alknet/docs/architecture/decisions/003-crate-decomposition.md

ADR-003: Crate Decomposition

Status

Accepted

Context

The previous alknet-core crate was a monolith containing transport, interface, server, client, call, auth, config, socks5, credentials, and HTTP — all in one crate with interdependent modules. This created coupling (interface types depended on auth, server depended on call, everything depended on config) and made it impossible to use individual components independently.

The new ALPN dispatch model eliminates the need for a shared interface layer. Each handler is self-contained — it receives a byte stream and manages its own protocol. This naturally decomposes into separate crates.

Key constraints:

• Protocol crates must depend on alknet-core for auth/identity/config — but not on each other
• alknet-vault is already standalone (no alknet-core dependency) and must remain so (see ADR-008)
• The CLI binary assembles everything — it's the only crate that depends on all handler crates
• Handlers with protocol-agnostic cores (SFTP, call protocol) preserve the WASM door — browser clients can implement the wire format over WebTransport (see ADR-009, ADR-013)
• alknet-call includes the call protocol client and adapter traits, not just the server side — this enables alknet-agent and alknet-napi to use it for remote invocation
• Rust is the canonical implementation language. TypeScript is a reference/browser adaptation, not a parallel implementation (see ADR-013)

Decision

The workspace decomposes into the following crates:

Crate	Responsibility	Depends on
alknet-core	ProtocolHandler trait, ALPN router, endpoint, BiStream, AuthContext, IdentityProvider, config, ArcSwap dynamic config	tokio, quinn, rustls, irpc, iroh (feature-gated, added by ADR-010)
alknet-vault	Local key vault: BIP39/SLIP-0010/AES-GCM key derivation, encryption	(standalone, no alknet-core)
alknet-ssh	SshAdapter (russh, SOCKS5, port forwarding)	alknet-core, russh
alknet-call	CallAdapter (JSON-RPC via irpc, operation registry, pub/sub, access control, call protocol client, adapter traits)	alknet-core, irpc
alknet-agent	Agent service: LLM execution loop (forked aisdk), tool dispatch via call protocol, provider key retrieval via vault	alknet-call
alknet-git	GitAdapter (gix, pkt-line protocol)	alknet-core, gix
alknet-sftp	SftpAdapter (russh-sftp protocol core)	alknet-core, russh-sftp
alknet-msg	MessageAdapter (E2E encryption, mixnet)	alknet-core
alknet-http	HttpAdapter (axum, REST API, MCP endpoint)	alknet-core, axum
alknet-dns	DnsAdapter (hickory-proto, pkarr, service discovery)	alknet-core, hickory-proto
alknet-napi	Node.js native addon — thin NAPI projection of the call protocol client	alknet-call, napi-rs
alknet	CLI binary — registers handlers, starts endpoint	all handler crates, alknet-vault

Dependency flow:

alknet-vault (standalone)
alknet-core ← all handler crates ← alknet (CLI)
alknet-call ← alknet-agent
alknet-call ← alknet-napi

No handler crate depends on another handler crate. Cross-handler communication goes through the call protocol (alknet-call) or through alknet-core's endpoint.

alknet-agent depends on alknet-call (not alknet-core directly) because it uses the call protocol client for tool dispatch and the operation registry for tool registration. It receives LLM provider keys through capabilities injected at the assembly layer (from alknet-vault), never from environment variables and never over the call protocol. See ADR-008 and ADR-014.

alknet-napi is a thin projection layer — it exposes the Rust call protocol client to Node.js via NAPI. It does not contain business logic or adapter implementations. See ADR-013.

Consequences

Positive:

• Each handler can be developed, tested, and versioned independently
• WASM-compatible handlers (sftp, call) don't pull in heavy dependencies (russh, axum)
• alknet-vault remains standalone — no circular dependency risk
• New handlers are added by creating a crate and registering it with the endpoint
• Clean separation of concerns — each crate has one job

Negative:

• More crates to manage in the workspace — workspace Cargo.toml and version coordination
• Shared types (AuthContext, BiStream) must live in alknet-core — if they change, all handlers recompile
• The CLI binary has a large dependency tree (all handlers) — but this is expected for a binary that assembles everything
• Testing cross-handler behavior requires integration tests in the CLI or a test utility crate

References

• Pivot proposal: docs/research/pivot/alpn-service-architecture.md
• ADR-001: ALPN-based protocol dispatch
• ADR-002: ProtocolHandler trait
• ADR-004: Auth as shared core (IdentityProvider)
• ADR-005: irpc as call protocol foundation

Amendments

Amendment 1 (2026-06-29): alknet-call is a protocol-foundation crate

The Decision table lists alknet-call as a handler crate that "depends on alknet-core, irpc." The dependency-flow diagram and the "No handler crate depends on another handler crate" rule were written before alknet-http (which implements from_openapi/from_mcp/to_openapi/ to_mcp and therefore needs alknet-call's OperationSpec, Handler, HandlerRegistration, and OperationAdapter trait) was specced.

Clarification: alknet-call is both a handler crate (it implements ProtocolHandler on ALPN alknet/call) and the protocol-foundation crate that alknet-agent, alknet-napi, and alknet-http consume for the operation registry, adapter contract, and call client. The "no handler crate depends on another handler crate" rule applies to peer handler crates (e.g., alknet-http does not depend on alknet-ssh); alknet-call is a protocol-foundation crate in the same spirit that alknet-core is, just at a different layer (operations/RPC vs. transport/auth/config).

alknet-http depending on alknet-call is "HTTP uses the call protocol types," not "HTTP depends on SSH." This is within the spirit of this ADR's decomposition. The alknet-call → alknet-http edge is recorded in the alknet-http spec (crates/http/overview.md) and in the adapter location map (crates/call/client-and-adapters.md).