frame: cqlvalue, added missing length checks in AsX methods

Fixes #277

frame/cqlvalue.go

@@ -199,6 +199,17 @@ func (c CqlValue) AsFloat64() (float64, error) {
 		uint64(c.Value[7])), nil
 }
 
+func readString(raw []byte) (newRaw []byte, read string, err error) {
+	if len(raw) < 4 {
+		return nil, "", fmt.Errorf("expected at least 4 bytes, got %d", len(raw))
+	}
+	size := binary.BigEndian.Uint32(raw)
+	if len(raw) < int(size+4) {
+		return nil, "", fmt.Errorf("expected at least %d bytes, got %d", size+4, len(raw))
+	}
+	return raw[size+4:], string(raw[4 : size+4]), nil
+}
+
 func (c CqlValue) AsStringSlice() ([]string, error) {
 	if c.Type.ID != SetID && c.Type.ID != ListID {
 		return nil, fmt.Errorf("%v can't be interpreted as a slice", c)
@@ -224,12 +235,15 @@ func (c CqlValue) AsStringSlice() ([]string, error) {
 	raw = raw[4:]
 
 	for i := range res {
-		if len(raw) < 4 {
-			return nil, fmt.Errorf("expected at least 4 bytes, got %d", len(raw))
+		var err error
+		raw, res[i], err = readString(raw)
+		if err != nil {
+			return nil, err
 		}
-		size := binary.BigEndian.Uint32(raw)
-		res[i] = string(raw[4 : size+4])
-		raw = raw[size+4:]
+	}
+
+	if len(raw) > 0 {
+		return nil, fmt.Errorf("got %d unexpected trailing bytes", len(raw))
 	}
 
 	return res, nil
@@ -252,16 +266,24 @@ func (c CqlValue) AsStringMap() (map[string]string, error) {
 
 	res := make(map[string]string, n)
 	for i := 0; i < n; i++ {
-		keyN := binary.BigEndian.Uint32(raw)
-		key := string(raw[4 : keyN+4])
-		raw = raw[keyN+4:]
-
-		valueN := binary.BigEndian.Uint32(raw)
-		value := string(raw[4 : valueN+4])
-		raw = raw[valueN+4:]
+		var key, value string
+		var err error
+		raw, key, err = readString(raw)
+		if err != nil {
+			return nil, err
+		}
+		raw, value, err = readString(raw)
+		if err != nil {
+			return nil, err
+		}
 
 		res[key] = value
 	}
+
+	if len(raw) > 0 {
+		return nil, fmt.Errorf("got %d unexpected trailing bytes", len(raw))
+	}
+
 	return res, nil
 }