Implementing an ECM Protocol Client Library

Client Library Architecture

ECM Protocol client libraries abstract protocol details, providing idiomatic interfaces for developers. This guide covers implementing a compliant client from the ground up.

Core Components

Transport Layer

Implement pluggable transport:

interface Transport {
  async request(method: string, path: string, body?: any): Promise<Response>;
  async stream(path: string): AsyncIterator<Message>;
  close(): void;
}

class HTTPTransport implements Transport {
  constructor(baseUrl: string, options: HTTPOptions) {...}
  // Implementation...
}

class GRPCTransport implements Transport {
  constructor(endpoint: string, options: GRPCOptions) {...}
  // Implementation...
}

Serialization

Handle ECM message serialization:

class ECMSerializer {
  serialize(context: Context): string {
    return JSON.stringify({
      ecm_version: "1.0",
      payload: context,
      timestamp: new Date().toISOString()
    });
  }
  
  deserialize(data: string): Context {
    const envelope = JSON.parse(data);
    this.validateVersion(envelope.ecm_version);
    return envelope.payload;
  }
}

Context Operations

CRUD Implementation

class ContextClient {
  constructor(transport: Transport) {
    this.transport = transport;
  }
  
  async put(context: Context): Promise<ContextRef> {
    const response = await this.transport.request(
      'POST', '/contexts', context
    );
    return response.body as ContextRef;
  }
  
  async get(id: string): Promise<Context | null> {
    try {
      const response = await this.transport.request(
        'GET', \`/contexts/\${id}\`
      );
      return response.body as Context;
    } catch (error) {
      if (error.status === 404) return null;
      throw error;
    }
  }
  
  async query(filter: ContextFilter): Promise<Context[]> {
    const response = await this.transport.request(
      'POST', '/contexts/query', filter
    );
    return response.body.contexts;
  }
}

Concurrency Control

ETag Handling

async update(id: string, context: Context, etag?: string): Promise<ContextRef> {
  const headers = etag ? { 'If-Match': etag } : {};
  
  try {
    const response = await this.transport.request(
      'PUT', \`/contexts/\${id}\`, context, { headers }
    );
    return response.body;
  } catch (error) {
    if (error.status === 409) {
      throw new ConcurrencyError('Context modified since read');
    }
    throw error;
  }
}

Subscription Support

Real-Time Updates

subscribe(filter: ContextFilter, handler: (event: ContextEvent) => void): Subscription {
  const stream = this.transport.stream(\`/contexts/subscribe?\${encode(filter)}\`);
  
  const subscription = {
    cancel: () => stream.close()
  };
  
  (async () => {
    for await (const message of stream) {
      handler(this.serializer.deserialize(message));
    }
  })();
  
  return subscription;
}

Error Handling

Error Classification

Map protocol errors to client exceptions: 404 to ContextNotFoundError, 409 to ConcurrencyError, 400 to ValidationError, 401/403 to AuthenticationError/AuthorizationError, 429 to RateLimitError.

Testing

Test client comprehensively:

Unit tests: With mocked transport
Integration tests: Against test server
Protocol compliance: Verify against spec
Error handling: All error scenarios

Conclusion

A well-implemented ECM Protocol client provides clean abstraction over protocol details. Focus on transport pluggability, proper error handling, and comprehensive testing for a production-ready library.

> Implementing an ECM Protocol Client Library