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docs(http): draft alknet-http architecture specs and ADRs 036-039

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First speccing pass for alknet-http (HTTP interface crate: h2/http1.1/h3
server + from_openapi/to_openapi/from_mcp/to_mcp adapters).

Specs (crates/http/):
- README.md, overview.md — crate index, two-roles-in-one-crate framing,
  adapter location map, feature gates (h3, mcp), no-env-vars invariant
- http-server.md — HttpAdapter for h2/http1.1, axum over QUIC stream,
  Bearer auth, SSE projection for subscriptions, /healthz, stealth decoy
- http-adapters.md — from_openapi (reqwest) and to_openapi (projection),
  error fidelity (HTTP_<status> per ADR-023), type definitions
- http-mcp.md — from_mcp/to_mcp (feature-gated), streamable-HTTP-only
- webtransport.md — h3/WebTransport handler, browser streaming path,
  HTTP/3 request vs WebTransport session distinguished at framing layer

ADRs:
- ADR-036 HTTP-to-Call Operation Mapping (Proposed) — direct path
  mapping; to_openapi is projection, not router (the load-bearing one-way
  door from Phase 0 DH-3)
- ADR-037 MCP Stdio Transport Exclusion (Proposed) — streamable HTTP
  only; stdio is not built (RCE-vector security position)
- ADR-038 HTTP/3 and WebTransport as First-Class HTTP Transports
  (Proposed) — corrects the Phase 0 DH-2 deferral framing; h3 is in
  scope, not deferred, per ADR-009 §'What this framework is NOT'
- ADR-039 HTTP Server and Client Host Colocated in alknet-http
  (Proposed) — one crate for server + client host (shared HTTP deps,
  shared operation-spec->HTTP mapping)
- ADR-003 Amendment 1 — clarifies alknet-call is a protocol-foundation
  crate (the alknet-http -> alknet-call dependency edge)

Open questions (OQ-38, OQ-39, OQ-40 added under 'Theme: alknet-http'):
- OQ-38 WebTransport relay-as-proxy scope (genuine scope question, not
  a deferral — the decision is made when the use case becomes concrete)
- OQ-39 to_openapi published-spec versioning (one-way after first
  publication)
- OQ-40 reqwest client config and connection pooling (two-way-door)

Architecture README and overview updated with doc table, ADR table
(036-039), current-state note, and crate graph (alknet-http ->
alknet-call edge).

Reviewed by architecture-reviewer subagent: 3 critical, 4 warning, 5
suggestion issues found and fixed (missing ADR-039, WebTransport stream
routing conflation, undefined types, stale OQ-37 deferral language,
README OQ table completeness, Bearer-only attribution, cross-references,
ADR-038 ALPN quote, feature-gate placeholder, MCP temporal language).
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---
status: draft
last_updated: 2026-06-29
---
# alknet-http — Overview
The HTTP interface crate: serves inbound HTTP on standard ALPNs and hosts
the HTTP-backed call-protocol adapters. This document covers the crate's
two roles, its dependency edges, and the adapter location map. Component
details are in the sibling documents.
## What
`alknet-http` is the HTTP protocol handler for the ALPN-as-service
architecture. It serves two roles in one crate:
1. **HTTP server** — a `ProtocolHandler` (`HttpAdapter`) that accepts
HTTP/2, HTTP/1.1, and HTTP/3 (WebTransport) connections on the
standard IANA ALPNs (`h2`, `http/1.1`, `h3`). It serves REST APIs, the
`to_openapi`/`to_mcp` projections of local call-protocol operations,
the `/healthz` operational endpoint, and the decoy surface for
stealth mode.
2. **HTTP client host** — the home of the HTTP-transport-backed call
adapters: `from_openapi` (import external HTTP APIs as call
operations, using `reqwest` for outbound calls) and `from_mcp` (import
remote MCP tools over streamable HTTP, using `reqwest`). The reverse
projections `to_openapi` (generate an OpenAPI doc from the local
registry's `External` operations) and `to_mcp` (expose local ops as
MCP tools over streamable HTTP, using `axum`) also live here.
