fix: error on different frag lens

conn_test.go

@@ -9,6 +9,50 @@ import (
 	"testing"
 )
 
+func TestHTTPDialDifferentFragLen(t *testing.T) {
+	cli := http.Client{
+		Transport: &http.Transport{
+			DialTLS: func(network, addr string) (net.Conn, error) {
+				conn, err := net.DialTCP("tcp", nil, net.TCPAddrFromAddrPort(
+					netip.MustParseAddrPort("52.222.136.117:443"),
+				))
+				if err != nil {
+					return nil, err
+				}
+				t.Log("net.Dial succeeded")
+				tlsConn := tls.Client(NewConn(conn), &tls.Config{
+					ServerName:         "huggingface.co",
+					MinVersion:         tls.VersionTLS12,
+					InsecureSkipVerify: true,
+				})
+				err = tlsConn.Handshake()
+				if err != nil {
+					_ = tlsConn.Close()
+					return nil, err
+				}
+				return tlsConn, nil
+			},
+		},
+	}
+	for i := 0; i < 10; i++ {
+		// will fail when i=0 in CN
+		DefaultFirstFragmentLen = i
+		resp, err := cli.Get("https://huggingface.co/")
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer resp.Body.Close()
+		if resp.StatusCode != http.StatusOK {
+			t.Fatal("status code:", resp.StatusCode)
+		}
+		data, err := io.ReadAll(resp.Body)
+		if err != nil {
+			t.Fatal(err)
+		}
+		t.Log(string(data))
+	}
+}
+
 func TestHTTPDialTLS13(t *testing.T) {
 	cli := http.Client{
 		Transport: &http.Transport{