cpio.go

// Copyright 2013-2017 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 cpio implements utilities for reading and writing cpio archives.
//
// Currently, only newc-formatted cpio archives are supported through cpio.Newc.
//
// Reading from or writing to a file:
//
//    f, err := os.Open(...)
//    if err ...
//    recReader := cpio.Newc.Reader(f)
//    err := ForEachRecord(recReader, func(r cpio.Record) error {
//
//    })
//
//    // Or...
//    recWriter := cpio.Newc.Writer(f)
//
//
// Reading from or writing to an in-memory archive:
//
//    a := cpio.InMemArchive()
//    err := a.WriteRecord(...)
//
//    recReader := a.Reader() // Reads from the "beginning."
//
//    if a.Contains("bar/foo") {
//
//    }
package cpio

import (
	"fmt"
	"io"
	"os"
	"syscall"
	"time"

	"github.com/u-root/u-root/pkg/ls"
	"github.com/u-root/u-root/pkg/uio"
	"golang.org/x/sys/unix"
)

var (
	formatMap = make(map[string]RecordFormat)
	Debug     = func(string, ...interface{}) {}
)

// Record represents a CPIO record, which represents a Unix file.
type Record struct {
	// ReaderAt contains the content of this CPIO record.
	io.ReaderAt

	// Info is metadata describing the CPIO record.
	Info

	// metadata about this item's place in the file
	RecPos  int64  // Where in the file this record is
	RecLen  uint64 // How big the record is.
	FilePos int64  // Where in the CPIO the file's contents are.
}

// String implements a fmt.Stringer for Record.
//
// String returns a string formatted like `ls` would format it.
func (r Record) String() string {
	s := ls.LongStringer{
		Human: true,
		Name:  ls.NameStringer{},
	}
	return s.FileString(LSInfoFromRecord(r))
}

// Info holds metadata about files.
type Info struct {
	Ino      uint64
	Mode     uint64
	UID      uint64
	GID      uint64
	NLink    uint64
	MTime    uint64
	FileSize uint64
	Dev      uint64
	Major    uint64
	Minor    uint64
	Rmajor   uint64
	Rminor   uint64
	Name     string
}

func (i Info) String() string {
	return fmt.Sprintf("%s: Ino %d Mode %#o UID %d GID %d NLink %d MTime %v FileSize %d Major %d Minor %d Rmajor %d Rminor %d",
		i.Name,
		i.Ino,
		i.Mode,
		i.UID,
		i.GID,
		i.NLink,
		time.Unix(int64(i.MTime), 0).UTC(),
		i.FileSize,
		i.Major,
		i.Minor,
		i.Rmajor,
		i.Rminor)
}

// A RecordReader reads one record from an archive.
type RecordReader interface {
	ReadRecord() (Record, error)
}

// A RecordWriter writes one record to an archive.
type RecordWriter interface {
	WriteRecord(Record) error
}

// A RecordFormat gives readers and writers for dealing with archives from io
// objects.
//
// CPIO files have a number of records, of which newc is the most widely used
// today.
type RecordFormat interface {
	Reader(r io.ReaderAt) RecordReader
	Writer(w io.Writer) RecordWriter
}

// Format returns the RecordFormat with that name, if it exists.
func Format(name string) (RecordFormat, error) {
	op, ok := formatMap[name]
	if !ok {
		return nil, fmt.Errorf("%q is not in cpio format map %v", name, formatMap)
	}
	return op, nil
}

func modeFromLinux(mode uint64) os.FileMode {
	m := os.FileMode(mode & 0777)
	switch mode & syscall.S_IFMT {
	case syscall.S_IFBLK:
		m |= os.ModeDevice
	case syscall.S_IFCHR:
		m |= os.ModeDevice | os.ModeCharDevice
	case syscall.S_IFDIR:
		m |= os.ModeDir
	case syscall.S_IFIFO:
		m |= os.ModeNamedPipe
	case syscall.S_IFLNK:
		m |= os.ModeSymlink
	case syscall.S_IFREG:
		// nothing to do
	case syscall.S_IFSOCK:
		m |= os.ModeSocket
	}
	if mode&syscall.S_ISGID != 0 {
		m |= os.ModeSetgid
	}
	if mode&syscall.S_ISUID != 0 {
		m |= os.ModeSetuid
	}
	if mode&syscall.S_ISVTX != 0 {
		m |= os.ModeSticky
	}
	return m
}

// LSInfoFromRecord converts a Record to be usable with the ls package for
// listing files.
func LSInfoFromRecord(rec Record) ls.FileInfo {
	var target string

	mode := modeFromLinux(rec.Mode)
	if mode&os.ModeType == os.ModeSymlink {
		if l, err := uio.ReadAll(rec); err != nil {
			target = err.Error()
		} else {
			target = string(l)
		}
	}

	return ls.FileInfo{
		Name:          rec.Name,
		Mode:          mode,
		Rdev:          unix.Mkdev(uint32(rec.Rmajor), uint32(rec.Rminor)),
		UID:           uint32(rec.UID),
		GID:           uint32(rec.GID),
		Size:          int64(rec.FileSize),
		MTime:         time.Unix(int64(rec.MTime), 0).UTC(),
		SymlinkTarget: target,
	}
}