Add Dialer.Host field (#196)

dialer.go

@@ -87,6 +87,13 @@ type Dialer struct {
 	// land.
 	Header HandshakeHeader
 
+	// Host is an optional string that could be used to specify the host during
+	// HTTP upgrade request by setting 'Host' header.
+	//
+	// Default value is an empty string, which results in setting 'Host' header
+	// equal to the URL hostname given to Dialer.Dial().
+	Host string
+
 	// OnStatusError is the callback that will be called after receiving non
 	// "101 Continue" HTTP response status. It receives an io.Reader object
 	// representing server response bytes. That is, it gives ability to parse
@@ -310,7 +317,7 @@ func (d Dialer) Upgrade(conn io.ReadWriter, u *url.URL) (br *bufio.Reader, hs Ha
 	nonce := make([]byte, nonceSize)
 	initNonce(nonce)
 
-	httpWriteUpgradeRequest(bw, u, nonce, d.Protocols, d.Extensions, d.Header)
+	httpWriteUpgradeRequest(bw, u, nonce, d.Protocols, d.Extensions, d.Header, d.Host)
 	if err := bw.Flush(); err != nil {
 		return br, hs, err
 	}

http.go

@@ -286,12 +286,16 @@ func httpWriteUpgradeRequest(
 	protocols []string,
 	extensions []httphead.Option,
 	header HandshakeHeader,
+	host string,
 ) {
 	bw.WriteString("GET ")
 	bw.WriteString(u.RequestURI())
 	bw.WriteString(" HTTP/1.1\r\n")
 
-	httpWriteHeader(bw, headerHost, u.Host)
+	if host == "" {
+		host = u.Host
+	}
+	httpWriteHeader(bw, headerHost, host)
 
 	httpWriteHeaderBts(bw, headerUpgrade, specHeaderValueUpgrade)
 	httpWriteHeaderBts(bw, headerConnection, specHeaderValueConnection)

http_test.go

@@ -99,10 +99,15 @@ func BenchmarkHttpWriteUpgradeRequest(b *testing.B) {
 		protocols  []string
 		extensions []httphead.Option
 		headers    HandshakeHeaderFunc
+		host       string
 	}{
 		{
 			url: makeURL("ws://example.org"),
 		},
+		{
+			url:  makeURL("ws://example.org"),
+			host: "test-host",
+		},
 	} {
 		bw := bufio.NewWriter(ioutil.Discard)
 		nonce := make([]byte, nonceSize)
@@ -122,6 +127,7 @@ func BenchmarkHttpWriteUpgradeRequest(b *testing.B) {
 					test.protocols,
 					test.extensions,
 					headers,
+					test.host,
 				)
 			}
 		})