tar/storage: work with raw (invalid utf8) names

When the entry name is not UTF-8, for example ISO-8859-1, then store the
raw bytes.
To accommodate this, we will have getters and setters for the entry's
name now. Since this most heavily affects the json marshalling, we'll
double check the sanity of the name before storing it in the JSONPacker.

tar/storage/entry.go

@@ -1,5 +1,11 @@
 package storage
 
+import (
+	"fmt"
+
+	"github.com/vbatts/tar-split/tar/common"
+)
+
 // Entries is for sorting by Position
 type Entries []Entry
 
@@ -33,7 +39,44 @@ const (
 type Entry struct {
 	Type     Type   `json:"type"`
 	Name     string `json:"name,omitempty"`
+	NameRaw  []byte `json:"name_raw,omitempty"`
 	Size     int64  `json:"size,omitempty"`
 	Payload  []byte `json:"payload"` // SegmentType stores payload here; FileType stores crc64 checksum here;
 	Position int    `json:"position"`
 }
+
+// SetName will check name for valid UTF-8 string, and set the appropriate
+// field. See https://github.com/vbatts/tar-split/issues/17
+func (e *Entry) SetName(name string) {
+	if common.IsValidUtf8String(name) {
+		e.Name = name
+	} else {
+		e.NameRaw = []byte(name)
+	}
+}
+
+// SetNameBytes will check name for valid UTF-8 string, and set the appropriate
+// field
+func (e *Entry) SetNameBytes(name []byte) {
+	if !common.IsValidUtf8Btyes(name) {
+		e.NameRaw = name
+	} else {
+		e.Name = string(name)
+	}
+}
+
+// GetName returns the string for the entry's name, regardless of the field stored in
+func (e *Entry) GetName() string {
+	if len(e.NameRaw) > 0 {
+		return fmt.Sprintf("%s", e.NameRaw)
+	}
+	return e.Name
+}
+
+// GetNameBytes returns the bytes for the entry's name, regardless of the field stored in
+func (e *Entry) GetNameBytes() []byte {
+	if len(e.NameRaw) > 0 {
+		return e.NameRaw
+	}
+	return []byte(e.Name)
+}