package iox

import (
	`io`
)

/*
CopyBufN is a mix between io.CopyN and io.CopyBuffer.

Despite what the docs may suggest, io.CopyN does NOT *read* n bytes from src AND write n bytes to dst.
Instead, it always reads 32 KiB from src, and writes n bytes to dst.

There are, of course, cases where this is deadfully undesired.

One can, of course, use io.CopyBuffer, but this is a bit annoying since you then have to provide a buffer yourself.

This convenience-wraps io.CopyBuffer to have a similar signature to io.CopyN but properly uses n for both reading and writing.
*/
func CopyBufN(dst io.Writer, src io.Reader, n int64) (written int64, err error) {

	var b []byte

	if n <= 0 {
		err = ErrBufTooSmall
		return
	}

	b = make([]byte, n)

	written, err = io.CopyBuffer(dst, src, b)

	return
}

// CopyBufWith allows for specifying a buffer allocator function, otherwise acts as CopyBufN.
func CopyBufWith(dst io.Writer, src io.Reader, bufFunc func() (b []byte)) (written int64, err error) {

	written, err = io.CopyBuffer(dst, src, bufFunc())

	return
}