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// Copyright 2018 the u-root 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 uio
import (
"fmt"
"io"
"os"
)
// ReadOneByte reads one byte from given io.ReaderAt.
func ReadOneByte(r io.ReaderAt) error {
buf := make([]byte, 1)
n, err := r.ReadAt(buf, 0)
if err != nil {
return err
}
if n != 1 {
return fmt.Errorf("expected to read 1 byte, but got %d", n)
}
return nil
}
// LazyOpener is a lazy io.Reader.
//
// LazyOpener will use a given open function to derive an io.Reader when Read
// is first called on the LazyOpener.
type LazyOpener struct {
r io.Reader
s string
err error
open func() (io.Reader, error)
}
// NewLazyOpener returns a lazy io.Reader based on `open`.
func NewLazyOpener(filename string, open func() (io.Reader, error)) *LazyOpener {
if len(filename) == 0 {
return nil
}
return &LazyOpener{s: filename, open: open}
}
// Read implements io.Reader.Read lazily.
//
// If called for the first time, the underlying reader will be obtained and
// then used for the first and subsequent calls to Read.
func (lr *LazyOpener) Read(p []byte) (int, error) {
if lr.r == nil && lr.err == nil {
lr.r, lr.err = lr.open()
}
if lr.err != nil {
return 0, lr.err
}
return lr.r.Read(p)
}
// String implements fmt.Stringer.
func (lr *LazyOpener) String() string {
if len(lr.s) > 0 {
return lr.s
}
if lr.r != nil {
return fmt.Sprintf("%v", lr.r)
}
return "unopened mystery file"
}
// Close implements io.Closer.Close.
func (lr *LazyOpener) Close() error {
if c, ok := lr.r.(io.Closer); ok {
return c.Close()
}
return nil
}
// LazyOpenerAt is a lazy io.ReaderAt.
//
// LazyOpenerAt will use a given open function to derive an io.ReaderAt when
// ReadAt is first called.
type LazyOpenerAt struct {
r io.ReaderAt
s string
err error
limit int64
open func() (io.ReaderAt, error)
}
// NewLazyFile returns a lazy ReaderAt opened from path.
func NewLazyFile(path string) *LazyOpenerAt {
if len(path) == 0 {
return nil
}
return NewLazyOpenerAt(path, func() (io.ReaderAt, error) {
return os.Open(path)
})
}
// NewLazyLimitFile returns a lazy ReaderAt opened from path with a limit reader on it.
func NewLazyLimitFile(path string, limit int64) *LazyOpenerAt {
if len(path) == 0 {
return nil
}
return NewLazyLimitOpenerAt(path, limit, func() (io.ReaderAt, error) {
return os.Open(path)
})
}
// NewLazyOpenerAt returns a lazy io.ReaderAt based on `open`.
func NewLazyOpenerAt(filename string, open func() (io.ReaderAt, error)) *LazyOpenerAt {
return &LazyOpenerAt{s: filename, open: open, limit: -1}
}
// NewLazyLimitOpenerAt returns a lazy io.ReaderAt based on `open`.
func NewLazyLimitOpenerAt(filename string, limit int64, open func() (io.ReaderAt, error)) *LazyOpenerAt {
return &LazyOpenerAt{s: filename, open: open, limit: limit}
}
// String implements fmt.Stringer.
func (loa *LazyOpenerAt) String() string {
if len(loa.s) > 0 {
return loa.s
}
if loa.r != nil {
return fmt.Sprintf("%v", loa.r)
}
return "unopened mystery file"
}
// File returns the backend file of the io.ReaderAt if it
// is backed by a os.File.
func (loa *LazyOpenerAt) File() *os.File {
if f, ok := loa.r.(*os.File); ok {
return f
}
return nil
}
// ReadAt implements io.ReaderAt.ReadAt.
func (loa *LazyOpenerAt) ReadAt(p []byte, off int64) (int, error) {
if loa.r == nil && loa.err == nil {
loa.r, loa.err = loa.open()
}
if loa.err != nil {
return 0, loa.err
}
if loa.limit > 0 {
if off >= loa.limit {
return 0, io.EOF
}
if int64(len(p)) > loa.limit-off {
p = p[0 : loa.limit-off]
}
}
return loa.r.ReadAt(p, off)
}
// Close implements io.Closer.Close.
func (loa *LazyOpenerAt) Close() error {
if c, ok := loa.r.(io.Closer); ok {
return c.Close()
}
return nil
}
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