github.com/spotify/syslog-redirector-golang@v0.0.0-20140320174030-4859f03d829a/src/pkg/net/dnsconfig_unix.go (about)

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // +build darwin dragonfly freebsd linux netbsd openbsd
     6  
     7  // Read system DNS config from /etc/resolv.conf
     8  
     9  package net
    10  
    11  type dnsConfig struct {
    12  	servers  []string // servers to use
    13  	search   []string // suffixes to append to local name
    14  	ndots    int      // number of dots in name to trigger absolute lookup
    15  	timeout  int      // seconds before giving up on packet
    16  	attempts int      // lost packets before giving up on server
    17  	rotate   bool     // round robin among servers
    18  }
    19  
    20  // See resolv.conf(5) on a Linux machine.
    21  // TODO(rsc): Supposed to call uname() and chop the beginning
    22  // of the host name to get the default search domain.
    23  // We assume it's in resolv.conf anyway.
    24  func dnsReadConfig() (*dnsConfig, error) {
    25  	file, err := open("/etc/resolv.conf")
    26  	if err != nil {
    27  		return nil, &DNSConfigError{err}
    28  	}
    29  	conf := new(dnsConfig)
    30  	conf.servers = make([]string, 3)[0:0] // small, but the standard limit
    31  	conf.search = make([]string, 0)
    32  	conf.ndots = 1
    33  	conf.timeout = 5
    34  	conf.attempts = 2
    35  	conf.rotate = false
    36  	for line, ok := file.readLine(); ok; line, ok = file.readLine() {
    37  		f := getFields(line)
    38  		if len(f) < 1 {
    39  			continue
    40  		}
    41  		switch f[0] {
    42  		case "nameserver": // add one name server
    43  			a := conf.servers
    44  			n := len(a)
    45  			if len(f) > 1 && n < cap(a) {
    46  				// One more check: make sure server name is
    47  				// just an IP address.  Otherwise we need DNS
    48  				// to look it up.
    49  				name := f[1]
    50  				switch len(ParseIP(name)) {
    51  				case 16:
    52  					name = "[" + name + "]"
    53  					fallthrough
    54  				case 4:
    55  					a = a[0 : n+1]
    56  					a[n] = name
    57  					conf.servers = a
    58  				}
    59  			}
    60  
    61  		case "domain": // set search path to just this domain
    62  			if len(f) > 1 {
    63  				conf.search = make([]string, 1)
    64  				conf.search[0] = f[1]
    65  			} else {
    66  				conf.search = make([]string, 0)
    67  			}
    68  
    69  		case "search": // set search path to given servers
    70  			conf.search = make([]string, len(f)-1)
    71  			for i := 0; i < len(conf.search); i++ {
    72  				conf.search[i] = f[i+1]
    73  			}
    74  
    75  		case "options": // magic options
    76  			for i := 1; i < len(f); i++ {
    77  				s := f[i]
    78  				switch {
    79  				case len(s) >= 6 && s[0:6] == "ndots:":
    80  					n, _, _ := dtoi(s, 6)
    81  					if n < 1 {
    82  						n = 1
    83  					}
    84  					conf.ndots = n
    85  				case len(s) >= 8 && s[0:8] == "timeout:":
    86  					n, _, _ := dtoi(s, 8)
    87  					if n < 1 {
    88  						n = 1
    89  					}
    90  					conf.timeout = n
    91  				case len(s) >= 8 && s[0:9] == "attempts:":
    92  					n, _, _ := dtoi(s, 9)
    93  					if n < 1 {
    94  						n = 1
    95  					}
    96  					conf.attempts = n
    97  				case s == "rotate":
    98  					conf.rotate = true
    99  				}
   100  			}
   101  		}
   102  	}
   103  	file.close()
   104  
   105  	return conf, nil
   106  }