From a48d2346ee1c4140d8dbe0e65d65a2555770e737 Mon Sep 17 00:00:00 2001
From: sminamot <shosfs@gmail.com>
Date: Mon, 26 Nov 2018 00:59:43 +0900
Subject: [PATCH 1/2] :tada: created

---
 kadai3-2/sminamot/main.go | 173 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 173 insertions(+)
 create mode 100644 kadai3-2/sminamot/main.go

diff --git a/kadai3-2/sminamot/main.go b/kadai3-2/sminamot/main.go
new file mode 100644
index 0000000..19d4c8d
--- /dev/null
+++ b/kadai3-2/sminamot/main.go
@@ -0,0 +1,173 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"path/filepath"
+	"time"
+
+	"golang.org/x/sync/errgroup"
+)
+
+const processNum = 4
+const tmpDir = "./tmp"
+
+type RangeClients []RangeClient
+
+type RangeClient struct {
+	Index      int
+	FilePath   string
+	StartBytes int64
+	EndBytes   int64
+}
+
+func NewRangeClients(fileBytes int64, fileName string) RangeClients {
+	rc := make(RangeClients, 0, processNum)
+	b := int64(fileBytes / processNum)
+	sb := int64(0)
+	for i := 0; i < processNum; i++ {
+		r := RangeClient{
+			Index:      i,
+			FilePath:   fmt.Sprintf("%s/%s_%d", tmpDir, fileName, i),
+			StartBytes: sb,
+			EndBytes:   sb + b,
+		}
+		if i == processNum-1 {
+			r.EndBytes = fileBytes
+		}
+		rc = append(rc, r)
+		sb += b + 1
+	}
+	return rc
+}
+
+func main() {
+	os.Exit(Run())
+}
+
+func Run() int {
+	if len(os.Args) < 2 {
+		fmt.Fprintln(os.Stderr, "Usage: ./main TARGET_URL")
+		return 1
+	}
+	targetUrl := os.Args[1]
+
+	res, err := http.Head(targetUrl)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		return 1
+	}
+	if res.Header.Get("Accept-Ranges") != "bytes" {
+		fmt.Fprintf(os.Stderr, "not support range header, url:%s", targetUrl)
+		return 1
+	}
+	rcs := NewRangeClients(res.ContentLength, filepath.Base(targetUrl))
+
+	// create tmp directory
+	if err := os.MkdirAll(tmpDir, 0755); err != nil {
+		fmt.Fprintln(os.Stderr, "could not create tmp directory")
+	}
+	// remove tmp directory with defer
+	defer os.RemoveAll(tmpDir)
+
+	eg, ctx := errgroup.WithContext(context.Background())
+	ctx, cancel := context.WithCancel(ctx)
+	defer cancel()
+
+	for _, rc := range rcs {
+		rc := rc
+		eg.Go(func() error {
+			res, err := rc.download(ctx, targetUrl)
+			if err != nil {
+				return err
+			}
+			defer res.Body.Close()
+
+			return rc.outputFile(ctx, res)
+		})
+	}
+
+	if err := eg.Wait(); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		return 1
+	}
+
+	fh, err := os.Create(filepath.Base(targetUrl))
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+	}
+	defer fh.Close()
+
+	// bind files
+	for _, rc := range rcs {
+		fp, err := os.Open(rc.FilePath)
+		if err != nil {
+			fmt.Fprintln(os.Stderr, err)
+		}
+		defer fp.Close()
+		io.Copy(fh, fp)
+	}
+
+	return 0
+}
+
+func (rc *RangeClient) download(ctx context.Context, t string) (*http.Response, error) {
+	type requestResult struct {
+		res *http.Response
+		err error
+	}
+
+	req, err := http.NewRequest("GET", t, nil)
+	tr := &http.Transport{}
+	client := &http.Client{Transport: tr}
+	if err != nil {
+		return nil, err
+	}
+
+	req.Header.Set("Range", fmt.Sprintf("bytes=%d-%d", rc.StartBytes, rc.EndBytes))
+
+	resCh := make(chan requestResult)
+	go func() {
+		time.Sleep(5 * time.Second)
+		res, err := client.Do(req)
+		resCh <- requestResult{
+			res: res,
+			err: err,
+		}
+	}()
+
+	select {
+	case <-ctx.Done():
+		tr.CancelRequest(req)
+		return nil, ctx.Err()
+	case result := <-resCh:
+		return result.res, result.err
+	}
+}
+
+func (rc *RangeClient) outputFile(ctx context.Context, res *http.Response) error {
+	fp, err := os.OpenFile(rc.FilePath, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0666)
+	if err != nil {
+		return err
+	}
+	defer fp.Close()
+
+	errCh := make(chan error)
+	go func() {
+		_, err := io.Copy(fp, res.Body)
+		errCh <- err
+	}()
+
+	select {
+	case <-ctx.Done():
+		return ctx.Err()
+	case err := <-errCh:
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}

From bdd7663528c067a8fb194b2a826b3e5064ae33b3 Mon Sep 17 00:00:00 2001
From: sminamot <shosfs@gmail.com>
Date: Mon, 26 Nov 2018 00:59:50 +0900
Subject: [PATCH 2/2] :clipboard: add README

---
 kadai3-2/sminamot/README.md | 12 ++++++++++++
 1 file changed, 12 insertions(+)
 create mode 100644 kadai3-2/sminamot/README.md

diff --git a/kadai3-2/sminamot/README.md b/kadai3-2/sminamot/README.md
new file mode 100644
index 0000000..5470511
--- /dev/null
+++ b/kadai3-2/sminamot/README.md
@@ -0,0 +1,12 @@
+# 分割ダウンローダーの作成
+
+## Usage
+```
+$ go build -o main
+$ ./main TARGET_URL
+```
+
+* `./tmp`ディレクトリを作り4分割のダウンロードを行う
+  * ファイル名は`<対象ファイル名>_{0..3}`
+* 分割ダウンロードが完了後に4つのファイルをマージする
+* HTTPリクエストや(分割ダウンロードの)ファイル書き込みに失敗した場合、他で実行中のgoroutine処理を終了する