{* ../../docs_src/stream_data/tutorial001_py310.py ln[44:47] hl[47] *}

## A Custom `PNGStreamingResponse` { #a-custom-pngstreamingresponse }

In the examples above, the data bytes were streamed, but the response didn't have a `Content-Type` header, so the client didn't know what type of data it was receiving.

You can create a custom sub-class of `StreamingResponse` that sets the `Content-Type` header to the type of data you're streaming.

        assertNotNull(ioException);
        assertTrue(ioException.getCause() instanceof java.io.IOException);

        // Test with custom exception
        Throwable customCause = new FessSystemException("Custom Fess error");
        GsaConfigException customException = new GsaConfigException("GSA custom error", customCause);
        assertNotNull(customException);
        assertTrue(customException.getCause() instanceof FessSystemException);

            }
        }

        return bean;
    }

    /**
     * Parses an XML element looking for the name of a custom implementation.
     *
     * @param parser The XML parser
     * @return Name of the custom implementation; otherwise {@code null}
     */
    private static String parseImplementation(final XmlPullParser parser) {

{* ../../docs_src/query_params_str_validations/tutorial014_an_py310.py hl[10] *}

## Custom Validation { #custom-validation }

There could be cases where you need to do some **custom validation** that can't be done with the parameters shown above.

In those cases, you can use a **custom validator function** that is applied after the normal validation (e.g. after validating that the value is a `str`).

## Base64 vs Files { #base64-vs-files }

Consider first if you can use [Request Files](../tutorial/request-files.md) for uploading binary data and [Custom Response - FileResponse](./custom-response.md#fileresponse--fileresponse-) for sending binary data, instead of encoding it in JSON.

JSON can only contain UTF-8 encoded strings, so it can't contain raw bytes.

To add metadata to your OpenAPI schema, including a license, version, contact, etc, read the docs for [Tutorial - Metadata and Docs URLs](../tutorial/metadata.md).

## OpenAPI Custom URL { #openapi-custom-url }

To customize the OpenAPI URL (or remove it), read the docs for [Tutorial - Metadata and Docs URLs](../tutorial/metadata.md#openapi-url).

## OpenAPI Docs URLs { #openapi-docs-urls }

But now you know how it works, so you can use relative imports in your own apps no matter how complex they are. 🤓

### Add some custom `tags`, `responses`, and `dependencies` { #add-some-custom-tags-responses-and-dependencies }

We are not adding the prefix `/items` nor the `tags=["items"]` to each *path operation* because we added them to the `APIRouter`.

	ReadBufferSize = 64 << 10
)

// ConnSettings - contains connection settings.
type ConnSettings struct {
	DialContext DialContext // Custom dialContext, DialTimeout is ignored if this is already setup.
	LookupHost  LookupHost  // Custom lookupHost, is nil on containerized deployments.
	DialTimeout time.Duration

	// TLS Settings
	RootCAs          *x509.CertPool
	CipherSuites     []uint16

import (
	"context"
	"net"
	"time"
)

// LookupHost is a function to make custom lookupHost for optional cached DNS requests
type LookupHost func(ctx context.Context, host string) (addrs []string, err error)

// DialContextWithLookupHost is a helper function which returns `net.DialContext` function.
// It randomly fetches an IP via custom LookupHost function and dials it by the given dial

        assertDoesNotThrow(() -> request.setFileId(alternating), "Should handle alternating pattern file ID");
    }

    @Test
    @DisplayName("Should create custom implementation of RequestWithFileId")
    void testCustomImplementation() {
        // Given - custom implementation
        class CustomRequestWithFileId implements RequestWithFileId {
            private byte[] fileId;
            private int setCount = 0;