i2c: Adds i2c.Addr type and flag.Value interface. (#362)

* i2c: Adds i2c.Addr type and flag.Value interface.

Add i2c.Addr
Add i2c.Addr Set()
Add Tests.

conn/i2c/i2c.go

@@ -19,6 +19,7 @@
 package i2c
 
 import (
+	"errors"
 	"io"
 	"strconv"
 
@@ -109,6 +110,21 @@ func (d *Dev) Duplex() conn.Duplex {
 	return conn.Half
 }
 
-//
+// Addr is an I²C slave address.
+type Addr uint16
+
+// Set sets the Addr to a value represented by the string s. Values maybe in
+// decimal or hexadecimal form. Set implements the flag.Value interface.
+func (a *Addr) Set(s string) error {
+	// Allow for only maximum of 10 bits for i2c addresses.
+	u, err := strconv.ParseUint(s, 0, 10)
+	if err != nil {
+		return errI2CSetError
+	}
+	*a = Addr(u)
+	return nil
+}
+
+var errI2CSetError = errors.New("invalid i2c address")
 
 var _ conn.Conn = &Dev{}

conn/i2c/i2c_test.go

@@ -104,3 +104,27 @@ func (f *fakeBus) SetSpeed(freq physic.Frequency) error {
 	f.freq = freq
 	return f.err
 }
+
+func TestAddr_Set(t *testing.T) {
+	tests := []struct {
+		str  string
+		want Addr
+		err  error
+	}{
+		{"0x18", 0x18, nil},
+		{"24", 24, nil},
+		{"0x3ff", 0x3ff, nil},
+		{"0x400", 0, errI2CSetError},
+		{"-1", 0, errI2CSetError},
+	}
+
+	for _, tt := range tests {
+		var a Addr
+		if err := a.Set(tt.str); err != tt.err {
+			t.Errorf("i2cAddr.Set(%s) error %v", tt.str, err)
+		}
+		if tt.err == nil && a != tt.want {
+			t.Errorf("i2cAddr.Set(%s) expected %d but got %d", tt.str, tt.want, a)
+		}
+	}
+}