Simplify feed parser and format detection

- Avoid doing multiple buffer copies
- Move parser and format detection logic to its own package

reader/parser/parser.go

@@ -0,0 +1,58 @@
+// Copyright 2018 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 parser // import "miniflux.app/reader/parser"
+
+import (
+	"strings"
+
+	"miniflux.app/errors"
+	"miniflux.app/logger"
+	"miniflux.app/model"
+	"miniflux.app/reader/atom"
+	"miniflux.app/reader/json"
+	"miniflux.app/reader/rdf"
+	"miniflux.app/reader/rss"
+)
+
+// ParseFeed analyzes the input data and returns a normalized feed object.
+func ParseFeed(data string) (*model.Feed, *errors.LocalizedError) {
+	data = stripInvalidXMLCharacters(data)
+
+	switch DetectFeedFormat(data) {
+	case FormatAtom:
+		return atom.Parse(strings.NewReader(data))
+	case FormatRSS:
+		return rss.Parse(strings.NewReader(data))
+	case FormatJSON:
+		return json.Parse(strings.NewReader(data))
+	case FormatRDF:
+		return rdf.Parse(strings.NewReader(data))
+	default:
+		return nil, errors.NewLocalizedError("Unsupported feed format")
+	}
+}
+
+func stripInvalidXMLCharacters(input string) string {
+	return strings.Map(func(r rune) rune {
+		if isInCharacterRange(r) {
+			return r
+		}
+
+		logger.Debug("Strip invalid XML characters: %U", r)
+		return -1
+	}, input)
+}
+
+// Decide whether the given rune is in the XML Character Range, per
+// the Char production of http://www.xml.com/axml/testaxml.htm,
+// Section 2.2 Characters.
+func isInCharacterRange(r rune) (inrange bool) {
+	return r == 0x09 ||
+		r == 0x0A ||
+		r == 0x0D ||
+		r >= 0x20 && r <= 0xDF77 ||
+		r >= 0xE000 && r <= 0xFFFD ||
+		r >= 0x10000 && r <= 0x10FFFF
+}