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)
├── 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)
│
└── 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-napi depends only on alknet-call (call protocol client)
• alknet (CLI) is the only crate that depends on all handler crates and alknet-vault

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, pkarr service discovery
h3	HttpAdapter (WebTransport upgrade)	Browser-compatible WebTransport, then ALPN upgrade
h2 / http/1.1	HttpAdapter	Standard HTTP for browsers, curl

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 exposes its operations through alknet/call. The vault is a capability source — derived keys and decrypted credentials are injected into operation contexts at the assembly layer, not passed as vault references to handlers. See ADR-008 for the integration rationale.

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.

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 TypeScript predecessor can import OpenAPI schemas and expose operations as HTTP endpoints or MCP tools. This bidirectional capability carries forward.

See ADR-005 for the full rationale.

WASM Compatibility

WASM is not an immediate implementation target, but it is a design constraint on one-way doors (see ADR-009). Decisions that would permanently prevent WASM targets from participating as peers require explicit justification.

This means:

• Core types (BiStream, Connection, ProtocolHandler, AuthContext) must not assume tokio or quinn
• Protocol parsers that are pure data transformations remain transport-agnostic
• The cost of keeping the WASM door open is low (trait vs concrete type, abstracted I/O) and the cost of closing it is high

Handlers with transport-agnostic cores are particularly WASM-friendly:

• russh-sftp's protocol core is already transport-agnostic
• hickory-proto is #![no_std] with wasm-bindgen feature
• The call protocol's JSON framing is inherently cross-language
• Git's pkt-line is simple enough to implement anywhere

A browser gets a WebTransport stream and speaks SFTP, Git, or call protocol directly — but only if we haven't closed that door with concrete type choices.

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
IdentityProvider	Trait for resolving credentials to identity
AuthToken	Opaque authentication token
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) 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. See ADR-009.

WASM Door Preservation

WASM compatibility is not an active deliverable, but it is a design constraint. Decisions that would permanently close the WASM door (e.g., concrete quinn types in public APIs) require explicit justification. The cost of keeping the door open is low; the cost of closing it is irreversibly high.

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, exposed via call protocol, vault is a capability source
009	One-Way Door Decision Framework	Classify decisions by reversal cost; one-way doors need ADRs

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 via call protocol — see ADR-008)

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.