110 lines
2.8 KiB
Go
110 lines
2.8 KiB
Go
package io
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import (
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"encoding/binary"
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"io"
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"reflect"
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)
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// BinWriter is a convenient wrapper around a io.Writer and err object.
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// Used to simplify error handling when writing into a io.Writer
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// from a struct with many fields.
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type BinWriter struct {
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w io.Writer
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Err error
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}
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// NewBinWriterFromIO makes a BinWriter from io.Writer.
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func NewBinWriterFromIO(iow io.Writer) *BinWriter {
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return &BinWriter{w: iow}
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}
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// WriteLE writes into the underlying io.Writer from an object v in little-endian format.
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func (w *BinWriter) WriteLE(v interface{}) {
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if w.Err != nil {
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return
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}
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w.Err = binary.Write(w.w, binary.LittleEndian, v)
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}
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// WriteBE writes into the underlying io.Writer from an object v in big-endian format.
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func (w *BinWriter) WriteBE(v interface{}) {
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if w.Err != nil {
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return
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}
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w.Err = binary.Write(w.w, binary.BigEndian, v)
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}
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// WriteArray writes a slice or an array arr into w.
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func (w *BinWriter) WriteArray(arr interface{}) {
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switch val := reflect.ValueOf(arr); val.Kind() {
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case reflect.Slice, reflect.Array:
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typ := val.Type().Elem()
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method, ok := typ.MethodByName("EncodeBinary")
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if !ok || !isEncodeBinaryMethod(method) {
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panic(typ.String() + " does not have EncodeBinary(*BinWriter)")
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}
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if w.Err != nil {
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return
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}
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w.WriteVarUint(uint64(val.Len()))
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for i := 0; i < val.Len(); i++ {
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method := val.Index(i).MethodByName("EncodeBinary")
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method.Call([]reflect.Value{reflect.ValueOf(w)})
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}
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default:
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panic("not an array")
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}
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}
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func isEncodeBinaryMethod(method reflect.Method) bool {
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t := method.Type
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return t != nil &&
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t.NumIn() == 2 && t.In(1) == reflect.TypeOf((*BinWriter)(nil)) &&
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t.NumOut() == 0
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}
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// WriteVarUint writes a uint64 into the underlying writer using variable-length encoding.
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func (w *BinWriter) WriteVarUint(val uint64) {
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if w.Err != nil {
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return
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}
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if val < 0xfd {
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w.Err = binary.Write(w.w, binary.LittleEndian, uint8(val))
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return
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}
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if val < 0xFFFF {
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w.Err = binary.Write(w.w, binary.LittleEndian, byte(0xfd))
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w.Err = binary.Write(w.w, binary.LittleEndian, uint16(val))
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return
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}
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if val < 0xFFFFFFFF {
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w.Err = binary.Write(w.w, binary.LittleEndian, byte(0xfe))
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w.Err = binary.Write(w.w, binary.LittleEndian, uint32(val))
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return
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}
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w.Err = binary.Write(w.w, binary.LittleEndian, byte(0xff))
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w.Err = binary.Write(w.w, binary.LittleEndian, val)
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}
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// WriteVarBytes writes a variable byte into the underlying io.Writer without prefix.
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func (w *BinWriter) WriteVarBytes(b []byte) {
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w.WriteLE(b)
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}
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// WriteBytes writes a variable length byte array into the underlying io.Writer.
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func (w *BinWriter) WriteBytes(b []byte) {
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w.WriteVarUint(uint64(len(b)))
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w.WriteLE(b)
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}
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// WriteString writes a variable length string into the underlying io.Writer.
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func (w *BinWriter) WriteString(s string) {
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w.WriteBytes([]byte(s))
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}
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