Both directions share the same HTTP dependencies (`axum` for serving,
`reqwest` for calling out), which is why they live in one crate rather
than being split into a server crate and a client crate. See
[ADR-039](../../decisions/039-http-server-and-client-host-colocated.md)
for the full rationale.
## Why
The crate's purpose is to be the HTTP interface library for downstream
crates that need to expose an HTTP interface. A downstream consumer (the
CLI binary, a hub deployment, a browser-facing service) wires
`HttpAdapter` into the `HandlerRegistry` for the standard HTTP ALPNs and
gets a full HTTP surface: REST projection of the call protocol, OpenAPI
discovery, MCP tool exposure, and WebTransport for browsers.
The key architectural insight that shapes the crate: **HTTP is both a
server surface and a client transport for adapters.** The server side
serves HTTP to external clients (browsers, curl, axios); the client side
makes outbound HTTP calls to external APIs (OpenAI, Anthropic, vast.ai)
through the `from_openapi`/`from_mcp` forwarding handlers. Both
directions share HTTP dependencies and HTTP-specific concerns (TLS,
headers, streaming, SSE), so they belong in one crate. See
[ADR-039](../../decisions/039-http-server-and-client-host-colocated.md)
for the colocation decision.
## Dependencies
```
alknet-http
├── alknet-core (ProtocolHandler, Connection, AuthContext, IdentityProvider, Capabilities)
├── alknet-call (OperationAdapter, OperationSpec, Handler, HandlerRegistration,
│ OperationRegistry, AdapterError, OperationProvenance)
├── axum (HTTP server — Router, extractors, middleware)
├── reqwest (HTTP client — from_openapi/from_mcp forwarding)
├── hyper (HTTP/1.1 + HTTP/2 framing; axum is built on hyper)
├── wtransport (HTTP/3 + WebTransport — feature-gated behind `h3`)
└── rmcp (MCP streamable HTTP — feature-gated behind `mcp`)
```
### The `alknet-call` dependency (ADR-003 Amendment 1)
`alknet-http` depends on `alknet-call`. ADR-003's rule is "no handler
crate depends on another handler crate," but `alknet-call` is both a
handler (it implements `ProtocolHandler` on `alknet/call`) *and* the
protocol-foundation crate that `alknet-agent`, `alknet-napi`, and now
`alknet-http` consume. `alknet-http` depending on `alknet-call` is
"HTTP uses the call protocol types" (`OperationSpec`, `Handler`,
`HandlerRegistration`, `OperationAdapter`), not "HTTP depends on SSH."
See [ADR-003 Amendment 1](../../decisions/003-crate-decomposition.md).
`alknet-call` stays lean — it has no `reqwest`, no `axum`, no HTTP
dependencies. The `from_openapi`/`from_mcp` forwarding handlers are
opaque `Arc<dyn Handler>` from the registry's perspective: constructed by
`alknet_http::from_openapi()` at registration time, stored in
`HandlerRegistration`, dispatched by the `CallAdapter` which doesn't
know `reqwest` is involved.
## ALPNs
| ALPN | Handler | Transport | Browser? |
|------|---------|-----------|----------|
| `http/1.1` | `HttpAdapter` | HTTP/1.1 over QUIC stream | No |
| `h2` | `HttpAdapter` | HTTP/2 over QUIC stream | No |
| `h3` | `HttpAdapter` | HTTP/3 / WebTransport | Yes (X.509 required) |
These are standard IANA ALPN strings, not `alknet/`-prefixed. Any HTTP
client connects without knowing about alknet — the TLS handshake
negotiates `h2` or `http/1.1` normally, and the `HttpAdapter` serves
HTTP. This is the stealth mapping (ADR-010): clients that don't offer
alknet ALPNs get the HTTP handler, just like port scanners in stealth
mode.
The `HttpAdapter` registers for all three ALPNs (when the corresponding
features are enabled). The endpoint's `HandlerRegistry` maps each ALPN to
the same `HttpAdapter` instance; the handler branches on
`connection.remote_alpn()` to pick the right framing.
