...
Run Format

Source file src/net/dnsconfig_unix.go

  // Copyright 2009 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 linux netbsd openbsd solaris
  
  // Read system DNS config from /etc/resolv.conf
  
  package net
  
  import (
  	"os"
  	"sync/atomic"
  	"time"
  )
  
  var (
  	defaultNS   = []string{"127.0.0.1:53", "[::1]:53"}
  	getHostname = os.Hostname // variable for testing
  )
  
  type dnsConfig struct {
  	servers    []string      // server addresses (in host:port form) to use
  	search     []string      // rooted suffixes to append to local name
  	ndots      int           // number of dots in name to trigger absolute lookup
  	timeout    time.Duration // wait before giving up on a query, including retries
  	attempts   int           // lost packets before giving up on server
  	rotate     bool          // round robin among servers
  	unknownOpt bool          // anything unknown was encountered
  	lookup     []string      // OpenBSD top-level database "lookup" order
  	err        error         // any error that occurs during open of resolv.conf
  	mtime      time.Time     // time of resolv.conf modification
  	soffset    uint32        // used by serverOffset
  }
  
  // See resolv.conf(5) on a Linux machine.
  func dnsReadConfig(filename string) *dnsConfig {
  	conf := &dnsConfig{
  		ndots:    1,
  		timeout:  5 * time.Second,
  		attempts: 2,
  	}
  	file, err := open(filename)
  	if err != nil {
  		conf.servers = defaultNS
  		conf.search = dnsDefaultSearch()
  		conf.err = err
  		return conf
  	}
  	defer file.close()
  	if fi, err := file.file.Stat(); err == nil {
  		conf.mtime = fi.ModTime()
  	} else {
  		conf.servers = defaultNS
  		conf.search = dnsDefaultSearch()
  		conf.err = err
  		return conf
  	}
  	for line, ok := file.readLine(); ok; line, ok = file.readLine() {
  		if len(line) > 0 && (line[0] == ';' || line[0] == '#') {
  			// comment.
  			continue
  		}
  		f := getFields(line)
  		if len(f) < 1 {
  			continue
  		}
  		switch f[0] {
  		case "nameserver": // add one name server
  			if len(f) > 1 && len(conf.servers) < 3 { // small, but the standard limit
  				// One more check: make sure server name is
  				// just an IP address. Otherwise we need DNS
  				// to look it up.
  				if parseIPv4(f[1]) != nil {
  					conf.servers = append(conf.servers, JoinHostPort(f[1], "53"))
  				} else if ip, _ := parseIPv6(f[1], true); ip != nil {
  					conf.servers = append(conf.servers, JoinHostPort(f[1], "53"))
  				}
  			}
  
  		case "domain": // set search path to just this domain
  			if len(f) > 1 {
  				conf.search = []string{ensureRooted(f[1])}
  			}
  
  		case "search": // set search path to given servers
  			conf.search = make([]string, len(f)-1)
  			for i := 0; i < len(conf.search); i++ {
  				conf.search[i] = ensureRooted(f[i+1])
  			}
  
  		case "options": // magic options
  			for _, s := range f[1:] {
  				switch {
  				case hasPrefix(s, "ndots:"):
  					n, _, _ := dtoi(s[6:])
  					if n < 0 {
  						n = 0
  					} else if n > 15 {
  						n = 15
  					}
  					conf.ndots = n
  				case hasPrefix(s, "timeout:"):
  					n, _, _ := dtoi(s[8:])
  					if n < 1 {
  						n = 1
  					}
  					conf.timeout = time.Duration(n) * time.Second
  				case hasPrefix(s, "attempts:"):
  					n, _, _ := dtoi(s[9:])
  					if n < 1 {
  						n = 1
  					}
  					conf.attempts = n
  				case s == "rotate":
  					conf.rotate = true
  				default:
  					conf.unknownOpt = true
  				}
  			}
  
  		case "lookup":
  			// OpenBSD option:
  			// http://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man5/resolv.conf.5
  			// "the legal space-separated values are: bind, file, yp"
  			conf.lookup = f[1:]
  
  		default:
  			conf.unknownOpt = true
  		}
  	}
  	if len(conf.servers) == 0 {
  		conf.servers = defaultNS
  	}
  	if len(conf.search) == 0 {
  		conf.search = dnsDefaultSearch()
  	}
  	return conf
  }
  
  // serverOffset returns an offset that can be used to determine
  // indices of servers in c.servers when making queries.
  // When the rotate option is enabled, this offset increases.
  // Otherwise it is always 0.
  func (c *dnsConfig) serverOffset() uint32 {
  	if c.rotate {
  		return atomic.AddUint32(&c.soffset, 1) - 1 // return 0 to start
  	}
  	return 0
  }
  
  func dnsDefaultSearch() []string {
  	hn, err := getHostname()
  	if err != nil {
  		// best effort
  		return nil
  	}
  	if i := byteIndex(hn, '.'); i >= 0 && i < len(hn)-1 {
  		return []string{ensureRooted(hn[i+1:])}
  	}
  	return nil
  }
  
  func hasPrefix(s, prefix string) bool {
  	return len(s) >= len(prefix) && s[:len(prefix)] == prefix
  }
  
  func ensureRooted(s string) string {
  	if len(s) > 0 && s[len(s)-1] == '.' {
  		return s
  	}
  	return s + "."
  }
  

View as plain text