alknet/docs/architecture/overview.md

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Alknet Overview

What Alknet Is

Alknet is a self-hostable networking toolkit built on QUIC+TLS with ALPN-based protocol dispatch. A single endpoint accepts connections on one port, and the ALPN string negotiated during the TLS handshake routes each connection to the correct protocol handler. Every service — SSH, SFTP, Git, HTTP, DNS, messaging, RPC — is an ALPN on a shared endpoint.

This is the core insight: a service IS an ALPN. One endpoint, one port, many protocols — dispatched by the TLS handshake, not by application-level peeking or separate listeners.

Why ALPN Dispatch

The previous architecture used a three-layer model (StreamInterface/MessageInterface, ListenerConfig, OperationEnv) that required separate listener types, application-level protocol detection via byte-peeking, and complex dispatch paths. ALPN negotiation eliminates all of this:

• Protocol detection happens at the TLS layer — no byte-peeking
• A single endpoint replaces multiple listener types
• Adding a protocol is registering an ALPN string
• Each handler owns its entire wire format

See ADR-001 for the full rationale.

Crate Graph

alknet-vault (standalone, no alknet-core dependency)
│
alknet-core
│   ├── ProtocolHandler trait
│   ├── ALPN router / endpoint
│   ├── BiStream trait, Connection type
│   ├── AuthContext, IdentityProvider
│   └── StaticConfig, DynamicConfig (ArcSwap)
│
├── alknet-ssh        (depends on alknet-core, russh)
├── alknet-call       (depends on alknet-core, irpc)
│   ├── CallAdapter (server: ProtocolHandler for alknet/call)
│   ├── Call client (send/receive over QUIC)
│   ├── OperationSpec, OperationRegistry, AccessControl
│   └── Adapter traits (from_*, to_*)
│
├── alknet-agent      (depends on alknet-call)
│   ├── LLM execution loop (forked aisdk, simplified)
│   ├── Tool dispatch via call protocol
│   └── Provider credentials via capabilities (no env vars, no vault on the wire)
│
├── alknet-git        (depends on alknet-core, gix)
├── alknet-sftp       (depends on alknet-core, russh-sftp)
├── alknet-msg        (depends on alknet-core)
├── alknet-http       (depends on alknet-core, axum)
├── alknet-dns        (depends on alknet-core, hickory-proto)
│
├── alknet-napi       (depends on alknet-call, napi-rs)
│   └── Thin NAPI projection of call protocol client to Node.js
│
└── alknet            (CLI binary, depends on all handler crates + alknet-vault)

Dependency rules:

• No handler crate depends on another handler crate
• All handler crates depend on alknet-core
• alknet-vault has zero alknet crate dependencies
• alknet-agent depends on alknet-call (not alknet-core) — it uses the call protocol client for tool dispatch
• alknet-napi depends only on alknet-call — thin NAPI projection, no business logic
• alknet (CLI) is the only crate that depends on all handler crates and alknet-vault
• Rust is the canonical implementation language — TypeScript is a reference/browser adaptation, not a parallel implementation (see ADR-013)

See ADR-003 for the full decomposition rationale.

ProtocolHandler Trait

The central abstraction. Every handler implements one trait:

#[async_trait]
pub trait ProtocolHandler: Send + Sync + 'static {
    fn alpn(&self) -> &'static [u8];
    async fn handle(&self, connection: Connection, auth: &AuthContext) -> Result<(), HandlerError>;
}

• alpn() returns the handler's ALPN identifier (e.g., b"alknet/ssh", b"alknet/call")
• handle() receives a Connection (not a single stream) and an AuthContext (which may be partial — see authentication section), returning HandlerError on failure
• Handlers that need a single stream call connection.accept_bi() once; handlers that multiplex (SSH, call) open/accept streams as needed
• Each handler manages its own wire format

This differs from the original ADR-002 signature which passed BiStream. See ADR-007 for the rationale: handlers like SSH and call need connection-level ownership to manage multiple streams.

See ADR-002 and ADR-007 for the full rationale.

