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[Launchpad Bug Tracker <1271684@xxxxxxxxxxxxxxxxxx>]

** Branch linked: lp:~barry/ubuntu-system-image/systemimage2.3

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https://bugs.launchpad.net/bugs/1271684

Title:
  File verification uses lots of memory

Status in Ubuntu Download Manager:
  Fix Released
Status in Ubuntu system image (server/client/updater):
  Fix Committed
Status in “ubuntu-download-manager” package in Ubuntu:
  Fix Released

Bug description:
  The file verification after downloading and checking the GPG signature
  of a file needs a lot of memory.

  The code looks like the whole file is read into memory to calculate
  the sha256 hash, using more than 250MB of RAM in my case (while only
  ~100M are free on this ported device). This causes a lot of swapping
  and a few minutes long freeze. In one out of three attempts, system-
  settings closed during the freeze (oom kill?) and I had to restart the
  verification.

  In two places in state.py, hashlib is used like this :
              # Verify the checksums.
              for dst, checksum in checksums:
                  with open(dst, 'rb') as fp:
                      got = hashlib.sha256(fp.read()).hexdigest()
                      [...]

  This could be changed to something like this (completely untested!):
              # Verify the checksums.
              chunk_size = 1024*1024
              for dst, checksum in checksums:
                  hash =  hashlib.sha256()
                  with open(dst, 'rb') as fp:
                      chunk = fp.read(chunk_size)
                      while chunk != '':
                          hash.update(chunk)
                          chunk = fp.read(chunk_size)
                      got = hash.hexdigest()
                      [...]

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