Utilities for generating cross-domain policy files¶
Internally, all policy files generated by django-flashpolicies are represented by instances of flashpolicies.policies.Policy, which understands how to handle the various permitted options in policy files and can generate the correct XML. This documentation covers Policy objects and their API, but is not and should not be taken to be documentation on the format and options for cross-domain policy files; Adobe’s cross-domain policy specification is the canonical source for that information.
For most cases, simply instantiating a Policy object with one or more domains will accomplish the desired effect. The property xml_dom will yield an xml.dom.minidom.Document object representing the policy’s XML; for information on working with these objects, consult the documentation for the xml.dom.minidom module in the Python standard library.
There are two similar but different ways to serialize the underlying XML. One is simply to use str() on a Policy instance, like so:
>>> from flashpolicies import policies >>> my_policy = policies.Policy('media.example.com', 'api.example.com') >>> print(str(my_policy)) <?xml version="1.0" ?> <!DOCTYPE cross-domain-policy SYSTEM 'http://www.adobe.com/xml/dtds/cross-domain-policy.dtd'> <cross-domain-policy> <allow-access-from domain="media.example.com"/> <allow-access-from domain="api.example.com"/> </cross-domain-policy>
The other is to call the serialize() method. The difference between these options is:
- str() will, as is required by Python’s semantics, produce a result of type str. Which, on Python 3, is a Unicode string; this means the output is not in any particular encoding, and will omit the encoding declaration of the XML prolog.
- serialize() will, on the other hand, always return a sequence of UTF-8-encoded bytes. This is the type str on Python 2, and the type bytes on Python 3. In accordance with this, the output of serialize() will include an encoding declaration in its XML prolog.
In general, str() should be used to inspect a Policy for debugging or educational purposes, while serialize() should be used any time the output will actually be treated as a policy file (i.e., if writing your own policy-serving view, or if serializing the policy to a file). The built-in serve() view uses serialize().
- class flashpolicies.policies.Policy¶
Wrapper object for creating and manipulating a Flash cross-domain policy.
In the simplest case – specifying one or more domains from which to allow access – simply pass the domains when initializing. For example:
my_policy = Policy('media.example.com', 'api.example.com')
A read-only property which returns an XML representation of this policy, as an xml.dom.minidom.Document object.
Serialize this policy to a UTF-8-encoded byte string (i.e., str on Python 2, bytes on Python 3), suitable for serving over HTTP or writing to a file.
- allow_domain(domain, to_ports=None, secure=True)¶
Allow access for Flash content served from a particular domain.
- domain – The domain from which to allow access. May be either a full domain name (e.g., "example.com") or a wildcard (e.g., "example.com"). Due to serious potential security concerns, it is strongly recommended that you avoid wildcard domain values.
- to_ports – (only for socket policy files) A list of ports the domain will be permitted to access. Each value in the list may be either a port number (e.g., "80"), a range of ports (e.g., "80-120") or the wildcard value "*", which will permit all ports.
- secure – If True, will require the security level of the HTTP protocol for Flash content to match that of this policy file; for example, if the policy file was retrieved via HTTPS, Flash content from domain must also be retrieved via HTTPS. If False, this matching of security levels will be disabled. It is strongly recommended that you not disable the matching of security levels.
- allow_headers(domain, headers, secure=True)¶
Allow Flash content from a particular domain to push data via HTTP headers.
- headers – A list of HTTP header names in which data may be submitted.
Allow access from digitally-signed documents.
Parameters: fingerprint – The fingerprint of the signing key to allow.
The XML resulting from use of this method will include both the key fingerprint and the name of an algorithm used to calculate the fingerprint. At the moment, "sha-1" is the only value defined in the cross-domain policy specification for the fingerprint-algorithm attribute of the certificate element (which is the element produced by this method), and so an argument for this is omitted; if additional algorithms are added to the specification, support will be added in a backwards-compatible fashion (likely through an argument defaulting to SHA-1).
Set metapolicy information (only applicable to master policy files), determining which other policy files may be used on the same domain.
Parameters: permitted – The metapolicy to use. Acceptable values are those listed in the cross-domain policy specification, and are also available as a set of constants defined in this module. Passing an invalid value will raise TypeError.
By default, Flash assumes a default metapolicy of "master-only" (except for socket policies, which assume a default of "all"), so if this is the desired metapolicy (and, for security reasons, it often is), this method does not need to be called.
Note that a metapolicy of "none" forbids all access, even if one or more domains have previously been specified as allowed. As such, setting the metapolicy to "none" will remove all access previously granted by allow_domain() or allow_headers(). Additionally, attempting to grant access via allow_domain() or allow_headers() will, when the metapolicy is "none", raise TypeError.
For ease of working with metapolicies, the following constants are defined, and correspond to the acceptable values for metapolicies as defined in the cross-domain policy specification.
All policy files available on the current domain are permitted. Actual value is the string "all".
Only policy files served from the current domain with an HTTP Content-Type of text/x-cross-domain-policy are permitted. Actual value is the string "by-content-type".
Only policy files served from the current domain as files named crossdomain.xml are permitted. Actual value is the string "by-ftp-filename".
Only the master policy file for this domain – the policy served from the URL /crossdomain.xml – is permitted. Actual value is the string "master-only".
No policy files are permitted, including the master policy file. Actual value is the string "none".
A tuple containing the above constants, for convenient validation of metapolicy values.