alknet/docs/architecture/crates/call/operation-registry.md

status, last_updated

status	last_updated
draft	2026-06-17

Operation Registry

OperationSpec, Handler, OperationRegistry, AccessControl, service discovery, and irpc integration.

What

The operation registry maps operation names to specs and handlers. It is the dispatch core of the call protocol — when a call.requested event arrives, the registry looks up the operation by name, checks access control, invokes the handler, and returns the result.

The registry is populated at startup by the CLI binary (or by the assembly layer in embedded contexts). Operations cannot be added or removed at runtime. This is consistent with OQ-04 (static registration at startup) and the HandlerRegistry model in alknet-core.

Why

The operation registry provides:

• Discoverability: Clients can query /services/list and /services/schema to learn what operations exist before calling them
• Access control: Each operation declares its required scopes and resources; the registry enforces ACL before invoking the handler
• Type safety: JSON Schema for input and output enables validation and client code generation
• Composability: Handlers can invoke other operations through OperationEnv (local dispatch — remote dispatch is a separate architectural concern, see Constraints)

The registry design is informed by the @alkdev/operations TypeScript package, which demonstrated the same capabilities in JavaScript runtimes. The Rust implementation in alknet-call is canonical — it preserves the behavioral contract (namespace + operation name → invoke with input, return output) while defining the adapter contract (from_, to_) in Rust (see ADR-013).

Architecture

OperationSpec

Every registered operation has a spec that declares its name, type, schemas, and access control:

pub struct OperationSpec {
    pub name: String,              // e.g., "fs/readFile", "vault/derive" (no leading slash)
    pub namespace: String,         // e.g., "fs", "vault"
    pub op_type: OperationType,   // Query, Mutation, Subscription
    pub input_schema: Value,      // JSON Schema for input
    pub output_schema: Value,     // JSON Schema for output
    pub access_control: AccessControl,
}

pub enum OperationType {
    Query,         // Read-only, idempotent (e.g., "fs/readFile", "services/list")
    Mutation,      // Side effects (e.g., "bash/exec", "vault/unlock")
    Subscription,  // Streaming (e.g., "events/subscribe")
}

Operation names use slash-based paths without a leading slash, aligned with URL path conventions: fs/readFile, vault/derive, services/list. The leading slash is added when needed for display (spec.path() returns /fs/readFile) and for wire format (the call.requested payload uses /fs/readFile). See OQ-13 for the path format decision (single-node service/op vs head/worker node/service/op).

The namespace field is derived from the name: for fs/readFile it's fs, for vault/derive it's vault. It's a convenience accessor for ACL matching and service grouping.

AccessControl

pub struct AccessControl {
    pub required_scopes: Vec<String>,          // AND-checked: caller must have ALL
    pub required_scopes_any: Option<Vec<String>>, // OR-checked: caller must have at LEAST ONE
    pub resource_type: Option<String>,          // e.g., "service"
    pub resource_action: Option<String>,        // e.g., "read"
}

When a call.requested event arrives:

1. The CallAdapter resolves the caller's Identity from AuthContext (and possibly an AuthToken in the payload)
2. The registry checks access_control.check(identity) before invoking the handler
3. If access is denied, the adapter returns call.error with code FORBIDDEN
4. If the identity is None and the operation has restrictions, the adapter returns call.error with code FORBIDDEN and message "authentication required"

Operations with empty AccessControl (no required scopes, no resource checks) are accessible to all callers, including unauthenticated ones.

Trusted calls skip ACL: When a handler invokes another operation through OperationEnv, the nested call is marked trusted: true and skips access control checks. This prevents double-checking: if /agent/chat is allowed and it internally calls /auth/verify, the auth check is trusted.

Handler

pub type Handler = Arc<dyn Fn(Value, OperationContext) -> Pin<Box<dyn Future<Output = ResponseEnvelope> + Send>> + Send + Sync>;

Handlers are async — many operations (vault key derivation, file I/O, irpc service calls) are inherently asynchronous. The handler receives an async runtime context and returns a Future<Output = ResponseEnvelope>.

