Improve XML decoder to remove illegal characters

reader/xml/decoder.go

@@ -0,0 +1,50 @@
+// Copyright 2019 Frédéric Guillot. All rights reserved.
+// Use of this source code is governed by the Apache 2.0
+// license that can be found in the LICENSE file.
+
+package xml // import "miniflux.app/reader/xml"
+
+import (
+	"bytes"
+	"encoding/xml"
+	"fmt"
+	"io"
+	"io/ioutil"
+
+	"miniflux.app/reader/encoding"
+)
+
+// NewDecoder returns a XML decoder that filters illegal characters.
+func NewDecoder(data io.Reader) *xml.Decoder {
+	decoder := xml.NewDecoder(data)
+	decoder.Entity = xml.HTMLEntity
+	decoder.Strict = false
+	decoder.CharsetReader = func(charset string, input io.Reader) (io.Reader, error) {
+		utf8Reader, err := encoding.CharsetReader(charset, input)
+		if err != nil {
+			return nil, err
+		}
+		rawData, err := ioutil.ReadAll(utf8Reader)
+		if err != nil {
+			return nil, fmt.Errorf("Unable to read data: %q", err)
+		}
+		filteredBytes := bytes.Map(filterValidXMLChar, rawData)
+		return bytes.NewReader(filteredBytes), nil
+	}
+
+	return decoder
+}
+
+// This function is copied from encoding/xml package,
+// and is used to check if all the characters are legal.
+func filterValidXMLChar(r rune) rune {
+	if r == 0x09 ||
+		r == 0x0A ||
+		r == 0x0D ||
+		r >= 0x20 && r <= 0xD7FF ||
+		r >= 0xE000 && r <= 0xFFFD ||
+		r >= 0x10000 && r <= 0x10FFFF {
+		return r
+	}
+	return -1
+}