add amamzon ws helper module

--HG--
extra : convert_revision : svn%3Ab85faa78-f9eb-468e-a121-7cced6da292c%40403

scrapy/trunk/scrapy/contrib/aws.py

@@ -0,0 +1,89 @@
+import re
+import time
+import hmac
+import base64
+import hashlib
+
+
+METADATA_PREFIX = 'x-amz-meta-'
+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 ['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
+    if not interesting_headers.has_key('content-type'):
+        interesting_headers['content-type'] = ''
+    if not interesting_headers.has_key('content-md5'):
+        interesting_headers['content-md5'] = ''
+
+    # just in case someone used this.  it's not necessary in this lib.
+    if interesting_headers.has_key('x-amz-date'):
+        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 merge_meta(headers, metadata):
+    final_headers = headers.copy()
+    for k in metadata.keys():
+        if k.lower() in ['content-md5', 'content-type', 'date']:
+            final_headers[k] = metadata[k]
+        else:
+            final_headers[METADATA_PREFIX + k] = metadata[k]
+
+    return final_headers
+
+def get_aws_metadata(headers):
+    metadata = {}
+    for hkey in headers.keys():
+        if hkey.lower().startswith(METADATA_PREFIX):
+            metadata[hkey[len(METADATA_PREFIX):]] = headers[hkey]
+            del headers[hkey]
+    return metadata
+
+
+def add_aws_auth_header(headers, method, path):
+    if not headers.has_key('Date'):
+        headers['Date'] = time.strftime("%a, %d %b %Y %H:%M:%S GMT", time.gmtime())
+
+    c_string = canonical_string(method, path, headers)
+    _hmac = hmac.new(settings.AWS_SECRET_ACCESS_KEY, digestmod=hashlib.sha1)
+    _hmac.update(c_string)
+    b64_hmac = base64.encodestring(_hmac.digest()).strip()
+    headers['Authorization'] = "AWS %s:%s" % (settings.AWS_ACCESS_KEY_ID, b64_hmac)
+