## Adapter Location Map
The decomposition principle (settled in
[client-and-adapters.md](../call/client-and-adapters.md)): the adapter
trait lives where the types live (`alknet-call`); the adapter
implementations live where their transport dependencies live.
```
alknet-call (lean — no HTTP client, no HTTP server)
├── OperationAdapter trait (the contract — async, ADR-017 §5)
├── from_call (QUIC — discovers remote ops via call protocol)
├── from_jsonschema (pure parse — caller fetches the doc, passes it in)
└── CallClient (outbound connection opener)
alknet-http (owns HTTP server + HTTP client)
├── HttpAdapter (axum server — inbound HTTP on h2/http1.1/h3)
├── from_openapi (parse OpenAPI doc + reqwest forwarding handler)
├── to_openapi (generate OpenAPI doc from local registry)
├── from_mcp (feature-gated) (import remote MCP tools over streamable HTTP — reqwest)
└── to_mcp (feature-gated) (expose local ops as MCP tools over streamable HTTP — axum)
```
`alknet-call` never sees the HTTP client. The `from_openapi`/`from_mcp`
forwarding handlers are opaque `Arc<dyn Handler>` from the registry's
perspective. `alknet-call` stays lean; `alknet-http` owns both HTTP
directions.
## Feature Gates
```toml
[features]
default = ["h2", "http1"] # the non-browser HTTP surface
h3 = ["dep:wtransport"] # HTTP/3 + WebTransport (browser path; X.509 required)
mcp = ["dep:rmcp"] # from_mcp / to_mcp (streamable HTTP only — ADR-037)
```
- `h2` + `http1` (default): the `axum` + `hyper` HTTP/1.1 + HTTP/2
server. This is the surface non-browser clients use.
- `h3`: the `wtransport` (or quinn HTTP/3 extension) dependency. Adds
the `h3` ALPN handler and the WebTransport streaming path. See
[webtransport.md](webtransport.md) and
[ADR-038](../../decisions/038-http3-and-webtransport-as-first-class.md).
- `mcp`: the `rmcp` dependency with streamable HTTP transport features
only. Adds `from_mcp`/`to_mcp`. See [http-mcp.md](http-mcp.md) and
[ADR-037](../../decisions/037-mcp-stdio-transport-exclusion.md).
A deployment that only needs the REST surface (no browsers, no MCP) uses
the default features. A browser-facing hub enables `h3`. A deployment
that wants MCP tool import/export enables `mcp`.
## The No-Env-Vars Invariant
The `from_openapi`/`from_mcp` forwarding handlers are the **credential
injection point** for the no-env-vars architecture. The path (from the
gap analysis):
```
vault → assembly layer → Capabilities → HandlerRegistration.capabilities
→ OperationContext.capabilities → from_openapi handler reads
context.capabilities.get("openai") → injects into HTTP Authorization
header → reqwest request goes out with vault-derived credential
```
This makes aisdk's `std::env::var("OPENAI_API_KEY")` reads unreachable —
the assembly layer never calls `Default::default()` on a provider; it
constructs them with vault-derived credentials, or routes HTTP calls
through `from_openapi` operations that carry the credential in
`Capabilities`.
**This is a spec-level invariant**: no handler reads outbound
credentials from any source other than `OperationContext.capabilities`.
The `from_openapi`/`from_mcp` implementations in `alknet-http` are
verified against this invariant. See ADR-014 and
[client-and-adapters.md](../call/client-and-adapters.md).
## Architecture (component pointers)
- **[http-server.md](http-server.md)** — the `HttpAdapter` for `h2`/
`http/1.1`: how axum is run over a QUIC bidirectional stream, Bearer
auth resolution, the `/healthz` raw route, stealth decoy, and the
HTTP-to-call dispatch (ADR-036).
- **[http-adapters.md](http-adapters.md)** — `from_openapi` (parse
OpenAPI, build forwarding handlers with `reqwest`) and `to_openapi`
(generate an OpenAPI doc from the registry's `External` operations).
Error fidelity per ADR-023.
