Allow the scraper to parse XHTML documents

Only "text/html" was authorized before.

reader/scraper/scraper.go

@@ -34,7 +34,7 @@ func Fetch(websiteURL, rules, userAgent string) (string, error) {
 		return "", errors.New("scraper: unable to download web page")
 	}
 
-	if !strings.Contains(response.ContentType, "text/html") {
+	if !isWhitelistedContentType(response.ContentType) {
 		return "", fmt.Errorf("scraper: this resource is not a HTML document (%s)", response.ContentType)
 	}
 
@@ -99,3 +99,9 @@ func getPredefinedScraperRules(websiteURL string) string {
 
 	return ""
 }
+
+func isWhitelistedContentType(contentType string) bool {
+	contentType = strings.ToLower(contentType)
+	return strings.HasPrefix(contentType, "text/html") ||
+		strings.HasPrefix(contentType, "application/xhtml+xml")
+}

reader/scraper/scraper_test.go

@@ -19,3 +19,24 @@ func TestGetPredefinedRules(t *testing.T) {
 		t.Error("A rule not defined should not return anything")
 	}
 }
+
+func TestWhitelistedContentTypes(t *testing.T) {
+	scenarios := map[string]bool{
+		"text/html":                            true,
+		"TeXt/hTmL":                            true,
+		"application/xhtml+xml":                true,
+		"text/html; charset=utf-8":             true,
+		"application/xhtml+xml; charset=utf-8": true,
+		"text/css":                             false,
+		"application/javascript":               false,
+		"image/png":                            false,
+		"application/pdf":                      false,
+	}
+
+	for inputValue, expectedResult := range scenarios {
+		actualResult := isWhitelistedContentType(inputValue)
+		if actualResult != expectedResult {
+			t.Errorf(`Unexpected result for content type whitelist, got "%v" instead of "%v"`, actualResult, expectedResult)
+		}
+	}
+}