Field name for data.
     */
    public static final String DATA = "data";

    /**
     * Field name for encoding.
     */

     * This is a required field indicating when the job began.
     */
    @Required
    public String startTime;

    /**
     * The timestamp when the job completed execution.
     * This field indicates when the job finished, if it has completed.
     */
    public String endTime;

    /**
     * Initializes the form with default null values.