Commit b598a7fc authored by Russ Cox's avatar Russ Cox

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/18258Reviewed-by: default avatarBrad Fitzpatrick <bradfitz@golang.org>
parent fb394017
......@@ -9,7 +9,7 @@ import (
"time"
)
const cacheMaxAge = 5 * time.Minute
const cacheMaxAge = 5 * time.Second
func parseLiteralIP(addr string) string {
var ip IP
......@@ -44,47 +44,59 @@ var hosts struct {
expire time.Time
path string
mtime time.Time
size int64
}
func readHosts() {
now := time.Now()
hp := testHookHostsPath
if len(hosts.byName) == 0 || now.After(hosts.expire) || hosts.path != hp {
hs := make(map[string][]string)
is := make(map[string][]string)
var file *file
if file, _ = open(hp); file == nil {
return
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]
}
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)
}
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
file.close()
}
// 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.
......
......@@ -10,6 +10,7 @@ package net
import (
"io"
"os"
"time"
_ "unsafe" // For go:linkname
)
......@@ -71,6 +72,14 @@ func open(name string) (*file, error) {
return &file{fd, make([]byte, 0, os.Getpagesize()), false}, nil
}
func stat(name string) (mtime time.Time, size int64, err error) {
st, err := os.Stat(name)
if err != nil {
return time.Time{}, 0, err
}
return st.ModTime(), st.Size(), nil
}
// byteIndex is strings.IndexByte. It returns the index of the
// first instance of c in s, or -1 if c is not present in s.
// strings.IndexByte is implemented in runtime/asm_$GOARCH.s
......
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