mesh-sdk/go/process/call.go

package process

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"strings"
	"time"

	"github.com/nats-io/nats.go"

	"git.novox.be/novox/mesh-sdk/go/busretry"
	"git.novox.be/novox/mesh-sdk/go/calladdress"
)

// CallTimeout bounds a call to a tool or a seat verb (mesh-tools node-tools/internal/bus/bus.go:35,
// RequestTimeout): what a module already expects.
var CallTimeout = 30 * time.Second

// Call invokes a tool or a seat verb as this process's own account (novox/hq ADR 0436 clause 4), on the
// caller-named subject, falling back to the subject that names no caller when nothing answers it —
// exactly the provisioner client's own pattern (mesh-catalog modules/mesh-provisioner-client/cmd/
// mesh-provisioner-client/secrets.go:59-61, 93-97, 119, 125-133). key is "seat:<seat>.<verb>" for a seat's
// verb, or "<module>.<tool>" for a module's own tool, as a process's bus.invokes names it. The reply is
// {result, error, node} (mesh-tools node-tools/internal/bus/bus.go answerOf); a non-empty error is the
// call's failure. It offers no way to answer a call — a process reaches the bus only as itself, and
// never serves anything. A key naming its machine after '@' (`seat:node-service-manager.stop@novox`) is CallOn of that
// machine; any other malformed key is refused before anything is published (calladdress; novox/hq issue 774).
func (c *Conn) Call(key string, body any) (json.RawMessage, error) {
	called, fallback, err := callSubjectsOn(key, "", c.callerToken())
	if err != nil {
		return nil, err
	}
	return c.callOn(called, fallback, body)
}

// CallOn is Call to the tool or seat verb of one named machine (novox/hq ADR 0469 §3; issue 1470): the tool
// runner of that node alone answers, on mesh.mod.<module>.call.<tool>.<node>.<token> (a seat verb:
// mesh.seat.<seat>.call.<verb>.<node>.<token>), falling back to the subject that names no caller
// (mesh-tools node-tools/internal/bus/caller.go:15-19). node is one subject token: an empty one, or one
// holding '.', '*', '>' or white space, is refused before anything is published.
func (c *Conn) CallOn(node, key string, body any) (json.RawMessage, error) {
	if err := calladdress.CheckNode(node); err != nil {
		return nil, err
	}
	called, fallback, err := callSubjectsOn(key, node, c.callerToken())
	if err != nil {
		return nil, err
	}
	return c.callOn(called, fallback, body)
}

// callOn asks called, then fallback when nothing answers it; while the bus itself answers nothing (a user-list reload
// drops the account's imports for a few seconds, busretry) both are asked again, within busretry.Bound. A call nobody
// answers on a bus that answers is not asked again: its callee is not running. A call that may have been delivered (a
// timeout, any answer) is never asked again.
func (c *Conn) callOn(called, fallback string, body any) (json.RawMessage, error) {
	data, err := json.Marshal(body)
	if err != nil {
		return nil, err
	}
	return callWith(c.request, c.blackedOut, called, fallback, data)
}

// callWith is callOn over a request and a blackout probe. Only the transport's own errors can count as undelivered: a
// callee's answer is *busretry.Answered, whatever its words, so a call that reached its callee is never asked again.
func callWith(request func(string, []byte) (json.RawMessage, error), blackout func() bool, called, fallback string,
	data []byte) (json.RawMessage, error) {
	return busretry.Do("the call on "+fallback, func() (json.RawMessage, error) {
		result, err := request(called, data)
		if errors.Is(err, nats.ErrNoResponders) {
			result, err = request(fallback, data)
		}
		return result, err
	}, blackout)
}

// answered is the error a callee answered with: delivered, never asked again (busretry.Answered).
func answered(words string) error { return &busretry.Answered{Words: words} }

// blackedOut says the bus answers this account nothing at all: its JetStream API, which every account imports, has no
// responder or says it is not enabled.
func (c *Conn) blackedOut() bool {
	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
	defer cancel()
	msg, err := c.nc.RequestWithContext(ctx, "$JS.API.INFO", nil)
	if err != nil {
		return busretry.Undelivered(err)
	}
	return strings.Contains(string(msg.Data), `"err_code":10039`) || strings.Contains(string(msg.Data), "jetstream not enabled")
}

// callerToken is this account's user name as the last token of a call it publishes, each dot written ~
// (mesh-tools node-tools/internal/bus/caller.go:43, CallerToken).
func (c *Conn) callerToken() string { return strings.ReplaceAll(c.account.User, ".", "~") }

// callSubjects is the caller-named subject key is called on, and its plain fallback (mesh-tools
// node-tools/internal/bus/caller.go CalledSubject, toolShape, calledPattern).
func callSubjects(key, token string) (called, fallback string, err error) {
	return callSubjectsOn(key, "", token)
}

// callSubjectsOn is callSubjects for one named node ("" names none, and then the key's own '@' names it): the node is a
// token between the tool and the caller on the called subject, and the last one of the fallback. A key naming another
// machine than node is refused.
func callSubjectsOn(key, node, token string) (called, fallback string, err error) {
	a, err := calladdress.Parse(key)
	if err != nil {
		return "", "", err
	}
	switch {
	case a.Node != "" && node != "" && a.Node != node:
		return "", "", fmt.Errorf("%q names the machine %s, and it is asked of %s", key, a.Node, node)
	case a.Node != "":
		node = a.Node
	}
	at := ""
	if node != "" {
		at = "." + node
	}
	if a.Seat != "" {
		return "mesh.seat." + a.Seat + ".call." + a.Verb + at + "." + token, "mesh.seat." + a.Seat + ".tool." + a.Verb + at, nil
	}
	return "mesh.mod." + a.Module + ".call." + a.Tool + at + "." + token, "mesh.mod." + a.Module + ".tool." + a.Tool + at, nil
}

// request asks one subject once and reads its reply ({result, error, node}); a reply naming an error is
// the call's failure, not a transport one.
func (c *Conn) request(subject string, data []byte) (json.RawMessage, error) {
	ctx, cancel := context.WithTimeout(context.Background(), CallTimeout)
	defer cancel()
	msg, err := c.nc.RequestWithContext(ctx, subject, data)
	if err != nil {
		return nil, err
	}
	var r struct {
		Result json.RawMessage `json:"result"`
		Error  string          `json:"error"`
		Node   string          `json:"node"`
	}
	if err := json.Unmarshal(msg.Data, &r); err != nil {
		return nil, fmt.Errorf("%s answered something that is not a seat's answer: %w", subject, err)
	}
	if r.Error != "" {
		return nil, answered(r.Error)
	}
	return r.Result, nil
}