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+To: Notmuch Mail <notmuch@notmuchmail.org>\r
+Message-ID: <20120321090722.6892.24383@brick.lan>\r
+From: Patrick Totzke <patricktotzke@googlemail.com>\r
+User-Agent: alot/0.3\r
+Subject: [RFC][alot] design decisions\r
+Date: Wed, 21 Mar 2012 09:07:22 +0000\r
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+\r
+Hi all,\r
+\r
+with alot 0.3 released, I started thinking seriously about proper=E2=84=A2 =\r
+MIME-display and gnupg\r
+integration for alot. I have to make a few design decisions here and could =\r
+really use\r
+some informed opinions from more experienced UI developers. My question in =\r
+particular is: =\r
+\r
+\r
+ How do I best integrate calls to external mime-handlers into my MVC event =\r
+driven code?\r
+\r
+I mostly know how to implement the individual parts but I struggle coming u=\r
+p with a\r
+consistent way of organizing it all without compromising my current layout.\r
+\r
+\r
+Background\r
+----------\r
+\r
+Model. Alot uses an abstraction layer over notmuch's thread, message and da=\r
+tabase objects\r
+to make them less fragile and generally behave more OOP-y: You can e.g. dir=\r
+ectly call\r
+message.add_tags(['foo','bar']) and so on. This is made possible by a "Data=\r
+baseManager"\r
+that maintains centralized and queued access to the notmuch index and deals=\r
+ with notmuch\r
+exceptions like a locked index [0].\r
+\r
+View/Controler. We use an event-driven interface (urwid.TwistedEventLoop, [=\r
+1]) that\r
+handles user input and maintains a tree of widgets that knows how to render=\r
+ itself.\r
+Twisted offers a neat concept of "Deferreds" to organize call- and errbacks=\r
+ that we\r
+already make use of [2]. Alot has a "MessageWidget" that displays a single=\r
+ message.\r
+\r
+We can easily access and parse email messages into MIME-trees (msg.get_emai=\r
+l() returns a\r
+email.message object; pythons email module allows extensive and RFC complia=\r
+nt dealing with\r
+this [3]).\r
+\r
+We already offer full compatibility with the mailcap protocol to constuct s=\r
+hell commands\r
+of external MIME handlers.\r
+\r
+We know how to call external commands asynchronously; `alot.helper.call_cmd=\r
+_async` does this\r
+and returns a Deferred to which we can connect callback functions.\r
+\r
+\r
+Objective\r
+---------\r
+We want to turn a email.message into nicely rendered text and display it as=\r
+ a widget.\r
+Calls to renderers should be done asynchronously, so that displaying large =\r
+threads\r
+does not block the interface unnecessarily.\r
+The text representation should be stored in a way that can be incrementally=\r
+ updated\r
+for use with message parts decrypted at a later point.\r
+\r
+\r
+Bad Solutions\r
+-------------\r
+\r
+1. Current solution: walk the MIME-tree depth-first, use blocking calls to =\r
+handlers\r
+and create a fixed "body" string that is displayed in the widget.\r
+A silly and hackish solution that we want to get rid of for obvious reasons.\r
+\r
+2. Use a "PartWidget" that is able to display a node in the MIME-tree:\r
+Its constructor creates the representation in a RFC compliant way, that is,\r
+it decodes 'text/plain' parts, stacks other widgets of the same kind on top=\r
+ of each other\r
+for multipart parts or calls external renderer to get a text representation.\r
+\r
+Cons:\r
+ * widgets should not be clever and contain/construct any kind of additiona=\r
+l info\r
+ * its hard to update these widgets when a part gets decrypted; =\r
+\r
+ * decrypted parts are not available outside the displaying widget, widgets=\r
+ get\r
+ replaced completely when one rebuilds the buffer (refresh cmd)\r
+Pros:\r
+ * we can use Deferreds relatively painlessly in the ui (as opposed to the =\r
+db-wrapper)\r
+\r
+3. Accumulate rendered text in a tree structure *inside* message-objects an=\r
+d let that\r
+massage update the widget that displays it. One could let the widget regist=\r
+er\r
+some update-callback with the widget that rebuilds the widgets content.\r
+These callbacks are called after the external handler has finished and the =\r
+message-\r
+internal text-representation has been updated.\r
+\r
+Pros: =\r
+\r
+ * rendered text/decrypted message parts end up in the message and are avai=\r
+lable to process\r
+ and redisplay at will\r
+Cons:\r
+ * the calls to MIME-handlers are dealt with as Deferreds which depend on t=\r
+he twisted event\r
+ loop and indirectly on urwid. This is exactly the kind of tight coupling=\r
+ I'm trying to avoid:\r
+ Messages should be independent of the interface.\r
+ * Messages with multiple externally rendered parts will rebuild their widg=\r
+ets more than once\r
+ * references to old widgets (replaced e.g. after a buffer rebuild) will be=\r
+ kept, which keeps\r
+ them from being garbage-collected\r
+\r
+I'm surely missing an easy and elegant solution here.\r
+Any pointers or comments are much appreciated.\r
+Thanks,\r
+/p\r
+\r
+\r
+[0]: http://alot.readthedocs.org/en/latest/api/database.html\r
+[1]: http://excess.org/urwid/\r
+[2]: http://twistedmatrix.com/documents/current/core/howto/defer.html\r
+[3]: http://docs.python.org/library/email\r
projects / notmuch-archives.git / commitdiff