cp.go

// Copyright 2016-2017 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.

// Copy files.
//
// Synopsis:
//     cp [-rRfivwP] FROM... TO
//
// Options:
//     -w n: number of worker goroutines
//     -R: copy file hierarchies
//     -r: alias to -R recursive mode
//     -i: prompt about overwriting file
//     -f: force overwrite files
//     -v: verbose copy mode
//     -P: don't follow symlinks
package main

import (
	"bufio"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"os"
	"path/filepath"
	"runtime"
	"strings"

	flag "github.com/spf13/pflag"
)

// buffSize is the length of buffer during
// the parallel copy using worker function
const buffSize = 8192

var (
	flags struct {
		recursive bool
		ask       bool
		force     bool
		verbose   bool
		symlink   bool
		nwork     int
	}
	input = bufio.NewReader(os.Stdin)
	// offchan is a channel used for indicate the nextbuffer to read with worker()
	offchan = make(chan int64, 0)
	// zerochan is a channel used for indicate the start of a new read file
	zerochan = make(chan int, 0)
)

func init() {
	defUsage := flag.Usage
	flag.Usage = func() {
		os.Args[0] = "cp [-wRrifvP] file[s] ... dest"
		defUsage()
	}
	flag.IntVarP(&flags.nwork, "workers", "w", runtime.NumCPU(), "number of worker goroutines")
	flag.BoolVarP(&flags.recursive, "RECURSIVE", "R", false, "copy file hierarchies")
	flag.BoolVarP(&flags.recursive, "recursive", "r", false, "alias to -R recursive mode")
	flag.BoolVarP(&flags.ask, "interactive", "i", false, "prompt about overwriting file")
	flag.BoolVarP(&flags.force, "force", "f", false, "force overwrite files")
	flag.BoolVarP(&flags.verbose, "verbose", "v", false, "verbose copy mode")
	flag.BoolVarP(&flags.symlink, "no-dereference", "P", false, "don't follow symlinks")
	go nextOff()
}

// promptOverwrite ask if the user wants overwrite file
func promptOverwrite(dst string) (bool, error) {
	fmt.Printf("cp: overwrite %q? ", dst)
	answer, err := input.ReadString('\n')
	if err != nil {
		return false, err
	}

	if strings.ToLower(answer)[0] != 'y' {
		return false, nil
	}

	return true, nil
}

// copyFile copies file between src (source) and dst (destination)
// todir: if true insert src INTO dir dst
func copyFile(src, dst string, todir bool) error {
	if todir {
		file := filepath.Base(src)
		dst = filepath.Join(dst, file)
	}

	srcb, err := os.Lstat(src)
	if err != nil {
		return fmt.Errorf("can't stat %v: %v", src, err)
	}

	// don't follow symlinks, copy symlink
	if L := os.ModeSymlink; flags.symlink && srcb.Mode()&L == L {
		linkPath, err := filepath.EvalSymlinks(src)
		if err != nil {
			return fmt.Errorf("can't eval symlink %v: %v", src, err)
		}
		return os.Symlink(linkPath, dst)
	}

	if srcb.IsDir() {
		if flags.recursive {
			return copyDir(src, dst)
		}
		return fmt.Errorf("%q is a directory, try use recursive option", src)
	}

	dstb, err := os.Stat(dst)
	if err != nil && !os.IsNotExist(err) {
		return fmt.Errorf("%q: can't handle error %v", dst, err)
	}

	if dstb != nil {
		if sameFile(srcb.Sys(), dstb.Sys()) {
			return fmt.Errorf("%q and %q are the same file", src, dst)
		}
		if flags.ask && !flags.force {
			overwrite, err := promptOverwrite(dst)
			if err != nil {
				return err
			}
			if !overwrite {
				return nil
			}
		}
	}

	mode := srcb.Mode() & 0777
	s, err := os.Open(src)
	if err != nil {
		return fmt.Errorf("can't open %q: %v", src, err)
	}
	defer s.Close()

	d, err := os.OpenFile(dst, os.O_RDWR|os.O_CREATE|os.O_TRUNC, mode)
	if err != nil {
		return fmt.Errorf("can't create %q: %v", dst, err)
	}
	defer d.Close()

	return copyOneFile(s, d, src, dst)
}

// copyOneFile copy the content between two files
func copyOneFile(s *os.File, d *os.File, src, dst string) error {
	zerochan <- 0
	fail := make(chan error, flags.nwork)
	for i := 0; i < flags.nwork; i++ {
		go worker(s, d, fail)
	}

