如何恢复中断的下载 - 第2部分 [英] how to resume an interrupted download - part 2

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问题描述

这是我以前的问题的延续当我不是注册用户时，我发布了。作为一个复习，我正在尝试从我的雅虎恢复一个大文件的下载网站服务器下载时中断。我以前认为中断是由于超过100秒超时限制（因为雅虎强制用户编写脚本的时间限制）。但是，当我测量下载中断的时间时，我发现中断时间有很大变化（有时下载速度不间断地运行不到100秒，有时甚至长达七分钟）。所以我不知道超时的原因，我只是想解决他们。

This is a continuation of my previous question which I posted when I wasn't a registered user. As a refresher, I'm trying to resume the downloading of a large file from my Yahoo! web site server when the download gets interrupted. I previously thought the interruption was due to a 100 second timeout limit (because Yahoo! enforces that time limit on user written scripts). However, when I measured the timing of the download interrupts, I saw that the interrupt timing varies a lot (sometimes the download runs uninterrupted for less than 100 seconds and sometimes up to seven minutes). So I don't know the reason for the timeouts and I'm just trying to work around them.

我尝试了 naikus （谢谢），根据http头域的转储，似乎我的雅虎网站服务器确实识别范围属性，该属性应允许下载在中断的偏移处恢复。不幸的是，虽然字节范围在恢复的连接中的http标头中显示正确，但传输的内容始终在文件开头重新启动。 （我的测试文件是一个50,000个4字节整数的数组，从0开始递增。我下载的文件总是在发生下载中断的每个偏移处开始重新计数。）

I tried the suggestion by naikus (thank you) and, according to the dump of http header fields, it appears that my Yahoo! web site server does recognize the "range" property that should allow the download to resume at the offset of the interruption. Unfortunately, although the byte range appears correct in the http header in the resumed connections, the transferred content always restarts at the beginning of the file. (My test file is an array of 50,000 4-byte integers that increments starting at 0. My downloaded file always starts recounting at 0 at every offset at which a download interrupt occurred.)

是否有一些其他的http连接属性请求我应该得到雅虎服务器实际跳转到头文件字节范围中指定的文件偏移量？这是代码及其转储：

         // Setup connection.
         URL url = new URL(strUrl[0]);
         URLConnection connection = url.openConnection();
         downloaded = Integer.parseInt(strUrl[3]);
         if (downloaded > 0) {
             connection.setRequestProperty("Range", "bytes="+downloaded+"-");
             connection.connect();
             fileLength = mDownloadFileLength;
             Log.d("AsyncDownloadFile", 
                 "new download seek: " + downloaded +
                 "; lengthFile: " + fileLength);
         }
         else {
             connection.connect();
             downloaded = 0;
             fileLength = connection.getContentLength();
             mDownloadFileLength = fileLength;
         }
         Map<String, List<String>> map = connection.getHeaderFields();
         Log.d("AsyncDownloadFile", "header fields: " + map.toString());

         // Setup streams and buffers.
         input = new BufferedInputStream(url.openStream(), 8192);
         outFile = new RandomAccessFile(strUrl[1], "rw");
         if (downloaded > 0)  
             outFile.seek(downloaded);
         byte data[] = new byte[1024];

         // Download file.
         for (int count=0, i=0; (count=input.read(data, 0, 1024)) != -1; i++) { 
             outFile.write(data, 0, count);
             downloaded += count; 
             if (downloaded >= fileLength)
                 break;

             // Display progress.
             Log.d("AsyncDownloadFile", "bytes: " + downloaded);
             if ((i%10) == 0)
                 publishProgress((int)(downloaded*100/fileLength));
             if (mFlagDisableAsyncTask) {
                 downloaded = 0;
                 break;
             }
         }

         // Close streams.
         outFile.close();
         input.close();





转储：

dump: 

@ 4:08:24  
D/AsyncDownloadFile( 2372): header fields: {p3p=[policyref="http://info.yahoo.co
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA PO
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-mo
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[2000000], age=[0], serve
r=[YTS/1.17.13], accept-ranges=[bytes], date=[Fri, 06 Aug 2010 20:08:33 GMT]}  
D/AsyncDownloadFile( 2372): bytes: 1024  
D/AsyncDownloadFile( 2372): bytes: 1033  
D/AsyncDownloadFile( 2372): bytes: 2057  
D/AsyncDownloadFile( 2372): bytes: 2493  
D/AsyncDownloadFile( 2372): bytes: 3517  
D/AsyncDownloadFile( 2372): bytes: 3953  

.
.
.

