github.com/c0deoo1/golang1.5@v0.0.0-20220525150107-c87c805d4593/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  	port, err, ok := cgoLookupPort(network, service)
    78  	if !ok {
    79  		port, err = goLookupPort(network, service)
    80  	}
    81  	return port, err
    82  }
    83  
    84  func lookupCNAME(name string) (string, error) {
    85  	cname, err, ok := cgoLookupCNAME(name)
    86  	if !ok {
    87  		cname, err = goLookupCNAME(name)
    88  	}
    89  	return cname, err
    90  }
    91  
    92  func lookupSRV(service, proto, name string) (string, []*SRV, error) {
    93  	var target string
    94  	if service == "" && proto == "" {
    95  		target = name
    96  	} else {
    97  		target = "_" + service + "._" + proto + "." + name
    98  	}
    99  	cname, rrs, err := lookup(target, dnsTypeSRV)
   100  	if err != nil {
   101  		return "", nil, err
   102  	}
   103  	srvs := make([]*SRV, len(rrs))
   104  	for i, rr := range rrs {
   105  		rr := rr.(*dnsRR_SRV)
   106  		srvs[i] = &SRV{Target: rr.Target, Port: rr.Port, Priority: rr.Priority, Weight: rr.Weight}
   107  	}
   108  	byPriorityWeight(srvs).sort()
   109  	return cname, srvs, nil
   110  }
   111  
   112  func lookupMX(name string) ([]*MX, error) {
   113  	_, rrs, err := lookup(name, dnsTypeMX)
   114  	if err != nil {
   115  		return nil, err
   116  	}
   117  	mxs := make([]*MX, len(rrs))
   118  	for i, rr := range rrs {
   119  		rr := rr.(*dnsRR_MX)
   120  		mxs[i] = &MX{Host: rr.Mx, Pref: rr.Pref}
   121  	}
   122  	byPref(mxs).sort()
   123  	return mxs, nil
   124  }
   125  
   126  func lookupNS(name string) ([]*NS, error) {
   127  	_, rrs, err := lookup(name, dnsTypeNS)
   128  	if err != nil {
   129  		return nil, err
   130  	}
   131  	nss := make([]*NS, len(rrs))
   132  	for i, rr := range rrs {
   133  		nss[i] = &NS{Host: rr.(*dnsRR_NS).Ns}
   134  	}
   135  	return nss, nil
   136  }
   137  
   138  func lookupTXT(name string) ([]string, error) {
   139  	_, rrs, err := lookup(name, dnsTypeTXT)
   140  	if err != nil {
   141  		return nil, err
   142  	}
   143  	txts := make([]string, len(rrs))
   144  	for i, rr := range rrs {
   145  		txts[i] = rr.(*dnsRR_TXT).Txt
   146  	}
   147  	return txts, nil
   148  }
   149  
   150  func lookupAddr(addr string) ([]string, error) {
   151  	ptrs, err, ok := cgoLookupPTR(addr)
   152  	if !ok {
   153  		ptrs, err = goLookupPTR(addr)
   154  	}
   155  	return ptrs, err
   156  }