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Source file src/net/hosts.go

Documentation: net

     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  package net
     6  
     7  import (
     8  	"sync"
     9  	"time"
    10  )
    11  
    12  const cacheMaxAge = 5 * time.Second
    13  
    14  func parseLiteralIP(addr string) string {
    15  	var ip IP
    16  	var zone string
    17  	ip = parseIPv4(addr)
    18  	if ip == nil {
    19  		ip, zone = parseIPv6Zone(addr)
    20  	}
    21  	if ip == nil {
    22  		return ""
    23  	}
    24  	if zone == "" {
    25  		return ip.String()
    26  	}
    27  	return ip.String() + "%" + zone
    28  }
    29  
    30  // hosts contains known host entries.
    31  var hosts struct {
    32  	sync.Mutex
    33  
    34  	// Key for the list of literal IP addresses must be a host
    35  	// name. It would be part of DNS labels, a FQDN or an absolute
    36  	// FQDN.
    37  	// For now the key is converted to lower case for convenience.
    38  	byName map[string][]string
    39  
    40  	// Key for the list of host names must be a literal IP address
    41  	// including IPv6 address with zone identifier.
    42  	// We don't support old-classful IP address notation.
    43  	byAddr map[string][]string
    44  
    45  	expire time.Time
    46  	path   string
    47  	mtime  time.Time
    48  	size   int64
    49  }
    50  
    51  func readHosts() {
    52  	now := time.Now()
    53  	hp := testHookHostsPath
    54  
    55  	if now.Before(hosts.expire) && hosts.path == hp && len(hosts.byName) > 0 {
    56  		return
    57  	}
    58  	mtime, size, err := stat(hp)
    59  	if err == nil && hosts.path == hp && hosts.mtime.Equal(mtime) && hosts.size == size {
    60  		hosts.expire = now.Add(cacheMaxAge)
    61  		return
    62  	}
    63  
    64  	hs := make(map[string][]string)
    65  	is := make(map[string][]string)
    66  	var file *file
    67  	if file, _ = open(hp); file == nil {
    68  		return
    69  	}
    70  	for line, ok := file.readLine(); ok; line, ok = file.readLine() {
    71  		if i := byteIndex(line, '#'); i >= 0 {
    72  			// Discard comments.
    73  			line = line[0:i]
    74  		}
    75  		f := getFields(line)
    76  		if len(f) < 2 {
    77  			continue
    78  		}
    79  		addr := parseLiteralIP(f[0])
    80  		if addr == "" {
    81  			continue
    82  		}
    83  		for i := 1; i < len(f); i++ {
    84  			name := absDomainName([]byte(f[i]))
    85  			h := []byte(f[i])
    86  			lowerASCIIBytes(h)
    87  			key := absDomainName(h)
    88  			hs[key] = append(hs[key], addr)
    89  			is[addr] = append(is[addr], name)
    90  		}
    91  	}
    92  	// Update the data cache.
    93  	hosts.expire = now.Add(cacheMaxAge)
    94  	hosts.path = hp
    95  	hosts.byName = hs
    96  	hosts.byAddr = is
    97  	hosts.mtime = mtime
    98  	hosts.size = size
    99  	file.close()
   100  }
   101  
   102  // lookupStaticHost looks up the addresses for the given host from /etc/hosts.
   103  func lookupStaticHost(host string) []string {
   104  	hosts.Lock()
   105  	defer hosts.Unlock()
   106  	readHosts()
   107  	if len(hosts.byName) != 0 {
   108  		// TODO(jbd,bradfitz): avoid this alloc if host is already all lowercase?
   109  		// or linear scan the byName map if it's small enough?
   110  		lowerHost := []byte(host)
   111  		lowerASCIIBytes(lowerHost)
   112  		if ips, ok := hosts.byName[absDomainName(lowerHost)]; ok {
   113  			ipsCp := make([]string, len(ips))
   114  			copy(ipsCp, ips)
   115  			return ipsCp
   116  		}
   117  	}
   118  	return nil
   119  }
   120  
   121  // lookupStaticAddr looks up the hosts for the given address from /etc/hosts.
   122  func lookupStaticAddr(addr string) []string {
   123  	hosts.Lock()
   124  	defer hosts.Unlock()
   125  	readHosts()
   126  	addr = parseLiteralIP(addr)
   127  	if addr == "" {
   128  		return nil
   129  	}
   130  	if len(hosts.byAddr) != 0 {
   131  		if hosts, ok := hosts.byAddr[addr]; ok {
   132  			hostsCp := make([]string, len(hosts))
   133  			copy(hostsCp, hosts)
   134  			return hostsCp
   135  		}
   136  	}
   137  	return nil
   138  }
   139  

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