[WIP] kadai3-2 by ravelll

kadai3/ravelll/2/main.go

@@ -0,0 +1,108 @@
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"net/url"
+	"os"
+	"path/filepath"
+)
+
+const (
+	BatchByteSize = 500
+)
+
+func main() {
+	contentURL := os.Args[1]
+	os.Exit(download(contentURL))
+}
+
+func checkContentLength(contentURL string) (int64, error) {
+	req, err := http.Head(contentURL)
+	if err != nil {
+		return 0, err
+	}
+
+	return req.ContentLength, nil
+}
+
+func rangeHeaderVal(i int, partNum int) string {
+	if i == partNum-1 {
+		return fmt.Sprintf(
+			"bytes=%d-", i*BatchByteSize)
+	}
+
+	return fmt.Sprintf(
+		"bytes=%d-%d", i*BatchByteSize, (i+1)*BatchByteSize-1)
+}
+
+func request(contentURL string) (string, error) {
+	partedBody := make([]string, 0, 20)
+
+	contentLength, err := checkContentLength(contentURL)
+	if err != nil {
+		return "", err
+	}
+
+	partNum := int((contentLength / BatchByteSize) + 1)
+
+	for i := 0; partNum > i; i++ {
+		client := http.Client{}
+		req, err := http.NewRequest("GET", contentURL, nil)
+		req.Header.Add("Range", rangeHeaderVal(i, partNum))
+		downloaded, err := client.Do(req)
+		respBody, err := ioutil.ReadAll(downloaded.Body)
+		if err != nil {
+			return "", err
+		}
+
+		partedBody = append(partedBody, string(respBody))
+	}
+
+	var body string
+
+	for i := 0; i < len(partedBody); i++ {
+		body += partedBody[i]
+	}
+
+	return body, nil
+}
+
+func getFilename(contentURL string) (string, error) {
+	parsed, err := url.Parse(contentURL)
+	if err != nil {
+		log.Fatal(err)
+		return "", err
+	}
+	_, filename := filepath.Split(parsed.EscapedPath())
+	return filename, nil
+}
+
+func download(contentURL string) int {
+	if contentURL == "" {
+		fmt.Println("Error: no url specified.")
+		return 1
+	}
+
+	filename, filenameErr := getFilename(contentURL)
+	if filenameErr != nil {
+		return 1
+	}
+
+	responseBody, reqErr := request(contentURL)
+	if reqErr != nil {
+		return 1
+	}
+
+	output, createErr := os.Create(filename)
+	defer output.Close()
+	if createErr != nil {
+		return 1
+	}
+
+	output.WriteString(responseBody)
+
+	return 0
+}