如何“暂停”和“恢复”下载工作？答案

【问题标题】：How to `pause`, and `resume` download work?如何“暂停”和“恢复”下载工作？
【发布时间】：2012-08-27 23:06:33
【问题描述】：

通常，从服务器下载文件是这样的：

fp = open(file, 'wb')
req = urllib2.urlopen(url)
for line in req:
    fp.write(line)
fp.close()

在下载过程中，下载过程必须完成。如果进程停止或中断，则需要重新开始下载进程。所以，我想让我的程序暂停和恢复下载，我该如何实现呢？谢谢。

【问题讨论】：

标签： python binary download

【解决方案1】：

Web 服务器必须支持 Range 请求标头才能允许暂停/恢复下载：

Range: <unit>=<range-start>-<range-end>

然后客户端可以通过Range请求头来获取指定的字节，例如：

Range: bytes=0-1024

在这种情况下，服务器可以用200 OK 响应，表明它不支持Range 请求，或者它可以像这样回复206 Partial Content：

HTTP/1.1 206 Partial Content
Accept-Ranges: bytes
Content-Length: 1024
Content-Range: bytes 64-512/1024

Response body.... till 512th byte of the file

见：

【讨论】：

【解决方案2】：

在python中，你可以这样做：

import urllib, os

class myURLOpener(urllib.FancyURLopener):
    """Create sub-class in order to overide error 206.  This error means a
       partial file is being sent,
       which is ok in this case.  Do nothing with this error.
    """
    def http_error_206(self, url, fp, errcode, errmsg, headers, data=None):
        pass

loop = 1
dlFile = "2.6Distrib.zip"
existSize = 0
myUrlclass = myURLOpener()
if os.path.exists(dlFile):
    outputFile = open(dlFile,"ab")
    existSize = os.path.getsize(dlFile)
    #If the file exists, then only download the remainder
    myUrlclass.addheader("Range","bytes=%s-" % (existSize))
else:
    outputFile = open(dlFile,"wb")

webPage = myUrlclass.open("http://localhost/%s" % dlFile)

#If the file exists, but we already have the whole thing, don't download again
if int(webPage.headers['Content-Length']) == existSize:
    loop = 0
    print "File already downloaded"

numBytes = 0
while loop:
    data = webPage.read(8192)
    if not data:
        break
    outputFile.write(data)
    numBytes = numBytes + len(data)

webPage.close()
outputFile.close()

for k,v in webPage.headers.items():
    print k, "=", v
print "copied", numBytes, "bytes from", webPage.url

您可以找到来源：http://code.activestate.com/recipes/83208-resuming-download-of-a-file/

它只适用于 http dls

【讨论】：