Java Networking Protocols and Message Handling in Distributed Systems

Protocol.java

All message type IDs as int constants so both sides agree on tags.

Message IDs in one file

Avoids mismatches; every sender/receiver uses the same numeric tags.

NodeInfo.java

Stores host, port, and a stable id (e.g., host:port) for maps/sets and logs.

NodeInfo equals/hashCode

So it behaves correctly in HashMap/HashSet for membership and lookups.

MessageIO.java

Centralized, bug-free binary IO for primitives and length-prefixed UTF-8 strings.

Centralize binary IO

Consistency and fewer serialization bugs across all messages.

Messages.java

POJO classes for each message + sendX(...) encoders and readMessage(...) decoder.

Single readMessage(...)

One source of truth for parsing; switches on Protocol ID.

Atomic writes in messages

Synchronizing on the DataOutputStream in each sendX(...).

GraphUtils.java

Edges, adjacency builders, and Kruskal MST for overlay/topology tasks.

Separate graph code from node code

Keeps networking classes focused on sockets/threads; makes graph logic testable.

Registry.java

Registers nodes, forms the overlay, sends link weights, initiates tasks, collects summaries.

Registry communication to nodes

Sends control messages (e.g., TaskInitiate, PullTrafficSummary) defined in Messages.

MessagingNode.java

Connects to registry, manages peer sockets, routes/relays data, tracks and reports stats.

Data message contents

Source ID, destination ID, payload, and a hop-by-hop route.

Distinct control and data paths

Control (registry) vs. data (peer-to-peer) traffic have different lifecycles and threading.

Overlay MST purpose

A minimal, loop-free backbone for routing/printing required by the assignment.

Immutable/simple POJOs for messages

Easier to serialize, test, and reason about.

Disagreement on message field order

Decoding breaks—hence strict, centralized encoders/decoder in Messages.

Main benefit of file order

You can compile/run incrementally: protocol → wireformat → graph → registry → nodes.