Added in "ModeFromString" for turning standard serial port mode notat…

serial.go

@@ -199,3 +199,50 @@ func (e PortError) Error() string {
 func (e PortError) Code() PortErrorCode {
 	return e.code
 }
+
+// ModeFromString uses a string description of a serial mode (such as "8N1")
+// to partially populate a Mode structure.
+// See https://en.wikipedia.org/wiki/8-N-1 for details
+func ModeFromString(smode string, mode *Mode) error {
+	if len(smode) > 0 {
+		switch smode[0] {
+		case '8':
+			mode.DataBits = 8
+		case '7':
+			mode.DataBits = 7
+		case '6':
+			mode.DataBits = 6
+		case '5':
+			mode.DataBits = 5
+		default:
+			return &PortError{code: InvalidDataBits}
+		}
+	}
+	if len(smode) > 1 {
+		switch smode[1] {
+		case 'E':
+			mode.Parity = EvenParity
+		case 'N':
+			mode.Parity = NoParity
+		case 'O':
+			mode.Parity = OddParity
+		case 'M':
+			mode.Parity = MarkParity
+		case 'S':
+			mode.Parity = SpaceParity
+		default:
+			return &PortError{code: InvalidParity}
+		}
+	}
+	if len(smode) > 2 {
+		switch smode[2] {
+		case '1':
+			mode.StopBits = OneStopBit
+		case '2':
+			mode.StopBits = TwoStopBits
+		default:
+			return &PortError{code: InvalidStopBits}
+		}
+	}
+	return nil
+}

serial_test.go

@@ -0,0 +1,39 @@
+package serial
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestModeFromString(t *testing.T) {
+	good_cases := map[string]*Mode{
+		"8N1": {DataBits: 8, Parity: NoParity, StopBits: OneStopBit},
+		"7S2": {DataBits: 7, Parity: SpaceParity, StopBits: TwoStopBits},
+	}
+
+	bad_cases := map[string]*PortError{
+		"9N1": {code: InvalidDataBits},
+		"8N3": {code: InvalidStopBits},
+		"8R1": {code: InvalidParity},
+	}
+
+	for s, m := range good_cases {
+		mode := &Mode{}
+		err := ModeFromString(s, mode)
+		if err != nil {
+			t.Errorf("Failed to convert mode %q: %s", s, err)
+		} else if !reflect.DeepEqual(mode, m) {
+			t.Errorf("Mode %q should convert to %+v, got %+v", s, m, mode)
+		}
+	}
+
+	for s, e := range bad_cases {
+		mode := &Mode{}
+		err := ModeFromString(s, mode)
+		if err == nil {
+			t.Errorf("Mode %q should be invalid, got %v", s, mode)
+		} else if pe, ok := err.(*PortError); !ok || pe.code != e.code {
+			t.Errorf("Mode %q should fail with %v, got %v", s, e, err)
+		}
+	}
+}