Allow omitting the DPT scale field (#84)

Author: icholy

dpt.go

@@ -18,10 +18,13 @@ type DPT struct {
 func newDPT(s BaseSentence) (DPT, error) {
 	p := NewParser(s)
 	p.AssertType(TypeDPT)
-	return DPT{
+	dpt := DPT{
 		BaseSentence: s,
 		Depth:        p.Float64(0, "depth"),
 		Offset:       p.Float64(1, "offset"),
-		RangeScale:   p.Float64(2, "range scale"),
-	}, p.Err()
+	}
+	if len(p.Fields) > 2 {
+		dpt.RangeScale = p.Float64(2, "range scale")
+	}
+	return dpt, p.Err()
 }

dpt_test.go

@@ -30,6 +30,15 @@ var dpttests = []struct {
 			RangeScale: MustParseDecimal("0.1"),
 		},
 	},
+	{
+		name: "good sentence with 2 fields",
+		raw:  "$INDPT,2.3,0.0*46",
+		msg: DPT{
+			Depth:      MustParseDecimal("2.3"),
+			Offset:     MustParseDecimal("0.0"),
+			RangeScale: MustParseDecimal("0"),
+		},
+	},
 	{
 		name: "bad validity",
 		raw:  "$SDDPT,0.5,0.5,*AA",