// Copyright 2015 The Go Authors.  All rights reserved.// Use of this source code is governed by a BSD-style// license that can be found in the LICENSE file. package elf import (	"io"	"os") // errorReader returns error from all operations.type errorReader struct {	error} func (r errorReader) Read(p []byte) (n int, err error) {	return 0, r.error} func (r errorReader) ReadAt(p []byte, off int64) (n int, err error) {	return 0, r.error} func (r errorReader) Seek(offset int64, whence int) (int64, error) {	return 0, r.error} func (r errorReader) Close() error {	return r.error} // readSeekerFromReader converts an io.Reader into an io.ReadSeeker.// In general Seek may not be efficient, but it is optimized for// common cases such as seeking to the end to find the length of the// data.type readSeekerFromReader struct {	reset  func() (io.Reader, error)	r      io.Reader	size   int64	offset int64} func (r *readSeekerFromReader) start() {	x, err := r.reset()	if err != nil {		r.r = errorReader{err}	} else {		r.r = x	}	r.offset = 0} func (r *readSeekerFromReader) Read(p []byte) (n int, err error) {	if r.r == nil {		r.start()	}	n, err = r.r.Read(p)	r.offset += int64(n)	return n, err} func (r *readSeekerFromReader) Seek(offset int64, whence int) (int64, error) {	var newOffset int64	switch whence {	case 0:		newOffset = offset	case 1:		newOffset = r.offset + offset	case 2:		newOffset = r.size + offset	default:		return 0, os.ErrInvalid	} 	switch {	case newOffset == r.offset:		return newOffset, nil 	case newOffset < 0, newOffset > r.size:		return 0, os.ErrInvalid 	case newOffset == 0:		r.r = nil 	case newOffset == r.size:		r.r = errorReader{io.EOF} 	default:		if newOffset < r.offset {			// Restart at the beginning.			r.start()		}		// Read until we reach offset.		var buf [512]byte		for r.offset < newOffset {			b := buf[:]			if newOffset-r.offset < int64(len(buf)) {				b = buf[:newOffset-r.offset]			}			if _, err := r.Read(b); err != nil {				return 0, err			}		}	}	r.offset = newOffset	return r.offset, nil}