- **[http-mcp.md](http-mcp.md)** — `from_mcp`/`to_mcp` (feature-gated),
streamable HTTP only (ADR-037), the rmcp integration.
- **[webtransport.md](webtransport.md)** — the `h3` ALPN handler,
WebTransport session/stream handling, the browser streaming path
(ADR-038).
## Design Decisions
| Decision | ADR | Summary |
|----------|-----|---------|
| HTTP-to-call operation mapping | [ADR-036](../../decisions/036-http-to-call-operation-mapping.md) | Direct path mapping; `to_openapi` is projection, not router |
| MCP stdio transport exclusion | [ADR-037](../../decisions/037-mcp-stdio-transport-exclusion.md) | Streamable HTTP only; stdio is not built (RCE vector) |
| HTTP/3 + WebTransport first-class | [ADR-038](../../decisions/038-http3-and-webtransport-as-first-class.md) | `h3` in scope, not deferred; browser streaming uses QUIC streams |
| HTTP server + client host colocated | [ADR-039](../../decisions/039-http-server-and-client-host-colocated.md) | One crate for server + adapters (shared HTTP deps, shared mapping) |
| `alknet-call` is protocol-foundation | [ADR-003](../../decisions/003-crate-decomposition.md) Am. 1 | `alknet-http` depends on `alknet-call` (types, not peer handler) |
| Bearer auth via `resolve_from_token` | [ADR-004](../../decisions/004-auth-as-shared-core.md) | HTTP handler credential source + resolution (settled) |
| Stealth mode = HTTP handler on standard ALPNs | [ADR-010](../../decisions/010-alpn-router-and-endpoint.md) | Decoy for unknown paths (settled) |
| Adapter-registered ops are `Internal` | [ADR-015](../../decisions/015-privilege-model-and-authority-context.md) | `from_openapi`/`from_mcp` produce `Internal` leaves (settled) |
| `OperationAdapter` trait is async | [ADR-017](../../decisions/017-call-protocol-client-and-adapter-contract.md) | HTTP adapters implement the async trait (settled) |
| `to_*` adapters are projections | [ADR-017](../../decisions/017-call-protocol-client-and-adapter-contract.md) | `to_openapi`/`to_mcp` consume the registry, don't produce entries (settled) |
| Error schema fidelity | [ADR-023](../../decisions/023-operation-error-schemas.md) | `from_openapi` maps HTTP status → `HTTP_<status>` codes; `to_openapi` projects back (settled) |
| Browsers require X.509 | [ADR-027](../../decisions/027-tls-identity-redesign-acme-rawkey-decoupling.md) | `h3`/WebTransport needs X.509 (settled) |
| Browsers are not alknet peers | [ADR-034](../../decisions/034-outgoing-only-x509-and-three-peer-roles.md) | Browser over WebTransport/HTTPS = bearer token, no `PeerId` (settled) |
## Open Questions
See [open-questions.md](../../open-questions.md) for full details.
- **OQ-13** (resolved): Operation path format `/{service}/{op}` — the
HTTP path.
- **OQ-26** (resolved): `AdapterError` variants — reused by HTTP
adapters; `#[non_exhaustive]` allows extension.
- **OQ-37** (resolved): Browsers are not peers; `h3` hub is a
mixed-fingerprint `PeerEntry`.
- **OQ-38** (open, scope): WebTransport relay-as-proxy — does the proxy
live in `alknet-http` or a separate relay crate?
- **OQ-39** (open): `to_openapi` published-spec versioning — versioning
strategy for generated OpenAPI specs.
- **OQ-40** (open): reqwest client config and connection pooling —
two-way-door config shape.
## References
- `docs/research/alknet-http/phase-0-findings.md` — Phase 0 research
- `docs/research/alknet-call-completion/gap-analysis.md` — adapter
location map, no-env-vars invariant
- `/workspace/@alkdev/operations/src/from_openapi.ts`,
`/workspace/@alkdev/operations/src/from_mcp.ts` — TypeScript prior art
- `/workspace/rust-sdk/` — MCP Rust SDK (rmcp); streamable HTTP examples
- `/workspace/wtransport/` — pure-Rust WebTransport reference