package main

import (
	"io"
	"log"
	"math/rand"
)

func main() {
	reader := NewStreamOfStuff()
	bufferedReader := NewBufferedReader(reader)
	lenBits := make([]byte, 1)
	for i := 0; i < 10; i++ {
		if n, err := bufferedReader.Read(lenBits); err != nil || n != len(lenBits) {
			panic(err)
		}
		payload := make([]byte, int(lenBits[0]))
		if n, err := bufferedReader.Read(payload); err != nil || n != len(payload) {
			panic(err)
		}
		log.Printf("[%d] (%d) %q", i, len(payload), payload)
	}
}

type BufferedReader struct {
	buffer []byte
	reader io.Reader
}

func (r *BufferedReader) Read(b []byte) (int, error) {
	for len(b) > len(r.buffer) {
		more := make([]byte, 8)
		n, err := r.reader.Read(more)
		if err != nil {
			return 0, err
		}
		r.buffer = append(r.buffer, more[:n]...)
	}
	n := len(b)
	if copied := copy(b, r.buffer[:n]); copied != n {
		panic(copied)
	}
	r.buffer = r.buffer[n:]
	return n, nil
}

func NewBufferedReader(r io.Reader) io.Reader {
	return &BufferedReader{
		buffer: []byte{},
		reader: r,
	}
}

func NewStreamOfStuff() io.Reader {
	return jitterReader{}
}

type jitterReader struct{}

func (jitterReader jitterReader) Read(b []byte) (int, error) {
	n := rand.Int()%len(b) + 1
	for i := 0; i < n; i++ {
		b[i] = 'a' + byte(rand.Int()%26)
	}
	return n, nil
}