blob: 799cd7c8ac626eefb9449710b3d769b36355847f [file] [log] [blame]
// 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.
//go:build !linux && !windows && !darwin
// Package mmap provides a way to memory-map a file.
package mmap
import (
// ReaderAt reads a memory-mapped file.
// Like any io.ReaderAt, clients can execute parallel ReadAt calls, but it is
// not safe to call Close and reading methods concurrently.
type ReaderAt struct {
f *os.File
len int
// Close closes the reader.
func (r *ReaderAt) Close() error {
return r.f.Close()
// Len returns the length of the underlying memory-mapped file.
func (r *ReaderAt) Len() int {
return r.len
// At returns the byte at index i.
func (r *ReaderAt) At(i int) byte {
if i < 0 || r.len <= i {
panic("index out of range")
var b [1]byte
r.ReadAt(b[:], int64(i))
return b[0]
// ReadAt implements the io.ReaderAt interface.
func (r *ReaderAt) ReadAt(p []byte, off int64) (int, error) {
return r.f.ReadAt(p, off)
// Open memory-maps the named file for reading.
func Open(filename string) (*ReaderAt, error) {
f, err := os.Open(filename)
if err != nil {
return nil, err
fi, err := f.Stat()
if err != nil {
return nil, err
size := fi.Size()
if size < 0 {
return nil, fmt.Errorf("mmap: file %q has negative size", filename)
if size != int64(int(size)) {
return nil, fmt.Errorf("mmap: file %q is too large", filename)
return &ReaderAt{
f: f,
len: int(fi.Size()),
}, nil