net.Conn转换函数应该保留原始数据分割吗？

To clarify, a net.Conn transform() function transforms data write to/read from a connection, an example is as follow:

type TransformedConn struct {
  net.Conn
}

func (c *TransformedConn) Read(p []byte) (int, error) {
  n, err := c.Conn.Read(p)
  transform(p)
  return n, err
}

func (c *TransformedConn) Write(p []byte) (int, error) {
  t := append([]byte{}, p...) // as `p` must not be modified per io.Writer doc
  transform(t)
  return c.Conn.Write(t)
}

Similarly, crypto/cipher.StreamReader and crypto/cipher.StreamWriter perform a similar operation.

As required by io.Writer.Write(), it cannot modify the input buffer. In case the size of the buffer is huge, creating a buffer of the same size will be very expensive. So I'm wondering if it's ok for such transform function to write data out in smaller chunks, to allow us using a smaller scratch space?

I've found such chunking technique will cause some program to fail, especially the ones use io.ReadFull() and io.ReadAtLeast(). Because they implicitly expect that the data to arrive will from a single read() call.

Could someone point me a doc or a spec on how to write such transform functions?

Thanks!