A handler receives:

• input: Value — the deserialized payload from the call.requested event (always serde_json::Value)
• context: OperationContext — request ID, identity, metadata, env

And returns a ResponseEnvelope containing the result or an error.

OperationContext

pub struct OperationContext {
    pub request_id: String,
    pub parent_request_id: Option<String>,
    pub identity: Option<Identity>,
    pub metadata: HashMap<String, Value>,
    pub env: OperationEnv,
    pub trusted: bool,
}

• request_id: Correlates with the call.requested event's id field
• parent_request_id: Set when this call was initiated by another operation (via OperationEnv)
• identity: The authenticated identity making the call (from IdentityProvider)
• metadata: Additional context (connection info, tracing IDs)
• env: The operation environment for composing calls to other operations
• trusted: When true, ACL checks are skipped (set by OperationEnv, not by callers). The trusted field uses module-private construction — handlers construct OperationContext through OperationEnv::invoke() which sets trusted: true, or through the CallAdapter dispatch path which sets trusted: false. The field is not pub for writes; only pub fn is_trusted(&self) -> bool is exposed for reads.

OperationRegistry

pub struct OperationRegistry {
    operations: HashMap<String, (OperationSpec, Handler)>,
}

The registry maps operation names to (OperationSpec, Handler) pairs. Key methods:

• register(spec, handler): Add an operation at startup
• lookup(name): Find an operation by name, returning spec and handler
• invoke(name, input, context): Look up, check ACL, invoke handler, return result
• list_operations(): Return all registered specs (for /services/list)

The OperationRegistryBuilder provides a fluent API for constructing the registry at startup:

let registry = OperationRegistryBuilder::new()
    .with(services_list_spec(), Arc::new(services_list_handler))
    .with(services_schema_spec(), Arc::new(schema_handler))
    .with(vault_derive_spec(), Arc::new(vault_derive_handler))
    .with(vault_unlock_spec(), Arc::new(vault_unlock_handler))
    .build();

The CLI binary (or assembly layer) constructs the registry and passes it to the CallAdapter. Once built, the registry is immutable.

OperationEnv

#[async_trait]
pub trait OperationEnv: Send + Sync {
    async fn invoke(&self, namespace: &str, operation: &str, input: Value, parent: &OperationContext) -> ResponseEnvelope;
}

OperationEnv is the universal composition mechanism. A handler calls context.env.invoke("vault", "derive", input, &context) and gets a ResponseEnvelope back — regardless of whether the operation runs locally, via an irpc service, or on a remote node.

The parent parameter propagates the calling context: the nested call gets parent_request_id: Some(parent.request_id), inherits parent.identity, and is marked trusted: true.

Local dispatch only. The initial OperationEnv implementation dispatches directly through the local OperationRegistry:

pub struct LocalOperationEnv {
    registry: Arc<OperationRegistry>,
}

#[async_trait]
impl OperationEnv for LocalOperationEnv {
    async fn invoke(&self, namespace: &str, operation: &str, input: Value, parent: &OperationContext) -> ResponseEnvelope {
        let name = format!("{namespace}/{operation}");
        let context = OperationContext {
            request_id: format!("env-{name}"),
            parent_request_id: Some(parent.request_id.clone()),
            identity: parent.identity.clone(),  // Inherit caller's identity
            metadata: parent.metadata.clone(),   // Inherit caller's metadata
            env: self.clone(),
            trusted: true,                       // Nested calls skip ACL
        };
        self.registry.invoke(&name, input, context).await
    }
}

Future work may add irpc service dispatch and remote call protocol dispatch as additional backends. The handler-facing API stays the same.

