You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: request.go
    path of file: ./repos/alist/internal/net
    
    the code of the file until where you have to start completion: package net

import (
	"bytes"
	"context"
	"fmt"
	"io"
	"math"
	"net/http"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/alist-org/alist/v3/pkg/http_range"
	"github.com/aws/aws-sdk-go/aws/awsutil"
	log "github.com/sirupsen/logrus"
)

// DefaultDownloadPartSize is the default range of bytes to get at a time when
// using Download()
    
func (br *Buf) Read(p []byte) (n int, err error) {
	if err := br.ctx.Err(); err != nil {
		return 0, err
	}
	if len(p) == 0 {
		return 0, nil
	}
	if br.off >= br.size {
		return 0, io.EOF
	}
	br.rw.Lock()
	n, err = br.buffer.Read(p)
	br.rw.Unlock()
	if err == nil {
		br.off += n
		return n, err
	}
	if err != io.EOF {
		return n, err
	}
	if n != 0 {
		br.off += n
		return n, nil
	}
	// n==0, err==io.EOF
	// wait for new write for 200ms
	select {
	case <-br.ctx.Done():
		return 0, br.ctx.Err()
	//case <-br.notify:
	//	return 0, nil
	case <-time.After(time.Millisecond * 200):
		return 0, nil
	}
}