func Full(buf Buffer) bool {
	return buf.Len() == buf.Cap()
}
Full returns true iff buf.Len() == buf.Cap()
package buffer
import (
	"io"
	"os"
)
type Buffer interface {
	Len() int64  
	Cap() int64  
	io.Reader    
	io.Writer    
	Reset()      
}
type BufferAt interface {
	Buffer
	io.ReaderAt
	io.WriterAt
}
func len64(p []byte) int64 {
	return int64(len(p))
}
func Gap(buf Buffer) int64 {
	return buf.Cap() - buf.Len()
}