Factor out XDR en/decoding

xdr/writer.go

@@ -0,0 +1,95 @@
+package xdr
+
+import "io"
+
+func pad(l int) int {
+	d := l % 4
+	if d == 0 {
+		return 0
+	}
+	return 4 - d
+}
+
+var padBytes = []byte{0, 0, 0}
+
+type Writer struct {
+	w   io.Writer
+	tot uint64
+	err error
+	b   [8]byte
+}
+
+func NewWriter(w io.Writer) *Writer {
+	return &Writer{
+		w: w,
+	}
+}
+
+func (w *Writer) WriteString(s string) (int, error) {
+	return w.WriteBytes([]byte(s))
+}
+
+func (w *Writer) WriteBytes(bs []byte) (int, error) {
+	if w.err != nil {
+		return 0, w.err
+	}
+
+	w.WriteUint32(uint32(len(bs)))
+	if w.err != nil {
+		return 0, w.err
+	}
+
+	var l, n int
+	n, w.err = w.w.Write(bs)
+	l += n
+
+	if p := pad(len(bs)); w.err == nil && p > 0 {
+		n, w.err = w.w.Write(padBytes[:p])
+		l += n
+	}
+
+	w.tot += uint64(l)
+	return l, w.err
+}
+
+func (w *Writer) WriteUint32(v uint32) (int, error) {
+	if w.err != nil {
+		return 0, w.err
+	}
+	w.b[0] = byte(v >> 24)
+	w.b[1] = byte(v >> 16)
+	w.b[2] = byte(v >> 8)
+	w.b[3] = byte(v)
+
+	var l int
+	l, w.err = w.w.Write(w.b[:4])
+	w.tot += uint64(l)
+	return l, w.err
+}
+
+func (w *Writer) WriteUint64(v uint64) (int, error) {
+	if w.err != nil {
+		return 0, w.err
+	}
+	w.b[0] = byte(v >> 56)
+	w.b[1] = byte(v >> 48)
+	w.b[2] = byte(v >> 40)
+	w.b[3] = byte(v >> 32)
+	w.b[4] = byte(v >> 24)
+	w.b[5] = byte(v >> 16)
+	w.b[6] = byte(v >> 8)
+	w.b[7] = byte(v)
+
+	var l int
+	l, w.err = w.w.Write(w.b[:8])
+	w.tot += uint64(l)
+	return l, w.err
+}
+
+func (w *Writer) Tot() uint64 {
+	return w.tot
+}
+
+func (w *Writer) Err() error {
+	return w.err
+}