Qiniu MultiRange Download Example

multi_range_download.go

package main

import (
	"bytes"
	"errors"
	"fmt"
	"io"
	"mime"
	"mime/multipart"
	"net/http"
	"os"
	"strings"
)

// 注意：保证 Ranges 至少有两对，且 Ranges 最终不会覆盖整个文件
func MultiRangeGet(client *http.Client, url string, ranges [][2]int) ([]byte, error) {
	rangeHeaderValue := fmt.Sprintf("bytes=%s", generateRangeHeader(ranges))
	buffer := bytes.NewBuffer(make([]byte, 0, sumRangeSize(ranges)))

	req, err := http.NewRequest("GET", url, http.NoBody)
	if err != nil {
		return nil, err
	}
	req.Header.Add("Range", rangeHeaderValue)

	resp, err := client.Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	switch resp.StatusCode {
	case http.StatusOK:
		return nil, errors.New("Status code is 200, we don't support it here")
	case http.StatusPartialContent:
		contentType := resp.Header.Get("Content-Type")
		_, params, err := mime.ParseMediaType(contentType)
		if err != nil {
			return nil, err
		}
		multipartReader := multipart.NewReader(resp.Body, params["boundary"])
		for {
			part, err := multipartReader.NextPart()
			if err == io.EOF {
				break
			}
			if err != nil {
				return nil, err
			}
			_, partSize, err := parseContentRange(part.Header.Get("Content-Range"))
			if err != nil {
				return nil, err
			}
			copied, err := io.Copy(buffer, part)
			if err != nil {
				return nil, err
			}
			if copied != int64(partSize) {
				return nil, io.ErrUnexpectedEOF
			}
		}
	default:
		return nil, errors.New("Status code is neither 200 nor 206")
	}

	return buffer.Bytes(), nil
}

func generateRangeHeader(ranges [][2]int) string {
	parts := make([]string, 0, len(ranges))

	for _, rg := range ranges {
		parts = append(parts, fmt.Sprintf("%d-%d", rg[0], rg[0]+rg[1]-1))
	}

	return strings.Join(parts, ",")
}

func sumRangeSize(ranges [][2]int) int {
	sum := 0
	for _, rg := range ranges {
		sum += rg[1]
	}
	return sum
}

func parseContentRange(contentRange string) (int, int, error) {
	var from, to, total int

	parsed, err := fmt.Sscanf(contentRange, "bytes %d-%d/%d", &from, &to, &total)
	if err != nil || parsed != 3 {
		return 0, 0, fmt.Errorf("Content-Range is invalid: %s", err)
	}
	return from, to - from + 1, nil
}