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// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// +build darwin dragonfly freebsd !android,linux netbsd openbsd solaris
// +build cgo
package user
import (
"fmt"
"strconv"
"strings"
"syscall"
"unsafe"
)
// bytePtrToString takes a NUL-terminated array of bytes and convert
// it to a Go string.
func bytePtrToString(p *byte) string {
a := (*[10000]byte)(unsafe.Pointer(p))
i := 0
for a[i] != 0 {
i++
}
return string(a[:i])
}
func current() (*User, error) {
return lookupUnixUid(syscall.Getuid())
}
func lookupUser(username string) (*User, error) {
var pwd syscall.Passwd
var result *syscall.Passwd
p := syscall.StringBytePtr(username)
buf := alloc(userBuffer)
defer buf.free()
err := retryWithBuffer(buf, func() syscall.Errno {
syscall.Entersyscall()
rv := libc_getpwnam_r(p,
&pwd,
buf.ptr,
buf.size,
&result)
syscall.Exitsyscall()
if rv != 0 {
return syscall.GetErrno()
}
return 0
})
if err != nil {
return nil, fmt.Errorf("user: lookup username %s: %v", username, err)
}
if result == nil {
return nil, UnknownUserError(username)
}
return buildUser(&pwd), err
}
func lookupUserId(uid string) (*User, error) {
i, e := strconv.Atoi(uid)
if e != nil {
return nil, e
}
return lookupUnixUid(i)
}
func lookupUnixUid(uid int) (*User, error) {
var pwd syscall.Passwd
var result *syscall.Passwd
buf := alloc(userBuffer)
defer buf.free()
err := retryWithBuffer(buf, func() syscall.Errno {
syscall.Entersyscall()
rv := libc_getpwuid_r(syscall.Uid_t(uid),
&pwd,
buf.ptr,
buf.size,
&result)
syscall.Exitsyscall()
if rv != 0 {
return syscall.GetErrno()
}
return 0
})
if err != nil {
return nil, fmt.Errorf("user: lookup userid %d: %v", uid, err)
}
if result == nil {
return nil, UnknownUserIdError(uid)
}
return buildUser(&pwd), nil
}
func buildUser(pwd *syscall.Passwd) *User {
u := &User{
Uid: strconv.Itoa(int(pwd.Pw_uid)),
Gid: strconv.Itoa(int(pwd.Pw_gid)),
Username: bytePtrToString((*byte)(unsafe.Pointer(pwd.Pw_name))),
Name: bytePtrToString((*byte)(unsafe.Pointer(pwd.Pw_gecos))),
HomeDir: bytePtrToString((*byte)(unsafe.Pointer(pwd.Pw_dir))),
}
// The pw_gecos field isn't quite standardized. Some docs
// say: "It is expected to be a comma separated list of
// personal data where the first item is the full name of the
// user."
if i := strings.Index(u.Name, ","); i >= 0 {
u.Name = u.Name[:i]
}
return u
}
func currentGroup() (*Group, error) {
return lookupUnixGid(syscall.Getgid())
}
func lookupGroup(groupname string) (*Group, error) {
var grp syscall.Group
var result *syscall.Group
buf := alloc(groupBuffer)
defer buf.free()
p := syscall.StringBytePtr(groupname)
err := retryWithBuffer(buf, func() syscall.Errno {
syscall.Entersyscall()
rv := libc_getgrnam_r(p,
&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 groupname %s: %v", groupname, err)
}
if result == nil {
return nil, UnknownGroupError(groupname)
}
return buildGroup(&grp), nil
}
func lookupGroupId(gid string) (*Group, error) {
i, e := strconv.Atoi(gid)
if e != nil {
return nil, e
}
return lookupUnixGid(i)
}
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 buildGroup(grp *syscall.Group) *Group {
g := &Group{
Gid: strconv.Itoa(int(grp.Gr_gid)),
Name: bytePtrToString((*byte)(unsafe.Pointer(grp.Gr_name))),
}
return g
}
type bufferKind int
const (
userBuffer = bufferKind(syscall.SC_GETPW_R_SIZE_MAX)
groupBuffer = bufferKind(syscall.SC_GETGR_R_SIZE_MAX)
)
func (k bufferKind) initialSize() syscall.Size_t {
sz, _ := syscall.Sysconf(int(k))
if sz == -1 {
// DragonFly and FreeBSD do not have _SC_GETPW_R_SIZE_MAX.
// Additionally, not all Linux systems have it, either. For
// example, the musl libc returns -1.
return 1024
}
if !isSizeReasonable(int64(sz)) {
// Truncate. If this truly isn't enough, retryWithBuffer will error on the first run.
return maxBufferSize
}
return syscall.Size_t(sz)
}
type memBuffer struct {
ptr *byte
size syscall.Size_t
}
func alloc(kind bufferKind) *memBuffer {
sz := kind.initialSize()
b := make([]byte, sz)
return &memBuffer{
ptr: &b[0],
size: sz,
}
}
func (mb *memBuffer) resize(newSize syscall.Size_t) {
b := make([]byte, newSize)
mb.ptr = &b[0]
mb.size = newSize
}
func (mb *memBuffer) free() {
mb.ptr = nil
}
// retryWithBuffer repeatedly calls f(), increasing the size of the
// buffer each time, until f succeeds, fails with a non-ERANGE error,
// or the buffer exceeds a reasonable limit.
func retryWithBuffer(buf *memBuffer, f func() syscall.Errno) error {
for {
errno := f()
if errno == 0 {
return nil
} else if errno != syscall.ERANGE {
return errno
}
newSize := buf.size * 2
if !isSizeReasonable(int64(newSize)) {
return fmt.Errorf("internal buffer exceeds %d bytes", maxBufferSize)
}
buf.resize(newSize)
}
}
const maxBufferSize = 1 << 20
func isSizeReasonable(sz int64) bool {
return sz > 0 && sz <= maxBufferSize
}
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