github.com/q45/go@v0.0.0-20151101211701-a4fb8c13db3f/src/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 solaris
     6  
     7  // Read system DNS config from /etc/resolv.conf
     8  
     9  package net
    10  
    11  var defaultNS = []string{"127.0.0.1", "::1"}
    12  
    13  type dnsConfig struct {
    14  	servers    []string // servers to use
    15  	search     []string // suffixes to append to local name
    16  	ndots      int      // number of dots in name to trigger absolute lookup
    17  	timeout    int      // seconds before giving up on packet
    18  	attempts   int      // lost packets before giving up on server
    19  	rotate     bool     // round robin among servers
    20  	unknownOpt bool     // anything unknown was encountered
    21  	lookup     []string // OpenBSD top-level database "lookup" order
    22  	err        error    // any error that occurs during open of resolv.conf
    23  }
    24  
    25  // See resolv.conf(5) on a Linux machine.
    26  // TODO(rsc): Supposed to call uname() and chop the beginning
    27  // of the host name to get the default search domain.
    28  func dnsReadConfig(filename string) *dnsConfig {
    29  	conf := &dnsConfig{
    30  		ndots:    1,
    31  		timeout:  5,
    32  		attempts: 2,
    33  	}
    34  	file, err := open(filename)
    35  	if err != nil {
    36  		conf.servers = defaultNS
    37  		conf.err = err
    38  		return conf
    39  	}
    40  	defer file.close()
    41  	for line, ok := file.readLine(); ok; line, ok = file.readLine() {
    42  		if len(line) > 0 && (line[0] == ';' || line[0] == '#') {
    43  			// comment.
    44  			continue
    45  		}
    46  		f := getFields(line)
    47  		if len(f) < 1 {
    48  			continue
    49  		}
    50  		switch f[0] {
    51  		case "nameserver": // add one name server
    52  			if len(f) > 1 && len(conf.servers) < 3 { // small, but the standard limit
    53  				// One more check: make sure server name is
    54  				// just an IP address.  Otherwise we need DNS
    55  				// to look it up.
    56  				if parseIPv4(f[1]) != nil {
    57  					conf.servers = append(conf.servers, f[1])
    58  				} else if ip, _ := parseIPv6(f[1], true); ip != nil {
    59  					conf.servers = append(conf.servers, f[1])
    60  				}
    61  			}
    62  
    63  		case "domain": // set search path to just this domain
    64  			if len(f) > 1 {
    65  				conf.search = []string{f[1]}
    66  			}
    67  
    68  		case "search": // set search path to given servers
    69  			conf.search = make([]string, len(f)-1)
    70  			for i := 0; i < len(conf.search); i++ {
    71  				conf.search[i] = f[i+1]
    72  			}
    73  
    74  		case "options": // magic options
    75  			for _, s := range f[1:] {
    76  				switch {
    77  				case hasPrefix(s, "ndots:"):
    78  					n, _, _ := dtoi(s, 6)
    79  					if n < 1 {
    80  						n = 1
    81  					}
    82  					conf.ndots = n
    83  				case hasPrefix(s, "timeout:"):
    84  					n, _, _ := dtoi(s, 8)
    85  					if n < 1 {
    86  						n = 1
    87  					}
    88  					conf.timeout = n
    89  				case hasPrefix(s, "attempts:"):
    90  					n, _, _ := dtoi(s, 9)
    91  					if n < 1 {
    92  						n = 1
    93  					}
    94  					conf.attempts = n
    95  				case s == "rotate":
    96  					conf.rotate = true
    97  				default:
    98  					conf.unknownOpt = true
    99  				}
   100  			}
   101  
   102  		case "lookup":
   103  			// OpenBSD option:
   104  			// http://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man5/resolv.conf.5
   105  			// "the legal space-separated values are: bind, file, yp"
   106  			conf.lookup = f[1:]
   107  
   108  		default:
   109  			conf.unknownOpt = true
   110  		}
   111  	}
   112  	if len(conf.servers) == 0 {
   113  		conf.servers = defaultNS
   114  	}
   115  	return conf
   116  }
   117  
   118  func hasPrefix(s, prefix string) bool {
   119  	return len(s) >= len(prefix) && s[:len(prefix)] == prefix
   120  }