我尝试从网站下载图片,步骤如下:
http.Get
获取图片os.Create
在当前文件夹中创建新文件io.copyN
将图像复制到文件但如果io.CopyN
第一次失败,那似乎很奇怪,以后似乎永远不会成功
代码片段:
download_again:
copy_byte, copy_err := io.CopyN(file, res.Body, res.ContentLength)
fmt.Fprintf(os.Stderr, "img(%s) size: %d\n", name, res.ContentLength)
if copy_err == nil && res.ContentLength == copy_byte {
fmt.Fprintf(os.Stderr, "Success to download img(%s)[%f KB(%d B)]: %s\n", img_url, float64(copy_byte)/1024, copy_byte, name)
} else {
if try_i > download_times {
fmt.Fprintf(os.Stderr, "[fatal] fail to download img(%s) %s\n", img_url, name)
fout.WriteString(name + "\n")
return
}
fmt.Fprintf(os.Stderr, "error in download img(%s)[%f KB(%d B)]: %s, try %d times\n", img_url, float64(copy_byte)/1024, copy_byte, name, try_i)
try_i++
goto download_again
}
和输出消息:
img(11085) size: 273047
error in download img(./style/images/dszp/11085.jpg)[171.447266 KB(175562 B)]: 11085 , try 1 times
img(11085) size: 273047
error in download img(./style/images/dszp/11085.jpg)[0.000000 KB(0 B)]: 11085 , try 2 times
img(11085) size: 273047
error in download img(./style/images/dszp/11085.jpg)[0.000000 KB(0 B)]: 11085, try 3 times
img(11085) size: 273047
error in download img(./style/images/dszp/11085.jpg)[0.000000 KB(0 B)]: 11085, try 4 times
img(11085) size: 273047
error in download img(./style/images/dszp/11085.jpg)[0.000000 KB(0 B)]: 11085, try 5 times
img(11085) size: 273047
error in download img(./style/images/dszp/11085.jpg)[0.000000 KB(0 B)]: 11085, try 6 times
任何帮助将不胜感激:)
答案 0 :(得分:0)
您需要重试http请求。 (不只是io.CopyN
)
以下是可恢复下载的(主要是未经测试的)实现:
func downloadFile(dst *os.File, url string, offset int64) (int64, error) {
req, err := http.NewRequest("GET", url, nil)
if err != nil {
return 0, err
}
// try to use a range header
if offset > 0 {
req.Header.Set("Range", fmt.Sprintf("bytes=%d-", offset))
}
res, err := http.DefaultClient.Do(req)
if err != nil {
return 0, err
}
defer res.Body.Close()
// some http servers don't support range, so in that case we discard the first
// offset bytes
if offset > 0 && res.StatusCode != http.StatusPartialContent {
_, err = io.CopyN(ioutil.Discard, res.Body, offset)
if err != nil {
return offset, err
}
}
n, err := io.CopyN(dst, res.Body, res.ContentLength)
return offset + n, err
}
您可以将该函数传递给偏移量,它将尝试从该点开始(通过告知HTTP服务器或丢弃字节)。它还会返回您已经完成的进度,因此您可以将此函数包装在重试循环中:
func example() error {
f, err := os.Create("/tmp/pkg.png")
if err != nil {
return err
}
defer f.Close()
offset := int64(0)
delay := time.Second
// try 5 times
for i := 0; i < 5; i++ {
offset, err = downloadFile(f, "http://golang.org/doc/gopher/pkg.png", offset)
if err == nil {
return nil
}
// wait a little while before trying again
time.Sleep(delay)
delay *= 2
}
return fmt.Errorf("failed to download file after 5 tries")
}
顺便说一句,你应该避免使用goto
for循环。