forked from mirror/django-mailbox
153 lines
5.7 KiB
ReStructuredText
153 lines
5.7 KiB
ReStructuredText
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Message Storage Details
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=======================
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First, it may be helpful to know a little bit about how e-mail messages
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are actually sent across the wire:
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.. code-block:: http
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MIME-Version: 1.0
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Received: by 10.221.0.211 with HTTP; Sun, 20 Jan 2013 12:07:07 -0800 (PST)
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X-Originating-IP: [24.22.122.177]
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Date: Sun, 20 Jan 2013 12:07:07 -0800
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Delivered-To: test@adamcoddington.net
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Message-ID: <CAMdmm+jYCgrxrekAxszmDnBjAytcBym-Ec+uM-+HEtzuKy=M_g@mail.gmail.com>
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Subject: Message With Attachment
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From: Adam Coddington <test@adamcoddington.net>
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To: Adam Coddington <test@adamcoddington.net>
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Content-Type: multipart/mixed; boundary=047d7b33dd729737fe04d3bde348
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--047d7b33dd729737fe04d3bde348
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Content-Type: text/plain; charset=UTF-8
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This message has an attachment.
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--047d7b33dd729737fe04d3bde348
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Content-Type: image/png; name="heart.png"
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Content-Disposition: attachment; filename="heart.png"
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Content-Transfer-Encoding: base64
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X-Attachment-Id: f_hc6mair60
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iVBORw0KGgoAAAANSUhEUgAAAA4AAAAOCAYAAAFoTx1HAAAAzUlEQVQoz32RWxXDIBBEr4NIQEIl
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ICESkFAJkRAJSIgEpEQCEqYfu6QUkn7sCcyDGQiSACKSKCAkGwBJwhDwZQNMEiYAIBdQvk7rfaHf
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AO8NBJwCxTGhtFgTHVNaNaJeWFu44AXEHzKCktc7zZ0vss+bMoHSiM2b9mQoX1eZCgGqnWskY3gi
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XXAAxb8BqFiUgBNY7k49Tu/kV7UKPsefrjEOT9GmghYzrk9V03pjDGYKj3d0c06dKZkpTboRaD9o
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B+1m2m81d2Az948xzgdjLaFe95e83AAAAABJRU5ErkJggg==
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--047d7b33dd729737fe04d3bde348--
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Messages are grouped into multiple message payload parts, and should binary
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attachments exist, they are encoded into text using, generally, ``base64`` or
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``quoted-printable`` encodings.
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Earlier versions of this library would preserve the above text verbatim in the
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database, but neither of the above encodings are very efficient methods of
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storing binary data, and databases aren't really ideal for storing large
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chunks of binary data anyway.
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Modern versions of this library (>=2.1) will walk through the original message,
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write ``models.MessageAttachment`` records for each non-text attachment,
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and alter the message body removing the original payload component, but writing
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a custom header providing the library enough information to re-build the
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message in the event that one needs a python ``email.message.Message`` object.
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.. code-block:: http
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MIME-Version: 1.0
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Received: by 10.221.0.211 with HTTP; Sun, 20 Jan 2013 12:07:07 -0800 (PST)
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X-Originating-IP: [24.22.122.177]
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Date: Sun, 20 Jan 2013 12:07:07 -0800
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Delivered-To: test@adamcoddington.net
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Message-ID: <CAMdmm+jYCgrxrekAxszmDnBjAytcBym-Ec+uM-+HEtzuKy=M_g@mail.gmail.com>
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Subject: Message With Attachment
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From: Adam Coddington <test@adamcoddington.net>
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To: Adam Coddington <test@adamcoddington.net>
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Content-Type: multipart/mixed; boundary=047d7b33dd729737fe04d3bde348
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--047d7b33dd729737fe04d3bde348
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Content-Type: text/plain; charset=UTF-8
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This message has an attachment.
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--047d7b33dd729737fe04d3bde348
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X-Django-Mailbox-Interpolate-Attachment: 1308
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--047d7b33dd729737fe04d3bde348--
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The above payload is what would continue to be stored in the database.
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Although in this constructed example, this reduces the message's size only
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marginally, in most instances, attached files are much larger than the
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attachment shown here.
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.. note::
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Email message bodies are ``base-64`` encoded when stored in the database.
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Although the attachment is no longer preserved in the message body above,
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and only the ``X-Django-Mailbox-Interpolate-Attachment: 1308`` header remains
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in the place of the original attachment, the attachment was stored in a
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``django_mailbox.MesageAttachment`` record:
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.. list-table::
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:header-rows: 1
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* - Field
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- Value
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- Description
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* - Primary Key
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- ``1308``
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- Uniquely generated for each attachment.
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* - Headers
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- ``Content-Type: image/png; name="heart.png"
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Content-Disposition: attachment; filename="heart.png"
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Content-Transfer-Encoding: base64
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X-Attachment-Id: f_hc6mair60``
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- Raw headers from the actual message's payload part.
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* - File
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- ``(binary file object)``
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- References a stored-on-disk binary file corresponding with this
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attachment.
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And were one to run the ``django_mailbox.Message`` instance's
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``get_email_object`` method, the following message will be returned:
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.. code-block:: http
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MIME-Version: 1.0
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Received: by 10.221.0.211 with HTTP; Sun, 20 Jan 2013 12:07:07 -0800 (PST)
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X-Originating-IP: [24.22.122.177]
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Date: Sun, 20 Jan 2013 12:07:07 -0800
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Delivered-To: test@adamcoddington.net
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Message-ID: <CAMdmm+jYCgrxrekAxszmDnBjAytcBym-Ec+uM-+HEtzuKy=M_g@mail.gmail.com>
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Subject: Message With Attachment
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From: Adam Coddington <test@adamcoddington.net>
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To: Adam Coddington <test@adamcoddington.net>
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Content-Type: multipart/mixed; boundary=047d7b33dd729737fe04d3bde348
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--047d7b33dd729737fe04d3bde348
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Content-Type: text/plain; charset=UTF-8
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This message has an attachment.
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--047d7b33dd729737fe04d3bde348
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Content-Type: image/png; name="heart.png"
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Content-Disposition: attachment; filename="heart.png"
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X-Attachment-Id: f_hc6mair60
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Content-Transfer-Encoding: base64
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iVBORw0KGgoAAAANSUhEUgAAAA4AAAAOCAYAAAFoTx1HAAAAzUlEQVQoz32RWxXDIBBEr4NIQEIl
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ICESkFAJkRAJSIgEpEQCEqYfu6QUkn7sCcyDGQiSACKSKCAkGwBJwhDwZQNMEiYAIBdQvk7rfaHf
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AO8NBJwCxTGhtFgTHVNaNaJeWFu44AXEHzKCktc7zZ0vss+bMoHSiM2b9mQoX1eZCgGqnWskY3gi
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XXAAxb8BqFiUgBNY7k49Tu/kV7UKPsefrjEOT9GmghYzrk9V03pjDGYKj3d0c06dKZkpTboRaD9o
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B+1m2m81d2Az948xzgdjLaFe95e83AAAAABJRU5ErkJggg==
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--047d7b33dd729737fe04d3bde348--
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.. note::
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Note that although the above is functionally identical to the originally
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received message, there were changes in the order of headers in rehydrated
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message components, and whitespace changes are also possible (but not
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shown above).
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