使用go语言来下载蜻蜓fm上的歌曲，效率感觉还行

package main

import (
       "encoding/json"
       "errors"
       "fmt"
       "net/http"
       "io"
       "os"
       "path"
       "io/ioutil"
       "sync"
)

//翻唱FM的URL：http://www.qingting.fm/#/vchannels/136962/programs/5659080
//翻唱FM的ajax地址:http://www.qingting.fm/s/vchannels/136962/programs/5745196/ajax

var QingTingAjaxAddrFmt = "http://www.qingting.fm/s/vchannels/%d/programs/%d/ajax"

//Go语言中json的解析，如果没有固定的输入格式，尽量使用通用格式 map [] interface{}
//因为GO语言导出结构体默认使用首字母大写，而且需要和实际的格式进行对应，还不如使用map+interface+[]
//type QingTingSongSubItem struct {
//     Name       string           "歌曲名称"
//     ParentName string           "专辑名称"
//     QTSongs    []string        "歌曲URL"
//     ParentID   int              "父目录ID"
//     Duration   int              "时长"
//     Type       string           "类型"
//     ID         int              "类型"
//     Thumb      string           "缩略图"
//}
//
//type QingTingSongItem struct {
//     PlayInfo QingTingSongSubItem
//}
//
//type QingTingPlayInfo QingTingSongItem
//
//func (this *QingTingPlayInfo) Download(dirname string) (bool, error) {
//     return false, nil
//}
//
//func (this *QingTingPlayInfo) String() string{
//     return fmt.Sprintf("歌曲名称:%#v 专辑名称:%#v 歌曲URL地址:%#v 父目录ID:%#v 时长:%#v 类型:%#v 缩略图:%#v",
//            this.PlayInfo.Name,
//            this.PlayInfo.ParentName,
//            this.PlayInfo.QTSongs,
//            this.PlayInfo.ParentID,
//            this.PlayInfo.Duration,
//            this.PlayInfo.Type,
//            this.PlayInfo.ID,
//            this.PlayInfo.Thumb)
//}

type QingTingPlayInfo map[string]interface{}

func Download(this QingTingPlayInfo, dirname string, wg *sync.WaitGroup) (bool, error){
       defer wg.Done()

       //pthis := (map[string]interface{})(this)
       name := this["name"].(string)
       url :="http://od.qingting.fm" + this["urls"].([]interface{})[0].(string)
       filename := path.Join(dirname, name+".m4a")
       fmt.Printf("开始下载:%s 到：%s\n", url, filename)

       res, err := http.Get(url)
       if err != nil{
              fmt.Printf("下载错误：%s\n", err)
              return false,err
       }

       defer res.Body.Close()
       data, err := ioutil.ReadAll(res.Body)
       if err != nil{
              fmt.Printf("下载失败:%s\n", err)
              return false,err
       }

       err2 := ioutil.WriteFile(filename, data, 0666)
       if err2 != nil{
              fmt.Printf("下载失败:%s\n", err2)
              return false, err2
       }

       fmt.Printf("!!!下载成功:%s 到：%s\n", url, filename)
       return true, nil
}
//-----------------------------------------------------------------
type QingTingFM struct {
       Channel int "频道"
       ID      int "频道ID"
}

func (this *QingTingFM) Crawl() ([]QingTingPlayInfo, error) {
       jsonbyte, err := this.readJson()
       if err != nil {
              return nil, err
       }

       if jsonbyte == nil{
              return nil,errors.New("返回了无效数据")
       }

       //go语言和json的映射关系 :对应结构体数据 []对应数组
       pis := make([]QingTingPlayInfo,0)
       jerr := json.Unmarshal(jsonbyte, &pis)
       if jerr != nil{
              return nil,jerr
       }

       downloadDir := "music_go"
       os.MkdirAll(downloadDir, 0666)
       //for _,pi := range pis{
       //     fmt.Println(pi["name"])
       //}
       var wg sync.WaitGroup
       //连接缓存最大数目
       maxIndex := len(pis) - 1
       cacheMax := 5
       for i,pi := range pis{
              wg.Add(1)
              cacheMax++
              //wg必须是传引用，这里必须要限制异步个数，否则与服务器的连接过多，服务器会拒绝，从而导致下载失败
              go Download(pi,downloadDir, &wg)
              //使用缓存
              if cacheMax > 5 || maxIndex == i{
                     wg.Wait()
                     cacheMax = 0
              }
       }

       return pis, nil
}

func (this *QingTingFM) readJson() ([]byte, error) {
       //ajaxAddr := "http://www.golangtc.com/t/533c0ad2320b520cc400004f"
       //http.Get自动gzip解压缩数据流
       res, err := http.Get(this.getAajxAddr())
       if err != nil {
              return nil, err
       }

       readerCloser := res.Body
       //读取之后需要关闭
       defer readerCloser.Close()

       if res.StatusCode != 200 {
              return nil, errors.New("返回错误状态码")
       }

       bytes := make([]byte, 0, 1024)
       //buffer必须是数组，或者可以使用ioutil ReadAll来读取
       var buffera [128]byte
       buffer := buffera[:]

       for {
              readed, rerr := readerCloser.Read(buffer)
              if readed == 0 && rerr == nil{
                     return nil, errors.New("readed=0 rerr=nil")
              }

              //切片...，自动将数组解压成很多个参数输入
              //实现原理和...，变参支持的原理一样
              //这句应该在 ==io.EOF之前，如果写到后面，则会丢失最后部分的数据
              bytes = append(bytes,buffer[:readed]...)

              //数据流读取完毕
              if rerr == io.EOF{
                     break
              }

              if rerr != nil {
                     return nil, rerr
              }

       }

       //将bytes转换成string
       return bytes, nil
}

func (this *QingTingFM) getAajxAddr() string {
       return fmt.Sprintf(QingTingAjaxAddrFmt, this.Channel, this.ID)
}

//-----------------------------------------------------------------
func main() {
       qtfm := QingTingFM{Channel: 136962, ID: 5745196}
       qtfm.Crawl()
}

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