plone.rfc822 1.0b2

RFC822 marshalling for zope.schema fields

Introduction

This package provides primitives for turning content objects described by zope.schema fields into RFC (2)822 style messages, as managed by the Python standard library’s email module.

It consists of:

• A marker interface IPrimaryField which can be used to indicate the primary field of a schema. The primary field will be used as the message body.

• An interface IFieldMarshaler which describes marshalers that convert to and from strings suitable for encoding into an RFC 2822 style message. These are adapters on (context, field), where context is the content object and field is the schema field instance.

• Default implementations of IFieldMarshaler for the standard fields in the zope.schema package.

• Helper methods to construct messages from one or more schemata or a list of fields, and to parse a message and update a context object accordingly.

The helper methods are described by plone.rfc822.interfaces.IMessageAPI, and are importable directly from the plone.rfc822 package:

def constructMessageFromSchema(context, schema, charset='utf-8'):
    """Convenience method which calls ``constructMessage()`` with all the
    fields, in order, of the given schema interface
    """

def constructMessageFromSchemata(context, schemata, charset='utf-8'):
    """Convenience method which calls ``constructMessage()`` with all the
    fields, in order, of all the given schemata (a sequence of schema
    interfaces).
    """

def constructMessage(context, fields, charset='utf-8'):
    """Helper method to construct a message.

    ``context`` is a content object.

    ``fields`` is a sequence of (name, field) pairs for the fields which make
    up the message. This can be obtained from zope.schema.getFieldsInOrder,
    for example.

    ``charset`` is the message charset.

    The message body will be constructed from the primary field, i.e. the
    field which is marked with ``IPrimaryField``. If no such field exists,
    the message will have no body. If multiple fields exist, the message will
    be a multipart message. Otherwise, it will contain a scalar string
    payload.

    A field will be ignored if ``(context, field)`` cannot be multi-adapted
    to ``IFieldMarshaler``, or if the ``marshal()`` method returns None.
    """

def renderMessage(message, mangleFromHeader=False):
    """Render a message to a string
    """

def initializeObjectFromSchema(context, schema, message, defaultCharset='utf-8'):
    """Convenience method which calls ``initializeObject()`` with all the
    fields, in order, of the given schema interface
    """

def initializeObjectFromSchemata(context, schemata, message, defaultCharset='utf-8'):
    """Convenience method which calls ``initializeObject()`` with all the
    fields in order, of all the given schemata (a sequence of schema
    interfaces).
    """

def initializeObject(context, fields, message, defaultCharset='utf-8'):
    """Initialise an object from a message.

    ``context`` is the content object to initialise.

    ``fields`` is a sequence of (name, field) pairs for the fields which make
    up the message. This can be obtained from zope.schema.getFieldsInOrder,
    for example.

    ``message`` is a ``Message`` object.

    ``defaultCharset`` is the default character set to use.

    If the message is a multipart message, the primary fields will be read
    in order.
    """

The message format used adheres to the following rules:

• All non-primary fields are represented as headers. The header name is taken from the field name, and the value is an encoded string as returned by the marshal() method of the appropriate IFieldMarshal multi-adapter.

• If no IFieldMarshaler adapter can be found, the header is ignored.

• Similarly, if no fields are found for a given header when parsing a message, the header is ignored.

• If there is a single primary field, the message has a string payload, which is the marshalled value of the primary field. In this case, the Content-Type header of the message will be obtained from the primary field’s marshaler.

• If there are multiple primary fields, each is encoded into its own message, each with its own Content-Type header. The outer message will have a content type of multipart/mixed and headers for other fields.

• A ValueError error is raised if a message is being parsed which has more or fewer parts than there are primary fields.

• Duplicate field names are allowed, and will be encoded as duplicate headers. When parsing a message, there needs to be one field per header. That is, if a message contains two headers with the name ‘foo’, the list of field name/ instance pairs passed to the initializeObject() method should contain two pairs with the name ‘foo’. The first field will be used for the first header value, the second field will be used for the second header value. If a third ‘foo’ header appears, it will be ignored.

