fix(httpx): enforce http11 for both fallback and h2 probe clients

common/httpx/httpx.go

@@ -153,7 +153,7 @@ func New(options *Options) (*HTTPX, error) {
 		DisableKeepAlives: true,
 	}
 
-	if httpx.Options.Protocol == "http11" {
+	if httpx.Options.Protocol == HTTP11 {
 		// disable http2
 		_ = os.Setenv("GODEBUG", "http2client=0")
 		transport.TLSNextProto = map[string]func(string, *tls.Conn) http.RoundTripper{}
@@ -183,19 +183,26 @@ func New(options *Options) (*HTTPX, error) {
 		CheckRedirect: redirectFunc,
 	}, retryablehttpOptions)
 
-	transport2 := &http2.Transport{
-		TLSClientConfig: &tls.Config{
-			InsecureSkipVerify: true,
-			MinVersion:         tls.VersionTLS10,
-		},
-		AllowHTTP: true,
-	}
-	if httpx.Options.SniName != "" {
-		transport2.TLSClientConfig.ServerName = httpx.Options.SniName
-	}
-	httpx.client2 = &http.Client{
-		Transport: transport2,
-		Timeout:   httpx.Options.Timeout,
+	// honor explicit HTTP/1.1 mode by disabling retryablehttp-go's internal
+	// HTTP/2 fallback client and HTTPX's own HTTP/2 probing client
+	if httpx.Options.Protocol == HTTP11 {
+		httpx.client.HTTPClient2 = httpx.client.HTTPClient
+		httpx.client2 = httpx.client.HTTPClient
+	} else {
+		transport2 := &http2.Transport{
+			TLSClientConfig: &tls.Config{
+				InsecureSkipVerify: true,
+				MinVersion:         tls.VersionTLS10,
+			},
+			AllowHTTP: true,
+		}
+		if httpx.Options.SniName != "" {
+			transport2.TLSClientConfig.ServerName = httpx.Options.SniName
+		}
+		httpx.client2 = &http.Client{
+			Transport: transport2,
+			Timeout:   httpx.Options.Timeout,
+		}
 	}
 
 	httpx.htmlPolicy = bluemonday.NewPolicy()

common/httpx/httpx_protocol_test.go

@@ -0,0 +1,51 @@
+package httpx
+
+import (
+	"os"
+	"testing"
+
+	"golang.org/x/net/http2"
+
+	"github.com/stretchr/testify/require"
+)
+
+// TestNew_HTTP11DisablesRetryableHTTP2Fallback verifies that forcing HTTP/1.1 disables retryablehttp-go's HTTP/2 fallback and prevents HTTP/2 probing client creation.
+func TestNew_HTTP11DisablesRetryableHTTP2Fallback(t *testing.T) {
+	opts := DefaultOptions
+	opts.Protocol = HTTP11
+
+	originalGODEBUG, hadGODEBUG := os.LookupEnv("GODEBUG")
+	t.Cleanup(func() {
+		if hadGODEBUG {
+			_ = os.Setenv("GODEBUG", originalGODEBUG)
+		} else {
+			_ = os.Unsetenv("GODEBUG")
+		}
+	})
+
+	ht, err := New(&opts)
+	require.NoError(t, err)
+	require.NotNil(t, ht)
+	t.Cleanup(func() { ht.Dialer.Close() })
+	require.NotNil(t, ht.client)
+	require.Same(t, ht.client.HTTPClient, ht.client.HTTPClient2)
+	require.Same(t, ht.client.HTTPClient, ht.client2)
+	_, isHTTP2 := ht.client2.Transport.(*http2.Transport)
+	require.False(t, isHTTP2)
+}
+
+// TestNew_NonHTTP11KeepsRetryableHTTP2FallbackClient verifies that non-HTTP/1.1 mode keeps a dedicated HTTP/2 client2 transport and allows retryable fallback behavior.
+func TestNew_NonHTTP11KeepsRetryableHTTP2FallbackClient(t *testing.T) {
+	opts := DefaultOptions
+	opts.Protocol = HTTP2
+
+	ht, err := New(&opts)
+	require.NoError(t, err)
+	require.NotNil(t, ht)
+	t.Cleanup(func() { ht.Dialer.Close() })
+	require.NotNil(t, ht.client)
+	require.NotSame(t, ht.client.HTTPClient, ht.client.HTTPClient2)
+	require.NotSame(t, ht.client.HTTPClient, ht.client2)
+	_, isHTTP2 := ht.client2.Transport.(*http2.Transport)
+	require.True(t, isHTTP2)
+}