encoding/binary: implemented the Write function

The ByteOrder.Put* methods are already available, this change uses
them to implement the Write function.

R=golang-dev, agl1, rsc, r
https://golang.org/cl/152141

src/pkg/encoding/binary/binary.go

@@ -117,8 +117,8 @@ func (bigEndian) GoString() string	{ return "binary.BigEndian" }
 // A fixed-size value is either a fixed-size integer
 // (int8, uint8, int16, uint16, ...) or an array or struct
 // containing only fixed-size values.  Bytes read from
-// r are decoded using order and written to successive
-// fields of the data.
+// r are decoded using the specified byte order and written
+// to successive fields of the data.
 func Read(r io.Reader, order ByteOrder, data interface{}) os.Error {
 	v := reflect.NewValue(data).(*reflect.PtrValue).Elem();
 	size := sizeof(v.Type());
@@ -133,6 +133,27 @@ func Read(r io.Reader, order ByteOrder, data interface{}) os.Error {
 	return nil;
 }
 
+// Write writes the binary representation of data into w.
+// Data must be a fixed-size value or a pointer to
+// a fixed-size value.
+// A fixed-size value is either a fixed-size integer
+// (int8, uint8, int16, uint16, ...) or an array or struct
+// containing only fixed-size values.  Bytes written to
+// w are encoded using the specified byte order and read
+// from successive fields of the data.
+func Write(w io.Writer, order ByteOrder, data interface{}) os.Error {
+	v := reflect.Indirect(reflect.NewValue(data));
+	size := sizeof(v.Type());
+	if size < 0 {
+		return os.NewError("binary.Write: invalid type " + v.Type().String())
+	}
+	buf := make([]byte, size);
+	e := &encoder{order: order, buf: buf};
+	e.value(v);
+	_, err := w.Write(buf);
+	return err;
+}
+
 func sizeof(t reflect.Type) int {
 	switch t := t.(type) {
 	case *reflect.ArrayType:
@@ -182,38 +203,71 @@ type decoder struct {
 	buf	[]byte;
 }
 
+type encoder struct {
+	order	ByteOrder;
+	buf	[]byte;
+}
+
 func (d *decoder) uint8() uint8 {
 	x := d.buf[0];
 	d.buf = d.buf[1:len(d.buf)];
 	return x;
 }
 
+func (e *encoder) uint8(x uint8) {
+	e.buf[0] = x;
+	e.buf = e.buf[1:len(e.buf)];
+}
+
 func (d *decoder) uint16() uint16 {
 	x := d.order.Uint16(d.buf[0:2]);
 	d.buf = d.buf[2:len(d.buf)];
 	return x;
 }
 
+func (e *encoder) uint16(x uint16) {
+	e.order.PutUint16(e.buf[0:2], x);
+	e.buf = e.buf[2:len(e.buf)];
+}
+
 func (d *decoder) uint32() uint32 {
 	x := d.order.Uint32(d.buf[0:4]);
 	d.buf = d.buf[4:len(d.buf)];
 	return x;
 }
 
+func (e *encoder) uint32(x uint32) {
+	e.order.PutUint32(e.buf[0:4], x);
+	e.buf = e.buf[4:len(e.buf)];
+}
+
 func (d *decoder) uint64() uint64 {
 	x := d.order.Uint64(d.buf[0:8]);
 	d.buf = d.buf[8:len(d.buf)];
 	return x;
 }
 
+func (e *encoder) uint64(x uint64) {
+	e.order.PutUint64(e.buf[0:8], x);
+	e.buf = e.buf[8:len(e.buf)];
+}
+
 func (d *decoder) int8() int8	{ return int8(d.uint8()) }
 
+func (e *encoder) int8(x int8)	{ e.uint8(uint8(x)) }
+
 func (d *decoder) int16() int16	{ return int16(d.uint16()) }
 
+func (e *encoder) int16(x int16)	{ e.uint16(uint16(x)) }
+
 func (d *decoder) int32() int32	{ return int32(d.uint32()) }
 
+func (e *encoder) int32(x int32)	{ e.uint32(uint32(x)) }
+
 func (d *decoder) int64() int64	{ return int64(d.uint64()) }
 