• Since message headers are always lowercase, field names will be matched case-insensitively when parsing a message.

Supermodel handler

If plone.supermodel is installed, this package will register a namespace handler for the marshal namespace, with the URI http://namespaces.plone.org/supermodel/marshal. This can be used to mark a field as the primary field:

<model xmlns="http://namespaces.plone.org/supermodel/schema"
       xmlns:marshal="http://namespaces.plone.org/supermodel/marshal">
    <schema>
        <field type="zope.schema.Text" name="test" marshal:primary="true">
            <title>Test field</title>
        </field>
    </schema>
</model>

plone.supermodel may be installed as a dependency using the extra [supermodel], but this is probably only useful for running the tests. If the package is not installed, the handler will not be ignored.

Changelog

1.0b2 (2011-02-11)

• Add IPrimaryFieldInfo to look up primary field information on a content item.

1.0b1 (2009-10-08)

• Initial release

Message construction and parsing

This package contains helper methods to construct an RFC 2822 style message from a list of schema fields, and to parse a message and initialise an object based on its headers and body payload.

Before we begin, let’s load the default field marshalers and configure annotations, which we will use later in this test.

>>> configuration = """\
... <configure
...      xmlns="http://namespaces.zope.org/zope"
...      i18n_domain="plone.rfc822.tests">
...
...     <include package="zope.component" file="meta.zcml" />
...     <include package="zope.annotation" />
...
...     <include package="plone.rfc822" />
...
... </configure>
... """

>>> from StringIO import StringIO
>>> from zope.configuration import xmlconfig
>>> xmlconfig.xmlconfig(StringIO(configuration))

The primary field

The message body is assumed to originate from a “primary” field, which is indicated via a marker interface.

To illustrate the pattern, consider the following schema interface:

>>> from zope.interface import Interface, alsoProvides
>>> from plone.rfc822.interfaces import IPrimaryField
>>> from zope import schema

>>> class ITestContent(Interface):
...
...     title = schema.TextLine(title=u"Title")
...     description = schema.Text(title=u"Description")
...     body = schema.Text(title=u"Body text")
...     emptyfield = schema.TextLine(title=u"Empty field", missing_value=u'missing')

The primary field instance is marked like this:

>>> alsoProvides(ITestContent['body'], IPrimaryField)

Constructing a message

Let’s now say we have an instance providing this interface, which we want to marshal to a message.

>>> from zope.interface import implements
>>> class TestContent(object):
...     implements(ITestContent)
...     title = u""
...     description = u""
...     body = u""
...     emptyfield = None

>>> content = TestContent()
>>> content.title = u"Test title"
>>> content.description = u"""Test description
... with a newline"""
>>> content.body = u"<p>Test body</p>"

We could create a message form this instance and schema like this:

>>> from plone.rfc822 import constructMessageFromSchema
>>> msg = constructMessageFromSchema(content, ITestContent)

The output looks like this:

>>> from plone.rfc822 import renderMessage
>>> print renderMessage(msg)
title: Test title
description: =?utf-8?q?Test_description=0D=0Awith_a_newline?=
emptyfield:
Content-Type: text/plain; charset="utf-8"
<BLANKLINE>
<p>Test body</p>

Notice how the non-ASCII header values are UTF-8 encoded. The encoding algorithm is clever enough to only encode the value if it is necessary, leaving more readable field values otherwise.

The body here is of the default message type:

>>> msg.get_default_type()
'text/plain'

This is because none of the default field types manage a content type.

The body is also utf-8 encoded, because the primary field specified this encoding.

