Add 'ParsePos' function (#50)

Author: pborzenkov

ltx.go

@@ -71,6 +71,28 @@ func NewPos(txID TXID, postApplyChecksum uint64) Pos {
 	}
 }
 
+// ParsePos parses Pos from its string representation.
+func ParsePos(s string) (Pos, error) {
+	if len(s) != 33 {
+		return Pos{}, fmt.Errorf("invalid formatted position length: %q", s)
+	}
+
+	txid, err := ParseTXID(s[:16])
+	if err != nil {
+		return Pos{}, err
+	}
+
+	checksum, err := strconv.ParseUint(s[17:], 16, 64)
+	if err != nil {
+		return Pos{}, fmt.Errorf("invalid checksum format: %q", s[17:])
+	}
+
+	return Pos{
+		TXID:              txid,
+		PostApplyChecksum: checksum,
+	}, nil
+}
+
 // String returns a string representation of the position.
 func (p Pos) String() string {
 	return fmt.Sprintf("%s/%016x", p.TXID, p.PostApplyChecksum)

ltx_test.go

@@ -25,6 +25,28 @@ func TestNewPos(t *testing.T) {
 	}
 }
 
+func TestPos_String(t *testing.T) {
+	pos := ltx.NewPos(1000, 2000)
+	if got, want := pos.String(), "00000000000003e8/00000000000007d0"; got != want {
+		t.Fatalf("Pos = %s, want = %s", got, want)
+	}
+}
+
+func TestParsePos(t *testing.T) {
+	t.Run("OK", func(t *testing.T) {
+		if v, err := ltx.ParsePos("00000000000003e8/00000000000007d0"); err != nil {
+			t.Fatal(err)
+		} else if got, want := v, ltx.NewPos(1000, 2000); got != want {
+			t.Fatalf("got=%d, want %d", got, want)
+		}
+	})
+	t.Run("ErrTooShort", func(t *testing.T) {
+		if _, err := ltx.ParsePos("00000000000003e8"); err == nil || err.Error() != `invalid formatted position length: "00000000000003e8"` {
+			t.Fatal(err)
+		}
+	})
+}
+
 func TestHeader_Validate(t *testing.T) {
 	t.Run("OK", func(t *testing.T) {
 		hdr := ltx.Header{