what is it

A Buffer is a variable-sized buffer of bytes with [Buffer.Read] and [Buffer.Write] methods.

• The zero value for Buffer is an empty buffer ready to use.

type Buffer struct {
  buf      []byte // contents are the bytes buf[off : len(buf)]
  off      int    // read at &buf[off], write at &buf[len(buf)]
  lastRead readOp // last read operation, so that Unread* can work correctly.
}

Create new buffer/byte array ([]byte)

io.Reader is an interface that wraps the basic Read method.

• Read reads up to len(p) bytes into p
• It returns the number of bytes read (0 <= n <= len(p)) and any error encountered

type Reader interface {
  Read(p []byte) (n int, err error)
}

It is useful when

import (
  "bytes"
)

func main() []byte {
  buf := new(bytes.Buffer)

  return buf.Bytes()
}