[doc] add attachments documentation

client/src/leap/soledad/client/_document.py

@@ -107,8 +107,9 @@ class IDocumentWithAttachment(Interface):
         Return whether this document's content differs from the contents stored
         in local database.
 
-        :return: Whether this document is dirty or not.
-        :rtype: bool
+        :return: A deferred which fires with True or False, depending on
+                 whether this document is dirty or not.
+        :rtype: Deferred
         """
 
     def upload_attachment(self):

docs/sphinx/.gitignore

+_build

docs/sphinx/Makefile

+# Minimal makefile for Sphinx documentation
+#
+
+# You can set these variables from the command line.
+SPHINXOPTS    =
+SPHINXBUILD   = sphinx-build
+SPHINXPROJ    = Soledad
+SOURCEDIR     = .
+BUILDDIR      = _build
+
+# Put it first so that "make" without argument is like "make help".
+help:
+	@$(SPHINXBUILD) -M help "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
+
+.PHONY: help Makefile
+
+# Catch-all target: route all unknown targets to Sphinx using the new
+# "make mode" option.  $(O) is meant as a shortcut for $(SPHINXOPTS).
+%: Makefile
+	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)

docs/sphinx/attachments.rst

+Document Attachments
+====================
+
+.. contents:: Contents:
+   :local:
+
+The content of a Soledad document is assumed to be JSON. This is particularly
+bad for storing larger amounts of binary data, because:
+
+* the only way to store data in JSON is as unicode string, and this uses more
+  space than needed for binary data storage.
+
+* the process of synchronization of Soledad documents depends on completing the
+  transfer and decryption of the content of all new/updated documents before
+  synchronized documents are available for use.
+
+Document attachments were introduced as a means to store large payloads of
+binary data and have them be synchronized separate from the usual Soledad
+document synchronization process.
+
+Example
+-------
+
+The attachments API is currently available in the `Document` class, and the
+document needs to know about the store to be able to manage attachments. When
+you create a new document with soledad, that document will already know about
+the store that created it, and can put/get/delete an attachment:
+
+.. code-block:: python
+
+    from twisted.internet.defer import inlineCallbacks
+
+    @inlineCallbacks
+    def attachment_example(soledad):
+        doc = yield soledad.create_doc({})
+
+        state = yield doc.get_attachment_state()
+        dirty = yield doc.is_dirty()
+        assert state == AttachmentStates.NONE
+        assert dirty == False
+
+        yield doc.put_attachment(open('hackers.txt'))
+        state = yield doc.get_attachment_state()
+        dirty = yield doc.is_dirty()
+        assert state | AttachmentState.LOCAL
+        assert dirty == True
+
+        yield soledad.put_doc(doc)
+        dirty = yield doc.is_dirty()
+        assert dirty == False
+
+        yield doc.upload_attachment()
+        state = yield doc.get_attachment_state()
+        assert state | AttachmentState.REMOTE
+        assert state == AttachmentState.SYNCED
+
+        fd = yield doc.get_attachment()
+        assert fd.read() == open('hackers.txt').read()
+
+Implementation
+--------------
+
+The current implementation of document attachments store data in a separate
+SQLCipher database in the client (using SQLite's BLOB type) and in the
+filesystem in the server. Encryption of data before it's sent to the server is
+the same used by normal Soledad synchronization process (AES-256 GCM mode).
+
+Document attachment API
+-----------------------
+
+.. autoclass:: leap.soledad.client._document.AttachmentStates
+   :members:
+   :undoc-members:
+
+.. autointerface:: leap.soledad.client._document.IDocumentWithAttachment
+   :members:
+   :undoc-members:

docs/sphinx/conf.py

@@ -36,6 +36,7 @@ extensions = [
     'sphinx.ext.coverage',
     'sphinx.ext.imgmath',
     'sphinx.ext.viewcode',
+    'sphinxcontrib.zopeext.autointerface',
 ]
 
 # Add any paths that contain templates here, relative to this directory.

docs/sphinx/index.rst

@@ -14,6 +14,7 @@ all user's devices that access a LEAP provider.
    :maxdepth: 2
 
    client
+   attachments
    server
 
 Indices and tables

docs/sphinx/requirements.pip

+sphinx
+sphinxcontrib-zopeext