moby/vendor/github.com/containerd/continuity/groups_unix.go

package continuity

import (
	"bufio"
	"fmt"
	"io"
	"os"
	"strconv"
	"strings"
)

// TODO(stevvooe): This needs a lot of work before we can call it useful.

type groupIndex struct {
	byName map[string]*group
	byGID  map[int]*group
}

func getGroupIndex() (*groupIndex, error) {
	f, err := os.Open("/etc/group")
	if err != nil {
		return nil, err
	}
	defer f.Close()

	groups, err := parseGroups(f)
	if err != nil {
		return nil, err
	}

	return newGroupIndex(groups), nil
}

func newGroupIndex(groups []group) *groupIndex {
	gi := &groupIndex{
		byName: make(map[string]*group),
		byGID:  make(map[int]*group),
	}

	for i, group := range groups {
		gi.byGID[group.gid] = &groups[i]
		gi.byName[group.name] = &groups[i]
	}

	return gi
}

type group struct {
	name    string
	gid     int
	members []string
}

func getGroupName(gid int) (string, error) {
	f, err := os.Open("/etc/group")
	if err != nil {
		return "", err
	}
	defer f.Close()

	groups, err := parseGroups(f)
	if err != nil {
		return "", err
	}

	for _, group := range groups {
		if group.gid == gid {
			return group.name, nil
		}
	}

	return "", fmt.Errorf("no group for gid")
}

// parseGroups parses an /etc/group file for group names, ids and membership.
// This is unix specific.
func parseGroups(rd io.Reader) ([]group, error) {
	var groups []group
	scanner := bufio.NewScanner(rd)

	for scanner.Scan() {
		if strings.HasPrefix(scanner.Text(), "#") {
			continue // skip comment
		}

		parts := strings.SplitN(scanner.Text(), ":", 4)

		if len(parts) != 4 {
			return nil, fmt.Errorf("bad entry: %q", scanner.Text())
		}

		name, _, sgid, smembers := parts[0], parts[1], parts[2], parts[3]

		gid, err := strconv.Atoi(sgid)
		if err != nil {
			return nil, fmt.Errorf("bad gid: %q", gid)
		}

		members := strings.Split(smembers, ",")

		groups = append(groups, group{
			name:    name,
			gid:     gid,
			members: members,
		})
	}

	if scanner.Err() != nil {
		return nil, scanner.Err()
	}

	return groups, nil
}