From 6fb48dbd1fd0c5125edaa176d01ab38628028244 Mon Sep 17 00:00:00 2001
From: akwizgran <michael@briarproject.org>
Date: Thu, 22 Mar 2018 13:51:50 +0000
Subject: [PATCH] akwizgran created page: Blog Sharing Client

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 Blog-Sharing-Client.md | 53 ++++++++++++++++++++++++++++++++++++++++++
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 create mode 100644 Blog-Sharing-Client.md

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+The blog sharing client is a [BSP client](BSP) that allows users to share blogs with their contacts, who may accept or decline the invitations.
+
+### Group identifiers
+
+The client's identifier is `org.briarproject.briar.blog.sharing`.
+
+The client uses a separate group for each pair of contacts. The [group descriptor](BSP#group-identifiers) is a [BDF list](BDF) containing the unique IDs of the contacts' identities, sorted in ascending order as byte strings.
+
+### Message types
+
+The sharing protocol uses five message types. All communication happens solely between the inviter and the invitee. The messages referring to each forum constitute a session.
+
+**0: INVITE** - Sent by the inviter to the invitee. The message body is a BDF list with four elements: `messageType` (int), `previousMessageId` (unique ID or null), `descriptor` (list), and `message` (string or null).
+
+`previousMessageId` is the ID of the previous message in this session, if any. `descriptor` is the [descriptor of the blog](Blog-Client#group-identifiers) being shared. `message` is an optional message from the inviter to the invitee. The blog ID must be calculated from the descriptor, as it is used by subsequent messages in the session.
+
+The inviter sets the blog's visibility to VISIBLE when sending an invite message.
+
+**1: ACCEPT** - Sent by the invitee to the inviter in response to an invite. The message body is a BDF list with three elements: `messageType` (int), `blogId` (unique ID), and `previousMessageId` (unique ID).
+
+The invitee sets the blog's visibility to SHARED when sending an accept message. The inviter sets the blog's visibility to SHARED when receiving an accept message.
+
+**2: DECLINE** - Sent by the invitee to the inviter in response to an invite. The message body is a BDF list with three elements: `messageType` (int), `blogId` (unique ID), and `previousMessageId` (unique ID).
+
+The inviter sets the blog's visibility to INVISIBLE when receiving a decline message.
+
+**3: LEAVE** - Sent by either party when unsubscribing from the blog, if the blog's visibility is VISIBLE or SHARED. The message body is a BDF list with three elements: `messageType` (int), `blogId` (unique ID), and `previousMessageId` (unique ID).
+
+The sender sets the blog's visibility to INVISIBLE when sending a leave message. The recipient sets the blog's visibility to INVISIBLE when receiving a leave message.
+
+**4: ABORT** - Sent by either party when recieving a message that is valid but unexpected in the current state. The message body is a BDF list with three elements: `messageType` (int), `blogId` (unique ID), and `previousMessageId` (unique ID).
+
+The sender sets the blog's visibility to INVISIBLE when sending an abort message. The recipient sets the blog's visibility to INVISIBLE when receiving an abort message.
+
+### State machine
+
+![state-machine-4](/uploads/373807b51d3ba73d6f49a874b931ef0f/state-machine-4.png)
+
+[state-machine-4.odg](/uploads/4606c2f4b9d7f3c00482bdbf46fec250/state-machine-4.odg)
+
+Aborting from any state returns the session to the START state.
+
+### Validity policy
+
+* A message is valid if it is well-formed.
+
+### Storage policy
+
+* All messages are stored.
+
+### Sharing policy
+
+* All local messages are shared.