fix unbounded memory consumption vulnerability (#111)

Co-authored-by: Helena Mariano <31138349+helenamariano@users.noreply.github.com>

docx.go

@@ -40,7 +40,7 @@ func ConvertDocx(r io.Reader) (string, map[string]string, error) {
 		size = si.Size()
 		ra = f
 	} else {
-		b, err := ioutil.ReadAll(r)
+		b, err := ioutil.ReadAll(io.LimitReader(r, maxBytes))
 		if err != nil {
 			return "", nil, nil
 		}

limit.go

@@ -0,0 +1,3 @@
+package docconv
+
+const maxBytes = 20 << 20 // 20MB

odt.go

@@ -14,7 +14,7 @@ func ConvertODT(r io.Reader) (string, map[string]string, error) {
 	meta := make(map[string]string)
 	var textBody string
 
-	b, err := ioutil.ReadAll(r)
+	b, err := ioutil.ReadAll(io.LimitReader(r, maxBytes))
 	if err != nil {
 		return "", nil, err
 	}

pages.go

@@ -21,7 +21,7 @@ func ConvertPages(r io.Reader) (string, map[string]string, error) {
 	meta := make(map[string]string)
 	var textBody string
 
-	b, err := ioutil.ReadAll(r)
+	b, err := ioutil.ReadAll(io.LimitReader(r, maxBytes))
 	if err != nil {
 		return "", nil, fmt.Errorf("error reading data: %v", err)
 	}

xml.go

@@ -25,7 +25,7 @@ func ConvertXML(r io.Reader) (string, map[string]string, error) {
 func XMLToText(r io.Reader, breaks []string, skip []string, strict bool) (string, error) {
 	var result string
 
-	dec := xml.NewDecoder(r)
+	dec := xml.NewDecoder(io.LimitReader(r, maxBytes))
 	dec.Strict = strict
 	for {
 		t, err := dec.Token()
@@ -76,7 +76,7 @@ func XMLToText(r io.Reader, breaks []string, skip []string, strict bool) (string
 // XMLToMap converts XML to a nested string map.
 func XMLToMap(r io.Reader) (map[string]string, error) {
 	m := make(map[string]string)
-	dec := xml.NewDecoder(r)
+	dec := xml.NewDecoder(io.LimitReader(r, maxBytes))
 	var tagName string
 	for {
 		t, err := dec.Token()