## 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.

The contents are **encrypted**, even though they are being sent with the **HTTP protocol**.

It is a common practice to have **one program/HTTP server** running on the server (the machine, host, etc.) and **managing all the HTTPS parts**: receiving the **encrypted HTTPS requests**, sending the **decrypted HTTP requests** to the actual HTTP application running in the same server (the **FastAPI** application, in this case), take the **HTTP response** from the application, **encrypt it** using...

You can define background tasks to be run *after* returning a response.

This is useful for operations that need to happen after a request, but that the client doesn't really have to be waiting for the operation to complete before receiving the response.

This includes, for example:

* Email notifications sent after performing an action:

   * leaking resources callers must [close the response body][ResponseBody] or the response.
   *
   * Note that transport-layer success (receiving a HTTP response code, headers and body) does not
   * necessarily indicate application-layer success: `response` may still indicate an unhappy HTTP
   * response code like 404 or 500.
   *

                                 n_ask_attempts=_DEFAULT_PROMPT_ASK_ATTEMPTS):
  """Loop over user prompts for an ENV param until receiving a valid response.

  For the env param var_name, read from the environment or verify user input
  until receiving valid input. When done, set var_name in the environ_cp to its
  new value.

  Args:
    environ_cp: (Dict) copy of the os.environ.

            region.close();
            totalReleased.incrementAndGet();
        }
    }

    /**
     * Get a receive region from the pool or allocate a new one
     *
     * @return memory region for receiving
     * @throws IOException if allocation fails
     */
    public RdmaMemoryRegion getReceiveRegion() throws IOException {
        RdmaMemoryRegion region = availableReceiveRegions.poll();
        if (region != null) {

   *
   * This method returns false unless it is overridden by a subclass.
   *
   * ### Duplex Transmission
   *
   * With regular HTTP calls the request always completes sending before the response may begin
   * receiving. With duplex the request and response may be interleaved! That is, request body bytes
   * may be sent after response headers or body bytes have been received.
   *

CAREFUL: When utilizing two-way communication, it is important to ensure that the remote handler is not blocked on a send.
If the remote handler is blocked on a send, and the client is trying to send without the remote receiving,
the operation would become deadlocked if the channels are full.

### Typed handlers

Typed handlers are handlers that have a specific type for the request and response payloads.

```go

        // Tree handle is released after close
        verify(tree, atLeastOnce()).release();
    }

    @Test
    @DisplayName("open(): server returns NO_SUCH_FILE after receiving response -> iterator empty, closed")
    void openHandlesNoSuchFileGracefully() throws Exception {
        when(tree.send(any(Trans2FindFirst2.class), any(Trans2FindFirst2Response.class))).thenAnswer((InvocationOnMock inv) -> {

    // retry, we return true and try a new route.
    return true
  }

  /**
   * Figures out the HTTP request to make in response to receiving [userResponse]. This will
   * either add authentication headers, follow redirects or handle a client request timeout. If a
   * follow-up is either unnecessary or not applicable, this returns null.
   */