HTTP的并发下载 Accept-Ranges
大家都用过迅雷等下载工具，特点就是支持并发下载，断点续传。
主要讲三个方面，如何HTTP的并发下载、通过Golang进行多协程开发、如何断点续传。
想要并发下载，就是把下载内容分块，然后并行下载这些块。这就要求服务器能够支持分块获取数据。大迅雷、电驴这种都有自己的协议，thunder://这种，我们只研究原理，就说说HTTP协议对于并发的支持。
| HTTP头 | 对应值 | 含义 | ||||
| Content-Length | 14247 | HTTP响应的Body大小，下载的时候，Body就是文件，也可以认为是文件大小，单位是比特 | ||||
| Content-Disposition | inline; filename=”bryce.jpg” | 是MIME协议的扩展，MIME协议指示MIME用户代理如何显示附加的文件。当浏览器接收到头时，它会激活文件下载。这里还包含了文件名 | ||||
| Accept-Ranges | bytes | 允许客户端以bytes的形式获取文件 | ||||
| Range | bytes=0-511 | 分块获取数据，这里表示获取第0到第511的数据，共512字节 |
Nginx官网ngx_http_slice_module: Module ngx_http_slice_module
Nginx的ngx_http_slice_module模块是用来支持Range回源的。 ngx_http_slice_module从Nginx的1.9.8版本开始有的。启用ngx_http_slice_module模块需要在编译Nginx时，加参数--with-http_slice_module。
location / {
slice 1m;
proxy_cache cache;
proxy_cache_key $uri$is_args$args$slice_range;
proxy_set_header Range $slice_range;
proxy_cache_valid 200 206 1h;
proxy_pass http://localhost:8000;
}Module ngx_http_slice_module 缓存配置文件
#user nobody;
worker_processes 1;
events {
worker_connections 1024;
}
http {
log_format main '$remote_addr - $remote_user [$time_local] "$request" '
'$status $body_bytes_sent "$http_referer" '
'"$http_user_agent" "$http_x_forwarded_for"';
access_log logs/access.log main;
sendfile on;
keepalive_timeout 65;
#cache
proxy_cache_path /data/cache
keys_zone=cache_my:100m
levels=1:1
inactive=12d
max_size=200m;
server {
listen 80;
server_name localhost;
location / {
#slice
slice 1k;
proxy_cache cache_my;
proxy_cache_key $uri$is_args$args$slice_range;
add_header X-Cache-Status $upstream_cache_status;
proxy_set_header Range $slice_range;
proxy_cache_valid 200 206 3h;
proxy_pass http://192.168.1.10:80;
proxy_cache_purge PURGE from 127.0.0.1;
}
}
}
三、运行结果
查看的是源站的日志
index.html文件大小为5196
curl www.*****.com/index.html -r 0-1024
四 GO实例代码
package main
import (
"flag"
"fmt"
"io"
"log"
"math"
"mime"
"net/http"
"net/http/httputil"
"os"
"strings"
"sync"
"time"
)
const (
DEFAULT_DOWNLOAD_BLOCK int64 = 4096
)
type GoGet struct {
Url string
Cnt int
DownloadBlock int64
CostomCnt int
Latch int
Header http.Header
MediaType string
MediaParams map[string]string
FilePath string // 包括路径和文件名
GetClient *http.Client
ContentLength int64
DownloadRange [][]int64
File *os.File
TempFiles []*os.File
WG sync.WaitGroup
}
func NewGoGet() *GoGet {
get := new(GoGet)
get.FilePath = "./"
get.GetClient = new(http.Client)
flag.Parse()
get.Url = *urlFlag
get.DownloadBlock = DEFAULT_DOWNLOAD_BLOCK
return get
}
var urlFlag = flag.String("u", "http://7b1h1l.com1.z0.glb.clouddn.com/bryce.jpg", "Fetch file url")
// var cntFlag = flag.Int("c", 1, "Fetch concurrently counts")
func main() {
get := NewGoGet()
download_start := time.Now()
req, err := http.NewRequest("HEAD", get.Url, nil)
resp, err := get.GetClient.Do(req)
get.Header = resp.Header
if err != nil {
log.Panicf("Get %s error %v.\n", get.Url, err)
}
get.MediaType, get.MediaParams, _ = mime.ParseMediaType(get.Header.Get("Content-Disposition"))
get.ContentLength = resp.ContentLength
get.Cnt = int(math.Ceil(float64(get.ContentLength / get.DownloadBlock)))
if strings.HasSuffix(get.FilePath, "/") {
get.FilePath += get.MediaParams["filename"]
}
get.File, err = os.Create(get.FilePath)
if err != nil {
log.Panicf("Create file %s error %v.\n", get.FilePath, err)
}
log.Printf("Get %s MediaType:%s, Filename:%s, Size %d.\n", get.Url, get.MediaType, get.MediaParams["filename"], get.ContentLength)
if get.Header.Get("Accept-Ranges") != "" {
log.Printf("Server %s support Range by %s.\n", get.Header.Get("Server"), get.Header.Get("Accept-Ranges"))
} else {
log.Printf("Server %s doesn't support Range.\n", get.Header.Get("Server"))
}
log.Printf("Start to download %s with %d thread.\n", get.MediaParams["filename"], get.Cnt)
var range_start int64 = 0
for i := 0; i < get.Cnt; i++ {
if i != get.Cnt-1 {
get.DownloadRange = append(get.DownloadRange, []int64{range_start, range_start + get.DownloadBlock - 1})
} else {
// 最后一块
get.DownloadRange = append(get.DownloadRange, []int64{range_start, get.ContentLength - 1})
}
range_start += get.DownloadBlock
}
// Check if the download has paused.
