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"""Helper function for working with Amazon Web Services"""
import re
import time
import hmac
import base64
import hashlib
from urlparse import urlsplit
AMAZON_HEADER_PREFIX = 'x-amz-'
# generates the aws canonical string for the given parameters
def canonical_string(method, path, headers, expires=None):
interesting_headers = {}
for key in headers:
lk = key.lower()
if lk in set(['content-md5', 'content-type', 'date']) \
or lk.startswith(AMAZON_HEADER_PREFIX):
interesting_headers[lk] = headers[key].strip()
# these keys get empty strings if they don't exist
interesting_headers.setdefault('content-type', '')
interesting_headers.setdefault('content-md5', '')
# just in case someone used this. it's not necessary in this lib.
if 'x-amz-date' in interesting_headers:
interesting_headers['date'] = ''
# if you're using expires for query string auth, then it trumps date
# (and x-amz-date)
if expires:
interesting_headers['date'] = str(expires)
sorted_header_keys = interesting_headers.keys()
sorted_header_keys.sort()
buf = "%s\n" % method
for key in sorted_header_keys:
if key.startswith(AMAZON_HEADER_PREFIX):
buf += "%s:%s\n" % (key, interesting_headers[key])
else:
buf += "%s\n" % interesting_headers[key]
# don't include anything after the first ? in the resource...
buf += "%s" % path.split('?')[0]
# ...unless there is an acl or torrent parameter
if re.search("[&?]acl($|=|&)", path):
buf += "?acl"
elif re.search("[&?]logging($|=|&)", path):
buf += "?logging"
elif re.search("[&?]torrent($|=|&)", path):
buf += "?torrent"
elif re.search("[&?]location($|=|&)", path):
buf += "?location"
return buf
def sign_request(req, accesskey, secretkey):
if 'Date' not in req.headers:
req.headers['Date'] = time.strftime("%a, %d %b %Y %H:%M:%S GMT", time.gmtime())
parsed = urlsplit(req.url)
bucket = parsed.hostname.replace('.s3.amazonaws.com','')
key = '%s?%s' % (parsed.path, parsed.query) if parsed.query else parsed.path
fqkey = '/%s%s' % (bucket, key)
c_string = canonical_string(req.method, fqkey, req.headers)
_hmac = hmac.new(secretkey, digestmod=hashlib.sha1)
_hmac.update(c_string)
b64_hmac = base64.encodestring(_hmac.digest()).strip()
req.headers['Authorization'] = "AWS %s:%s" % (accesskey, b64_hmac)
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