Contracts

Invoke services through typed contracts. Call remote APIs, workflows, and functions with schema validation and async execution support.

Loading

local contract = require("contract")

Opening a Binding

Open a binding directly by ID:

local greeter, err = contract.open("app.services:greeter")
if err then
    return nil, err
end

local result, err = greeter:say_hello("Alice")

With scope context or query parameters:

-- With scope table
local svc, err = contract.open("app.services:user", {
    tenant_id = "acme",
    region = "us-east"
})

-- With query parameters (auto-converted: "true"→bool, numbers→int/float)
local api, err = contract.open("app.services:api?debug=true&timeout=5000")

Returns: Instance, error

Getting a Contract

Retrieve contract definition for introspection:

local c, err = contract.get("app.services:greeter")

print(c:id())  -- "app.services:greeter"

local methods = c:methods()
for _, m in ipairs(methods) do
    print(m.name, m.description)
end

local method, err = c:method("say_hello")

Method Definition

Finding Implementations

List all bindings that implement a contract:

local bindings, err = contract.find_implementations("app.services:greeter")

for _, binding_id in ipairs(bindings) do
    print(binding_id)
end

Or via contract object:

local c, err = contract.get("app.services:greeter")
local bindings, err = c:implementations()

Checking Implementation

Check if instance implements a contract:

if contract.is(instance, "app.services:greeter") then
    instance:say_hello("World")
end

Calling Methods

Sync call - blocks until complete:

local calc, err = contract.open("app.services:calculator")

local sum, err = calc:add(10, 20)
local product, err = calc:multiply(5, 6)

Async Calls

Add _async suffix for async execution:

local processor, err = contract.open("app.services:processor")

local future, err = processor:process_async(large_dataset)

-- Do other work...

-- Wait for result
local ch = future:response()
local payload, ok = ch:receive()
if ok then
    local result = payload:data()
end

See Futures for future methods.

Opening via Contract

Open binding through contract object:

local c, err = contract.get("app.services:user")

-- Default binding
local instance, err = c:open()

-- Specific binding
local instance, err = c:open("app.services:user_impl")

-- With scope
local instance, err = c:open(nil, {user_id = 123})
local instance, err = c:open("app.services:user_impl", {user_id = 123})

Adding Context

Create wrapper with pre-configured context:

local c, err = contract.get("app.services:user")

local wrapped = c:with_context({
    request_id = ctx.get("request_id"),
    user_id = current_user.id
})

local instance, err = wrapped:open()

Security Context

Set actor and scope for authorization:

local security = require("security")
local c, err = contract.get("app.services:admin")

local secured = c:with_actor(security.actor()):with_scope(security.scope())

local admin, err = secured:open()

Permissions

Errors