github.com/tcnksm/go@v0.0.0-20141208075154-439b32936367/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  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  func dnsReadConfig(filename string) (*dnsConfig, error) {
    24  	file, err := open(filename)
    25  	if err != nil {
    26  		return nil, &DNSConfigError{err}
    27  	}
    28  	defer file.close()
    29  	conf := &dnsConfig{
    30  		ndots:    1,
    31  		timeout:  5,
    32  		attempts: 2,
    33  	}
    34  	for line, ok := file.readLine(); ok; line, ok = file.readLine() {
    35  		f := getFields(line)
    36  		if len(f) < 1 {
    37  			continue
    38  		}
    39  		switch f[0] {
    40  		case "nameserver": // add one name server
    41  			if len(f) > 1 && len(conf.servers) < 3 { // small, but the standard limit
    42  				// One more check: make sure server name is
    43  				// just an IP address.  Otherwise we need DNS
    44  				// to look it up.
    45  				if parseIPv4(f[1]) != nil {
    46  					conf.servers = append(conf.servers, f[1])
    47  				} else if ip, _ := parseIPv6(f[1], true); ip != nil {
    48  					conf.servers = append(conf.servers, f[1])
    49  				}
    50  			}
    51  
    52  		case "domain": // set search path to just this domain
    53  			if len(f) > 1 {
    54  				conf.search = []string{f[1]}
    55  			}
    56  
    57  		case "search": // set search path to given servers
    58  			conf.search = make([]string, len(f)-1)
    59  			for i := 0; i < len(conf.search); i++ {
    60  				conf.search[i] = f[i+1]
    61  			}
    62  
    63  		case "options": // magic options
    64  			for i := 1; i < len(f); i++ {
    65  				s := f[i]
    66  				switch {
    67  				case hasPrefix(s, "ndots:"):
    68  					n, _, _ := dtoi(s, 6)
    69  					if n < 1 {
    70  						n = 1
    71  					}
    72  					conf.ndots = n
    73  				case hasPrefix(s, "timeout:"):
    74  					n, _, _ := dtoi(s, 8)
    75  					if n < 1 {
    76  						n = 1
    77  					}
    78  					conf.timeout = n
    79  				case hasPrefix(s, "attempts:"):
    80  					n, _, _ := dtoi(s, 9)
    81  					if n < 1 {
    82  						n = 1
    83  					}
    84  					conf.attempts = n
    85  				case s == "rotate":
    86  					conf.rotate = true
    87  				}
    88  			}
    89  		}
    90  	}
    91  	return conf, nil
    92  }
    93  
    94  func hasPrefix(s, prefix string) bool {
    95  	return len(s) >= len(prefix) && s[:len(prefix)] == prefix
    96  }