listdir.go

package main

import (
	"fmt"
	"log"
	"os"
	"path"
	"runtime"
	"strings"
	"syscall"
	"unsafe"
)

const (
	// readDirentBufSize for syscall.ReadDirent() to hold multiple
	// directory entries in one buffer. golang source uses 4096 as
	// buffer size whereas we want 25 times larger to save lots of
	// entries to avoid multiple syscall.ReadDirent() call.
	readDirentBufSize = 4096 * 25
)

// actual length of the byte array from the c - world.
func clen(n []byte) int {
	for i := 0; i < len(n); i++ {
		if n[i] == 0 {
			return i
		}
	}
	return len(n)
}

// parseDirents - inspired from
// https://golang.org/src/syscall/syscall_<os>.go
func parseDirents(dirPath string, buf []byte) (entries []string, err error) {
	bufidx := 0
	for bufidx < len(buf) {
		dirent := (*syscall.Dirent)(unsafe.Pointer(&buf[bufidx]))
		// On non-Linux operating systems for rec length of zero means
		// we have reached EOF break out.
		if runtime.GOOS != "linux" && dirent.Reclen == 0 {
			break
		}
		bufidx += int(dirent.Reclen)
		bytes := (*[10000]byte)(unsafe.Pointer(&dirent.Name[0]))
		var name = string(bytes[0:clen(bytes[:])])
		// Reserved names skip them.
		if name == "." || name == ".." {
			continue
		}

		switch dirent.Type {
		case syscall.DT_DIR:
			entries = append(entries, name+"/")
		case syscall.DT_REG:
			entries = append(entries, name)
		case syscall.DT_LNK, syscall.DT_UNKNOWN:
			// If its symbolic link, follow the link using os.Stat()

			// On Linux XFS does not implement d_type for on disk
			// format << v5. Fall back to Stat().
			var fi os.FileInfo
			fi, err = os.Stat(path.Join(dirPath, name))
			if err != nil {
				// If file does not exist, we continue and skip it.
				// Could happen if it was deleted in the middle while
				// this list was being performed.
				if os.IsNotExist(err) {
					err = nil
					continue
				}
				return nil, err
			}
			if fi.IsDir() {
				entries = append(entries, fi.Name()+"/")
			} else if fi.Mode().IsRegular() {
				entries = append(entries, fi.Name())
			}
		default:
			// Skip entries which are not file or directory.
			continue
		}
	}
	return entries, nil
}

// Return all the entries at the directory dirPath.
func readDir(dirPath string) (entries []string, err error) {
	buf := make([]byte, readDirentBufSize)
	d, err := os.Open(dirPath)
	if err != nil {
		// File is really not found.
		if os.IsNotExist(err) {
			return nil, err
		}

		// File path cannot be verified since one of the parents is a file.
		if strings.Contains(err.Error(), "not a directory") {
			return nil, err
		}
		return nil, err
	}
	defer d.Close()

	fd := int(d.Fd())
	for {
		nbuf, err := syscall.ReadDirent(fd, buf)
		if err != nil {
			return nil, err
		}
		if nbuf <= 0 {
			break
		}
		var tmpEntries []string
		if tmpEntries, err = parseDirents(dirPath, buf[:nbuf]); err != nil {
			return nil, err
		}
		entries = append(entries, tmpEntries...)
	}
	return
}

func main() {
	entries, err := readDir(".")
	if err != nil {
		log.Fatal(err)
	}
	for _, entry := range entries {
		_, err := os.Stat(entry + "/xl.json")
		if err != nil {
			log.Fatal(err)
		}
	}
	fmt.Println(len(entries))
}