If we want to use a different content type, we could set it explicitly:

>>> msg.set_type('text/html')
>>> print renderMessage(msg)
title: Test title
description: =?utf-8?q?Test_description=0D=0Awith_a_newline?=
emptyfield:
MIME-Version: 1.0
Content-Type: text/html; charset="utf-8"
<BLANKLINE>
<p>Test body</p>

Alternatively, if we know that any IText field on an object providing our ITestContent interface always stores HTML, could register a custom IFieldMarshaler adapter which would indicate this to the message constructor. Let’s take a look at that now.

Custom marshalers

The default marshaler can be obtained by multi-adapting the content object and the field instance to IFieldMarshaler:

>>> from zope.component import getMultiAdapter
>>> from plone.rfc822.interfaces import IFieldMarshaler
>>> getMultiAdapter((content, ITestContent['body'],), IFieldMarshaler)
<plone.rfc822.defaultfields.UnicodeValueFieldMarshaler object at ...>

Let’s now create our own marshaler by extending this class and overriding the getContentType():

>>> from plone.rfc822.defaultfields import UnicodeValueFieldMarshaler
>>> from zope.schema.interfaces import IText
>>> from zope.component import adapts

>>> class TestBodyMarshaler(UnicodeValueFieldMarshaler):
...     adapts(ITestContent, IText)
...
...     def getContentType(self):
...         return 'text/html'

Ordinarily, we’d register this with ZCML. For the purpose of the test, we’ll register it using the zope.component API.

>>> from zope.component import provideAdapter
>>> provideAdapter(TestBodyMarshaler)

Hint: If the schema contained multiple text fields, this adapter would apply to all of them. To avoid that, we could either mark the field with a custom marker interface (similary to the way we marked a field with IPrimaryField above), or have the marshaler check the field name.

Let’s now try again:

>>> msg = constructMessageFromSchema(content, ITestContent)
>>> print renderMessage(msg)
title: Test title
description: =?utf-8?q?Test_description=0D=0Awith_a_newline?=
emptyfield:
MIME-Version: 1.0
Content-Type: text/html; charset="utf-8"
<BLANKLINE>
<p>Test body</p>

Notice how the Content-Type has changed.

Consuming a message

A message can be used to initialise an object. The object has to be constructed first:

>>> newContent = TestContent()

We then need to obtain a Message object. The email module contains helper functions for this purpose.

>>> messageBody = """\
... title: Test title
... description: =?utf-8?q?Test_description=0D=0Awith_a_newline?=
... Content-Type: text/html
...
... <p>Test body</p>"""

>>> from email import message_from_string
>>> msg = message_from_string(messageBody)

The message can now be used to initialise the object according to the given schema. This should be the same schema as the one used to construct the message.

>>> from plone.rfc822 import initializeObjectFromSchema
>>> initializeObjectFromSchema(newContent, ITestContent, msg)

>>> newContent.title
u'Test title'
>>> newContent.description
u'Test description\nwith a newline'
>>> newContent.body
u'<p>Test body</p>'

We can also consume messages with a transfer encoding and a charset:

>>> messageBody = """\
... title: =?utf-8?q?Test_title?=
... description: =?utf-8?q?Test_description=0D=0Awith_a_newline?=
... emptyfield:
... Content-Transfer-Encoding: base64
... Content-Type: text/html; charset="utf-8"
... <BLANKLINE>
... PHA+VGVzdCBib2R5PC9wPg==
... <BLANKLINE>"""

>>> msg = message_from_string(messageBody)
>>> msg.get_content_type()
'text/html'
>>> msg.get_content_charset()
'utf-8'

>>> initializeObjectFromSchema(newContent, ITestContent, msg)

>>> newContent.title
u'Test title'
>>> newContent.description
u'Test description\nwith a newline'
>>> newContent.body
u'<p>Test body</p>'

Note: Empty fields will result in the field’s missing_value being used:

>>> newContent.emptyfield
u'missing'

Handling multiple primary fields and duplicate field names

It is possible that our type could have multiple primary fields or even duplicate field names.

