1. Rudimentary Client-Server Message Board Ricky Landry COP5611 – Operating Systems Design Principles University of Central Florida April 16, 2012

2. Fundamental Requirements
Ability to create topics
Ability to create comments associated with a topic
Ability to produce information on the author of a topic or comment
Ability to produce the timestamp of creation and last modification time of a topic or a comment
Ability to remove a topic or comment (only if requested by the author)

3. Critical Design Decisions
Client-Server Architecture
Multi-threaded Server
Stateless
Messaging Protocol
Java Swing Client Front-End (GUI)

4. Message Board Database
Server-side database was written specifically for the application to explore design challenges
Multi-threaded server design required mutually exclusive access to the database to handle concurrency and atomicity concerns
Accomplished through the use of object locks built into the Java language
synchronized(this){ … } wraps database access calls

5. Server Database Design
Singleton-patterned database consists of:
List of MbdbTopic objects, stored as a Hashtable
List of MbdbComment objects, stored as a Hashtable

6. Server Database Design
MbdbTopic object consists of:
topic name
author name
creation time
topic header
deleted state
list of the comment headers of child comments

7. Server Database Design
MbdbComment object consists of:
comment message
author name
creation time
comment header
deleted state
unique identifier of its parent topic

8. Server Database Design
TopicHeader and CommentHeader Objects contain:
Topic/Comment unique identifier
Topic/Comment last update time
Definition of TopicHeaderList and CommentHeaderList containers, respectively

9. Server Design
Used the Java Serialization API for serialized object transfer between server and client.
Listen socket is a Java ServerSocket object
When a connection is made, the new socket connected to the client is handed off to a worker thread spawned specifically for the client

10. Server Design

11. Protocol Design
Defines the following aspects of the client-server model:
Credentials
Topic message data payloads
Comment message data payloads
Message structure
Message types

12. Protocol Design Client-to-Server Message Types: CREATE_TOPIC
CREATE_COMMENT
REMOVE_TOPIC
REMOVE_COMMENT
GET_TOPIC_HEADERS
GET_TOPIC_OBJECT
GET_COMMENT_OBJECT
CREDENTIALS
CLOSING_CONNECTION

13. Protocol Design Server-to-Client Message Types: TOPIC_HEADERS_REPLY
TOPIC_OBJECT_REPLY
COMMENT_OBJECT_REPLY
AUTHETICATION_SUCCESS
AUTHETICATION_FAILURE
INVALID_TOPIC_ID
INVALID_COMMENT_ID
INVALID_REPLY_RECEIVED

14. Client Database Design
The client has its own database that contains the client state
Has four containers:
One containing MbdbTopic objects
One containing MbdbComment objects
One containing the read state for each topic
One containing the read state for each comment
Defines wrappers for Topic/Comment objects and their respective read state

15. Client Database Design

16. Client Controller Design
Responsible for client database management and access
Updates the client database with server data
Provides current (undeleted) client data to the front-end
Responsible for communication with the server
Responsible for managing client credentials

17. Client Front-End Design
Built using the Java Swing API
Provides basic interface to underlying function
Topic Window Mockup
Comment Window Mockup

18. Client Front-End Design

19. Client Front-End Design
Topic Window
Comment Window

20. Questions ?