kadai3-2 shuheiktgw

kadai3-2/shuheiktgw/gget/.gitignore

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+gget

kadai3-2/shuheiktgw/gget/README.md

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+gget
+====
+
+gget is a wget like command to download file, but downloads a file in parallel.
+
+## Usage
+```
+gget [options...] URL
+
+OPTIONS:
+  --parallel value, -p value  specifies the amount of parallelism (default: the number of CPU)
+  --help, -h                  prints help
+
+```
+
+## Install
+
+```
+go build
+./gget [options...] URL
+```

kadai3-2/shuheiktgw/gget/cli.go

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+package main
+
+import (
+	"flag"
+	"fmt"
+	"io"
+	"runtime"
+)
+
+const (
+	ExitCodeOK = iota
+	ExitCodeError
+	ExitCodeBadArgsError
+	ExitCodeParseFlagsError
+	ExitCodeInvalidFlagError
+)
+
+const name = "gget"
+
+// CLI represents CLI interface for gget
+type CLI struct {
+	outStream, errStream io.Writer
+}
+
+// Run runs gget command
+func (cli *CLI) Run(args []string) int {
+	var parallel int
+
+	flags := flag.NewFlagSet(name, flag.ContinueOnError)
+	flags.Usage = func() {
+		fmt.Fprint(cli.outStream, usage)
+	}
+
+	numCPU := runtime.NumCPU()
+	flags.IntVar(&parallel, "parallel", numCPU, "")
+	flags.IntVar(&parallel, "p", numCPU, "")
+
+	if err := flags.Parse(args[1:]); err != nil {
+		return ExitCodeParseFlagsError
+	}
+
+	if parallel < 1 {
+		fmt.Fprintf(cli.errStream, "Failed to set up gget: The number of parallels cannot be less than one\n")
+		return ExitCodeInvalidFlagError
+	}
+
+	parsedArgs := flags.Args()
+	if len(parsedArgs) != 1 {
+		fmt.Fprintf(cli.errStream, "Invalid arguments: you need to set exactly one URL\n")
+		return ExitCodeBadArgsError
+	}
+
+	request, err := NewRequest(parsedArgs[0], parallel)
+	if err != nil {
+		fmt.Fprintf(cli.errStream, "Error occurred while initializing a request: %s\n", err)
+		return ExitCodeError
+	}
+
+	if err := request.Do(); err != nil {
+		fmt.Fprintf(cli.errStream, "Error occurred while downloading the file: %s\n", err)
+		return ExitCodeError
+	}
+
+	return ExitCodeOK
+}
+
+var usage = `Usage: gget [options...] URL
+
+gget is a wget like command to download file, but downloads a file in parallel
+
+OPTIONS:
+  --parallel value, -p value  specifies the amount of parallelism (default: the number of CPU)
+  --help, -h                  prints help
+
+`

kadai3-2/shuheiktgw/gget/main.go

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+package main
+
+import "os"
+
+func main() {
+	cli := &CLI{outStream: os.Stdout, errStream: os.Stderr}
+	os.Exit(cli.Run(os.Args))
+}

kadai3-2/shuheiktgw/gget/request.go

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+package main
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"os"
+	"strings"
+
+	"golang.org/x/sync/errgroup"
+)
+
+// Request represents a request to download a file
+type Request struct {
+	URL    string
+	FName  string
+	Ranges []*Range
+}
+
+// Range tells tha range of file to download
+type Range struct {
+	start int64
+	end   int64
+}
+
+// NewRequest initializes Request object
+func NewRequest(rawURL string, parallel int) (*Request, error) {
+	u, err := url.Parse(rawURL)
+	if err != nil {
+		return nil, err
+	}
+
+	ss := strings.Split(u.Path, "/")
+	fname := ss[len(ss)-1]
+
+	res, err := http.Head(rawURL)
+	if err != nil {
+		return nil, err
+	}
+	defer res.Body.Close()
+
+	total := res.ContentLength
+	unit := total / int64(parallel)
+	ranges := make([]*Range, parallel)
+
+	for i := 0; i < parallel; i++ {
+		var start int64
+		if i == 0 {
+			start = 0
+		} else {
+			start = int64(i)*unit + 1
+		}
+
+		var end int64
+		if i == parallel-1 {
+			end = total
+		} else {
+			end = int64(i+1) * unit
+		}
+
+		ranges[i] = &Range{start: start, end: end}
+	}
+
+	return &Request{URL: rawURL, FName: fname, Ranges: ranges}, nil
+}
+
+// Do sends a real HTTP requests in parallel
+func (r *Request) Do() error {
+	eg, _ := errgroup.WithContext(context.TODO())
+
+	for idx := range r.Ranges {
+		// DO NOT refer to idx directly since function below
+		// is a closure and idx changes for each iterations
+		i := idx
+		eg.Go(func() error {
+			return r.do(i)
+		})
+	}
+
+	if err := eg.Wait(); err != nil {
+		return err
+	}
+
+	return r.mergeFiles()
+}
+
+func (r *Request) do(idx int) error {
+	req, err := http.NewRequest(http.MethodGet, r.URL, nil)
+	if err != nil {
+		return err
+	}
+
+	ran := r.Ranges[idx]
+	req.Header.Set("Range", fmt.Sprintf("bytes=%d-%d", ran.start, ran.end))
+
+	client := http.DefaultClient
+
+	res, err := client.Do(req)
+	if err != nil {
+		return err
+	}
+	defer res.Body.Close()
+
+	tmpFName := fmt.Sprintf("%s.%d", r.FName, idx)
+	file, err := os.Create(tmpFName)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	if _, err := io.Copy(file, res.Body); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (r *Request) mergeFiles() error {
+	f, err := os.Create(r.FName)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	for idx := range r.Ranges {
+		tmpFName := fmt.Sprintf("%s.%d", r.FName, idx)
+		tmpFile, err := os.Open(tmpFName)
+		if err != nil {
+			return err
+		}
+
+		io.Copy(f, tmpFile)
+		tmpFile.Close()
+		if err := os.Remove(tmpFName); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}