For example, consider the following schema interface, intended to be used in an annotation adapter:

>>> class IPersonalDetails(Interface):
...     description = schema.Text(title=u"Personal description")
...     currentAge = schema.Int(title=u"Age", min=0)
...     personalProfile = schema.Text(title=u"Profile")

>>> alsoProvides(IPersonalDetails['personalProfile'], IPrimaryField)

The annotation storage would look like this:

>>> from persistent import Persistent
>>> class PersonalDetailsAnnotation(Persistent):
...     implements(IPersonalDetails)
...     adapts(ITestContent)
...
...     def __init__(self):
...         self.description = None
...         self.currentAge = None
...         self.personalProfile = None

>>> from zope.annotation.factory import factory
>>> provideAdapter(factory(PersonalDetailsAnnotation))

We should now be able to adapt a content instance to IPersonalDetails, provided it is annotatable.

>>> from zope.annotation.interfaces import IAttributeAnnotatable
>>> alsoProvides(content, IAttributeAnnotatable)

>>> personalDetails = IPersonalDetails(content)
>>> personalDetails.description = u"<p>My description</p>"
>>> personalDetails.currentAge = 21
>>> personalDetails.personalProfile = u"<p>My profile</p>"

The default marshalers will attempt to adapt the context to the schema of a given field before getting or setting a value. If we pass multiple schemata (or a combined sequence of fields) to the message constructor, it will handle both duplicate field names (as duplicate headers) and multiple primary fields (as multipart message attachments).

Here are the fields it will see:

>>> from zope.schema import getFieldsInOrder
>>> allFields = getFieldsInOrder(ITestContent) + \
...             getFieldsInOrder(IPersonalDetails)

>>> [f[0] for f in allFields]
['title', 'description', 'body', 'emptyfield', 'description', 'currentAge', 'personalProfile']

>>> [f[0] for f in allFields if IPrimaryField.providedBy(f[1])]
['body', 'personalProfile']

Let’s now construct a message. Since we now have two fields called description, we will get two headers by that name. Since we have two primary fields, we will get a multipart message with two attachments.

>>> from plone.rfc822 import constructMessageFromSchemata
>>> msg = constructMessageFromSchemata(content, (ITestContent, IPersonalDetails,))
>>> msgString = renderMessage(msg)
>>> print msgString
title: Test title
description: =?utf-8?q?Test_description=0D=0Awith_a_newline?=
emptyfield:
description: <p>My description</p>
currentAge: 21
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="===============...=="
<BLANKLINE>
--===============...==
MIME-Version: 1.0
Content-Type: text/html; charset="utf-8"
<BLANKLINE>
<p>Test body</p>
--===============...==
MIME-Version: 1.0
Content-Type: text/html; charset="utf-8"
<BLANKLINE>
<p>My profile</p>
--===============...==--

(Note that we’ve used ellipses here for the doctest to work with the generated boundary string).

Notice how both messages have a MIME type of ‘text/html’ and no charset. That is because of the custom adapter for (ITestContent, IText) which we registered earlier.

We can obviously read this message as well. Note that in this case, the order of fields passed to initializeObject() is important, both to determine which field gets which description header, and to match the two attachments to the two primary fields:

>>> newContent = TestContent()
>>> alsoProvides(newContent, IAttributeAnnotatable)

>>> from plone.rfc822 import initializeObjectFromSchemata
>>> msg = message_from_string(msgString)
>>> initializeObjectFromSchemata(newContent, [ITestContent, IPersonalDetails], msg)

>>> newContent.title
u'Test title'

>>> newContent.description
u'Test description\nwith a newline'

>>> newContent.body
u'<p>Test body</p>'

>>> newPersonalDetails = IPersonalDetails(newContent)
>>> newPersonalDetails.description
u'<p>My description</p>'

>>> newPersonalDetails.currentAge
21

>>> newPersonalDetails.personalProfile
u'<p>My profile</p>'

Alternative ways to deal with multiple schemata

In the example above, we created a single enveloping message with headers corresponding to the fields in both our schemata, and only the primary fields separated out into different attached payloads.

