Messaging services

Questions

How should we bounce messages? Silently? Via an auto-generated message?
- On an error, send an error message to the sender's inbox.
How should we handle messages sent to groups rather than individuals? Should the message be broken into individuals messages (after checking for SEND_MESSAGE permission on the group)?

Objects

Name	DBO	Migration	DTO
MessageContent (Immutable after creation)	Primary key: ID Foreign key: CreatedBy (UserGroup) Foreign key: MessageBody (S3 File Handle ID) Etag CreatedOn	Backup via ID Note: Etag is required because MessageStatus is mutable.	Interface ID CreatedBy (principal ID) S3 File Handle ID CreatedOn
MessageToUser (Immutable after creation)	Foreign key: ID (MessageContent) Subject (nullable) Self foreign key: InReplyTo (ID) (nullable) Foreign key: InReplyToRootId Recursive foreign key to primary key	Secondary to MessageContent	Implements MessageContent Subject (string, optional) List of recipient IDs inReplyTo (optional)
MessageRecipient (Immutable after creation)	Foreign key: ID (MessageContent) Foreign key: Recipient ID (UserGroup)	Secondary to MessageContent
MessageStatus	Foreign key: ID (MessageContent) Foreign key: Recipient ID (UserGroup) States: UNREAD, READ, ARCHIVED	Secondary to MessageContent	ID Recipient State
Comment (Immutable after creation)	Foreign key: ID (MessageContent) Target type (Enum ObjectType) Target ID TBD: references to other Comments in the conversation*	Secondary to MessageContent	Implements MessageContent Target type Target ID
CommentVotes	Primary key: Message ID Up votes Down votes Is-comment-inappropriate votes	TBD	ID Up Down
MessagingSettings	Foreign key: User ID (UserGroup) Etag Blob of settings	TBD	ID Notification levels Update to an owned entity Update to some favorite entity Team Message from user Mail to everyone Etc... Message receipt email (if more than one) Auto-mark mail as read if forwarded to email Blacklist of blocked users
MessageBundle			Bundles the MessageToUser and Message Status

'* per Marcel, Comments may have a more complex set of references/relationships than Messages to Users have. Rather than just 'inReplyTo', it might be that one Comment is an 'answer' to another comment which is a question. Further, the multiple answers to a question may have 'previous' references which order them.

Other

Message ID generator
Message delivery will be via worker, i.e. asynchronous (in most cases) with respect to message creation
- Messages to a low number (1) of recipients should be immediately consistent
- Comments should always be immediately consistent
- Proposed RDS implementation
  - Add a migratable table with a single column of message IDs
  - Add a worker that periodically polls the table
  - If the table is not empty, process N rows from the top
  - Delete rows once finished processing
Email mechanism (use Amazon SES)
- Since we've decided to use SES, we should use their REST API rather than their SMTP API
- The Gmail server may still be useful for handling bounced messages

Services

Sort by recipient

Method	URI	underlying query (if any)	Body	Parameters	Return	Description	Permission
GET	/message/inbox	select * from messagecontent c, messagetouser m, messagestatus s where c.ID=m.messageContentID and s.messageContentID=c.ID and s.recipientID=<pid>		Sorting + pagination	Paginated results<MessageBundle>	Gets all messages the authenticated user has received	Authenticated User
GET	/message/outbox	select * from messagecontent c, messagetouser m where c.ID=m.messageContentID and c.createdBy=<pid> TODO: what is the best way to populate the recipients?		Sorting + pagination	Paginated results<Message>	Gets all messages the authenticated user has sent	Authenticated User
POST	/message	n/a	Message	inReplyTo=null (i.e. another Message)	Message	Sends a message. Note, message delivery permission is on a recipient-by-recipient basis, asynchronous to the message creation. Unauthorized delivery may result in silent failure or a bounce message (TBD).	Authenticated User Must be admin to send to AUTH_USERS
POST	/message/check	use existing userGroupDAO query to check recipients.	Message	inReplyTo=null (i.e. another Message)	Boolean ErrorResponse	Checks to see if the message is correctly formatted and that the sender has permission to send to the indicated recipients	Authenticated User
POST	/message/{id}/forward	n/a	RecipientBundle			Forwards a message to other recipients. This is equivalent to getting a (visible) message and POST-ing it to /message	Sender or Receiver
POST	/entity/{id}/comments	n/a	Message		Message	Convenience method for commenting on an entity. The service fills out fields like message ID, thread ID, and recipients, leaving just subject and body for the user.	Authenticated user with SEND_MESSAGE permission on entity
GET	/message/{id}	select * from messagecontent c, messagetouser m where c.ID=m.messageContentID and c.ID=<id>			Message	Gets a specific message	Sender or Receiver
GET	/message/{id}/conversation	TODO		Sorting + pagination	Paginated results<Message>	Gets messages belonging in the same thread as the message ID. The list is filtered according to the user's ID.	Sender or Receiver
GET	/entity/{id}/comments	select * from messagecontent mc, comment c, inreploytoroot r where mc.ID=c.messageContentID and c.TargetType='ENTITY" and c.TargetID=<id>		Sorting + pagination	Paginated results<Message>	Gets message belonging to the thread tied to the entity.	Authenticated user with READ permission on entity
GET	/message/{id}/status	select * from messagestatus where messagstatus.messageContentID=<id>			Message Status	Gets the status of a message	Receiver
PUT	/message/status	n/a	MessageStatus			Marks a message as: READ UNREAD ARCHIVED	Receiver
GET	/message/settings	TODO			MessageSettings	Gets the notification settings of the user	Authenticated User
PUT	/message/settings	TODO	MessageSettings			Changes notification settings	Authenticated User