Kadai3 2 gosagawa

kadai3-2/gosagawa/.gitignore

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+vendor/*

kadai3-2/gosagawa/README.md

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+# kadai3-2
+
+##分割ダウンロードを行う
+- Rangeアクセスを用いる
+- いくつかのゴルーチンでダウンロードしてマージする
+- エラー処理を工夫する
+  - golang.org/x/sync/errgourpパッケージなどを使ってみる
+- キャンセルが発生した場合の実装を行う
+
+##install
+
+```
+dep ensure
+```
+
+##usage
+
+```
+go run main.go
+```
+

kadai3-2/gosagawa/main.go

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+package main
+
+import (
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"runtime"
+	"strings"
+
+	"github.com/pkg/errors"
+	"golang.org/x/sync/errgroup"
+)
+
+func main() {
+
+	url := os.Args[1]
+	fmt.Println(url)
+
+	//TODO check args
+
+	//TODO check RangeAccess available
+
+	d, err := NewDownloader(url)
+	if err != nil {
+		fmt.Printf("\ndownload initialize error. %v", err)
+		os.Exit(1)
+	}
+
+	err = d.Download()
+	if err != nil {
+		fmt.Printf("\ndownload error. %v", err)
+		os.Exit(1)
+	}
+	err = d.Merge()
+	if err != nil {
+		fmt.Printf("\ndownload merge error. %v", err)
+		os.Exit(1)
+	}
+}
+
+type Downloader struct {
+	FileName   string
+	MaxProcess uint
+	Workers    []*worker
+}
+
+type worker struct {
+	processId            uint
+	bytesToStartReading  uint
+	bytesToFinishReading uint
+	resourceUrl          string
+	partFilePath         string
+}
+
+func NewDownloader(url string) (*Downloader, error) {
+	d := new(Downloader)
+	d.FileName = getFileName(url)
+	d.MaxProcess = uint(runtime.NumCPU())
+
+	res, err := http.Head(url)
+	if err != nil {
+		return nil, err
+	}
+
+	size := uint(res.ContentLength)
+
+	split := size / d.MaxProcess
+	for i := uint(0); i < d.MaxProcess; i++ {
+		w, err := NewWorker(d, size, i, split, url)
+		if err != nil {
+			return nil, errors.Wrap(err, "initialize worker error")
+		}
+		d.Workers = append(d.Workers, w)
+	}
+	fmt.Fprintf(os.Stdout, "Download start from %s\n", url)
+	return d, nil
+}
+
+func NewWorker(d *Downloader, size uint, i uint, split uint, url string) (*worker, error) {
+	bytesToStartReading := split * i
+	bytesToFinishReading := bytesToStartReading + split - 1
+	partFilePath := fmt.Sprintf("%s.%d", d.FileName, i)
+
+	if i == d.MaxProcess-1 {
+		bytesToFinishReading = size
+	}
+	w := &worker{
+		processId:            i,
+		bytesToStartReading:  bytesToStartReading,
+		bytesToFinishReading: bytesToFinishReading,
+		resourceUrl:          url,
+		partFilePath:         partFilePath,
+	}
+	return w, nil
+}
+
+func (d *Downloader) Download() error {
+	eg := errgroup.Group{}
+	for _, worker := range d.Workers {
+		w := worker
+		eg.Go(func() error {
+			return w.Request()
+		})
+	}
+
+	if err := eg.Wait(); err != nil {
+		return err
+	}
+	return nil
+}
+
+func (d *Downloader) Merge() error {
+	outputFilePath := fmt.Sprintf("%s", d.FileName)
+	outputFile, err := os.Create(outputFilePath)
+	if err != nil {
+		return errors.Wrap(err, "failed to create merge file")
+	}
+	defer outputFile.Close()
+	for i := uint(0); i < d.MaxProcess; i++ {
+		partFilePath := fmt.Sprintf("%s.%d", outputFilePath, i)
+		partFile, err := os.Open(partFilePath)
+		if err != nil {
+			return errors.Wrap(err, "failed to open part file")
+		}
+		io.Copy(outputFile, partFile)
+		partFile.Close()
+		if err := os.Remove(partFilePath); err != nil {
+			return errors.Wrap(err, "failed to remove a file")
+		}
+	}
+	return nil
+}
+
+func (w *worker) Request() error {
+	res, err := w.MakeResponse()
+	if err != nil {
+		return errors.Wrap(err, fmt.Sprintf("failed to split get requests: %d", w.processId))
+	}
+	defer res.Body.Close()
+	output, err := os.Create(w.partFilePath)
+	if err != nil {
+		return errors.Wrap(err, fmt.Sprintf("failed to create file %s", w.partFilePath))
+	}
+	defer output.Close()
+	io.Copy(output, res.Body)
+	return nil
+}
+
+func (w *worker) MakeResponse() (*http.Response, error) {
+	req, err := http.NewRequest("GET", w.resourceUrl, nil)
+	if err != nil {
+		return nil, errors.Wrap(err, fmt.Sprintf("failed to split NewRequest for get: %d", w.processId))
+	}
+	req.Header.Set("Range", fmt.Sprintf("bytes=%d-%d", w.bytesToStartReading, w.bytesToFinishReading))
+	return http.DefaultClient.Do(req)
+}
+
+func getFileName(resourceUrl string) string {
+	token := strings.Split(resourceUrl, "/")
+	filename := token[len(token)-1]
+	return filename
+}