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// Copyright 2016 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.
//
// This source code is an adaptation of:
// https://go.dev/src/os/user/lookup_unix.go
// to provide user lookup functionality against an arbitrary password file.
package passwdfile
import (
"bufio"
"bytes"
"errors"
"fmt"
"io"
"os"
"os/user"
"reflect"
"strconv"
"strings"
)
var colon = []byte(":")
// lineFunc returns a value, an error, or (nil, nil) to skip the row.
type lineFunc func(line []byte) (v any, err error)
// readColonFile parses r as an /etc/group or /etc/passwd style file, running
// fn for each row. readColonFile returns a value, an error, or (nil, nil) if
// the end of the file is reached without a match.
//
// readCols is the minimum number of colon-separated fields that will be passed
// to fn; in a long line additional fields may be silently discarded.
func readColonFile(r io.Reader, fn lineFunc, readCols int) (v any, err error) {
rd := bufio.NewReader(r)
// Read the file line-by-line.
for {
var isPrefix bool
var wholeLine []byte
// Read the next line. We do so in chunks (as much as reader's
// buffer is able to keep), check if we read enough columns
// already on each step and store final result in wholeLine.
for {
var line []byte
line, isPrefix, err = rd.ReadLine()
if err != nil {
// We should return (nil, nil) if EOF is reached
// without a match.
if err == io.EOF {
err = nil
}
return nil, err
}
// Simple common case: line is short enough to fit in a
// single reader's buffer.
if !isPrefix && len(wholeLine) == 0 {
wholeLine = line
break
}
wholeLine = append(wholeLine, line...)
// Check if we read the whole line (or enough columns)
// already.
if !isPrefix || bytes.Count(wholeLine, []byte{':'}) >= readCols {
break
}
}
// There's no spec for /etc/passwd or /etc/group, but we try to follow
// the same rules as the glibc parser, which allows comments and blank
// space at the beginning of a line.
wholeLine = bytes.TrimSpace(wholeLine)
if len(wholeLine) == 0 || wholeLine[0] == '#' {
continue
}
v, err = fn(wholeLine)
if v != nil || err != nil {
return v, err
}
// If necessary, skip the rest of the line
for ; isPrefix; _, isPrefix, err = rd.ReadLine() {
if err != nil {
// We should return (nil, nil) if EOF is reached without a match.
if err == io.EOF {
err = nil
}
return nil, err
}
}
}
}
// returns a *User for a row if that row's has the given value at the
// given index.
func matchUserIndexValue(value string, idx int) lineFunc {
var leadColon string
if idx > 0 {
leadColon = ":"
}
substr := []byte(leadColon + value + ":")
return func(line []byte) (v any, err error) {
if !bytes.Contains(line, substr) || bytes.Count(line, colon) < 6 {
return
}
// kevin:x:1005:1006::/home/kevin:/usr/bin/zsh
parts := strings.SplitN(string(line), ":", 7)
if len(parts) < 6 || parts[idx] != value || parts[0] == "" ||
parts[0][0] == '+' || parts[0][0] == '-' {
return
}
if _, err := strconv.Atoi(parts[2]); err != nil {
return nil, nil
}
if _, err := strconv.Atoi(parts[3]); err != nil {
return nil, nil
}
u := &user.User{
Username: parts[0],
Uid: parts[2],
Gid: parts[3],
Name: parts[4],
HomeDir: parts[5],
}
// 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."
u.Name, _, _ = strings.Cut(u.Name, ",")
return u, nil
}
}
func findUserID(uid string, r io.Reader) (*user.User, error) {
i, e := strconv.Atoi(uid)
if e != nil {
return nil, errors.New("user: invalid userid " + uid)
}
if v, err := readColonFile(r, matchUserIndexValue(uid, 2), 6); err != nil {
return nil, err
} else if v != nil {
u, ok := v.(*user.User)
if !ok {
return nil, fmt.Errorf("expected user info, but found %v", reflect.TypeOf(v))
}
return u, nil
}
return nil, user.UnknownUserIdError(i)
}
func findUsername(name string, r io.Reader) (*user.User, error) {
if v, err := readColonFile(r, matchUserIndexValue(name, 0), 6); err != nil {
return nil, err
} else if v != nil {
u, ok := v.(*user.User)
if !ok {
return nil, fmt.Errorf("expected user info, but found %v", reflect.TypeOf(v))
}
return u, nil
}
return nil, user.UnknownUserError(name)
}
func LookupUserInFile(userFile, username string) (*user.User, error) {
f, err := os.Open(userFile)
if err != nil {
return nil, err
}
defer f.Close()
return findUsername(username, f)
}
func LookupUserIDInFile(userFile, uid string) (*user.User, error) {
f, err := os.Open(userFile)
if err != nil {
return nil, err
}
defer f.Close()
return findUserID(uid, f)
}
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