@ 4:13:25  
D/AsyncDownloadFile( 2372): bytes: 386473  
D/AsyncDownloadFile( 2372): bytes: 387497  
D/AsyncDownloadFile( 2372): bytes: 387933  
D/AsyncDownloadFile( 2372): new download seek: 387933; lengthFile: 2000000  
D/AsyncDownloadFile( 2372): header fields: {p3p=[policyref="http://info.yahoo.co
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA PO
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-mo
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[1612067], age=[0], serve
r=[YTS/1.17.13], accept-ranges=[bytes], date=[Fri, 06 Aug 2010 20:13:29 GMT], co
ntent-range=[bytes 387933-1999999/2000000]}  
D/AsyncDownloadFile( 2372): bytes: 388957  
D/AsyncDownloadFile( 2372): bytes: 389981  
D/AsyncDownloadFile( 2372): bytes: 390409  
D/AsyncDownloadFile( 2372): bytes: 391433  
D/AsyncDownloadFile( 2372): bytes: 391869  
D/AsyncDownloadFile( 2372): bytes: 392893  

.
.
.

@ 4:18:45  
D/AsyncDownloadFile( 2372): bytes: 775413  
D/AsyncDownloadFile( 2372): bytes: 775849  
D/AsyncDownloadFile( 2372): bytes: 776873  
D/AsyncDownloadFile( 2372): bytes: 777309  
D/AsyncDownloadFile( 2372): new download seek: 777309; lengthFile: 2000000  
D/AsyncDownloadFile( 2372): header fields: {p3p=[policyref="http://info.yahoo.co
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA PO
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-mo
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[1222691], age=[0], serve
r=[YTS/1.17.13], accept-ranges=[bytes], date=[Fri, 06 Aug 2010 20:18:54 GMT], co
ntent-range=[bytes 777309-1999999/2000000]}  
D/dalvikvm( 2372): GC_FOR_MALLOC freed 11019 objects / 470560 bytes in 155ms  
D/AsyncDownloadFile( 2372): bytes: 778333  
D/AsyncDownloadFile( 2372): bytes: 779357  
D/AsyncDownloadFile( 2372): bytes: 779790  
D/AsyncDownloadFile( 2372): bytes: 780814  
D/AsyncDownloadFile( 2372): bytes: 781250  
D/AsyncDownloadFile( 2372): bytes: 782274  

.
.
.

@ 4:23:45  
D/AsyncDownloadFile( 2372): bytes: 1163334  
D/AsyncDownloadFile( 2372): bytes: 1163770  
D/AsyncDownloadFile( 2372): bytes: 1164794  
D/AsyncDownloadFile( 2372): bytes: 1165230  
D/AsyncDownloadFile( 2372): new download seek: 1165230; lengthFile: 2000000  
D/AsyncDownloadFile( 2372): header fields: {p3p=[policyref="http://info.yahoo.co
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA PO
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-mo
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[834770], age=[0], server
=[YTS/1.17.13], accept-ranges=[bytes], date=[Fri, 06 Aug 2010 20:23:47 GMT], con
tent-range=[bytes 1165230-1999999/2000000]}  
D/AsyncDownloadFile( 2372): bytes: 1166246  
D/AsyncDownloadFile( 2372): bytes: 1167270  
D/AsyncDownloadFile( 2372): bytes: 1167706  
D/AsyncDownloadFile( 2372): bytes: 1168730  
D/AsyncDownloadFile( 2372): bytes: 1169754  
D/AsyncDownloadFile( 2372): bytes: 1170778  

.
.
.

