I'm working on a Pyramid-based website that uses SQLite for its backend (via
SQLAlchemy). I want to add a link that will allow an user to download a backup
of the SQLite database. Here's what I have so far for the view handler:
> 1 import datetime
> 2 import cStringIO
> 3 import zipfile as Z
> 4 from pyramid.response import Response
> 5 import os
> 6
> 7 def backup(request):
> 8 conn_str = request.registry.settings['sqlalchemy.url']
> 9 i = conn_str.find('///')
> 10 dbpath = conn_str[i+3:]
> 11 dbname = os.path.basename(dbpath)
> 12 dbhead = os.path.splitext(dbname)[0]
> 13
> 14 d = datetime.date.today()
> 15 f = file(dbpath,'rb').read()
> 16
> 17 output = cStringIO.StringIO()
> 18
> 19 zf = Z.ZipFile(output, 'w', Z.ZIP_DEFLATED)
> 20 zf.writestr(dbname, f)
> 21 zf.close()
> 22
> 23 o = output.getvalue()
> 24 output.close()
> 25
> 26 response = Response(
> 27 content_type='application/zip',
> 28 content_disposition='attachment; filename=%s%02d%02d%02d.zip' %
> (dbhead, d.year % 100, d.month, d.day),
> 29 content_encoding='binary',
> 30 content_length=len(o),
> 31 body=o,
> 32 )
> 33 # response.app_iter = output.getvalue()
> 34
> 35 return response
The code delivers a zip file containing the current database. It works but I
have some concerns:
The code in lines 8 and 9 seems like a kludgy way to find the database file
name from the configuration file. Is there a better way to parse SQLAlchemy
connection strings? SQLAlchemy has a method for building connection strings
(sqlalchemy.engine.url.URL) but I couldn't find a parser.
Notice lines 31 (body parameter to Response constructor) and 33 (setting
response.app_iter member). The code works with either (but obviously not both),
but when testing with the local server (paster serve), setting the body
parameter, results in a significantly faster download. The zipped database
file is currently about 167k and downloads instantly with the body parameter,
but takes 4-5 seconds with app_iter. I assume this is because with app_iter,
the file is downloaded in multiple smaller chunks. Is there a limit on the size
of the data that can be sent via the body parameter?
Even though I specify a content_length parameter, when the browser is
downloading the file, it acts like it does not know the total download size.
The status says x bytes of ??? and the progress bar indicates an indeterminate
length. I've observed this with both Firefox and Safari. Is there a way to tell
the browser to total download length so the progress bar fills in properly?
Thanks,
Mark
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