ALPN Registry

ALPN	Handler	Description
alknet/ssh	SshAdapter	SSH-2 handshake, channel multiplexing, SOCKS5, port forwarding
alknet/call	CallAdapter	JSON-RPC via irpc: operations, streaming, pub/sub
alknet/git	GitAdapter	Git smart protocol over QUIC (gix, pkt-line)
alknet/sftp	SftpAdapter	SFTP protocol (russh-sftp core)
alknet/msg	MessageAdapter	E2E encrypted messaging, mixnet
alknet/http	HttpAdapter	axum REST API, dashboard, MCP endpoint
alknet/dns	DnsAdapter	DNS over QUIC/TLS, pkrr service discovery
h3	HttpAdapter (WebTransport upgrade)	Browser-compatible WebTransport, then ALPN upgrade
h2 / http/1.1	HttpAdapter	Standard HTTP for browsers, curl

Note

: alknet/agent is not in the ALPN registry. The agent service is a future consumer that builds on top of alknet-call (it depends on alknet-call, not alknet-core directly — see ADR-003). It uses the call protocol for tool dispatch and exposes agent operations (e.g., /agent/chat) as call-protocol operations in the OperationRegistry, not as a separate ALPN. The agent is a mental model that informed the core architecture (capabilities, scoped env, abort cascade) but is not specced yet — its design will change as it's built out against the implemented core crates.

Note

: alknet/vault is not in the ALPN registry. alknet-vault is a standalone local key vault with no alknet-core dependency. The CLI binary embeds it and accesses it at the assembly layer — unlocking the vault at startup, deriving and decrypting credentials, and injecting them into handler capabilities. The vault is not exposed over the call protocol. No vault operations are registered in the operation registry. See ADR-008 and ADR-014.

Authentication

All handlers resolve identity through the shared IdentityProvider in alknet-core:

pub trait IdentityProvider: Send + Sync + 'static {
    fn resolve_from_fingerprint(&self, fingerprint: &str) -> Option<Identity>;
    fn resolve_from_token(&self, token: &AuthToken) -> Option<Identity>;
}

Each handler extracts credentials differently (SSH key fingerprint, AuthToken, Bearer header) but resolves through the same provider. Auth resolution is hybrid: the endpoint resolves what it can (e.g., TLS client certificate → fingerprint), and the handler resolves what it must (e.g., AuthToken in the first call frame). The AuthContext passed to handle() may be partial — handlers complete authentication inside handle().

See ADR-004 for the full rationale.

Security Model: Secret Material Flow

Authentication (above) handles inbound identity — who is calling me. Secret material flow handles outbound credentials — what secrets a handler uses for its own outbound calls (LLM provider API keys, HTTP service tokens, signing keys). These are orthogonal concerns with different sources and lifetimes:

Axis	Question	Source	Lifetime
Identity (inbound)	Who is the caller?	AuthContext, per-request (TLS cert, auth token)	Per-request
Capabilities (outbound)	What secrets can I use outbound?	Assembly layer, from vault, injected at construction	Handler lifetime

The vault (alknet-vault) holds the master seed and derives keys and decrypts credentials. It is accessed only at the assembly layer — the CLI binary unlocks it at startup, derives/decrypts what each handler needs, and injects the results into handler capabilities. The vault is not exposed over the call protocol. No vault operations are registered in the operation registry. The master seed and derived private keys never cross the network.

This replaces the industry default of environment variables and plaintext config files for storing credentials. There is no std::env::var("API_KEY") path — the only way a handler gets a credential is through a capability, and the only way a capability is populated is through the assembly layer from the vault.

The call protocol carries no secret material — not in request payloads, not in response payloads, not in operation metadata. Operations that need to share public key material use a dedicated operation that returns only the public component.

See ADR-008 and ADR-014 for the full rationale.

Call Protocol

alknet-call uses irpc as its foundation. The wire format is length-prefixed JSON (EventEnvelope framing). Operations are registered in an irpc registry with JSON Schema discovery. The call protocol supports request/response, streaming subscriptions, and pub/sub.