@ 4:30:25  
D/AsyncDownloadFile( 2372): bytes: 1551255  
D/AsyncDownloadFile( 2372): bytes: 1551691  
D/AsyncDownloadFile( 2372): bytes: 1552715  
D/AsyncDownloadFile( 2372): bytes: 1553151  
D/AsyncDownloadFile( 2372): new download seek: 1553151; lengthFile: 2000000  
D/AsyncDownloadFile( 2372): header fields: {p3p=[policyref="http://info.yahoo.co
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA PO
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-mo
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[446849], age=[0], server
=[YTS/1.17.13], accept-ranges=[bytes], date=[Fri, 06 Aug 2010 20:30:44 GMT], con
tent-range=[bytes 1553151-1999999/2000000]}  
D/AsyncDownloadFile( 2372): bytes: 1554167  
D/AsyncDownloadFile( 2372): bytes: 1554184  
D/AsyncDownloadFile( 2372): bytes: 1555208  
D/AsyncDownloadFile( 2372): bytes: 1555644  
D/AsyncDownloadFile( 2372): bytes: 1556668  
D/AsyncDownloadFile( 2372): bytes: 1557104  

.
.
.

@ 4:37:10  
D/AsyncDownloadFile( 2372): bytes: 1939188  
D/AsyncDownloadFile( 2372): bytes: 1939624  
D/AsyncDownloadFile( 2372): bytes: 1940648  
D/AsyncDownloadFile( 2372): bytes: 1941084  
D/AsyncDownloadFile( 2372): new download seek: 1941084; lengthFile: 2000000  
D/dalvikvm( 2372): GC_FOR_MALLOC freed 13701 objects / 604600 bytes in 128ms
D/AsyncDownloadFile( 2372): header fields: {p3p=[policyref="http://info.yahoo.co
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA PO
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-mo
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[58916], age=[0], server=
[YTS/1.17.13], accept-ranges=[bytes], date=[Fri, 06 Aug 2010 20:37:16 GMT], cont
ent-range=[bytes 1941084-1999999/2000000]}  
D/AsyncDownloadFile( 2372): bytes: 1942108  
D/AsyncDownloadFile( 2372): bytes: 1942117  
D/AsyncDownloadFile( 2372): bytes: 1943141  
D/AsyncDownloadFile( 2372): bytes: 1943577  
D/AsyncDownloadFile( 2372): bytes: 1944601  
D/AsyncDownloadFile( 2372): bytes: 1945037  

.
.
.

@ 4:38:30  
D/AsyncDownloadFile( 2372): bytes: 1993217  
D/AsyncDownloadFile( 2372): bytes: 1994241  
D/AsyncDownloadFile( 2372): bytes: 1994677  
D/AsyncDownloadFile( 2372): bytes: 1995701  
D/AsyncDownloadFile( 2372): bytes: 1996137  
D/AsyncDownloadFile( 2372): bytes: 1997161  
D/AsyncDownloadFile( 2372): bytes: 1997597  
D/AsyncDownloadFile( 2372): bytes: 1998621  
D/AsyncDownloadFile( 2372): bytes: 1999057  
D/onPostExecute( 2372): download: unsuccessful  

- - -

从BalusC谢谢），我修改了连接设置，但是Yahoo!服务器在每次中断时继续重置为文件的开头。以下是更改的代码和生成的转储：

After the tip from BalusC (thanks), I modified the connection setup but the Yahoo! server continues to reset to the start of the file at each interrupt. Here's the changed code and the resulting dumps:

            // Setup connection.
            URL url = new URL(strUrl[0]);
            URLConnection connection = url.openConnection();
            downloaded = Integer.parseInt(strUrl[3]);
            if (downloaded == 0) {
                connection.connect();
                strLastModified = connection.getHeaderField("Last-Modified");
                fileLength = connection.getContentLength();
                mDownloadFileLength = fileLength;
            }
            else {
                connection.setRequestProperty("Range", "bytes=" + downloaded + "-");
                connection.setRequestProperty("If-Range", strLastModified);
                connection.connect();
                fileLength = mDownloadFileLength;
                Log.d("AsyncDownloadFile", 
                        "new download seek: " + downloaded +
                        "; lengthFile: " + fileLength);
            }
            map = connection.getHeaderFields();
            Log.d("AsyncDownloadFile", "header fields: " + map.toString());





