python类update()的实例源码

def presign(self, req, expires, iso_date=None):
        """
        Presign a request using SigV4 query params. Takes in an HTTP request
        and an expiration time in seconds and returns a URL.

        http://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-query-string-auth.html
        """
        if iso_date is None:
            iso_date = datetime.datetime.utcnow().strftime('%Y%m%dT%H%M%SZ')

        region = self.determine_region_name(req.host)
        service = self.determine_service_name(req.host)

        params = {
            'X-Amz-Algorithm': 'AWS4-HMAC-SHA256',
            'X-Amz-Credential': '%s/%s/%s/%s/aws4_request' % (
                self._provider.access_key,
                iso_date[:8],
                region,
                service
            ),
            'X-Amz-Date': iso_date,
            'X-Amz-Expires': expires,
            'X-Amz-SignedHeaders': 'host'
        }

        if self._provider.security_token:
            params['X-Amz-Security-Token'] = self._provider.security_token

        headers_to_sign = self.headers_to_sign(req)
        l = sorted(['%s' % n.lower().strip() for n in headers_to_sign])
        params['X-Amz-SignedHeaders'] = ';'.join(l)

        req.params.update(params)

        cr = self.canonical_request(req)

        # We need to replace the payload SHA with a constant
        cr = '\n'.join(cr.split('\n')[:-1]) + '\nUNSIGNED-PAYLOAD'

        # Date header is expected for string_to_sign, but unused otherwise
        req.headers['X-Amz-Date'] = iso_date

        sts = self.string_to_sign(req, cr)
        signature = self.signature(req, sts)

        # Add signature to params now that we have it
        req.params['X-Amz-Signature'] = signature

        return 'https://%s%s?%s' % (req.host, req.path,
                                    urllib.parse.urlencode(req.params))