github.com/d4l3k/go@v0.0.0-20151015000803-65fc379daeda/src/net/lookup_unix.go (about)

     1  // Copyright 2011 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  package net
     8  
     9  import "sync"
    10  
    11  var onceReadProtocols sync.Once
    12  
    13  // readProtocols loads contents of /etc/protocols into protocols map
    14  // for quick access.
    15  func readProtocols() {
    16  	if file, err := open("/etc/protocols"); err == nil {
    17  		for line, ok := file.readLine(); ok; line, ok = file.readLine() {
    18  			// tcp    6   TCP    # transmission control protocol
    19  			if i := byteIndex(line, '#'); i >= 0 {
    20  				line = line[0:i]
    21  			}
    22  			f := getFields(line)
    23  			if len(f) < 2 {
    24  				continue
    25  			}
    26  			if proto, _, ok := dtoi(f[1], 0); ok {
    27  				if _, ok := protocols[f[0]]; !ok {
    28  					protocols[f[0]] = proto
    29  				}
    30  				for _, alias := range f[2:] {
    31  					if _, ok := protocols[alias]; !ok {
    32  						protocols[alias] = proto
    33  					}
    34  				}
    35  			}
    36  		}
    37  		file.close()
    38  	}
    39  }
    40  
    41  // lookupProtocol looks up IP protocol name in /etc/protocols and
    42  // returns correspondent protocol number.
    43  func lookupProtocol(name string) (int, error) {
    44  	onceReadProtocols.Do(readProtocols)
    45  	proto, found := protocols[name]
    46  	if !found {
    47  		return 0, &AddrError{Err: "unknown IP protocol specified", Addr: name}
    48  	}
    49  	return proto, nil
    50  }
    51  
    52  func lookupHost(host string) (addrs []string, err error) {
    53  	order := systemConf().hostLookupOrder(host)
    54  	if order == hostLookupCgo {
    55  		if addrs, err, ok := cgoLookupHost(host); ok {
    56  			return addrs, err
    57  		}
    58  		// cgo not available (or netgo); fall back to Go's DNS resolver
    59  		order = hostLookupFilesDNS
    60  	}
    61  	return goLookupHostOrder(host, order)
    62  }
    63  
    64  func lookupIP(host string) (addrs []IPAddr, err error) {
    65  	order := systemConf().hostLookupOrder(host)
    66  	if order == hostLookupCgo {
    67  		if addrs, err, ok := cgoLookupIP(host); ok {
    68  			return addrs, err
    69  		}
    70  		// cgo not available (or netgo); fall back to Go's DNS resolver
    71  		order = hostLookupFilesDNS
    72  	}
    73  	return goLookupIPOrder(host, order)
    74  }
    75  
    76  func lookupPort(network, service string) (int, error) {
    77  	if systemConf().canUseCgo() {
    78  		if port, err, ok := cgoLookupPort(network, service); ok {
    79  			return port, err
    80  		}
    81  	}
    82  	return goLookupPort(network, service)
    83  }
    84  
    85  func lookupCNAME(name string) (string, error) {
    86  	if systemConf().canUseCgo() {
    87  		if cname, err, ok := cgoLookupCNAME(name); ok {
    88  			return cname, err
    89  		}
    90  	}
    91  	return goLookupCNAME(name)
    92  }
    93  
    94  func lookupSRV(service, proto, name string) (string, []*SRV, error) {
    95  	var target string
    96  	if service == "" && proto == "" {
    97  		target = name
    98  	} else {
    99  		target = "_" + service + "._" + proto + "." + name
   100  	}
   101  	cname, rrs, err := lookup(target, dnsTypeSRV)
   102  	if err != nil {
   103  		return "", nil, err
   104  	}
   105  	srvs := make([]*SRV, len(rrs))
   106  	for i, rr := range rrs {
   107  		rr := rr.(*dnsRR_SRV)
   108  		srvs[i] = &SRV{Target: rr.Target, Port: rr.Port, Priority: rr.Priority, Weight: rr.Weight}
   109  	}
   110  	byPriorityWeight(srvs).sort()
   111  	return cname, srvs, nil
   112  }
   113  
   114  func lookupMX(name string) ([]*MX, error) {
   115  	_, rrs, err := lookup(name, dnsTypeMX)
   116  	if err != nil {
   117  		return nil, err
   118  	}
   119  	mxs := make([]*MX, len(rrs))
   120  	for i, rr := range rrs {
   121  		rr := rr.(*dnsRR_MX)
   122  		mxs[i] = &MX{Host: rr.Mx, Pref: rr.Pref}
   123  	}
   124  	byPref(mxs).sort()
   125  	return mxs, nil
   126  }
   127  
   128  func lookupNS(name string) ([]*NS, error) {
   129  	_, rrs, err := lookup(name, dnsTypeNS)
   130  	if err != nil {
   131  		return nil, err
   132  	}
   133  	nss := make([]*NS, len(rrs))
   134  	for i, rr := range rrs {
   135  		nss[i] = &NS{Host: rr.(*dnsRR_NS).Ns}
   136  	}
   137  	return nss, nil
   138  }
   139  
   140  func lookupTXT(name string) ([]string, error) {
   141  	_, rrs, err := lookup(name, dnsTypeTXT)
   142  	if err != nil {
   143  		return nil, err
   144  	}
   145  	txts := make([]string, len(rrs))
   146  	for i, rr := range rrs {
   147  		txts[i] = rr.(*dnsRR_TXT).Txt
   148  	}
   149  	return txts, nil
   150  }
   151  
   152  func lookupAddr(addr string) ([]string, error) {
   153  	if systemConf().canUseCgo() {
   154  		if ptrs, err, ok := cgoLookupPTR(addr); ok {
   155  			return ptrs, err
   156  		}
   157  	}
   158  	return goLookupPTR(addr)
   159  }