Then your API will (let's imagine):

* Send the invoice to some customer of the external developer.
* Collect the money.
* Send a notification back to the API user (the external developer).
    * This will be done by sending a POST request (from *your API*) to some *external API* provided by that external developer (this is the "callback").

	// If x-amz-content-sha256 is set and the value is not
	// 'UNSIGNED-PAYLOAD' we should validate the content sha256.
	switch v[0] {
	case unsignedPayload, unsignedPayloadTrailer:
		return true
	case emptySHA256:
		// some broken clients set empty-sha256
		// with > 0 content-length in the body,
		// we should skip such clients and allow
		// blindly such insecure clients only if
		// S3 strict compatibility is disabled.

@app.get("/items/{item_id}")
async def read_item(item_id: str):
    if item_id not in items:
        raise HTTPException(
            status_code=404,
            detail="Item not found",
            headers={"X-Error": "Some custom header"},
        )
    return {"item": items[item_id]}


@app.get("/http-no-body-statuscode-exception")
async def no_body_status_code_exception():
    raise HTTPException(status_code=204)

     * This is usually set by the Maven launcher script using the "maven.home" system property.
     *
     * @return the Maven installation directory path
     */
    @Nonnull
    Path installationDirectory();

    /**
     * Returns the user's home directory.
     * This is typically obtained from the "user.home" system property.
     *
     * @return the user's home directory path
     */
    @Nonnull
    Path userHomeDirectory();

  // TODO(b/192446998): Remove this override after tools understand nullness better.
  public @Nullable V put(K key, @ParametricNullness V value) {
    return super.put(key, value);
  }

  @CanIgnoreReturnValue
  @Override
  @SuppressWarnings("RedundantOverride") // b/192446478: RedundantOverride ignores some annotations.

                plugins {
                  id 'elasticsearch.internal-distribution-archive-check'
                }"""
        }
        file("SomeFile.txt") << """
            some dummy txt file
        """

        buildFile << """
            allprojects {
                apply plugin:'base'
                ext.elasticLicenseUrl = "http://foo.bar"
            }

        MapTestSuiteBuilder.using(
                new TestTypeToInstanceMapGenerator() {
                  // Other tests will verify what real, warning-free usage looks like
                  // but here we have to do some serious fudging
                  @Override
                  @SuppressWarnings({"unchecked", "rawtypes"})
                  public Map<TypeToken, Object> create(Object... elements) {

  // TODO(b/192446998): Remove this override after tools understand nullness better.
  public @Nullable V put(K key, @ParametricNullness V value) {
    return super.put(key, value);
  }

  @CanIgnoreReturnValue
  @Override
  @SuppressWarnings("RedundantOverride") // b/192446478: RedundantOverride ignores some annotations.

        // 4 (dataCount) + 4 (dataOffset) + 1 (setupCount) + 2 (function)
        assertEquals(38, bytesWritten, "Number of bytes written should be 38 for primary transaction");

        // Verify some key values
        assertEquals(smbComNtTransaction.maxSetupCount, dst[0], "maxSetupCount should be written correctly");
        assertEquals(smbComNtTransaction.totalParameterCount, SmbComTransaction.readInt4(dst, 3),

# Custom Request and APIRoute class { #custom-request-and-apiroute-class }

In some cases, you may want to override the logic used by the `Request` and `APIRoute` classes.

In particular, this may be a good alternative to logic in a middleware.

For example, if you want to read or manipulate the request body before it is processed by your application.

/// danger

This is an "advanced" feature.