Refactor markup render system (#32533)

Remove unmaintainable sanitizer rules. No need to add special "class"
regexp rules anymore, use RenderInternal.SafeAttr instead, more details
(and examples) are in the tests

modules/markup/internal/internal_test.go

@@ -0,0 +1,61 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package internal
+
+import (
+	"bytes"
+	"html/template"
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRenderInternal(t *testing.T) {
+	cases := []struct {
+		input, protected, recovered string
+	}{
+		{
+			input:     `<div class="test">class="content"</div>`,
+			protected: `<div data-attr-class="sec:test">class="content"</div>`,
+			recovered: `<div class="test">class="content"</div>`,
+		},
+		{
+			input:     "<div\nclass=\"test\" data-xxx></div>",
+			protected: `<div data-attr-class="sec:test" data-xxx></div>`,
+			recovered: `<div class="test" data-xxx></div>`,
+		},
+	}
+	for _, c := range cases {
+		var r RenderInternal
+		out := &bytes.Buffer{}
+		in := r.init("sec", out)
+		protected := r.ProtectSafeAttrs(template.HTML(c.input))
+		assert.EqualValues(t, c.protected, protected)
+		_, _ = io.WriteString(in, string(protected))
+		_ = in.Close()
+		assert.EqualValues(t, c.recovered, out.String())
+	}
+
+	var r1, r2 RenderInternal
+	protected := r1.ProtectSafeAttrs(`<div class="test"></div>`)
+	assert.EqualValues(t, `<div class="test"></div>`, protected, "non-initialized RenderInternal should not protect any attributes")
+	_ = r1.init("sec", nil)
+	protected = r1.ProtectSafeAttrs(`<div class="test"></div>`)
+	assert.EqualValues(t, `<div data-attr-class="sec:test"></div>`, protected)
+	assert.EqualValues(t, "data-attr-class", r1.SafeAttr("class"))
+	assert.EqualValues(t, "sec:val", r1.SafeValue("val"))
+	recovered, ok := r1.RecoverProtectedValue("sec:val")
+	assert.True(t, ok)
+	assert.EqualValues(t, "val", recovered)
+	recovered, ok = r1.RecoverProtectedValue("other:val")
+	assert.False(t, ok)
+	assert.Empty(t, recovered)
+
+	out2 := &bytes.Buffer{}
+	in2 := r2.init("sec-other", out2)
+	_, _ = io.WriteString(in2, string(protected))
+	_ = in2.Close()
+	assert.EqualValues(t, `<div data-attr-class="sec:test"></div>`, out2.String(), "different secureID should not recover the value")
+}