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Source file src/net/hosts.go

Documentation: net

  // Copyright 2009 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  package net
  
  import (
  	"sync"
  	"time"
  )
  
  const cacheMaxAge = 5 * time.Second
  
  func parseLiteralIP(addr string) string {
  	var ip IP
  	var zone string
  	ip = parseIPv4(addr)
  	if ip == nil {
  		ip, zone = parseIPv6(addr, true)
  	}
  	if ip == nil {
  		return ""
  	}
  	if zone == "" {
  		return ip.String()
  	}
  	return ip.String() + "%" + zone
  }
  
  // hosts contains known host entries.
  var hosts struct {
  	sync.Mutex
  
  	// Key for the list of literal IP addresses must be a host
  	// name. It would be part of DNS labels, a FQDN or an absolute
  	// FQDN.
  	// For now the key is converted to lower case for convenience.
  	byName map[string][]string
  
  	// Key for the list of host names must be a literal IP address
  	// including IPv6 address with zone identifier.
  	// We don't support old-classful IP address notation.
  	byAddr map[string][]string
  
  	expire time.Time
  	path   string
  	mtime  time.Time
  	size   int64
  }
  
  func readHosts() {
  	now := time.Now()
  	hp := testHookHostsPath
  
  	if now.Before(hosts.expire) && hosts.path == hp && len(hosts.byName) > 0 {
  		return
  	}
  	mtime, size, err := stat(hp)
  	if err == nil && hosts.path == hp && hosts.mtime.Equal(mtime) && hosts.size == size {
  		hosts.expire = now.Add(cacheMaxAge)
  		return
  	}
  
  	hs := make(map[string][]string)
  	is := make(map[string][]string)
  	var file *file
  	if file, _ = open(hp); file == nil {
  		return
  	}
  	for line, ok := file.readLine(); ok; line, ok = file.readLine() {
  		if i := byteIndex(line, '#'); i >= 0 {
  			// Discard comments.
  			line = line[0:i]
  		}
  		f := getFields(line)
  		if len(f) < 2 {
  			continue
  		}
  		addr := parseLiteralIP(f[0])
  		if addr == "" {
  			continue
  		}
  		for i := 1; i < len(f); i++ {
  			name := absDomainName([]byte(f[i]))
  			h := []byte(f[i])
  			lowerASCIIBytes(h)
  			key := absDomainName(h)
  			hs[key] = append(hs[key], addr)
  			is[addr] = append(is[addr], name)
  		}
  	}
  	// Update the data cache.
  	hosts.expire = now.Add(cacheMaxAge)
  	hosts.path = hp
  	hosts.byName = hs
  	hosts.byAddr = is
  	hosts.mtime = mtime
  	hosts.size = size
  	file.close()
  }
  
  // lookupStaticHost looks up the addresses for the given host from /etc/hosts.
  func lookupStaticHost(host string) []string {
  	hosts.Lock()
  	defer hosts.Unlock()
  	readHosts()
  	if len(hosts.byName) != 0 {
  		// TODO(jbd,bradfitz): avoid this alloc if host is already all lowercase?
  		// or linear scan the byName map if it's small enough?
  		lowerHost := []byte(host)
  		lowerASCIIBytes(lowerHost)
  		if ips, ok := hosts.byName[absDomainName(lowerHost)]; ok {
  			ipsCp := make([]string, len(ips))
  			copy(ipsCp, ips)
  			return ipsCp
  		}
  	}
  	return nil
  }
  
  // lookupStaticAddr looks up the hosts for the given address from /etc/hosts.
  func lookupStaticAddr(addr string) []string {
  	hosts.Lock()
  	defer hosts.Unlock()
  	readHosts()
  	addr = parseLiteralIP(addr)
  	if addr == "" {
  		return nil
  	}
  	if len(hosts.byAddr) != 0 {
  		if hosts, ok := hosts.byAddr[addr]; ok {
  			hostsCp := make([]string, len(hosts))
  			copy(hostsCp, hosts)
  			return hostsCp
  		}
  	}
  	return nil
  }
  

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