1
func sendFile(writer http.ResponseWriter, request *http.Request, f *os.File) {
2
  defer f.Close()
3
  info, err := f.Stat()
4
  if err != nil {
5
    log.Println("sendFile1", err.Error())
6
    http.NotFound(writer, request)
7
    return
8
  }
9
  writer.Header().Add("Accept-Ranges", "bytes")
10
  writer.Header().Add("Content-Disposition", "attachment; filename="+info.Name())
11
  var start, end int64
12
  //fmt.Println(request.Header,"\n")
13
  if r := request.Header.Get("Range"); r != "" {
14
    if strings.Contains(r, "bytes=") && strings.Contains(r, "-") {
15

16
      fmt.Sscanf(r, "bytes=%d-%d", &start, &end)
17
      if end == 0 {
18
        end = info.Size() - 1
19
      }
20
      if start > end || start < 0 || end < 0 || end >= info.Size() {
21
        writer.WriteHeader(http.StatusRequestedRangeNotSatisfiable)
22
        log.Println("sendFile2 start:", start, "end:", end, "size:", info.Size())
23
        return
24
      }
25
      writer.Header().Add("Content-Length", strconv.FormatInt(end-start+1, 10))
26
      writer.Header().Add("Content-Range", fmt.Sprintf("bytes %v-%v/%v", start, end, info.Size()))
27
      writer.WriteHeader(http.StatusPartialContent)
28
    } else {
29
      writer.WriteHeader(http.StatusBadRequest)
30
      return
31
    }
32
  } else {
33
    writer.Header().Add("Content-Length", strconv.FormatInt(info.Size(), 10))
34
    start = 0
35
    end = info.Size() - 1
36
  }
37
  _, err = f.Seek(start, 0)
38
  if err != nil {
39
    log.Println("sendFile3", err.Error())
40
    writer.WriteHeader(http.StatusInternalServerError)
41
    return
42
  }
43
  n := 512
44
  buf := make([]byte, n)
45
  for {
46
    if end-start+1 < int64(n) {
47
      n = int(end - start + 1)
48
    }
49
    _, err := f.Read(buf[:n])
50
    if err != nil {
51
      log.Println("1:", err)
52
      if err != io.EOF {
53
        log.Println("error:", err)
54
      }
55
      return
56
    }
57
    err = nil
58
    _, err = writer.Write(buf[:n])
59
    if err != nil {
60
      //log.Println(err, start, end, info.Size(), n)
61
      return
62
    }
63
    start += int64(n)
64
    if start >= end+1 {
65
      return
66
    }
67
  }
68

69
}