	// iterate the errors from channel
	for i := 0; i < flags.nwork; i++ {
		err := <-fail
		if err != nil {
			return err
		}
	}

	if flags.verbose {
		fmt.Printf("%q -> %q\n", src, dst)
	}

	return nil
}

// createDir populate dir destination if not exists
// if exists verify is not a dir: return error if is file
// cannot overwrite: dir -> file
func createDir(src, dst string) error {
	dstInfo, err := os.Stat(dst)
	if err != nil && !os.IsNotExist(err) {
		return err
	}

	if err == nil {
		if !dstInfo.IsDir() {
			return fmt.Errorf("can't overwrite non-dir %q with dir %q", dst, src)
		}
		return nil
	}

	srcInfo, err := os.Stat(src)
	if err != nil {
		return err
	}
	if err := os.Mkdir(dst, srcInfo.Mode()); err != nil {
		return err
	}
	if flags.verbose {
		fmt.Printf("%q -> %q\n", src, dst)
	}

	return nil
}

// copyDir copy the file hierarchies
// used at cp when -r or -R flag is true
func copyDir(src, dst string) error {
	if err := createDir(src, dst); err != nil {
		return err
	}

	// list files from destination
	files, err := ioutil.ReadDir(src)
	if err != nil {
		return fmt.Errorf("can't list files from %q: %q", src, err)
	}

	// copy recursively the src -> dst
	for _, file := range files {
		fname := file.Name()
		fpath := filepath.Join(src, fname)
		newDst := filepath.Join(dst, fname)
		copyFile(fpath, newDst, false)
	}

	return err
}

// worker is a concurrent copy, used to copy part of the files
// in parallel
func worker(s *os.File, d *os.File, fail chan error) {
	var buf [buffSize]byte
	var bp []byte

	l := len(buf)
	bp = buf[0:]
	o := <-offchan
	for {
		n, err := s.ReadAt(bp, o)
		if err != nil && err != io.EOF {
			fail <- fmt.Errorf("reading %s at %v: %v", s.Name(), o, err)
			return
		}
		if n == 0 {
			break
		}

		nb := bp[0:n]
		n, err = d.WriteAt(nb, o)
		if err != nil {
			fail <- fmt.Errorf("writing %s: %v", d.Name(), err)
			return
		}
		bp = buf[n:]
		o += int64(n)
		l -= n
		if l == 0 {
			l = len(buf)
			bp = buf[0:]
			o = <-offchan
		}
	}
	fail <- nil
}

// nextOff handler for next buffers and sync goroutines
// zerochan imply the init of file
// offchan is the next buffer part to read
func nextOff() {
	off := int64(0)
	for {
		select {
		case <-zerochan:
			off = 0
		case offchan <- off:
			off += buffSize
		}
	}
}

// cp is a function whose eval the args
// and make decisions for copyfiles
func cp(args []string) (lastErr error) {
	todir := false
	from, to := args[:len(args)-1], args[len(args)-1]
	toStat, err := os.Stat(to)
	if err == nil {
		todir = toStat.IsDir()
	}
	if flag.NArg() > 2 && todir == false {
		log.Fatalf("is not a directory: %s\n", to)
	}

	for _, file := range from {
		if err := copyFile(file, to, todir); err != nil {
			log.Printf("cp: %v\n", err)
			lastErr = err
		}
	}

	return err
}

func main() {
	flag.Parse()
	if flag.NArg() < 2 {
		flag.Usage()
		os.Exit(1)
	}

	if err := cp(flag.Args()); err != nil {
		os.Exit(1)
	}

}