Created
March 18, 2020 13:11
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| package main | |
| import ( | |
| "bufio" | |
| "fmt" | |
| "io" | |
| "io/ioutil" | |
| "math" | |
| "net/http" | |
| "os" | |
| "path/filepath" | |
| "strconv" | |
| "sync" | |
| "time" | |
| ) | |
| func main() { | |
| start := time.Now() | |
| if len(os.Args) < 2 { | |
| fmt.Printf("Usage: %s <URL>\n", os.Args[0]) | |
| return | |
| } | |
| URL := os.Args[1] | |
| fileName := filepath.Base(URL) | |
| fo, err := os.Create(fileName) | |
| if err != nil { | |
| panic(err) | |
| } | |
| defer fo.Close() | |
| w := bufio.NewWriter(fo) | |
| defer w.Flush() | |
| downloadURL(URL, w, 0, 100) | |
| fmt.Printf("finished: %v\n", time.Since(start)) | |
| } | |
| func downloadURL(URL string, writer io.Writer, chunkSize uint64, maxRoutines uint64) error { | |
| res, _ := http.Head(URL) | |
| clen, _ := strconv.ParseUint(res.Header.Get("Content-Length"), 10, 64) | |
| if chunkSize == 0 { | |
| chunkSize = 2 * 1024 * 1024 | |
| } | |
| if maxRoutines == 0 { | |
| maxRoutines = 10 | |
| } | |
| totalChunks := uint64(math.Ceil(float64(clen) / float64(chunkSize))) | |
| lastChunkSize := clen % chunkSize | |
| stacks := make([][]byte, totalChunks) | |
| sem := make(chan struct{}, maxRoutines) | |
| var wg sync.WaitGroup | |
| var i uint64 | |
| for i = 0; i < totalChunks; i++ { | |
| wg.Add(1) | |
| sem <- struct{}{} // ensure | |
| min := chunkSize * i | |
| max := chunkSize * (i + 1) | |
| if i == totalChunks-1 { | |
| max = min + lastChunkSize | |
| } | |
| go func(min uint64, max uint64, idx uint64) { | |
| defer func() { | |
| wg.Done() | |
| <-sem | |
| }() | |
| rng := fmt.Sprintf("bytes=%d-%d", min, max-1) | |
| fmt.Printf("%04d: %s\n", idx, rng) | |
| req, _ := http.NewRequest(http.MethodGet, URL, nil) | |
| req.Header.Add("Range", rng) | |
| resp, err := http.DefaultClient.Do(req) | |
| if err != nil { | |
| return | |
| } | |
| defer resp.Body.Close() | |
| b, err := ioutil.ReadAll(resp.Body) | |
| if err != nil { | |
| return | |
| } | |
| stacks[idx] = b | |
| }(min, max, i) | |
| } | |
| wg.Wait() | |
| for _, body := range stacks { | |
| writer.Write(body) | |
| } | |
| return nil | |
| } |
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