146 lines
3.3 KiB
Go
146 lines
3.3 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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u64 []byte
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u32 []byte
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u16 []byte
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u8 []byte
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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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u64 := make([]byte, 8)
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u32 := u64[:4]
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u16 := u64[:2]
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u8 := u64[:1]
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return &BinWriter{w: iow, u64: u64, u32: u32, u16: u16, u8: u8}
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}
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// WriteU64LE writes an uint64 value into the underlying io.Writer in
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// little-endian format.
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func (w *BinWriter) WriteU64LE(u64 uint64) {
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binary.LittleEndian.PutUint64(w.u64, u64)
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w.WriteBytes(w.u64)
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}
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// WriteU32LE writes an uint32 value into the underlying io.Writer in
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// little-endian format.
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func (w *BinWriter) WriteU32LE(u32 uint32) {
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binary.LittleEndian.PutUint32(w.u32, u32)
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w.WriteBytes(w.u32)
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}
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// WriteU16LE writes an uint16 value into the underlying io.Writer in
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// little-endian format.
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func (w *BinWriter) WriteU16LE(u16 uint16) {
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binary.LittleEndian.PutUint16(w.u16, u16)
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w.WriteBytes(w.u16)
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}
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// WriteU16BE writes an uint16 value into the underlying io.Writer in
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// big-endian format.
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func (w *BinWriter) WriteU16BE(u16 uint16) {
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binary.BigEndian.PutUint16(w.u16, u16)
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w.WriteBytes(w.u16)
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}
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// WriteB writes a byte into the underlying io.Writer.
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func (w *BinWriter) WriteB(u8 byte) {
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w.u8[0] = u8
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w.WriteBytes(w.u8)
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}
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// WriteBool writes a boolean value into the underlying io.Writer encoded as
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// a byte with values of 0 or 1.
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func (w *BinWriter) WriteBool(b bool) {
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var i byte
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if b {
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i = 1
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}
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w.WriteB(i)
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}
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// WriteArray writes a slice or an array arr into w. Note that nil slices and
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// empty slices are gonna be treated the same resulting in equal zero-length
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// array encoded.
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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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if w.Err != nil {
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return
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}
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typ := val.Type().Elem()
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w.WriteVarUint(uint64(val.Len()))
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for i := 0; i < val.Len(); i++ {
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el, ok := val.Index(i).Interface().(encodable)
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if !ok {
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el, ok = val.Index(i).Addr().Interface().(encodable)
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if !ok {
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panic(typ.String() + " is not encodable")
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}
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}
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el.EncodeBinary(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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// 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.WriteB(byte(val))
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return
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}
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if val < 0xFFFF {
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w.WriteB(byte(0xfd))
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w.WriteU16LE(uint16(val))
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return
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}
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if val < 0xFFFFFFFF {
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w.WriteB(byte(0xfe))
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w.WriteU32LE(uint32(val))
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return
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}
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w.WriteB(byte(0xff))
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w.WriteU64LE(val)
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}
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// WriteBytes writes a variable byte into the underlying io.Writer without prefix.
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func (w *BinWriter) WriteBytes(b []byte) {
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if w.Err != nil {
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return
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}
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_, w.Err = w.w.Write(b)
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}
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// WriteVarBytes writes a variable length byte array into the underlying io.Writer.
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func (w *BinWriter) WriteVarBytes(b []byte) {
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w.WriteVarUint(uint64(len(b)))
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w.WriteBytes(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.WriteVarBytes([]byte(s))
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}
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