How to get filename from Content-Disposition in headers

Question

I am downloading a file with Mechanize and in response headers there is a string:

Content-Disposition: attachment; filename=myfilename.txt

Is there a quick standard way to get that filename value? What I have in mind now is this:

filename = f[1]['Content-Disposition'].split('; ')[1].replace('filename=', '')

But it looks like a quick'n'dirty solution.

Answer 1

First get the value of the header by using mechanize, then parse the header using the builtin cgi module.

To demonstrate:

>>> import mechanize
>>> browser = mechanize.Browser()
>>> response = browser.open('http://example.com/your/url')
>>> info = response.info()
>>> header = info.getheader('Content-Disposition')
>>> header
'attachment; filename=myfilename.txt'

The header value can then be parsed:

>>> import cgi               
>>> value, params = cgi.parse_header(header)
>>> value
'attachment'
>>> params
{'filename': 'myfilename.txt'}

params is a simple dict so params['filename'] is what you need. It doesn't matter whether the filename is wrapped in quotes or not.

Answer 2

These regular expressions are based on the grammar from RFC 6266, but modified to accept headers without disposition-type, e.g. Content-Disposition: filename=example.html

i.e. [ disposition-type ";" ] disposition-parm ( ";" disposition-parm )* / disposition-type

It will handle filename parameters with and without quotes, and unquote quoted pairs from values in quotes, e.g. filename="foo\"bar" -> foo"bar

It will handle filename* extended parameters and prefer a filename* extended parameter over a filename parameter regardless of the order they appear in the header

It strips folder name information, e.g. /etc/passwd -> passwd, and it defaults to the basename from the URL path in the absence of a filename parameter (or header, or if the parameter value is empty string)

The token and qdtext regular expressions are based on the grammar from RFC 2616, the mimeCharset and valueChars regular expressions are based on the grammar from RFC 5987, and the language regular expression is based on the grammar from RFC 5646

import re, urllib
from os import path
from urlparse import urlparse

# content-disposition = "Content-Disposition" ":"
#                        disposition-type *( ";" disposition-parm )
# disposition-type    = "inline" | "attachment" | disp-ext-type
#                     ; case-insensitive
# disp-ext-type       = token
# disposition-parm    = filename-parm | disp-ext-parm
# filename-parm       = "filename" "=" value
#                     | "filename*" "=" ext-value
# disp-ext-parm       = token "=" value
#                     | ext-token "=" ext-value
# ext-token           = <the characters in token, followed by "*">

token = '[-!#-\'*+.\dA-Z^-z|~]+'
qdtext='[]-~\t !#-[]'
mimeCharset='[-!#-&+\dA-Z^-z]+'
language='(?:[A-Za-z]{2,3}(?:-[A-Za-z]{3}(?:-[A-Za-z]{3}){,2})?|[A-Za-z]{4,8})(?:-[A-Za-z]{4})?(?:-(?:[A-Za-z]{2}|\d{3}))(?:-(?:[\dA-Za-z]{5,8}|\d[\dA-Za-z]{3}))*(?:-[\dA-WY-Za-wy-z](?:-[\dA-Za-z]{2,8})+)*(?:-[Xx](?:-[\dA-Za-z]{1,8})+)?|[Xx](?:-[\dA-Za-z]{1,8})+|[Ee][Nn]-[Gg][Bb]-[Oo][Ee][Dd]|[Ii]-[Aa][Mm][Ii]|[Ii]-[Bb][Nn][Nn]|[Ii]-[Dd][Ee][Ff][Aa][Uu][Ll][Tt]|[Ii]-[Ee][Nn][Oo][Cc][Hh][Ii][Aa][Nn]|[Ii]-[Hh][Aa][Kk]|[Ii]-[Kk][Ll][Ii][Nn][Gg][Oo][Nn]|[Ii]-[Ll][Uu][Xx]|[Ii]-[Mm][Ii][Nn][Gg][Oo]|[Ii]-[Nn][Aa][Vv][Aa][Jj][Oo]|[Ii]-[Pp][Ww][Nn]|[Ii]-[Tt][Aa][Oo]|[Ii]-[Tt][Aa][Yy]|[Ii]-[Tt][Ss][Uu]|[Ss][Gg][Nn]-[Bb][Ee]-[Ff][Rr]|[Ss][Gg][Nn]-[Bb][Ee]-[Nn][Ll]|[Ss][Gg][Nn]-[Cc][Hh]-[Dd][Ee]'
valueChars = '(?:%[\dA-F][\dA-F]|[-!#$&+.\dA-Z^-z|~])*'
dispositionParm = '[Ff][Ii][Ll][Ee][Nn][Aa][Mm][Ee]\s*=\s*(?:({token})|"((?:{qdtext}|\\\\[\t !-~])*)")|[Ff][Ii][Ll][Ee][Nn][Aa][Mm][Ee]\*\s*=\s*({mimeCharset})\'(?:{language})?\'({valueChars})|{token}\s*=\s*(?:{token}|"(?:{qdtext}|\\\\[\t !-~])*")|{token}\*\s*=\s*{mimeCharset}\'(?:{language})?\'{valueChars}'.format(**locals())

try:
  m = re.match('(?:{token}\s*;\s*)?(?:{dispositionParm})(?:\s*;\s*(?:{dispositionParm}))*|{token}'.format(**locals()), result.headers['Content-Disposition'])

except KeyError:
  name = path.basename(urllib.unquote(urlparse(url).path))

else:
  if not m:
    name = path.basename(urllib.unquote(urlparse(url).path))

  # Many user agent implementations predating this specification do not
  # understand the "filename*" parameter.  Therefore, when both "filename"
  # and "filename*" are present in a single header field value, recipients
  # SHOULD pick "filename*" and ignore "filename"

  elif m.group(8) is not None:
    name = urllib.unquote(m.group(8)).decode(m.group(7))

  elif m.group(4) is not None:
    name = urllib.unquote(m.group(4)).decode(m.group(3))

  elif m.group(6) is not None:
    name = re.sub('\\\\(.)', '\1', m.group(6))

  elif m.group(5) is not None:
    name = m.group(5)

  elif m.group(2) is not None:
    name = re.sub('\\\\(.)', '\1', m.group(2))

  else:
    name = m.group(1)

  # Recipients MUST NOT be able to write into any location other than one to
  # which they are specifically entitled

  if name:
    name = path.basename(name)

  else:
    name = path.basename(urllib.unquote(urlparse(url).path))

Answer 3

I would try something like:

import re
filename = re.findall("filename=(\S+)", f[1]['Content-Disposition'])

This handles quotes and URL escaping on the filenames.