import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.nio.charset.Charset;

/**
 * A destination to which bytes can be written, such as a file. Unlike an {@link OutputStream}, a
 * {@code ByteSink} is not an open, stateful stream that can be written to and closed. Instead, it
 * is an immutable <i>supplier</i> of {@code OutputStream} instances.
 *
 * <p>{@code ByteSink} provides two kinds of methods:
 *

import java.io.Writer;
import java.nio.charset.Charset;
import java.util.Iterator;
import java.util.stream.Stream;

/**
 * A destination to which characters can be written, such as a text file. Unlike a {@link Writer}, a
 * {@code CharSink} is not an open, stateful stream that can be written to and closed. Instead, it
 * is an immutable <i>supplier</i> of {@code Writer} instances.
 *
 * <p>{@code CharSink} provides two kinds of methods:
 *
 * <ul>

// It returns the index where bytes should be written and whether it succeeded.
func (b *Buffer) tryGrowByReslice(n int) (int, bool) {
	if l := len(b.buf); n <= cap(b.buf)-l {
		b.buf = b.buf[:l+n]
		return l, true
	}
	return 0, false
}

// grow grows the buffer to guarantee space for n more bytes.
// It returns the index where bytes should be written.
// If the buffer can't grow it will panic with ErrTooLarge.

		fmt.Println("ReadFrom Error:", err)
		return
	}

	if err = writer.Flush(); err != nil {
		fmt.Println("Flush Error:", err)
		return
	}

	fmt.Println("Bytes written:", n)
	fmt.Println("Buffer contents:", buf.String())
	// Output:
	// Bytes written: 41
	// Buffer contents: Hello, world!
	// This is a ReadFrom example.
}

// The simplest use of a Scanner, to read standard input as a set of lines.

{* ../../docs_src/background_tasks/tutorial002_an_py310.py hl[13,15,22,25] *}


In this example, the messages will be written to the `log.txt` file *after* the response is sent.

If there was a query in the request, it will be written to the log in a background task.

And then another background task generated at the *path operation function* will write a message using the `email` path parameter.

				t.Errorf("%s: buf.Flush = %v", context, e)
			}

			written := w.Bytes()
			if len(written) != nwrite {
				t.Errorf("%s: %d bytes written", context, len(written))
			}
			for l := 0; l < len(written); l++ {
				if written[l] != data[l] {
					t.Errorf("wrong bytes written")
					t.Errorf("want=%q", data[:len(written)])
					t.Errorf("have=%q", written)
				}
			}
		}
	}
}

  /**
   * Copies bytes from this hash code into {@code dest}.
   *
   * @param dest the byte array into which the hash code will be written
   * @param offset the start offset in the data
   * @param maxLength the maximum number of bytes to write
   * @return the number of bytes written to {@code dest}
   * @throws IndexOutOfBoundsException if there is not enough room in {@code dest}
   */
  @CanIgnoreReturnValue

  @Override
  public void writeChar(int v) throws IOException {
    writeShort(v);
  }

  /**
   * Writes a {@code String} as specified by {@link DataOutputStream#writeChars(String)}, except
   * each character is written using little-endian byte order.
   *
   * @throws IOException if an I/O error occurs
   */
  @Override
  public void writeChars(String s) throws IOException {
    for (int i = 0; i < s.length(); i++) {

  /**
   * Copies bytes from this hash code into {@code dest}.
   *
   * @param dest the byte array into which the hash code will be written
   * @param offset the start offset in the data
   * @param maxLength the maximum number of bytes to write
   * @return the number of bytes written to {@code dest}
   * @throws IndexOutOfBoundsException if there is not enough room in {@code dest}
   */
  @CanIgnoreReturnValue

///

/// tip

Notice that in this case we are using a standard Python `open()` function that interacts with a file.

So, it involves I/O (input/output), that requires "waiting" for things to be written to disk.

But `open()` doesn't use `async` and `await`.

So, we declare the event handler function with standard `def` instead of `async def`.

///

### `startup` and `shutdown` together