An alternative approach would be to separate each schema out into its own multipart message. To do that, we would simply use the constructMessage() function multiple times.

>>> mainMessage = constructMessageFromSchema(content, ITestContent)
>>> personalDetailsMessage = constructMessageFromSchema(content, IPersonalDetails)

>>> from email.MIMEMultipart import MIMEMultipart
>>> envelope = MIMEMultipart()
>>> envelope.attach(mainMessage)
>>> envelope.attach(personalDetailsMessage)

>>> envelopeString = renderMessage(envelope)
>>> print envelopeString
Content-Type: multipart/mixed; boundary="===============...=="
MIME-Version: 1.0
<BLANKLINE>
--===============...==
title: Test title
description: =?utf-8?q?Test_description=0D=0Awith_a_newline?=
emptyfield:
MIME-Version: 1.0
Content-Type: text/html; charset="utf-8"
<BLANKLINE>
<p>Test body</p>
--===============...==
description: <p>My description</p>
currentAge: 21
MIME-Version: 1.0
Content-Type: text/html; charset="utf-8"
<BLANKLINE>
<p>My profile</p>
--===============...==--

Which approach works best will depend largely on the intended recipient of the message.

Encoding the payload and handling filenames

Finally, let’s consider a more complex example, inspired by the field marshaler in plone.namedfile.

Let’s say we have a value type intended to represent a binary file with a filename and content type:

>>> from zope.interface import Interface, implements
>>> from zope import schema

>>> class IFileValue(Interface):
...     data = schema.Bytes(title=u"Raw data")
...     contentType = schema.ASCIILine(title=u"MIME type")
...     filename = schema.ASCIILine(title=u"Filename")

>>> class FileValue(object):
...     implements(IFileValue)
...     def __init__(self, data, contentType, filename):
...         self.data = data
...         self.contentType = contentType
...         self.filename = filename

Suppose we had a custom field type to represent this:

>>> from zope.schema.interfaces import IObject
>>> class IFileField(IObject):
...     pass

>>> class FileField(schema.Object):
...     implements(IFileField)
...     schema = IFileValue
...     def __init__(self, **kw):
...         if 'schema' in kw:
...             self.schema = kw.pop('schema')
...         super(FileField, self).__init__(schema=self.schema, **kw)

We can register a field marshaler for this field which will do the following:

• Insist that the field is only used as a primary field, since it makes little sense to encode a binary file in a header.

• Save the filename in a Content-Disposition header.

• Be capable of reading the filename again from this header.

• Encode the payload using base64

  >>> from plone.rfc822.interfaces import IFieldMarshaler
  >>> from email.Encoders import encode_base64
  

  >>> from zope.component import adapts
  >>> from plone.rfc822.defaultfields import BaseFieldMarshaler
  

  >>> class FileFieldMarshaler(BaseFieldMarshaler):
  ...     adapts(Interface, IFileField)
  ...
  ...     ascii = False
  ...
  ...     def encode(self, value, charset='utf-8', primary=False):
  ...         if not primary:
  ...             raise ValueError("File field cannot be marshaled as a non-primary field")
  ...         if value is None:
  ...             return None
  ...         return value.data
  ...
  ...     def decode(self, value, message=None, charset='utf-8', contentType=None, primary=False):
  ...         filename = None
  ...         # get the filename from the Content-Disposition header if possible
  ...         if primary and message is not None:
  ...             filename = message.get_filename(None)
  ...         return FileValue(value, contentType, filename)
  ...
  ...     def getContentType(self):
  ...         value = self._query()
  ...         if value is None:
  ...             return None
  ...         return value.contentType
  ...
  ...     def getCharset(self, default='utf-8'):
  ...         return None # this is not text data!
  ...
  ...     def postProcessMessage(self, message):
  ...         value = self._query()
  ...         if value is not None:
  ...             filename = value.filename
  ...             if filename:
  ...                 # Add a new header storing the filename if we have one
  ...                 message.add_header('Content-Disposition', 'attachment', filename=filename)
  ...         # Apply base64 encoding
  ...         encode_base64(message)
  

  >>> from zope.component import provideAdapter
  >>> provideAdapter(FileFieldMarshaler)
  

To illustrate marshaling, let’s create a content object that contains two file fields.

