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// Copyright 2015 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.
package net
import (
"errors"
"internal/bytealg"
"os"
"sync"
"time"
)
const (
nssConfigPath = "/etc/nsswitch.conf"
)
var nssConfig nsswitchConfig
type nsswitchConfig struct {
initOnce sync.Once // guards init of nsswitchConfig
// ch is used as a semaphore that only allows one lookup at a
// time to recheck nsswitch.conf
ch chan struct{} // guards lastChecked and modTime
lastChecked time.Time // last time nsswitch.conf was checked
mu sync.Mutex // protects nssConf
nssConf *nssConf
}
func getSystemNSS() *nssConf {
nssConfig.tryUpdate()
nssConfig.mu.Lock()
conf := nssConfig.nssConf
nssConfig.mu.Unlock()
return conf
}
// init initializes conf and is only called via conf.initOnce.
func (conf *nsswitchConfig) init() {
conf.nssConf = parseNSSConfFile("/etc/nsswitch.conf")
conf.lastChecked = time.Now()
conf.ch = make(chan struct{}, 1)
}
// tryUpdate tries to update conf.
func (conf *nsswitchConfig) tryUpdate() {
conf.initOnce.Do(conf.init)
// Ensure only one update at a time checks nsswitch.conf
if !conf.tryAcquireSema() {
return
}
defer conf.releaseSema()
now := time.Now()
if conf.lastChecked.After(now.Add(-5 * time.Second)) {
return
}
conf.lastChecked = now
var mtime time.Time
if fi, err := os.Stat(nssConfigPath); err == nil {
mtime = fi.ModTime()
}
if mtime.Equal(conf.nssConf.mtime) {
return
}
nssConf := parseNSSConfFile(nssConfigPath)
conf.mu.Lock()
conf.nssConf = nssConf
conf.mu.Unlock()
}
func (conf *nsswitchConfig) acquireSema() {
conf.ch <- struct{}{}
}
func (conf *nsswitchConfig) tryAcquireSema() bool {
select {
case conf.ch <- struct{}{}:
return true
default:
return false
}
}
func (conf *nsswitchConfig) releaseSema() {
<-conf.ch
}
// nssConf represents the state of the machine's /etc/nsswitch.conf file.
type nssConf struct {
mtime time.Time // time of nsswitch.conf modification
err error // any error encountered opening or parsing the file
sources map[string][]nssSource // keyed by database (e.g. "hosts")
}
type nssSource struct {
source string // e.g. "compat", "files", "mdns4_minimal"
criteria []nssCriterion
}
// standardCriteria reports all specified criteria have the default
// status actions.
func (s nssSource) standardCriteria() bool {
for i, crit := range s.criteria {
if !crit.standardStatusAction(i == len(s.criteria)-1) {
return false
}
}
return true
}
// nssCriterion is the parsed structure of one of the criteria in brackets
// after an NSS source name.
type nssCriterion struct {
negate bool // if "!" was present
status string // e.g. "success", "unavail" (lowercase)
action string // e.g. "return", "continue" (lowercase)
}
// standardStatusAction reports whether c is equivalent to not
// specifying the criterion at all. last is whether this criteria is the
// last in the list.
func (c nssCriterion) standardStatusAction(last bool) bool {
if c.negate {
return false
}
var def string
switch c.status {
case "success":
def = "return"
case "notfound", "unavail", "tryagain":
def = "continue"
default:
// Unknown status
return false
}
if last && c.action == "return" {
return true
}
return c.action == def
}
func parseNSSConfFile(file string) *nssConf {
f, err := open(file)
if err != nil {
return &nssConf{err: err}
}
defer f.close()
mtime, _, err := f.stat()
if err != nil {
return &nssConf{err: err}
}
conf := parseNSSConf(f)
conf.mtime = mtime
return conf
}
func parseNSSConf(f *file) *nssConf {
conf := new(nssConf)
for line, ok := f.readLine(); ok; line, ok = f.readLine() {
line = trimSpace(removeComment(line))
if len(line) == 0 {
continue
}
colon := bytealg.IndexByteString(line, ':')
if colon == -1 {
conf.err = errors.New("no colon on line")
return conf
}
db := trimSpace(line[:colon])
srcs := line[colon+1:]
for {
srcs = trimSpace(srcs)
if len(srcs) == 0 {
break
}
sp := bytealg.IndexByteString(srcs, ' ')
var src string
if sp == -1 {
src = srcs
srcs = "" // done
} else {
src = srcs[:sp]
srcs = trimSpace(srcs[sp+1:])
}
var criteria []nssCriterion
// See if there's a criteria block in brackets.
if len(srcs) > 0 && srcs[0] == '[' {
bclose := bytealg.IndexByteString(srcs, ']')
if bclose == -1 {
conf.err = errors.New("unclosed criterion bracket")
return conf
}
var err error
criteria, err = parseCriteria(srcs[1:bclose])
if err != nil {
conf.err = errors.New("invalid criteria: " + srcs[1:bclose])
return conf
}
srcs = srcs[bclose+1:]
}
if conf.sources == nil {
conf.sources = make(map[string][]nssSource)
}
conf.sources[db] = append(conf.sources[db], nssSource{
source: src,
criteria: criteria,
})
}
}
return conf
}
// parses "foo=bar !foo=bar"
func parseCriteria(x string) (c []nssCriterion, err error) {
err = foreachField(x, func(f string) error {
not := false
if len(f) > 0 && f[0] == '!' {
not = true
f = f[1:]
}
if len(f) < 3 {
return errors.New("criterion too short")
}
eq := bytealg.IndexByteString(f, '=')
if eq == -1 {
return errors.New("criterion lacks equal sign")
}
if hasUpperCase(f) {
lower := []byte(f)
lowerASCIIBytes(lower)
f = string(lower)
}
c = append(c, nssCriterion{
negate: not,
status: f[:eq],
action: f[eq+1:],
})
return nil
})
return
}
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