HTML: fix panic for malformed IE conditional comment, fixes #596

tdewolff · Aug 1, 2023 · 68d601f · 68d601f
1 parent 65bbd3b
commit 68d601f
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Showing 2 changed files with 9 additions and 4 deletions.
diff --git a/html/html.go b/html/html.go
@@ -95,11 +95,15 @@ func (o *Minifier) Minify(m *minify.M, w io.Writer, r io.Reader, _ map[string]st
 				if bytes.HasPrefix(t.Data, []byte("<!--[if ")) && bytes.HasSuffix(t.Data, []byte("<![endif]-->")) { // downlevel-hidden
 					begin := bytes.IndexByte(t.Data, '>') + 1
 					end := len(t.Data) - len("<![endif]-->")
-					w.Write(t.Data[:begin])
-					if err := o.Minify(m, w, buffer.NewReader(t.Data[begin:end]), nil); err != nil {
-						return minify.UpdateErrorPosition(err, z, t.Offset)
+					if begin < end {
+						w.Write(t.Data[:begin])
+						if err := o.Minify(m, w, buffer.NewReader(t.Data[begin:end]), nil); err != nil {
+							return minify.UpdateErrorPosition(err, z, t.Offset)
+						}
+						w.Write(t.Data[end:])
+					} else {
+						w.Write(t.Data) // malformed
 					}
-					w.Write(t.Data[end:])
 				} else {
 					w.Write(t.Data) // downlevel-revealed or short downlevel-hidden
 				}

diff --git a/html/html_test.go b/html/html_test.go
@@ -245,6 +245,7 @@ func TestHTMLKeepConditionalComments(t *testing.T) {
 		{`<!--[if IE 6]--> <b> </b> <!--[endif]-->`, `<!--[if IE 6]--><b></b><!--[endif]-->`},
 		{`<!--[if !mso]><!--> <b> </b> <!--<![endif]-->`, `<!--[if !mso]><!--><b></b><!--<![endif]-->`},
 		{`<!--[if gt IE 6]><!--> <b> </b> <![endif]-->`, `<!--[if gt IE 6]><!--><b></b><![endif]-->`},
+		{`<!--[if IE]foo<![endif]-->`, `<!--[if IE]foo<![endif]-->`}, // #596
 	}
 
 	m := minify.New()