The call protocol's adapter contract (from_openapi, from_mcp, from_call, to_openapi, to_mcp) enables bidirectional composition — operations can be imported from external sources and exported to external protocols. These adapter traits are defined in Rust in alknet-call. The existing TypeScript @alkdev/operations library informed the design and may be adapted for browser use (see ADR-013).

See ADR-005 for the full rationale.

WASM Compatibility

WASM is not an implementation target. It is a design constraint on one-way doors (see ADR-009): core types must not assume tokio or quinn, and protocol parsers that are pure data transformations remain transport-agnostic. The cost of keeping this door open is low (trait vs concrete type, abstracted I/O); the cost of closing it is irreversibly high. The browser path is through a JavaScript SDK adapted from the existing TypeScript @alkdev/operations library, speaking the EventEnvelope wire format over WebTransport streams — not through Rust-to-WASM compilation of the full stack (see ADR-013). Specific WASM targeting decisions are deferred to individual crate specs. See OQ-09.

Shared Types

The following types live in alknet-core and are used across handler crates:

Type	Purpose
ProtocolHandler	The trait every handler implements
Connection	QUIC connection (or mock) — handlers open/accept streams on it
BiStream	Trait: AsyncRead + AsyncWrite + Send + Unpin — bidirectional byte stream
AuthContext	Resolved identity for a connection (may be partial)
Identity	Authenticated peer identity (inbound)
IdentityProvider	Trait for resolving credentials to identity
AuthToken	Opaque authentication token
Capabilities	Outbound credentials injected by the assembly layer (non-serializable, zeroized)
Visibility	Operation visibility — External (wire-callable) or Internal (composition-only)
StaticConfig	Immutable configuration loaded at startup
DynamicConfig	Hot-reloadable configuration (ArcSwap)
ConfigReloadHandle	Handle for triggering config reloads

Design Principles

One-Way and Two-Way Doors

Not all decisions carry the same reversal cost. One-way door decisions (BiStream type, crate independence, secret material flow) require ADRs and possibly POCs before commitment. Two-way door decisions (static vs dynamic registration, single vs multi-transport) can be decided during implementation — start simple, add complexity when needed. WASM compatibility is a design constraint within this framework, not a separate principle: decisions that would permanently close the WASM door require explicit justification. See ADR-009.

One ALPN, One Connection, One Handler

Each ALPN gets its own QUIC connection. The handler owns the entire connection lifecycle. Handlers that need multiple streams (SSH, call) call connection.accept_bi() or connection.open_bi() as needed. There is no multiplexing layer between connections.

Handler Independence

No handler crate depends on another handler crate. Cross-handler communication goes through the call protocol (alknet/call) or through alknet-core's endpoint. The only crate that depends on all handlers is the CLI binary.

Design Decisions

All design decisions are documented as ADRs in decisions/.

ADR	Decision	Summary
001	ALPN-Based Protocol Dispatch	Single endpoint, ALPN negotiation routes to handlers
002	ProtocolHandler Trait	One trait replaces StreamInterface/MessageInterface
003	Crate Decomposition	One crate per protocol handler, core provides shared infra
004	Auth as Shared Core	IdentityProvider in core, handlers extract credentials
005	irpc as Call Protocol Foundation	Call protocol uses irpc for registry, framing, dispatch
006	ALPN String Convention and Connection Model	alknet/ prefix, one ALPN per connection
007	BiStream Type Definition	BiStream is a trait, handlers receive Connection not BiStream
008	Vault Integration Point	CLI-embedded, vault is a capability source accessed at assembly time
009	One-Way Door Decision Framework	Classify decisions by reversal cost; one-way doors need ADRs
010	ALPN Router and Endpoint	HandlerRegistry, accept loop, static registration
011	AuthContext Structure and Resolution Flow	AuthContext fields, hybrid resolution
012	Call Protocol Stream Model	Bidirectional streams, EventEnvelope, ID-based correlation
013	Rust as Canonical Implementation Language	Rust canonical, TypeScript reference adaptation
014	Secret Material Flow and Capability Injection	Capabilities carry outbound credentials; call protocol carries no secret material
015	Privilege Model and Authority Context	internal = authority switch not ACL skip; External/Internal visibility; handler identity + scoped env
016	Abort Cascade for Nested Calls	call.aborted cascades to descendants; default abort-dependents, continue-running opt-in
017	Call Protocol Client and Adapter Contract	CallClient opens connections; from_call imports remote ops; connection direction independent of call direction
018	Vault as Standalone Crate	Zero alknet crate dependencies; vault defines own types and errors
019	Vault Assembly-Layer-Only Access	The assembly layer (CLI binary) is the sole direct caller; handlers never hold a vault reference
020	HD Derivation for Encryption Keys	SLIP-0010 derivation from seed, not PBKDF2; salt field unused in v2
021	Key Rotation via Version-Indexed Paths	Version-indexed derivation paths; rotate re-encrypts between versions

