badrand.go

package main

import (
	"bytes"
	"fmt"
	"io"
	"math/big"
)

type BadRand struct {
	reader             io.Reader
	expectedTotalBytes uint
}

func NewBadRand(out int64, outputLen uint) *BadRand {
	x := big.NewInt(out)
	y := make([]byte, outputLen)
	tail := x.Bytes()

	for i, j := len(tail)-1, len(y)-1; i >= 0 && j > 0; i, j = i-1, j-1 {
		y[j] = tail[i]
	}

	return &BadRand{
		reader:             bytes.NewReader(y),
		expectedTotalBytes: outputLen,
	}
}

func (b *BadRand) Read(p []byte) (n int, err error) {
	return b.reader.Read(p)
}

func main() {
	fmt.Println("Hello, playground")

	//x := NewBadRand(1)
	//buf := make([]byte, 100)
	//n, err := io.ReadFull(x, buf)
	//if err != nil {
	//	fmt.Println("BAD!!")
	//}

	//fmt.Printf("Read %d bytes\n", n)

	x := NewBadRand(123, 40)

	out := make([]byte, 100)
	n, err := io.ReadFull(x, out)
	if err != nil {
		fmt.Println("BAD READ!")
	}

	fmt.Printf("%v bytes read\n", n)
	fmt.Printf("%v\n", out)
}