转储：

dump: 

@12:36:40 started  
D/AsyncDownloadFile(  413): header fields: {p3p=[policyref="http://info.yahoo.c
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTP
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA P
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-m
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[2000000], age=[0], serv
r=[YTS/1.17.13], accept-ranges=[bytes], date=[Sat, 07 Aug 2010 04:36:56 GMT]}  
D/AsyncDownloadFile(  413): bytes: 1024  
D/AsyncDownloadFile(  413): bytes: 2048  
D/AsyncDownloadFile(  413): bytes: 2476  
D/AsyncDownloadFile(  413): bytes: 3500  
D/AsyncDownloadFile(  413): bytes: 3936  

...

@12:39:20 interrupted  
D/AsyncDownloadFile(  413): bytes: 388068  
D/AsyncDownloadFile(  413): bytes: 389092  
D/AsyncDownloadFile(  413): bytes: 389376  
D/AsyncDownloadFile(  413): new download seek: 389376; lengthFile: 2000000  
D/AsyncDownloadFile(  413): header fields: {p3p=[policyref="http://info.yahoo.co
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA PO
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-mo
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[1610624], age=[0], serve
r=[YTS/1.17.13], accept-ranges=[bytes], date=[Sat, 07 Aug 2010 04:39:21 GMT], co
ntent-range=[bytes 389376-1999999/2000000]}  
D/AsyncDownloadFile(  413): bytes: 390400  
D/AsyncDownloadFile(  413): bytes: 390409  
D/AsyncDownloadFile(  413): bytes: 391433  
D/AsyncDownloadFile(  413): bytes: 391869  

...

@12:44:10 interrupted  
D/AsyncDownloadFile(  413): bytes: 775413  
D/AsyncDownloadFile(  413): bytes: 775849  
D/AsyncDownloadFile(  413): bytes: 776873  
D/AsyncDownloadFile(  413): bytes: 777309  
D/AsyncDownloadFile(  413): new download seek: 777309; lengthFile: 2000000  
D/AsyncDownloadFile(  413): header fields: {p3p=[policyref="http://info.yahoo.co
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA PO
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-mo
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[1222691], age=[0], serve
r=[YTS/1.17.13], accept-ranges=[bytes], date=[Sat, 07 Aug 2010 04:44:20 GMT], co
ntent-range=[bytes 777309-1999999/2000000]}  
D/dalvikvm(  413): GC_FOR_MALLOC freed 10869 objects / 465664 bytes in 122ms  
D/AsyncDownloadFile(  413): bytes: 778333  
D/AsyncDownloadFile(  413): bytes: 778342  
D/AsyncDownloadFile(  413): bytes: 779366  
D/AsyncDownloadFile(  413): bytes: 779802  

...

@12:49:30 interrupted  
D/AsyncDownloadFile(  413): bytes: 1163782  
D/AsyncDownloadFile(  413): bytes: 1164806  
D/AsyncDownloadFile(  413): bytes: 1165242  
D/AsyncDownloadFile(  413): new download seek: 1165242; lengthFile: 2000000  
D/AsyncDownloadFile(  413): header fields: {p3p=[policyref="http://info.yahoo.co
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA PO
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-mo
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[834758], age=[0], server
=[YTS/1.17.13], accept-ranges=[bytes], date=[Sat, 07 Aug 2010 04:49:43 GMT], con
tent-range=[bytes 1165242-1999999/2000000]}  
D/AsyncDownloadFile(  413): bytes: 1166266  
D/AsyncDownloadFile(  413): bytes: 1167290  
D/AsyncDownloadFile(  413): bytes: 1167718  
D/AsyncDownloadFile(  413): bytes: 1168742  

...