+func (e *encoder) int64(x int64)	{ e.uint64(uint64(x)) }
+
 func (d *decoder) value(v reflect.Value) {
 	switch v := v.(type) {
 	case *reflect.ArrayValue:
@@ -249,3 +303,39 @@ func (d *decoder) value(v reflect.Value) {
 		v.Set(math.Float64frombits(d.uint64()))
 	}
 }
+
+func (e *encoder) value(v reflect.Value) {
+	switch v := v.(type) {
+	case *reflect.ArrayValue:
+		l := v.Len();
+		for i := 0; i < l; i++ {
+			e.value(v.Elem(i))
+		}
+	case *reflect.StructValue:
+		l := v.NumField();
+		for i := 0; i < l; i++ {
+			e.value(v.Field(i))
+		}
+
+	case *reflect.Uint8Value:
+		e.uint8(v.Get())
+	case *reflect.Uint16Value:
+		e.uint16(v.Get())
+	case *reflect.Uint32Value:
+		e.uint32(v.Get())
+	case *reflect.Uint64Value:
+		e.uint64(v.Get())
+	case *reflect.Int8Value:
+		e.int8(v.Get())
+	case *reflect.Int16Value:
+		e.int16(v.Get())
+	case *reflect.Int32Value:
+		e.int32(v.Get())
+	case *reflect.Int64Value:
+		e.int64(v.Get())
+	case *reflect.Float32Value:
+		e.uint32(math.Float32bits(v.Get()))
+	case *reflect.Float64Value:
+		e.uint64(math.Float64bits(v.Get()))
+	}
+}

src/pkg/encoding/binary/binary_test.go

@@ -5,6 +5,7 @@
 package binary
 
 import (
+	"os";
 	"bytes";
 	"math";
 	"reflect";
@@ -63,24 +64,36 @@ var little = []byte{
 	39, 40, 41, 42,
 }
 
-func TestRead(t *testing.T) {
-	var sl, sb Struct;
-
-	err := Read(bytes.NewBuffer(big), BigEndian, &sb);
+func checkResult(t *testing.T, dir string, order, err os.Error, have, want interface{}) {
 	if err != nil {
-		t.Errorf("Read big-endian: %v", err);
-		goto little;
+		t.Errorf("%v %v: %v", dir, order, err);
+		return;
+	}
+	if !reflect.DeepEqual(have, want) {
+		t.Errorf("%v %v:\n\thave %+v\n\twant %+v", dir, order, have, want)
 	}
-	if !reflect.DeepEqual(sb, s) {
-		t.Errorf("Read big-endian:\n\thave %+v\n\twant %+v", sb, s)
 }
 
-little:
-	err = Read(bytes.NewBuffer(little), LittleEndian, &sl);
-	if err != nil {
-		t.Errorf("Read little-endian: %v", err)
-	}
-	if !reflect.DeepEqual(sl, s) {
-		t.Errorf("Read little-endian:\n\thave %+v\n\twant %+v", sl, s)
+func testRead(t *testing.T, order ByteOrder, b []byte, s1 interface{}) {
+	var s2 Struct;
+	err := Read(bytes.NewBuffer(b), order, &s2);
+	checkResult(t, "Read", order, err, s2, s1);
 }
+
+func testWrite(t *testing.T, order ByteOrder, b []byte, s1 interface{}) {
+	buf := new(bytes.Buffer);
+	err := Write(buf, order, s1);
+	checkResult(t, "Write", order, err, buf.Bytes(), b);
 }
+
+func TestBigEndianRead(t *testing.T)	{ testRead(t, BigEndian, big, s) }
+
+func TestLittleEndianRead(t *testing.T)	{ testRead(t, LittleEndian, little, s) }
+
+func TestBigEndianWrite(t *testing.T)	{ testWrite(t, BigEndian, big, s) }
+
+func TestLittleEndianWrite(t *testing.T)	{ testWrite(t, LittleEndian, little, s) }
+
+func TestBigEndianPtrWrite(t *testing.T)	{ testWrite(t, BigEndian, big, &s) }
+
+func TestLittleEndianPtrWrite(t *testing.T)	{ testWrite(t, LittleEndian, little, &s) }