Calling Agents with Runtime Reflection (Go)

Normal RPC through the callee’s definition package or a generated guest client (see golem-call-another-agent-go) is the baseline. Reflection adds three more levels, which compose through agent ids:

Every level uses the same verbs: Call waits for the result, Trigger does not, Schedule runs it later. Discovered and dynamic clients live in the reflection package (github.com/golemcloud/golem/sdks/go/golem/reflection).

Method-Only Clients

A method-only client declares methods and nothing else, so it calls any existing agent that has them, whatever its type:

type Pingable struct{} // the shape's identity type
 
var (
	Pinger = golem.DefineAgentClient[Pingable]()
	Ping   = Pinger.Method[golem.Unit, string]("ping")
)
 
func pingAll(ids []string) {
	for _, id := range ids {
		c, err := Pinger.Bind(id)
		if err != nil {
			continue
		}
		reply, err := Ping.Call(c, golem.Unit{})
		fmt.Println(id, reply, err)
	}
}

Bind checks nothing about the target, which the client does not describe; a target that is not deployed is reported by Bind, and a mismatch by the host or when the result is decoded. Binding does not create the agent, but the first call to a durable id does.

Full Clients

A full client also declares the target type’s name, constructor and lifecycle, so it creates and addresses instances like the agent’s own definition:

type CounterID struct{ Name string }
type AddIn struct{ By int64 }
 
var (
	Counter = golem.DefineFullAgentClient[CounterID]("CounterAgent", golem.AgentClientSpec{})
	Add     = Counter.Method[AddIn, int64]("add")
)
 
c, err := Counter.Get(CounterID{Name: "main"}) // an error when the target is not deployed
total, err := Add.Call(c, AddIn{By: 5})
 
c, err = Counter.Bind(agentID) // the id must name CounterAgent with a CounterID constructor
id, err := Counter.AgentID(CounterID{Name: "main"}, golem.None[golem.UUID]()) // without creating it

• Get, NewPhantom, Bind and AgentID work the same on an agent’s own definition (DefineAgent), except that there Get, NewPhantom and AgentID panic instead of returning an error: the target is in the same component, so a failure is a programming mistake.
• golem.AgentClientSpec{Mode: golem.Ephemeral} declares an ephemeral target: it has no durable identity, so Get and Bind are refused and NewPhantom addresses it.
• golem.DefineConfiguredFullAgentClient[Id, Cfg] declares the target’s configuration type, so Get(id, client.WithConfig(cfg)) passes typed creation-time overrides, checked at compile time against Cfg.

Generated guest clients are built on full clients.

Discover and Inspect

for _, t := range reflection.DiscoverAgentTypes() {
	fmt.Println(t.Name(), t.Mode(), t.SourceLanguage())
	for _, m := range t.Methods() {
		fmt.Println("  ", m.Name(), m.Description(), m.ReadOnly())
	}
}
 
counter, found := reflection.DiscoverAgentType("CounterAgent")
if !found {
	panic("CounterAgent is not deployed in this environment")
}
add, known := counter.Method("add")
if !known {
	panic("CounterAgent has no method add")
}
input := add.Input()                              // a schema.Ref of the parameter record
fmt.Println(golem.Must(input.ToJSONSchema(true))) // e.g. for an LLM

Input() is the parameter record (without host-filled fields such as the principal) and Output() the result type, golem.None when there is none; both are schema.Refs from github.com/golemcloud/golem/sdks/go/core/schema, which pack and unpack canonical JSON and render JSON Schema. Constructor().Input() describes the constructor the same way. A discovery miss (not deployed, not visible to the caller) reports false. A snapshot never refreshes itself; discover again when a newer deployment matters.

Call a Discovered Agent

client, err := counter.Get(map[string]any{"name": "main"})
if err != nil {
	panic(err)
}
total, invocation, err := client.Call("add", map[string]any{"by": "5"}) // s64 is a string
if err != nil {
	var rce *golem.RemoteCallError
	if errors.As(err, &rce) {
		fmt.Println(rce.Kind, rce.Message)
	}
	panic(err)
}
fmt.Println(client.AgentID(), total, invocation.IdempotencyKey)

• Get takes the constructor arguments by name and creates the agent if it does not exist; reflection.WithPhantomID(uuid) addresses a phantom instance and NewPhantom allocates one. Bind(agentID) addresses an existing id of this type.
• reflection.WithConfigJSON(path, value) overrides one declared configuration value at creation, as canonical JSON (reflection.WithConfigValue(path, schema.SchemaValue) takes a schema-model value); Get, NewPhantom and Bind accept it. Undeclared paths, secrets and invalid values are refused before anything is sent. An agent that already exists keeps the configuration it was created with.
• Call, Trigger and Schedule return the invocation’s golem.InvocationID (agent id and idempotency key) — for an ephemeral agent, the only record of which instance ran.
• CallAsync returns a *reflection.PendingCall: its ID is known at once, Get() returns the result (MustGet() panics on an error, and a second Get returns the same result), and Cancel() stops waiting (the call may already have run; Get then reports golem.ErrCallCancelled). It behaves like the *golem.Future that a typed CallAsync returns. A scheduled call is cancelled through the *golem.ScheduledInvocation that Schedule returns.
• Missing, unexpected or invalid arguments fail with *schema.ValidationError, listing every problem, before anything is sent.
• Remote failures are *golem.RemoteCallError; for a remote agent error, its Cause is a *golem.AgentError.

Agent IDs

typed := golem.Must(golem.ParseAgentID[CounterID](agentID))
fmt.Println(typed.TypeName, typed.ID.Name, typed.PhantomID.IsSome())
 
raw := golem.Must(reflection.ParseRawAgentID(agentID)) // no Go type needed
fmt.Println(raw.TypeName, golem.Must(raw.ConstructorJSON()))
 
t, found := reflection.DiscoverAgentTypeByID(agentID) // the type behind an existing agent
id := golem.Must(t.AgentID(map[string]any{"name": "other"}, golem.None[golem.UUID]()))

Parsing is strict and reports malformed ids; lookup by id never creates the agent. Agent ids are scoped to the caller’s environment.

Fully Dynamic

A dynamic client sends values the caller packed itself and validates nothing. Keep a discovered snapshot beside it for validation:

t, _ := reflection.DiscoverAgentType(agentType)
m, _ := t.Method(method)
input := golem.Must(m.Input().PackJSON(args))
 
client := golem.Must(reflection.BindAgentID(agentID))
out, _, err := client.Call(method, input)
if err != nil {
	panic(err)
}
if v, has := out.Get(); has {
	if result, declared := m.Output().Get(); declared {
		fmt.Println(golem.Must(result.UnpackJSON(v)))
	}
}

A dynamic client also has CallAsync, Trigger and Schedule. reflection.MakeAgentID(typeName, constructor, phantom) builds an id from a packed constructor, so a dynamic caller can address any instance; the first call to it creates a durable agent.

Canonical JSON

• Integers up to 32 bits are JSON numbers; s64, u64, duration nanoseconds and quantity mantissas are base-10 strings ("5"). A duration is {"nanoseconds": "…"}.
• An absent option is null; a result is {"ok": …} or {"err": …}; a variant case is its name, or {name: payload}; a map is [[k, v], …]; flags are an array of names; binary is unpadded base64url.
• Streams, futures and other capabilities cannot be packed as JSON; call such methods through a typed client.

Related Guides