try compatibility with pre 1.15 as noop

client.go

@@ -275,15 +275,7 @@ func (d *Dialer) DialContext(ctx context.Context, urlStr string, requestHeader h
 		}
 		if proxyURL != nil {
 			proxyDialer := &netDialerFunc{fn: netDial}
-			if proxyURL.Scheme == "https" {
-				proxyDialer.usesTLS = true
-				proxyDialer.fn = func(network, addr string) (net.Conn, error) {
-					t := tls.Dialer{}
-					t.Config = d.TLSClientConfig
-					t.NetDialer = &net.Dialer{}
-					return t.DialContext(ctx, network, addr)
-				}
-			}
+			modifyProxyDialer(ctx, d, proxyURL, proxyDialer)
 			dialer, err := proxy_FromURL(proxyURL, proxyDialer)
 			if err != nil {
 				return nil, nil, err

client_server_httpsproxy_test.go

@@ -0,0 +1,51 @@
+// +build go1.15
+
+package websocket
+
+import (
+	"crypto/tls"
+	"net/http"
+	"net/url"
+	"testing"
+)
+
+func TestHttpsProxy(t *testing.T) {
+
+	sTLS := newTLSServer(t)
+	defer sTLS.Close()
+	s := newServer(t)
+	defer s.Close()
+
+	surlTLS, _ := url.Parse(sTLS.Server.URL)
+
+	cstDialer := cstDialer // make local copy for modification on next line.
+	cstDialer.Proxy = http.ProxyURL(surlTLS)
+
+	connect := false
+	origHandler := sTLS.Server.Config.Handler
+
+	// Capture the request Host header.
+	sTLS.Server.Config.Handler = http.HandlerFunc(
+		func(w http.ResponseWriter, r *http.Request) {
+			if r.Method == "CONNECT" {
+				connect = true
+				w.WriteHeader(http.StatusOK)
+				return
+			}
+
+			if !connect {
+				t.Log("connect not received")
+				http.Error(w, "connect not received", http.StatusMethodNotAllowed)
+				return
+			}
+			origHandler.ServeHTTP(w, r)
+		})
+
+	cstDialer.TLSClientConfig = &tls.Config{RootCAs: rootCAs(t, sTLS.Server)}
+	ws, _, err := cstDialer.Dial(s.URL, nil)
+	if err != nil {
+		t.Fatalf("Dial: %v", err)
+	}
+	defer ws.Close()
+	sendRecv(t, ws)
+}

client_server_test.go

@@ -185,47 +185,6 @@ func TestProxyDial(t *testing.T) {
 	sendRecv(t, ws)
 }
 
-func TestHttpsProxy(t *testing.T) {
-
-	sTLS := newTLSServer(t)
-	defer sTLS.Close()
-	s := newServer(t)
-	defer s.Close()
-
-	surlTLS, _ := url.Parse(sTLS.Server.URL)
-
-	cstDialer := cstDialer // make local copy for modification on next line.
-	cstDialer.Proxy = http.ProxyURL(surlTLS)
-
-	connect := false
-	origHandler := sTLS.Server.Config.Handler
-
-	// Capture the request Host header.
-	sTLS.Server.Config.Handler = http.HandlerFunc(
-		func(w http.ResponseWriter, r *http.Request) {
-			if r.Method == "CONNECT" {
-				connect = true
-				w.WriteHeader(http.StatusOK)
-				return
-			}
-
-			if !connect {
-				t.Log("connect not received")
-				http.Error(w, "connect not received", http.StatusMethodNotAllowed)
-				return
-			}
-			origHandler.ServeHTTP(w, r)
-		})
-
-	cstDialer.TLSClientConfig = &tls.Config{RootCAs: rootCAs(t, sTLS.Server)}
-	ws, _, err := cstDialer.Dial(s.URL, nil)
-	if err != nil {
-		t.Fatalf("Dial: %v", err)
-	}
-	defer ws.Close()
-	sendRecv(t, ws)
-}
-
 func TestProxyAuthorizationDial(t *testing.T) {
 	s := newServer(t)
 	defer s.Close()

proxy.go

@@ -6,7 +6,6 @@ package websocket
 
 import (
 	"bufio"
-	"crypto/tls"
 	"encoding/base64"
 	"errors"
 	"net"
@@ -39,17 +38,7 @@ func init() {
 	proxy_RegisterDialerType("http", func(proxyURL *url.URL, forwardDialer proxy_Dialer) (proxy_Dialer, error) {
 		return &httpProxyDialer{proxyURL: proxyURL, forwardDial: forwardDialer.Dial, usesTLS: false}, nil
 	})
-	proxy_RegisterDialerType("https", func(proxyURL *url.URL, forwardDialer proxy_Dialer) (proxy_Dialer, error) {
-		fwd := forwardDialer.Dial
-		if dialerEx, ok := forwardDialer.(proxyDialerEx); !ok || !dialerEx.UsesTLS() {
-			tlsDialer := &tls.Dialer{
-				Config:    &tls.Config{},
-				NetDialer: &net.Dialer{},
-			}
-			fwd = tlsDialer.Dial
-		}
-		return &httpProxyDialer{proxyURL: proxyURL, forwardDial: fwd, usesTLS: true}, nil
-	})
+	registerDialerHttps()
 }
 
 type httpProxyDialer struct {

proxy_https.go

@@ -0,0 +1,36 @@
+// +build go1.15
+
+package websocket
+
+import (
+	"context"
+	"crypto/tls"
+	"net"
+	"net/url"
+)
+
+func registerDialerHttps() {
+	proxy_RegisterDialerType("https", func(proxyURL *url.URL, forwardDialer proxy_Dialer) (proxy_Dialer, error) {
+		fwd := forwardDialer.Dial
+		if dialerEx, ok := forwardDialer.(proxyDialerEx); !ok || !dialerEx.UsesTLS() {
+			tlsDialer := &tls.Dialer{
+				Config:    &tls.Config{},
+				NetDialer: &net.Dialer{},
+			}
+			fwd = tlsDialer.Dial
+		}
+		return &httpProxyDialer{proxyURL: proxyURL, forwardDial: fwd, usesTLS: true}, nil
+	})
+}
+
+func modifyProxyDialer(ctx context.Context, d *Dialer, proxyURL *url.URL, proxyDialer *netDialerFunc) {
+	if proxyURL.Scheme == "https" {
+		proxyDialer.usesTLS = true
+		proxyDialer.fn = func(network, addr string) (net.Conn, error) {
+			t := tls.Dialer{}
+			t.Config = d.TLSClientConfig
+			t.NetDialer = &net.Dialer{}
+			return t.DialContext(ctx, network, addr)
+		}
+	}
+}

proxy_https_legacy.go

@@ -0,0 +1,15 @@
+// +build !go1.15
+
+package websocket
+
+import (
+	"context"
+	"net/url"
+)
+
+func registerDialerHttps() {
+}
+
+func modifyProxyDialer(ctx context.Context, d *Dialer, proxyURL *url.URL, proxyDialer *netDialerFunc) {
+	return nil
+}