for i := 0; i < len(get.DownloadRange); i++ {
range_i := fmt.Sprintf("%d-%d", get.DownloadRange[i][0], get.DownloadRange[i][1])
temp_file, err := os.OpenFile(get.FilePath+"."+range_i, os.O_RDONLY|os.O_APPEND, 0)
if err != nil {
temp_file, _ = os.Create(get.FilePath + "." + range_i)
} else {
fi, err := temp_file.Stat()
if err == nil {
get.DownloadRange[i][0] += fi.Size()
}
}
get.TempFiles = append(get.TempFiles, temp_file)
}
go get.Watch()
get.Latch = get.Cnt
for i, _ := range get.DownloadRange {
get.WG.Add(1)
go get.Download(i)
}
get.WG.Wait()
for i := 0; i < len(get.TempFiles); i++ {
temp_file, _ := os.Open(get.TempFiles[i].Name())
cnt, err := io.Copy(get.File, temp_file)
if cnt <= 0 || err != nil {
log.Printf("Download #%d error %v.\n", i, err)
}
temp_file.Close()
}
get.File.Close()
log.Printf("Download complete and store file %s with %v.\n", get.FilePath, time.Now().Sub(download_start))
defer func() {
for i := 0; i < len(get.TempFiles); i++ {
err := os.Remove(get.TempFiles[i].Name())
if err != nil {
log.Printf("Remove temp file %s error %v.\n", get.TempFiles[i].Name(), err)
} else {
log.Printf("Remove temp file %s.\n", get.TempFiles[i].Name())
}
}
}()
}
func (get *GoGet) Download(i int) {
defer get.WG.Done()
if get.DownloadRange[i][0] > get.DownloadRange[i][1] {
return
}
range_i := fmt.Sprintf("%d-%d", get.DownloadRange[i][0], get.DownloadRange[i][1])
log.Printf("Download #%d bytes %s.\n", i, range_i)
defer get.TempFiles[i].Close()
req, err := http.NewRequest("GET", get.Url, nil)
req.Header.Set("Range", "bytes="+range_i)
resp, err := get.GetClient.Do(req)
defer resp.Body.Close()
if err != nil {
log.Printf("Download #%d error %v.\n", i, err)
} else {
cnt, err := io.Copy(get.TempFiles[i], resp.Body)
if cnt == int64(get.DownloadRange[i][1]-get.DownloadRange[i][0]+1) {
log.Printf("Download #%d complete.\n", i)
} else {
req_dump, _ := httputil.DumpRequest(req, false)
resp_dump, _ := httputil.DumpResponse(resp, true)
log.Panicf("Download error %d %v, expect %d-%d, but got %d.\nRequest: %s\nResponse: %s\n", resp.StatusCode, err, get.DownloadRange[i][0], get.DownloadRange[i][1], cnt, string(req_dump), string(resp_dump))
}
}
}
// http://stackoverflow.com/questions/15714126/how-to-update-command-line-output
func (get *GoGet) Watch() {
fmt.Printf("[=================>]\n")
}
单元测试
package tests
import (
"fmt"
"testing"
"github.com/mnhkahn/go_code/goget"
)
func TestProcess(t *testing.T) {
schedule := goget.NewGoGetSchedules(2)
schedule.SetDownloadBlock(1)
job := schedule.NextJob()
fmt.Println(job)
schedule.FinishJob(job)
job = schedule.NextJob()
fmt.Println(job)
schedule.FinishJob(job)
}判断是否支持 Accept-Ranges ： bytes
curl -i -X HEAD https://img-blog.csdnimg.cn/30f7496053534e77a036730ac40da861.pngCSDN 文件存储
阿里OSS
七牛存储
参考资料：
ngx_http_slice_module (ngx_http_slice_module) - Nginx 中文开发手册 - 开发者手册 - 云+社区 - 腾讯云
尝鲜：Nginx-1.9.8 推出的切片模块 - 纯真年代
CDN如何使用nginx负载均衡实现回源请求_BigChen_up的博客-CSDN博客_nginx 回源
Nginx进行Range缓存_zzhongcy的博客-CSDN博客_nginx range
Golang实现多线程并发下载 - Go语言中文网 - Golang中文社区