if errCode != ErrNone {
		return cred, "", "", time.Time{}, errCode
	}

	// Payload streaming.
	payload := streamingContentSHA256
	if trailers {
		payload = streamingContentSHA256Trailer
	}

	// Payload for STREAMING signature should be 'STREAMING-AWS4-HMAC-SHA256-PAYLOAD'
	if payload != req.Header.Get(xhttp.AmzContentSha256) {
		return cred, "", "", time.Time{}, ErrContentSHA256Mismatch
	}

                .result());
    }

    /**
     * Create a new protected words entry for the specified dictionary.
     *
     * @param dictId identifier of the dictionary
     * @param body create request payload
     * @return JSON response containing creation result and new entry ID
     */
    // POST /api/admin/dict/protwords/setting/{dictId}
    @Execute

Let's start with a simple FastAPI application:

{* ../../docs_src/generate_clients/tutorial001_py39.py hl[7:9,12:13,16:17,21] *}

Notice that the *path operations* define the models they use for request payload and response payload, using the models `Item` and `ResponseMessage`.

### API Docs { #api-docs }

If you go to `/docs`, you will see that it has the **schemas** for the data to be sent in requests and received in responses:

    private @interface ValidCronRequired {
        String message() default "Must be a valid non-blank cron expression";

        Class<?>[] groups() default {};

        Class<? extends jakarta.validation.Payload>[] payload() default {};
    }

    private static class ComposedBean {
        @ValidCronRequired
        private String composedCron;

        public String getComposedCron() {

        void testVerifyFailedState() {
            assertFalse(testBlock.isVerifyFailed());
        }

        @Test
        @DisplayName("Test raw payload handling")
        void testRawPayloadHandling() {
            byte[] payload = new byte[] { 1, 2, 3, 4, 5 };

            assertNull(testBlock.getRawPayload());
            assertFalse(testBlock.isRetainPayload());

        // Arrange
        byte[] payload = new byte[] { 5, 6 };

        // Act
        spyBlob.set(payload);

        // Assert
        verify(spyBlob, times(1)).set(payload);
        assertSame(payload, spyBlob.get(), "Spy should behave like real object exposing same array");
        assertEquals(2, spyBlob.length(), "length() should reflect the set payload length");
    }

                // Implementation for raw payload
            }

            @Override
            public byte[] getRawPayload() {
                // Implementation for getting raw payload
                return null;
            }

            @Override
            public boolean isRetainPayload() {
                // Implementation for retain payload flag
                return false;
            }

// The remaining payload and versions are returned.
func checkXL2V1(buf []byte) (payload []byte, major, minor uint16, e error) {
	if len(buf) <= 8 {
		return payload, 0, 0, fmt.Errorf("xlMeta: no data")
	}

	if !bytes.Equal(buf[:4], xlHeader[:]) {
		return payload, 0, 0, fmt.Errorf("xlMeta: unknown XLv2 header, expected %v, got %v", xlHeader[:4], buf[:4])
	}

        if (isRetainPayload()) {
            final byte[] payload = new byte[len];
            System.arraycopy(buffer, start, payload, 0, len);
            setRawPayload(payload);
        }

        if (!verifySignature(buffer, start, len)) {

        }
        // The region before offset and after the payload must remain untouched.
        for (int i = 0; i < offset; i++) {
            final int idx = i;
            assertEquals(0, dst[i], () -> "pre-offset byte " + idx + " modified");
        }
        for (int i = offset + 8; i < dst.length; i++) {
            final int idx = i;
            assertEquals(0, dst[i], () -> "post-payload byte " + idx + " modified");
        }
    }