net/http: reuse http proxy connections for different http requests

Comment on cache keys above connectMethod says "http to proxy, http
anywhere after that", however in reality target address was always
included, which prevented http requests to different target
addresses to reuse the same http proxy connection.

R=golang-dev, r, rsc, bradfitz
CC=golang-dev
https://golang.org/cl/5901064

src/pkg/net/http/proxy_test.go

@@ -5,6 +5,7 @@
 package http
 
 import (
+	"net/url"
 	"os"
 	"testing"
 )
@@ -46,3 +47,32 @@ func TestUseProxy(t *testing.T) {
 		}
 	}
 }
+
+var cacheKeysTests = []struct {
+	proxy  string
+	scheme string
+	addr   string
+	key    string
+}{
+	{"", "http", "foo.com", "|http|foo.com"},
+	{"", "https", "foo.com", "|https|foo.com"},
+	{"http://foo.com", "http", "foo.com", "http://foo.com|http|"},
+	{"http://foo.com", "https", "foo.com", "http://foo.com|https|foo.com"},
+}
+
+func TestCacheKeys(t *testing.T) {
+	for _, tt := range cacheKeysTests {
+		var proxy *url.URL
+		if tt.proxy != "" {
+			u, err := url.Parse(tt.proxy)
+			if err != nil {
+				t.Fatal(err)
+			}
+			proxy = u
+		}
+		cm := connectMethod{proxy, tt.scheme, tt.addr}
+		if cm.String() != tt.key {
+			t.Fatalf("{%q, %q, %q} cache key %q; want %q", tt.proxy, tt.scheme, tt.addr, cm.String(), tt.key)
+		}
+	}
+}

src/pkg/net/http/transport.go

@@ -450,10 +450,14 @@ type connectMethod struct {
 
 func (ck *connectMethod) String() string {
 	proxyStr := ""
+	targetAddr := ck.targetAddr
 	if ck.proxyURL != nil {
 		proxyStr = ck.proxyURL.String()
+		if ck.targetScheme == "http" {
+			targetAddr = ""
+		}
 	}
-	return strings.Join([]string{proxyStr, ck.targetScheme, ck.targetAddr}, "|")
+	return strings.Join([]string{proxyStr, ck.targetScheme, targetAddr}, "|")
 }
 
 // addr returns the first hop "host:port" to which we need to TCP connect.