Distributed Message Passing

A publish-subscribe messaging system with a centralized coordinator, built in C++ using TCP sockets. Participants register with the coordinator and can send messages to all other active participants, with support for disconnect/reconnect and message expiration.

Features

• Centralized coordinator: Manages participant registration and message routing
• Publish-subscribe model: Messages sent by any participant are broadcast to all others
• Message expiration (TTL): Messages expire after a configurable time-to-live duration; expired messages are not delivered on reconnect
• Fault tolerance: Participants can disconnect and reconnect, receiving any missed messages that have not yet expired
• Dual-socket architecture: Separate command and message sockets per participant
• Thread pool concurrency: Both coordinator and participants use thread pools for handling concurrent connections and message delivery
• Message logging: Participants log received messages to a local file

Architecture

• coordinator -- Central server that accepts participant connections. Maintains a registry of active participants and their message file descriptors. When a participant sends a message, the coordinator broadcasts it to all other connected participants. Tracks which participants have received each message for reliable reconnect delivery.
• participant -- Connects to the coordinator and provides an interactive command prompt. Opens a listening socket for receiving messages from the coordinator.

Protocol

Participants send #-delimited messages to the coordinator over the command socket: <id>#<command> [args]#<ip>. The coordinator parses these and dispatches to the appropriate handler (register, deregister, disconnect, reconnect, msend).

Building

make        # builds both coordinator and participant
make clean  # removes binaries and build artifacts

Requires a C++ compiler with C++20 support and pthreads.

Usage

1. Start the coordinator:

   ./coordinator config/coordinator.txt

2. In separate terminals, start participants:

   ./participant config/participant1.txt
   ./participant config/participant2.txt

3. On each participant, register with the coordinator:

   participant> register <listen_port>
   

4. Send messages:

   participant> msend Hello everyone
   

5. Other commands:

   • disconnect -- Disconnect from the group (can reconnect later)
   • reconnect <listen_port> -- Rejoin and receive missed non-expired messages
   • deregister -- Permanently leave the group

Configuration Files

Coordinator config (config/coordinator.txt):

<port>
<message_ttl_seconds>

Participant config (config/participant1.txt):

<participant_id>
<log_file_name>
<coordinator_ip> <coordinator_port>