net: return rooted DNS names on Plan 9

This change returns rooted DNS names on Plan 9,
for consistency with other operating systems.

Updates #12193.

Change-Id: If983920c5b9a8f67d4ccb51bb295fac8dfb87e88
Reviewed-on: https://go-review.googlesource.com/15581Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: David du Colombier <0intro@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Mikio Hara <mikioh.mikioh@gmail.com>

src/net/lookup_plan9.go

@@ -190,6 +190,17 @@ func lookupPort(network, service string) (port int, err error) {
 	return 0, unknownPortError
 }
 
+// ensureEndDot adds '.' at the end of name unless it is already there.
+func ensureEndDot(name string) string {
+	if name == "" {
+		return "."
+	}
+	if name[len(name)-1] == '.' {
+		return name
+	}
+	return name + "."
+}
+
 func lookupCNAME(name string) (cname string, err error) {
 	lines, err := queryDNS(name, "cname")
 	if err != nil {
@@ -225,8 +236,8 @@ func lookupSRV(service, proto, name string) (cname string, addrs []*SRV, err err
 		if !(portOk && priorityOk && weightOk) {
 			continue
 		}
-		addrs = append(addrs, &SRV{f[5], uint16(port), uint16(priority), uint16(weight)})
-		cname = f[0]
+		addrs = append(addrs, &SRV{ensureEndDot(f[5]), uint16(port), uint16(priority), uint16(weight)})
+		cname = ensureEndDot(f[0])
 	}
 	byPriorityWeight(addrs).sort()
 	return
@@ -243,7 +254,7 @@ func lookupMX(name string) (mx []*MX, err error) {
 			continue
 		}
 		if pref, _, ok := dtoi(f[2], 0); ok {
-			mx = append(mx, &MX{f[3], uint16(pref)})
+			mx = append(mx, &MX{ensureEndDot(f[3]), uint16(pref)})
 		}
 	}
 	byPref(mx).sort()
@@ -260,7 +271,7 @@ func lookupNS(name string) (ns []*NS, err error) {
 		if len(f) < 3 {
 			continue
 		}
-		ns = append(ns, &NS{f[2]})
+		ns = append(ns, &NS{ensureEndDot(f[2])})
 	}
 	return
 }
@@ -272,7 +283,7 @@ func lookupTXT(name string) (txt []string, err error) {
 	}
 	for _, line := range lines {
 		if i := byteIndex(line, '\t'); i >= 0 {
-			txt = append(txt, line[i+1:])
+			txt = append(txt, ensureEndDot(line[i+1:]))
 		}
 	}
 	return
@@ -292,7 +303,7 @@ func lookupAddr(addr string) (name []string, err error) {
 		if len(f) < 3 {
 			continue
 		}
-		name = append(name, f[2])
+		name = append(name, ensureEndDot(f[2]))
 	}
 	return
 }