Service Discovery

Two built-in operations expose what the node offers:

Operation name	Display path	Type	Description
services/list	/services/list	Query	List registered operation names and metadata
services/schema	/services/schema	Query	Get the OperationSpec for a specific operation

These are read-only — no admin operations are exposed through the call protocol itself.

services/list returns:

{
  "operations": [
    { "name": "fs/readFile", "namespace": "fs", "op_type": "query" },
    { "name": "vault/derive", "namespace": "vault", "op_type": "mutation" },
    { "name": "events/subscribe", "namespace": "events", "op_type": "subscription" }
  ]
}

services/schema accepts { "name": "fs/readFile" } and returns the full OperationSpec including input/output JSON Schemas.

irpc Integration

irpc and the operation registry serve different scopes:

Layer	Mechanism	Serialization	Scope
Call protocol (external)	EventEnvelope over QUIC streams	JSON	Cross-language, cross-node
irpc services (internal)	VaultProtocol derive macro, Service trait	postcard (binary)	Rust-to-Rust, in-process or in-cluster
Local dispatch (in-process)	Direct function call through OperationRegistry	None	Same process

The call protocol can wrap irpc services. When /vault/derive receives a call.requested event, the handler:

1. Deserializes the JSON payload
2. Calls VaultProtocol::DeriveEd25519 via irpc (in-process, type-safe, postcard)
3. Serializes the result back to JSON
4. Returns call.responded on the stream

This layering preserves irpc's type safety for internal calls while keeping the external interface cross-language.

Operation Registration at Startup

The CLI binary (or assembly layer) registers operations before starting the endpoint:

let registry = OperationRegistryBuilder::new()
    // Built-in service discovery
    .with(services_list_spec(), Arc::new(services_list_handler))
    .with(services_schema_spec(), Arc::new(services_schema_handler))
    // Vault operations (exposed via call protocol, backed by irpc)
    .with(vault_derive_spec(), Arc::new(vault_derive_handler))
    .with(vault_unlock_spec(), Arc::new(vault_unlock_handler))
    .with(vault_lock_spec(), Arc::new(vault_lock_handler))
    .build();

let call_adapter = CallAdapter::new(Arc::new(registry), identity_provider);

The registry is immutable after construction. Adding operations requires restarting the process. This is consistent with OQ-04 and the HandlerRegistry model in alknet-core.

Constraints

• The registry is immutable after construction. No runtime registration or deregistration. Two-way door — ArcSwap<OperationRegistry> can be added later.
• Operation specs use JSON Schema. The call protocol's external interface is always JSON. irpc's postcard serialization is internal only.
• OperationEnv::invoke() dispatches through the local registry. Remote dispatch (federation, head/worker routing) would be a separate mechanism at a different layer — not a prefix added to operation paths. irpc service dispatch is contracted but not built.
• The call protocol does not depend on any database. Operation specs are in-memory, populated at startup.
• OperationContext.trusted is set by OperationEnv, not by callers. A handler cannot mark its own call as trusted.

Design Decisions

Decision	ADR	Summary
irpc as call protocol foundation	ADR-005	irpc provides framing and service dispatch
Call protocol stream model	ADR-012	Bidirectional streams, EventEnvelope, ID-based correlation
Static handler registration	ADR-010	Registry is immutable after construction
Vault integration via call protocol	ADR-008	Vault ops exposed as call protocol operations

Open Questions

See open-questions.md for full details.

• OQ-13 (resolved): Operation path format is /{service}/{op}. Remote dispatch is a separate mechanism, not a path prefix.
• OQ-14 (resolved): Batch is a client-side pattern of correlated call.requested events, not a protocol primitive.

References

• call-protocol.md — CallAdapter, EventEnvelope, stream model, PendingRequestMap
• ADR-005: irpc as call protocol foundation
• ADR-008: Vault integration point
• ADR-010: ALPN router and endpoint (static registration)
• ADR-012: Call protocol stream model
• Reference implementation: /workspace/@alkdev/alknet-main/crates/alknet-core/src/call/