I'm back with yet another stupid newbie question.

I wrote a file downloader module (cleverly hidden in a QProgressDialog) that downloads files from the internet. While it works fine on small files, I have discovered that on huge files (e.g., 900 MB) it will often fail to download the entire file. The last 1000 bytes or so will be missing. If I repeat the download four or five times it will eventually get the file, but obviously I am doing something wrong. Perhaps somebody here can spot my error.
The downloader is:

Qt Code: 
  1. #!/usr/bin/env python
  2. # -*- coding: utf-8 -*-
  3. from PyQt4.QtNetwork import *
  4. from PyQt4.QtCore import *
  5. from PyQt4.QtGui import *
  6.  
  7.  
  8. #==========
  9. class UpdateDownloader(QProgressDialog):
  10.     #==========
  11.     def __init__(self, theUpdateNode, updateServer, downloadPath, parent=None):
  12.         QProgressDialog.__init__(self, parent)
  13.  
  14.         self.urlString = "%s/%s" % (updateServer, theUpdateNode.URL)
  15.         self.fileName = QString(downloadPath)
  16.         self.title = theUpdateNode.title
  17.         self.outFile = None
  18.         self.httpGetId = 0
  19.         self.httpRequestAborted = False
  20.         self.http = QHttp(self)
  21.         self.successfulDownload = True
  22.         self.contentLength = 0
  23.  
  24.         self.setCancelButton(None)
  25.         self.http.requestFinished.connect(self.httpRequestFinished)
  26.         self.http.dataReadProgress.connect(self.updateDataReadProgress)
  27.         self.http.responseHeaderReceived.connect(self.readResponseHeader)
  28.  
  29.     #==========
  30.     def httpRequestFinished(self, requestId, error):
  31.         if requestId != self.httpGetId:
  32.             return
  33.  
  34.         filesize = self.outFile.size()
  35.         self.outFile.close()
  36.  
  37.         if error:
  38.             self.outFile.remove()
  39. #            QMessageBox.information(self, self.tr("Download"),
  40. #                    self.tr("Download failed: %1.").arg(self.http.errorString()))
  41.             self.successfulDownload = False
  42.         else:
  43.             if filesize != self.contentLength:
  44. #                QMessageBox.information(self, "Download",
  45. #                        "Download failed: filesize is ", filesize, " should be ", self.contentLength))
  46.                 self.successfulDownload = False
  47.             else:
  48.                 self.successfulDownload = True
  49.  
  50.         self.outFile = None
  51.         self.done(0)
  52.  
  53.     #==========
  54.     def updateDataReadProgress(self, bytesRead, totalBytes):
  55.         self.setMaximum(totalBytes)
  56.         self.setValue(bytesRead)
  57.  
  58.     #==========
  59.     def readResponseHeader(self, responseHeader):
  60.         self.contentLength = responseHeader.contentLength()
  61.         # Check for genuine error conditions.
  62.         if responseHeader.statusCode() not in (200, 300, 301, 302, 303, 307):
  63. #            QMessageBox.information(self, self.tr("Download"),
  64. #                                          self.tr("Download failed: %1.")
  65. #                                          .arg(responseHeader.reasonPhrase()))
  66.             self.http.abort()
  67.             if self.outFile is not None:
  68.                 self.outFile.close()
  69.                 self.outFile.remove()
  70.                 self.outFile = None
  71.             self.successfulDownload = False
  72.             self.done(0)
  73.  
  74.     #==========
  75.     def downloadFile(self):
  76.         url = QUrl(self.urlString)
  77.         if QFile.exists(self.fileName):
  78.             QFile.remove(self.fileName)
  79.  
  80.         self.outFile = QFile(self.fileName)
  81.         if not self.outFile.open(QIODevice.WriteOnly):
  82. #            QMessageBox.information(self, self.tr("Updates"),
  83. #                    self.tr("Unable to save the file %1: %2.").arg(self.fileName).arg(self.outFile.errorString()))
  84.             self.outFile = None
  85.             self.successfulDownload = False
  86.             self.done(0)
  87.             return
  88.  
  89.         if url.scheme().toLower() == 'https':
  90.             mode = QHttp.ConnectionModeHttps
  91.         else:
  92.             mode = QHttp.ConnectionModeHttp
  93.  
  94.         port = url.port()
  95.  
  96.         if port == -1:
  97.             port = 0
  98.  
  99.         self.http.setHost(url.host(), mode, port)
  100.  
  101.         if not url.userName().isEmpty():
  102.             self.http.setUser(url.userName(), url.password())
  103.  
  104.         path = QUrl.toPercentEncoding(url.path(), "!$&'()*+,;=:@/")
  105.         if path.isEmpty():
  106.             path = "/"
  107.         path = QString(path)
  108.         self.httpGetId = self.http.get(path, self.outFile)
  109.  
  110.         self.setWindowTitle(self.tr("Download"))
  111.         self.setLabelText(self.tr("Downloading %1.").arg(self.title))
  112.         self.show()
  113.  
  114.     #==========
  115.     def doDownload(self):
  116.         self.downloadFile()
  117.         self.exec_()
  118.         self.hide()
  119.         return self.successfulDownload
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it is called thusly:
Qt Code: 
  1. from UpdateDownloader import UpdateDownloader
  2.  
  3. updateNode.URL = "archive1.zip"
  4. updateNode.title = "The initial archive file"
  5. downloadPath = "%s/%s" % (self.host.DOWNLOAD_DIR, updateNode.URL)
  6. downloadSuccessful = UpdateDownloader(updateNode, UPDATE_COM, downloadPath).doDownload()
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