test(xml): add test cases regarding XML encoding

internal/reader/xml/decoder.go

@@ -21,18 +21,23 @@ func NewXMLDecoder(data io.ReadSeeker) *xml.Decoder {
 	buffer := &bytes.Buffer{}
 	io.Copy(buffer, data)
 
-	enc := getEncoding(buffer.Bytes())
+	if hasUTF8XMLDeclaration(buffer.Bytes()) {
-	if enc == nil || bytes.EqualFold(enc, []byte("utf-8")) {
+		// TODO: detect actual encoding from bytes if not UTF-8 and convert to UTF-8 if needed.
-		// filter invalid chars now, since decoder.CharsetReader isn't called for utf-8 content
+		// For now we just expect the invalid characters to be stripped out.
+
+		// Filter invalid chars now, since decoder.CharsetReader isn't called for utf-8 content
 		filteredBytes := filterValidXMLChars(buffer.Bytes())
+
 		decoder = xml.NewDecoder(bytes.NewReader(filteredBytes))
 	} else {
 		data.Seek(0, io.SeekStart)
-		// invalid characters will be filtered later via decoder.CharsetReader
 		decoder = xml.NewDecoder(data)
+
+		// The XML document will be converted to UTF-8 by encoding.CharsetReader
+		// Invalid characters will be filtered later via decoder.CharsetReader
+		decoder.CharsetReader = charsetReaderFilterInvalidUtf8
 	}
 
-	decoder.CharsetReader = charsetReaderFilterInvalidUtf8
 	decoder.Entity = xml.HTMLEntity
 	decoder.Strict = false
 
@@ -46,7 +51,7 @@ func charsetReaderFilterInvalidUtf8(charset string, input io.Reader) (io.Reader,
 	}
 	rawData, err := io.ReadAll(utf8Reader)
 	if err != nil {
-		return nil, fmt.Errorf("encoding: unable to read data: %w", err)
+		return nil, fmt.Errorf("xml: unable to read data: %w", err)
 	}
 	filteredBytes := filterValidXMLChars(rawData)
 	return bytes.NewReader(filteredBytes), nil
@@ -110,3 +115,8 @@ func getEncoding(b []byte) []byte {
 	}
 	return v[1 : idx+1]
 }
+
+func hasUTF8XMLDeclaration(data []byte) bool {
+	enc := getEncoding(data)
+	return enc == nil || bytes.EqualFold(enc, []byte("utf-8"))
+}

internal/reader/xml/decoder_test.go

@@ -6,11 +6,78 @@ package xml // import "miniflux.app/v2/internal/reader/xml"
 import (
 	"encoding/xml"
 	"fmt"
+	"os"
 	"strings"
 	"testing"
 	"unicode/utf8"
 )
 
+func TestXMLDocumentWithISO88591Encoding(t *testing.T) {
+	fp, err := os.Open("testdata/iso88591.xml")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer fp.Close()
+
+	type myXMLDocument struct {
+		XMLName xml.Name `xml:"note"`
+		To      string   `xml:"to"`
+		From    string   `xml:"from"`
+	}
+
+	var doc myXMLDocument
+
+	decoder := NewXMLDecoder(fp)
+	err = decoder.Decode(&doc)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	expectedTo := "Anaïs"
+	expectedFrom := "Jürgen"
+
+	if doc.To != expectedTo {
+		t.Errorf(`Incorrect "to" field, expected: %q, got: %q`, expectedTo, doc.To)
+	}
+	if doc.From != expectedFrom {
+		t.Errorf(`Incorrect "from" field, expected: %q, got: %q`, expectedFrom, doc.From)
+	}
+}
+
+func TestXMLDocumentWithISO88591FileEncodingButUTF8Prolog(t *testing.T) {
+	fp, err := os.Open("testdata/iso88591_utf8_mismatch.xml")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer fp.Close()
+
+	type myXMLDocument struct {
+		XMLName xml.Name `xml:"note"`
+		To      string   `xml:"to"`
+		From    string   `xml:"from"`
+	}
+
+	var doc myXMLDocument
+
+	decoder := NewXMLDecoder(fp)
+	err = decoder.Decode(&doc)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// TODO: detect actual encoding from bytes if not UTF-8 and convert to UTF-8 if needed.
+	// For now we just expect the invalid characters to be stripped out.
+	expectedTo := "Anas"
+	expectedFrom := "Jrgen"
+
+	if doc.To != expectedTo {
+		t.Errorf(`Incorrect "to" field, expected: %q, got: %q`, expectedTo, doc.To)
+	}
+	if doc.From != expectedFrom {
+		t.Errorf(`Incorrect "from" field, expected: %q, got: %q`, expectedFrom, doc.From)
+	}
+}
+
 func TestXMLDocumentWithIllegalUnicodeCharacters(t *testing.T) {
 	type myxml struct {
 		XMLName xml.Name `xml:"rss"`

internal/reader/xml/testdata/iso88591.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="iso8859-1"?>
+<note>
+  <to>Anaïs</to>
+  <from>Jürgen</from>
+</note>

internal/reader/xml/testdata/iso88591_utf8_mismatch.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<note>
+  <to>Anaïs</to>
+  <from>Jürgen</from>
+</note>