title: how to resume an interrupted download - part 2
body: <p>This is a continuation of <a href="https://stackoverflow.com/questions/3411480/how-to-resume-an-interrupted-download/3411558#3411558">my previous question</a> 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.</p>
  
  <p>I tried the suggestion by <a href="https://stackoverflow.com/users/306602/naikus">naikus</a> (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.)</p>
  
  <p><b>Is there some other http connection property request I should be making to get the Yahoo! server to actually skip to the file offset specified in the header's byte range?</b>  Here's the code and what it dumps:</p>
  
  <pre><code>         // Setup connection.
           URL url = new URL(strUrl[0]);
           URLConnection connection = url.openConnection();
           downloaded = Integer.parseInt(strUrl[3]);
           if (downloaded &gt; 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&lt;String, List&lt;String&gt;&gt; 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 &gt; 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 &gt;= 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();
  </code></pre>
  
  <hr>
  
  <p>dump:  </p>
  
  <pre><code>@ 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  
  
  - - -  
  </code></pre>
  
  <p>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:</p>
  
  <pre><code>            // 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());
  </code></pre>
  
  <hr>
  
  <p>dump:  </p>
  
  <pre><code>@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  
  </code></pre>