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net: check /etc/hosts for modifications every 5 seconds, not 5 minutes
But also cache the previous parsed form and don't reread if the size and modification time are both unchanged from before. On systems with stable /etc/hosts this should result in more stat calls but only a single parsing of /etc/hosts. On systems with variable /etc/hosts files (like some Docker systems) this should result in quicker adoption of changes. Fixes #13340. Change-Id: Iba93b204be73d6d903cd17c58038a4fcfd0952b9 Reviewed-on: https://go-review.googlesource.com/18258 Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
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fb394017f1
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@ -9,7 +9,7 @@ import (
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"time"
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)
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const cacheMaxAge = 5 * time.Minute
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const cacheMaxAge = 5 * time.Second
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func parseLiteralIP(addr string) string {
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var ip IP
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@ -44,47 +44,59 @@ var hosts struct {
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expire time.Time
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path string
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mtime time.Time
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size int64
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}
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func readHosts() {
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now := time.Now()
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hp := testHookHostsPath
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if len(hosts.byName) == 0 || now.After(hosts.expire) || hosts.path != hp {
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hs := make(map[string][]string)
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is := make(map[string][]string)
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var file *file
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if file, _ = open(hp); file == nil {
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return
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}
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for line, ok := file.readLine(); ok; line, ok = file.readLine() {
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if i := byteIndex(line, '#'); i >= 0 {
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// Discard comments.
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line = line[0:i]
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}
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f := getFields(line)
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if len(f) < 2 {
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continue
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}
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addr := parseLiteralIP(f[0])
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if addr == "" {
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continue
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}
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for i := 1; i < len(f); i++ {
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name := absDomainName([]byte(f[i]))
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h := []byte(f[i])
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lowerASCIIBytes(h)
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key := absDomainName(h)
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hs[key] = append(hs[key], addr)
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is[addr] = append(is[addr], name)
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}
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}
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// Update the data cache.
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hosts.expire = now.Add(cacheMaxAge)
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hosts.path = hp
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hosts.byName = hs
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hosts.byAddr = is
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file.close()
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if now.Before(hosts.expire) && hosts.path == hp && len(hosts.byName) > 0 {
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return
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}
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mtime, size, err := stat(hp)
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if err == nil && hosts.path == hp && hosts.mtime.Equal(mtime) && hosts.size == size {
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hosts.expire = now.Add(cacheMaxAge)
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return
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}
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hs := make(map[string][]string)
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is := make(map[string][]string)
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var file *file
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if file, _ = open(hp); file == nil {
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return
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}
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for line, ok := file.readLine(); ok; line, ok = file.readLine() {
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if i := byteIndex(line, '#'); i >= 0 {
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// Discard comments.
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line = line[0:i]
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}
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f := getFields(line)
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if len(f) < 2 {
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continue
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}
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addr := parseLiteralIP(f[0])
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if addr == "" {
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continue
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}
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for i := 1; i < len(f); i++ {
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name := absDomainName([]byte(f[i]))
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h := []byte(f[i])
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lowerASCIIBytes(h)
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key := absDomainName(h)
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hs[key] = append(hs[key], addr)
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is[addr] = append(is[addr], name)
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}
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}
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// Update the data cache.
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hosts.expire = now.Add(cacheMaxAge)
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hosts.path = hp
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hosts.byName = hs
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hosts.byAddr = is
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hosts.mtime = mtime
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hosts.size = size
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file.close()
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}
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// lookupStaticHost looks up the addresses for the given host from /etc/hosts.
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@ -10,6 +10,7 @@ package net
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import (
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"io"
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"os"
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"time"
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_ "unsafe" // For go:linkname
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)
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@ -71,6 +72,14 @@ func open(name string) (*file, error) {
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return &file{fd, make([]byte, 0, os.Getpagesize()), false}, nil
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}
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func stat(name string) (mtime time.Time, size int64, err error) {
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st, err := os.Stat(name)
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if err != nil {
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return time.Time{}, 0, err
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}
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return st.ModTime(), st.Size(), nil
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}
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// byteIndex is strings.IndexByte. It returns the index of the
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// first instance of c in s, or -1 if c is not present in s.
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// strings.IndexByte is implemented in runtime/asm_$GOARCH.s
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