@12:55:30 interrupted  
D/AsyncDownloadFile(  413): bytes: 1552722  
D/AsyncDownloadFile(  413): bytes: 1553158  
D/AsyncDownloadFile(  413): bytes: 1554182  
D/AsyncDownloadFile(  413): bytes: 1554618  
D/AsyncDownloadFile(  413): new download seek: 1554618; lengthFile: 2000000  
D/AsyncDownloadFile(  413): header fields: {p3p=[policyref="http://info.yahoo.co
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA PO
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-mo
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[445382], age=[0], server
=[YTS/1.17.13], accept-ranges=[bytes], date=[Sat, 07 Aug 2010 04:55:39 GMT], con
tent-range=[bytes 1554618-1999999/2000000]}  
D/AsyncDownloadFile(  413): bytes: 1555642  
D/AsyncDownloadFile(  413): bytes: 1556666  
D/AsyncDownloadFile(  413): bytes: 1557094  
D/AsyncDownloadFile(  413): bytes: 1558118  

...

@12:57:20 interrupted  
D/AsyncDownloadFile(  413): bytes: 1941834  
D/AsyncDownloadFile(  413): bytes: 1942858  
D/AsyncDownloadFile(  413): bytes: 1943882  
D/AsyncDownloadFile(  413): bytes: 1943994  
D/AsyncDownloadFile(  413): new download seek: 1943994; lengthFile: 2000000  
D/AsyncDownloadFile(  413): header fields: {p3p=[policyref="http://info.yahoo.co
m/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi
 OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA PO
L HEA PRE LOC GOV"], content-type=[application/zip], connection=[close], last-mo
dified=[Fri, 06 Aug 2010 14:47:50 GMT], content-length=[56006], age=[0], server=
[YTS/1.17.13], accept-ranges=[bytes], date=[Sat, 07 Aug 2010 04:57:15 GMT], cont
ent-range=[bytes 1943994-1999999/2000000]}  
D/dalvikvm(  413): GC_FOR_MALLOC freed 13617 objects / 602200 bytes in 165ms  
D/AsyncDownloadFile(  413): bytes: 1945018  
D/AsyncDownloadFile(  413): bytes: 1946042  
D/AsyncDownloadFile(  413): bytes: 1946470  
D/AsyncDownloadFile(  413): bytes: 1947494  

...

@12:58:10 finished  
D/AsyncDownloadFile(  413): bytes: 1996103  
D/AsyncDownloadFile(  413): bytes: 1997127  
D/AsyncDownloadFile(  413): bytes: 1997563  
D/AsyncDownloadFile(  413): bytes: 1998587  
D/AsyncDownloadFile(  413): bytes: 1999023  
D/onPostExecute(  413): downloaded: unsuccessful


推荐答案

恢复下载，您不仅需要发送 范围 请求标头，还有 If-Range 请求头，它应包含唯一的文件标识符或文件修改时间戳。

To resume a download, you need to send not only the Range request header, but also the If-Range request header which should contain either the unique file identifier or the file modification timestamp.

如果服务器返回一个 ETag 响应头在初始下载，那么你应该使用它在 If-Range 后续恢复请求的头。或者如果它返回 Last-Modified 响应标题，那么你应该在 If-Range 请求标题中使用它。

If the server returns an ETag response header on the initial download, then you should use it in the If-Range header of the subsequent resume requests. Or if it returns a Last-Modified response header, then you should use it in the If-Range request header instead.

查看您的日志，服务器发送了一个 Last-Modified 响应头。所以你应该在简历请求的 If-Range 头文件中发回。

Looking at your logs, the server has sent a Last-Modified response header. So you should send it back along in an If-Range header of the resume request.

// Initial download.
String lastModified = connection.getHeaderField("Last-Modified");

// ...

// Resume download.
connection.setRequestProperty("If-Range", lastModified);

服务器将使用此信息来验证是否要求完全相同的文件。

The server will use this information to verify if you're requesting exactly the same file.

这篇关于如何恢复中断的下载 - 第2部分的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！

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