net/url: sort keys in Encode; don't enumerate map randomly

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/6303098

src/pkg/net/url/url.go

@@ -7,7 +7,9 @@
 package url
 
 import (
+	"bytes"
 	"errors"
+	"sort"
 	"strconv"
 	"strings"
 )
@@ -538,14 +540,24 @@ func (v Values) Encode() string {
 	if v == nil {
 		return ""
 	}
-	parts := make([]string, 0, len(v)) // will be large enough for most uses
-	for k, vs := range v {
+	var buf bytes.Buffer
+	keys := make([]string, 0, len(v))
+	for k := range v {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	for _, k := range keys {
+		vs := v[k]
 		prefix := QueryEscape(k) + "="
 		for _, v := range vs {
-			parts = append(parts, prefix+QueryEscape(v))
+			if buf.Len() > 0 {
+				buf.WriteByte('&')
+			}
+			buf.WriteString(prefix)
+			buf.WriteString(QueryEscape(v))
 		}
 	}
-	return strings.Join(parts, "&")
+	return buf.String()
 }
 
 // resolvePath applies special path segments from refs and applies

src/pkg/net/url/url_test.go

@@ -453,20 +453,24 @@ func TestEscape(t *testing.T) {
 //}
 
 type EncodeQueryTest struct {
-	m         Values
-	expected  string
-	expected1 string
+	m        Values
+	expected string
 }
 
 var encodeQueryTests = []EncodeQueryTest{
-	{nil, "", ""},
-	{Values{"q": {"puppies"}, "oe": {"utf8"}}, "q=puppies&oe=utf8", "oe=utf8&q=puppies"},
-	{Values{"q": {"dogs", "&", "7"}}, "q=dogs&q=%26&q=7", "q=dogs&q=%26&q=7"},
+	{nil, ""},
+	{Values{"q": {"puppies"}, "oe": {"utf8"}}, "oe=utf8&q=puppies"},
+	{Values{"q": {"dogs", "&", "7"}}, "q=dogs&q=%26&q=7"},
+	{Values{
+		"a": {"a1", "a2", "a3"},
+		"b": {"b1", "b2", "b3"},
+		"c": {"c1", "c2", "c3"},
+	}, "a=a1&a=a2&a=a3&b=b1&b=b2&b=b3&c=c1&c=c2&c=c3"},
 }
 
 func TestEncodeQuery(t *testing.T) {
 	for _, tt := range encodeQueryTests {
-		if q := tt.m.Encode(); q != tt.expected && q != tt.expected1 {
+		if q := tt.m.Encode(); q != tt.expected {
 			t.Errorf(`EncodeQuery(%+v) = %q, want %q`, tt.m, q, tt.expected)
 		}
 	}