1  package codec
  2  
  3  import (
  4  	"encoding/binary"
  5  	"fmt"
  6  	"math"
  7  )
  8  
  9  type Decoder struct {
 10  	buf []byte
 11  	pos int // current (unread) byte position
 12  }
 13  
 14  func Decode(b []byte) *Decoder {
 15  	return &Decoder{buf: b}
 16  }
 17  
 18  func (d *Decoder) Has(n int) bool {
 19  	return d.pos+n <= len(d.buf)
 20  }
 21  
 22  func (d *Decoder) Bytes(num int) []byte {
 23  	p := d.pos
 24  	d.pos += num
 25  	return d.buf[p : p+num]
 26  }
 27  
 28  // All remaining bytes in the buffer
 29  func (d *Decoder) Rest() []byte {
 30  	p := d.pos
 31  	d.pos = len(d.buf)
 32  	return d.buf[p:]
 33  }
 34  
 35  func (d *Decoder) Bool() bool {
 36  	v := d.buf[d.pos]
 37  	d.pos += 1
 38  	return v != 0
 39  }
 40  
 41  func (d *Decoder) UInt8() uint8 {
 42  	p := d.pos
 43  	d.pos += 1
 44  	return d.buf[p]
 45  }
 46  
 47  func (d *Decoder) UInt16le() uint16 {
 48  	p := d.pos
 49  	d.pos += 2
 50  	return binary.LittleEndian.Uint16(d.buf[p : p+2])
 51  }
 52  
 53  func (d *Decoder) UInt16be() uint16 {
 54  	p := d.pos
 55  	d.pos += 2
 56  	return binary.BigEndian.Uint16(d.buf[p : p+2])
 57  }
 58  
 59  func (d *Decoder) UInt32le() uint32 {
 60  	p := d.pos
 61  	d.pos += 4
 62  	return binary.LittleEndian.Uint32(d.buf[p : p+4])
 63  }
 64  
 65  func (d *Decoder) UInt32be() uint32 {
 66  	p := d.pos
 67  	d.pos += 4
 68  	return binary.BigEndian.Uint32(d.buf[p : p+4])
 69  }
 70  
 71  func (d *Decoder) UInt64le() uint64 {
 72  	p := d.pos
 73  	d.pos += 8
 74  	return binary.LittleEndian.Uint64(d.buf[p : p+8])
 75  }
 76  
 77  func (d *Decoder) Int64le() int64 {
 78  	p := d.pos
 79  	d.pos += 8
 80  	return int64(binary.LittleEndian.Uint64(d.buf[p : p+8]))
 81  }
 82  func (d *Decoder) VarUInt() uint64 {
 83  	val := d.buf[d.pos]
 84  	d.pos += 1
 85  	if val < 253 {
 86  		return uint64(val)
 87  	}
 88  	if val == 253 {
 89  		return uint64(d.UInt16le())
 90  	}
 91  	if val == 254 {
 92  		return uint64(d.UInt32le())
 93  	}
 94  	return d.UInt64le()
 95  }
 96  
 97  func (d *Decoder) VarString() string {
 98  	len := d.VarUInt()
 99  	if len > math.MaxInt {
100  		panic(fmt.Sprintf("decoded string length too long (greater than max-int): %v", len))
101  	}
102  	data := d.Bytes(int(len))
103  	return string(data)
104  }
105  
106  func (d *Decoder) PadString(size int) string {
107  	data := d.Bytes(size)
108  	if size > 0 {
109  		end := size - 1
110  		for data[end] == 0 && end > 0 {
111  			end--
112  		}
113  		return string(data[:end+1])
114  	}
115  	return ""
116  }