Open Questions

Open questions are tracked in open-questions.md. Key questions affecting this document:

• OQ-01: BiStream type definition (resolved: trait, Connection parameter — see ADR-007)
• OQ-02: AuthContext resolution timing (resolved: hybrid — see ADR-004)
• OQ-03: ALPN string naming convention (resolved: see ADR-006)
• OQ-04: Dynamic handler registration at runtime vs static at startup (two-way door, defer to implementation)
• OQ-08: Vault integration point (resolved: CLI-embedded, assembly-layer only — see ADR-008, ADR-014, ADR-018, ADR-019)
• OQ-16: Safe vault operations for call protocol exposure (resolved: none for now — see ADR-014)
• OQ-20: Encryption key derivation (resolved: HD derivation, not PBKDF2 — see ADR-020)
• OQ-21: Remote vault administration (deferred: network unlock not supported — see ADR-019)
• OQ-22: Key rotation (resolved: version-indexed paths, rotate method — see ADR-021)

Failure Modes

Failure	Behavior
ALPN negotiation fails (no intersection)	TLS handshake fails — correct behavior, the client and server have no protocol in common
Handler handle() returns HandlerError	Endpoint logs the error, closes the QUIC stream. Other streams on the same connection are unaffected
Handler panics	The handler's task is caught by tokio's panic handling. The stream is closed. Other streams and connections are unaffected
IdentityProvider returns None	AuthContext is partial. If the handler requires authentication and cannot extract credentials from the stream, it closes the stream with an auth error
Config reload fails	ArcSwap<DynamicConfig> keeps the previous valid config. Error is logged. No service interruption
BiStream read/write error	QUIC stream-level error. The handler detects this as an I/O error and returns from handle(). The connection itself may remain open for other streams

What Stays from the Previous Implementation

The reference implementation at /workspace/@alkdev/alknet-main/ contains working code that carries forward, adapted to the new model:

Module	Lines	Destination	Notes
src/auth/*	~1450	alknet-core	Identity, IdentityProvider, keys — simplified per ADR-004
src/config/*	~950	alknet-core	StaticConfig, DynamicConfig, ArcSwap — adapted for ALPN handler config
src/transport/*	~1500	alknet-core	Transport trait, TCP/TLS/iroh — becomes endpoint connection acceptors
src/call/*	~1200	alknet-call	EventEnvelope, registry, framing — becomes ProtocolHandler on alknet/call
src/interface/ssh.rs	982	alknet-ssh	SSH channel handling
src/server/handler.rs	974	alknet-ssh	SSH server handler
src/server/channel_proxy.rs	555	alknet-ssh	Channel proxy
src/server/serve.rs	1526	alknet-core (reference)	Accept loop pattern informs ALPN router, but gets rewritten
src/client/*	~1900	alknet-ssh	SOCKS5 client, connect logic
src/socks5/*	~800	alknet-ssh	SOCKS5 protocol

The old code is reference, not constraint. Understand what it did and why, then implement against the new ProtocolHandler trait and ALPN router.