func lookupUnixGid(gid int) (*Group, error) {
var grp syscall.Group
var result *syscall.Group
buf := alloc(groupBuffer)
defer buf.free()
err := retryWithBuffer(buf, func() syscall.Errno {
syscall.Entersyscall()
rv := libc_getgrgid_r(syscall.Gid_t(gid),
&grp,
buf.ptr,
buf.size,
&result)
syscall.Exitsyscall()
if rv != 0 {
return syscall.GetErrno()
}
return 0
})
if err != nil {
return nil, fmt.Errorf("user: lookup groupid %d: %v", gid, err)
}
if result == nil {
return nil, UnknownGroupIdError(strconv.Itoa(gid))
}
return buildGroup(&grp), nil
}
func listGroups(u *User) ([]string, error) {
ug, err := strconv.Atoi(u.Gid)
if err != nil {
return nil, fmt.Errorf("user: list groups for %s: invalid gid %q", u.Username, u.Gid)
}
userGID := syscall.Gid_t(ug)
nameC, err := syscall.BytePtrFromString(u.Username)
if err != nil {
return nil, fmt.Errorf("user: invalid user name %q: %v", strconv.Quote(u.Username), err)
}
n := int32(256)
gidsC := make([]syscall.Gid_t, n)
syscall.Entersyscall()
rv := libc_getgrouplist(nameC, userGID, &gidsC[0], &n)
syscall.Exitsyscall()
if rv == -1 {
// More than initial buffer, but now n contains the correct size.
const maxGroups = 2048
if n > maxGroups {
return nil, fmt.Errorf("user: list groups for %s: member of more than %d groups", u.Username, maxGroups)
}
gidsC = make([]syscall.Gid_t, n)
syscall.Entersyscall()
rv := libc_getgrouplist(nameC, userGID, &gidsC[0], &n)
syscall.Exitsyscall()
if rv == -1 {
return nil, fmt.Errorf("user: list groups for %s failed (changed groups?)", u.Username)
}
}
gidsC = gidsC[:n]
gids := make([]string, 0, n)
for _, g := range gidsC[:n] {
gids = append(gids, strconv.Itoa(int(g)))
}
return gids, nil
}