Comparison with Alternatives

Building a scalable OCPP Central System or Station client involves navigating multiple architectural trade-offs: memory management, connection tracking, horizontal clustering, and protocol compliance.

ocpp-ws-io isn't the only option. Here's how it differs from other popular Node.js OCPP libraries.

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1. @voltbras/ts-ocpp

@voltbras/ts-ocpp is a popular, strongly typed, TypeScript-first OCPP library.

Where they excel:

• Excellent out-of-the-box TypeScript types.
• Simple class-based OOP API design.
• Larger community and more mature adoption.

What ocpp-ws-io addresses differently:

• Clustering: ts-ocpp stores connections in memory class instances. When scaling across multiple pods or load balancer nodes, you need to build your own message brokering. ocpp-ws-io provides a RedisAdapter (Stream + Pub/Sub) for unicast routing across nodes.
• Rate Limiting: ocpp-ws-io includes socket-level token bucket rate limiters that can drop high-frequency messages (e.g., MeterValues) before parsing, while allowing critical messages through.
• Path-based Routing: ts-ocpp uses class-based handlers. ocpp-ws-io offers Express-style path routing (OCPPRouter) with scoped middleware and authentication per route.

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2. ocpp-eliftech

ocpp-eliftech is one of the oldest JavaScript/Node packages for OCPP implementation.

Where they excel:

• Long track record — it has been used in production for years.
• Complete implementation of OCPP 1.6-J.
• Minimal and unopinionated design.

What ocpp-ws-io addresses differently:

• Modern TypeScript: ocpp-eliftech relies on older Promise patterns and prototypical inheritance. ocpp-ws-io uses TypeScript async/await and provides auto-generated types for all OCPP methods.
• Schema Validation: ocpp-ws-io implements runtime JSON schema validation using AJV, mapping violations to OCPP-J error codes (e.g., FormatViolation vs PropertyConstraintViolation).
• Idempotency Keys: To prevent duplicate processing on network retries, ocpp-ws-io supports deterministic message IDs (idempotencyKey) on call().
• Observability: ocpp-ws-io provides built-in Prometheus metrics (/metrics) and health endpoints (/health).

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3. rpc-websockets

While not an OCPP library, many teams pipe raw WebSocket JSON-RPC through rpc-websockets and build OCPP logic on top.

Where they excel:

• Lightweight and protocol-agnostic JSON-RPC execution.
• No OCPP-specific constraints imposed on the developer.

What ocpp-ws-io addresses differently:

• OCPP Awareness: rpc-websockets doesn't understand CallError (Type [4]) or how OCPP error payloads differ from generic JSON-RPC. With ocpp-ws-io, OCPP-J framing (Call, CallResult, CallError) is handled natively.
• Subprotocol Negotiation: ocpp-ws-io manages ocpp1.6 vs ocpp2.0.1 subprotocol negotiation at the HTTP upgrade layer and routes calls into version-typed handlers.
• Spec Compliance: Generic RPC libraries allow fire-and-forget (noReply: true). OCPP requires every message to be correlated and tracked. ocpp-ws-io enforces this while providing NOREPLY as an explicit opt-out.

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4. ocpp-rpc

ocpp-rpc is another widely used OCPP JSON-RPC library for Node.js.

Where they excel:

• Strict validation matching the official OCPP JSON schemas.
• Clean separation between CSMS and Charge Point roles.

What ocpp-ws-io addresses differently:

• WebSocket Routing: Both libraries use the ws library directly. ocpp-ws-io adds Express-style path routing (OCPPRouter) at the WebSocket layer — scoped middleware, authentication, and path matchers (e.g., /api/v2/chargers/*) without requiring an external HTTP framework.
• Clustering: ocpp-rpc leaves multi-node pub/sub bridging to you. ocpp-ws-io provides a RedisAdapter for presence tracking and stream-based unicast routing across nodes.

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5. Scalability Approach

When scaling horizontally, the architecture of your WebSocket library matters. Here is how ocpp-ws-io approaches common scaling concerns.

Horizontal Scalability

Throughput Design

• Selective validation bypass: High-frequency messages like Heartbeat can skip JSON schema validation via strictModeMethods, reducing CPU overhead for trusted traffic.
• Redis pipeline batching: broadcastBatch() groups unicast commands per target node and dispatches them in a single Redis.pipeline() call, collapsing N individual round-trips into one per node.

Resource Management

• Session TTLs: Dead connections are evicted after a configurable sessionTtlMs rather than being immediately dropped, preserving state across temporary disconnects.
• Socket-level rate limiting: Token bucket rate limiters operate at the transport layer, dropping traffic before payload parsing.
• Built-in observability: healthEndpoint: true exposes /health and Prometheus /metrics on the native HTTP server.

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When to Use What

ocpp-ws-io is an open-source tool built to solve specific infrastructure problems. If those problems aren't yours, the other libraries listed here are excellent choices.