1 files changed, 45 insertions, 13 deletions

diff --git a/src/pkg/net/lookup.go b/src/pkg/net/lookup.go
index bec93ec08..20f20578c 100644
--- a/src/pkg/net/lookup.go
+++ b/src/pkg/net/lookup.go
@@ -4,9 +4,20 @@
 
 package net
 
-import (
-	"time"
-)
+import "time"
+
+// protocols contains minimal mappings between internet protocol
+// names and numbers for platforms that don't have a complete list of
+// protocol numbers.
+//
+// See http://www.iana.org/assignments/protocol-numbers
+var protocols = map[string]int{
+	"icmp": 1, "ICMP": 1,
+	"igmp": 2, "IGMP": 2,
+	"tcp": 6, "TCP": 6,
+	"udp": 17, "UDP": 17,
+	"ipv6-icmp": 58, "IPV6-ICMP": 58, "IPv6-ICMP": 58,
+}
 
 // LookupHost looks up the given host using the local resolver.
 // It returns an array of that host's addresses.
@@ -14,9 +25,36 @@ func LookupHost(host string) (addrs []string, err error) {
 	return lookupHost(host)
 }
 
-func lookupHostDeadline(host string, deadline time.Time) (addrs []string, err error) {
+// LookupIP looks up host using the local resolver.
+// It returns an array of that host's IPv4 and IPv6 addresses.
+func LookupIP(host string) (addrs []IP, err error) {
+	return lookupIPMerge(host)
+}
+
+var lookupGroup singleflight
+
+// lookupIPMerge wraps lookupIP, but makes sure that for any given
+// host, only one lookup is in-flight at a time. The returned memory
+// is always owned by the caller.
+func lookupIPMerge(host string) (addrs []IP, err error) {
+	addrsi, err, shared := lookupGroup.Do(host, func() (interface{}, error) {
+		return lookupIP(host)
+	})
+	if err != nil {
+		return nil, err
+	}
+	addrs = addrsi.([]IP)
+	if shared {
+		clone := make([]IP, len(addrs))
+		copy(clone, addrs)
+		addrs = clone
+	}
+	return addrs, nil
+}
+
+func lookupIPDeadline(host string, deadline time.Time) (addrs []IP, err error) {
 	if deadline.IsZero() {
-		return lookupHost(host)
+		return lookupIPMerge(host)
 	}
 
 	// TODO(bradfitz): consider pushing the deadline down into the
@@ -34,12 +72,12 @@ func lookupHostDeadline(host string, deadline time.Time) (addrs []string, err er
 	t := time.NewTimer(timeout)
 	defer t.Stop()
 	type res struct {
-		addrs []string
+		addrs []IP
 		err   error
 	}
 	resc := make(chan res, 1)
 	go func() {
-		a, err := lookupHost(host)
+		a, err := lookupIPMerge(host)
 		resc <- res{a, err}
 	}()
 	select {
@@ -51,12 +89,6 @@ func lookupHostDeadline(host string, deadline time.Time) (addrs []string, err er
 	return
 }
 
-// LookupIP looks up host using the local resolver.
-// It returns an array of that host's IPv4 and IPv6 addresses.
-func LookupIP(host string) (addrs []IP, err error) {
-	return lookupIP(host)
-}
-
 // LookupPort looks up the port for the given network and service.
 func LookupPort(network, service string) (port int, err error) {
 	return lookupPort(network, service)