Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update

Motivation and Context

Enables interoperability with Docker Engine daemons. Adds minimal client for connectivity verification and version retrieval over Unix sockets.

Implementation:

• DockerEngineClient with async/await API using Swift NIO
• Connects to /var/run/docker.sock by default, configurable
• HTTP-over-Unix-socket with simplified response parsing
• Proper error types: socketNotFound, connectionFailed, invalidResponse, requestFailed

API Example:

let client = DockerEngineClient()
let connected = try await client.connect()
let version = try await client.getVersion()

Known Limitations (Documented):

• Simplified HTTP parsing (no chunked encoding support)
• Polling-based reads (~50ms max latency)
• EventLoopGroup per-request overhead
• Suitable for infrequent connectivity checks, not high-throughput

Future enhancements: EventLoopGroup reuse, proper NIO handlers, comprehensive HTTP parsing.

Files:

• Sources/Services/ContainerAPIService/Client/DockerEngineClient.swift (204 lines)
• Tests/ContainerAPIClientTests/DockerEngineClientTests.swift (60 lines)
• Documentation: docker-engine-client-example.md, updates to how-to.md, technical-overview.md

Testing

• Tested locally (requires macOS 15+ with Apple silicon)
• Added/updated tests (unit tests for initialization, failures, errors)
• Added/updated docs (comprehensive examples and limitations)

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