>>> class IFileContent(Interface):
...     file1 = FileField()
...     file2 = FileField()

>>> class FileContent(object):
...     implements(IFileContent)
...     file1 = None
...     file2 = None

>>> fileContent = FileContent()
>>> fileContent.file1 = FileValue('dummy file', 'text/plain', 'dummy1.txt')
>>> fileContent.file2 = FileValue('<html><body>test</body></html>', 'text/html', 'dummy2.html')

At this point, neither of these fields is marked as a primary field. Let’s see what happens when we attempt to construct a message from this schema.

>>> from plone.rfc822 import constructMessageFromSchema
>>> message = constructMessageFromSchema(fileContent, IFileContent)
>>> print renderMessage(message)
<BLANKLINE>
<BLANKLINE>

As expected, we got no message headers and no message body. Let’s now mark one field as primary:

>>> from plone.rfc822.interfaces import IPrimaryField
>>> from zope.interface import alsoProvides
>>> alsoProvides(IFileContent['file1'], IPrimaryField)

>>> message = constructMessageFromSchema(fileContent, IFileContent)
>>> messageBody = renderMessage(message)
>>> print messageBody
MIME-Version: 1.0
Content-Type: text/plain
Content-Disposition: attachment; filename="dummy1.txt"
Content-Transfer-Encoding: base64
<BLANKLINE>
ZHVtbXkgZmlsZQ==

Here, we have a base64 encoded payload, a Content-Disposition header, and a Content-Type header according to the primary field.

We can also reconstruct the object from this message.

>>> from plone.rfc822 import initializeObjectFromSchema
>>> from email import message_from_string

>>> inputMessage = message_from_string(messageBody)
>>> newFileContent = FileContent()
>>> initializeObjectFromSchema(newFileContent, IFileContent, inputMessage)

>>> newFileContent.file1.data
'dummy file'
>>> newFileContent.file1.contentType
'text/plain'
>>> newFileContent.file1.filename
'dummy1.txt'

>>> newFileContent.file2 is None
True

Let’s now show what would happen if we encoded both files in the message. In this case, we should get a multipart document with two payloads.

>>> alsoProvides(IFileContent['file2'], IPrimaryField)
>>> message = constructMessageFromSchema(fileContent, IFileContent)
>>> messageBody = renderMessage(message)
>>> print messageBody # doctest: +ELLIPSIS
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="===============...=="
<BLANKLINE>
--===============...==
MIME-Version: 1.0
Content-Type: text/plain
Content-Disposition: attachment; filename="dummy1.txt"
Content-Transfer-Encoding: base64
<BLANKLINE>
ZHVtbXkgZmlsZQ==
--===============...==
MIME-Version: 1.0
Content-Type: text/html
Content-Disposition: attachment; filename="dummy2.html"
Content-Transfer-Encoding: base64
<BLANKLINE>
PGh0bWw+PGJvZHk+dGVzdDwvYm9keT48L2h0bWw+
--===============...==--

And again, we can reconstruct the object, this time with both fields:

>>> inputMessage = message_from_string(messageBody)
>>> newFileContent = FileContent()
>>> initializeObjectFromSchema(newFileContent, IFileContent, inputMessage)

>>> newFileContent.file1.data
'dummy file'
>>> newFileContent.file1.contentType
'text/plain'
>>> newFileContent.file1.filename
'dummy1.txt'

>>> newFileContent.file2.data
'<html><body>test</body></html>'
>>> newFileContent.file2.contentType
'text/html'
>>> newFileContent.file2.filename
'dummy2.html'