1 files changed, 62 insertions, 33 deletions

diff --git a/libgo/go/net/hosts.go b/libgo/go/net/hosts.go
index 27958c7cc50..c4de1b6a972 100644
--- a/libgo/go/net/hosts.go
+++ b/libgo/go/net/hosts.go
@@ -9,7 +9,7 @@ import (
 	"time"
 )
 
-const cacheMaxAge = 5 * time.Minute
+const cacheMaxAge = 5 * time.Second
 
 func parseLiteralIP(addr string) string {
 	var ip IP
@@ -27,51 +27,76 @@ func parseLiteralIP(addr string) string {
 	return ip.String() + "%" + zone
 }
 
-// Simple cache.
+// 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 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++ {
-				h := f[i]
-				hs[h] = append(hs[h], addr)
-				is[addr] = append(is[addr], h)
-			}
+		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.
@@ -80,7 +105,11 @@ func lookupStaticHost(host string) []string {
 	defer hosts.Unlock()
 	readHosts()
 	if len(hosts.byName) != 0 {
-		if ips, ok := hosts.byName[host]; ok {
+		// 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 {
 			return ips
 		}
 	}