mesh-controller/cmd/mesh-controller/seatverbs.go

package main

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"os/exec"
	"strings"

	"github.com/novox/mesh-controller/internal/catalogue"
	"github.com/novox/mesh-controller/internal/link"
)

// The mesh's own verbs, served as the mesh-controller seat's tools (novox/hq ADR 0154, design 33).
//
// **Each tool runs the command it names, in this same binary, and answers what it printed.** That is
// ADR 0035 taken literally: the logic lives once, in the command, and a surface is an adapter with no
// decisions in it. Running a fresh process rather than calling the function keeps two things true
// that calling it would not — every command opens and closes its own stores the way it does from a
// shell, and nothing a command prints to the process's standard output can leak into another call's
// answer. It also means a refusal is the same refusal in the same words, because it is the same
// output.

// verbAnswer is what a verb answers: what the command printed, whether it succeeded, and — where the
// command speaks JSON — the same as data.
type verbAnswer struct {
	Output string `json:"output"`
	OK     bool   `json:"ok"`
	Answer any    `json:"answer,omitempty"`
}

// argvFor is the command line a verb and its arguments become. Only the verbs the seat declares, and
// only the arguments each declares: a caller cannot reach a flag the schema did not name.
func argvFor(verb string, args map[string]any) ([]string, error) {
	str := func(key string) string {
		v, _ := args[key].(string)
		return strings.TrimSpace(v)
	}
	need := func(keys ...string) error {
		for _, k := range keys {
			if str(k) == "" {
				return fmt.Errorf("%s needs %q", verb, k)
			}
		}
		return nil
	}
	switch verb {
	case "status":
		return []string{"status", "--json"}, nil
	case "nodes":
		return []string{"node", "list"}, nil
	case "node":
		if err := need("node"); err != nil {
			return nil, err
		}
		return []string{"node", "show", str("node")}, nil
	case "modules":
		return []string{"module", "list"}, nil
	case "seats":
		return []string{"seats", "--json"}, nil
	case "builds":
		if m := str("module"); m != "" {
			return []string{"builds", m}, nil
		}
		return []string{"builds"}, nil
	case "plan":
		if err := need("node"); err != nil {
			return nil, err
		}
		return []string{"plan", str("node"), "--json"}, nil
	case "assign", "unassign":
		if err := need("node", "module"); err != nil {
			return nil, err
		}
		return []string{verb, str("node"), str("module")}, nil
	case "push":
		// Sent and not waited for: the asker reads `status` for what the machine did, which is
		// what a person at a shell does too. A tool call that blocked for a push's whole apply would
		// time out on every machine that takes a minute, and say nothing about the ones that did not.
		if n := str("node"); n != "" {
			return []string{"push", n, "--wait", "0"}, nil
		}
		return []string{"push", "--behind", "--wait", "0"}, nil
	case "build":
		if err := need("repository"); err != nil {
			return nil, err
		}
		argv := []string{"build", str("repository"), "--wait", "0"}
		if p := str("path"); p != "" {
			argv = append(argv, "--path", p)
		}
		if r := str("ref"); r != "" {
			argv = append(argv, "--ref", r)
		}
		return argv, nil
	}
	return nil, fmt.Errorf("%q is not a verb the %s seat serves", verb, catalogue.ControllerSeatName)
}

// jsonVerbs are the verbs whose command speaks JSON, so the answer carries it as data as well.
var jsonVerbs = map[string]bool{"status": true, "seats": true, "plan": true}

// runVerb runs this binary with the given command line and gathers what it said.
func runVerb(ctx context.Context, argv []string) (verbAnswer, error) {
	self, err := os.Executable()
	if err != nil {
		return verbAnswer{}, err
	}
	cmd := exec.CommandContext(ctx, self, argv...)
	// The same environment: the stores' credentials, the bus, the broker — everything a command run
	// from a shell in this container would have, because it is that.
	cmd.Env = os.Environ()
	var out bytes.Buffer
	cmd.Stdout = &out
	cmd.Stderr = &out
	runErr := cmd.Run()
	answer := verbAnswer{Output: out.String(), OK: runErr == nil}
	if jsonVerbs[argv[0]] && runErr == nil {
		var parsed any
		if json.Unmarshal(bytes.TrimSpace(out.Bytes()), &parsed) == nil {
			answer.Answer = parsed
		}
	}
	var exit *exec.ExitError
	if runErr != nil && !errors.As(runErr, &exit) {
		// Not the command refusing — the command not running at all, which is this process's fault.
		return answer, fmt.Errorf("could not run %s: %w", strings.Join(argv, " "), runErr)
	}
	return answer, nil
}

// seatToolHandlers are the handlers for every verb the mesh-controller seat declares, from the
// store's row, so a verb the row does not carry is not served and a verb it carries that this binary
// cannot run is said at start rather than at the first call.
func seatToolHandlers() (map[string]link.ToolHandler, error) {
	seat, known := catalogue.SeatNamed(catalogue.ControllerSeatName)
	if !known {
		return nil, fmt.Errorf("this mesh defines no %s seat", catalogue.ControllerSeatName)
	}
	handlers := map[string]link.ToolHandler{}
	for _, v := range seat.Serves {
		verb := v.Name
		if verb == "tools" {
			handlers[verb] = func(ctx context.Context, _ json.RawMessage) (any, error) {
				return seatTools(), nil
			}
			continue
		}
		if _, err := argvFor(verb, map[string]any{"node": "x", "module": "x", "repository": "x"}); err != nil {
			return nil, fmt.Errorf("the %s seat's row declares %q, which this control plane cannot run: %w",
				catalogue.ControllerSeatName, verb, err)
		}
		handlers[verb] = func(ctx context.Context, raw json.RawMessage) (any, error) {
			args := map[string]any{}
			if len(raw) > 0 {
				if err := json.Unmarshal(raw, &args); err != nil {
					return nil, fmt.Errorf("the arguments are not a JSON object: %w", err)
				}
			}
			argv, err := argvFor(verb, args)
			if err != nil {
				return nil, err
			}
			return runVerb(ctx, argv)
		}
	}
	return handlers, nil
}

// seatTools is what `tools` answers: every seat with a protocol, and the tools each serves, from the
// mesh's own records — no holder in the path, so it is true while a holder restarts (design 33 §5).
func seatTools() map[string]any {
	var seats []map[string]any
	for _, s := range catalogue.SeatsWithAProtocol() {
		if len(s.Serves) == 0 {
			continue
		}
		var tools []map[string]any
		for _, v := range s.Serves {
			tools = append(tools, map[string]any{
				"name": v.Name, "description": v.Description, "input": v.Input, "output": v.Output,
			})
		}
		seats = append(seats, map[string]any{"seat": s.Name, "scope": s.Scope, "tools": tools})
	}
	return map[string]any{"seats": seats}
}