proposal: bufio: add `(*reader).ResetWithSize` to initialize as fields and use with `Peek`

[Jorropo]

I would like to embed the bufio as reader in my fields to avoid pointers to pointers, reduce allocations and memory used:

 type mything struct{
  someStuff thisIsSomeStuff
- reader *bufio.Reader
+ reader bufio.Reader
 }

This is doable by calling thing.reader.Reset(r) however I also need to use (*reader).Peek but I can't specify the size.
So instead I write: thing.reader = *bufio.NewReaderWithSize(r, maximumBlockSize) which feels wrong.

Proposal:

// ResetWithSize is like [Reset] but it will allocate a new buffer if the current buffer is smaller than required.
func (*Reader) ResetWithSize(r io.Reader, size int)

Potential implementation:

// ResetWithSize is like [Reset] but it will allocate a new buffer if the current buffer is smaller than required.
func (b *Reader) ResetWithSize(r io.Reader, size int) {
 if len(b.buf) < size {
  b.buf = make([]byte, size)
 }
 b.reset(r)
}

[bcmills]

It does seem strange that Reset allocates a new buffer but hard-codes defaultBufSize. 🤔

I wonder if it would be better to provide a more general Resize(size int) method, with the constraint that the new size must be less than or equal to the number of bytes already buffered (as reported by Buffered). It seems like that would work equally well for this use-case, and may address others as well.