mesh-catalog/modules/dunst/cmd/dunst-tools/actions.go

package main

// Answers from a notification (novox/hq ADR 0253, to-be 46 §11 "the desk"): `send` takes actions, each a
// token and a label. dunst offers them on the notification (a middle click, or its context menu, which
// is the node-launcher's menu); the one the operator chooses is emitted as this module's event
// `action-chosen` {id, token, machine}, and the operator channel's holder acts on it. It is this module's
// event until seats publish events of their own (to-be 46 phase 3), when it becomes the node-notifier
// seat's.
//
// notify-send waits for the answer (`--wait`) in this process: the id is answered at once, and the
// answer, if any, comes later. An answer is never invented: a notification closed, expired or replaced
// emits nothing, and a wait ends after AnswerWait. A restart of this bundle ends the waits it held,
// which the README says; the notification stays shown and its answers do nothing then.

import (
	"bufio"
	"errors"
	"fmt"
	"io"
	"os"
	"os/exec"
	"regexp"
	"strconv"
	"strings"
	"syscall"
	"time"

	stdio "git.novox.be/novox/mesh-sdk/go"
)

// Choice is one action a notification offers.
type Choice struct {
	Token string `json:"token"`
	Label string `json:"label"`
}

const (
	// MostChoices is how many actions one notification offers.
	MostChoices = 4
	// AnswerWait is how long an answer is waited for.
	AnswerWait = 7 * 24 * time.Hour
	// ChosenEvent is the event an answer is said as; StartedEvent says this bundle started, so the answers
	// an earlier one waited for are lost and the operator channel shows them again (novox/hq ADR 0258).
	ChosenEvent  = "action-chosen"
	StartedEvent = "started"
)

// sayStarted says, once this bundle serves, that it started on this machine; retried while the runtime
// cannot take it yet, and said in the log when it never could.
func sayStarted() {
	body := map[string]any{"machine": os.Getenv("MESH_NODE")}
	var err error
	for wait := time.Second; wait <= time.Minute; wait *= 2 {
		time.Sleep(wait)
		if err = emit(StartedEvent, body); err == nil {
			return
		}
	}
	fmt.Fprintf(os.Stderr, "[dunst] could not say it started (answers waited for before are lost until the "+
		"operator channel shows them again): %v\n", err)
}

var tokenShape = regexp.MustCompile(`^[A-Za-z0-9_-]{1,64}$`)

// emit says an event as this module; a seam a test replaces.
var emit = func(event string, body any) error { return stdio.Emit(event, body) }

// choicesOf reads `actions`: a list of {token, label}.
func choicesOf(args map[string]any) ([]Choice, error) {
	v, present := args["actions"]
	if !present || v == nil {
		return nil, nil
	}
	list, ok := v.([]any)
	if !ok {
		return nil, errors.New("actions is a list of {token, label}")
	}
	if len(list) > MostChoices {
		return nil, fmt.Errorf("at most %d actions", MostChoices)
	}
	var out []Choice
	seen := map[string]bool{}
	for _, it := range list {
		o, ok := it.(map[string]any)
		if !ok {
			return nil, errors.New("actions is a list of {token, label}")
		}
		tok, _ := o["token"].(string)
		label, _ := o["label"].(string)
		label = strings.TrimSpace(label)
		switch {
		case !tokenShape.MatchString(tok):
			return nil, fmt.Errorf("an action's token is letters, digits, - and _, at most 64: %q", tok)
		case seen[tok]:
			return nil, fmt.Errorf("the token %q is given twice", tok)
		case label == "" || len(label) > 40 || strings.ContainsAny(label, "\n="):
			return nil, fmt.Errorf("an action's label is one short line without '=': %q", label)
		}
		seen[tok] = true
		out = append(out, Choice{Token: tok, Label: label})
	}
	return out, nil
}

// actionArgs are notify-send's arguments for the choices, and its wait.
func actionArgs(choices []Choice) []string {
	args := []string{"--wait"}
	for _, c := range choices {
		args = append(args, "--action="+c.Token+"="+c.Label)
	}
	return args
}

// sendWaiting runs notify-send with the choices, answers the id it prints first, and waits for the
// answer in the background: the next line it prints, if it is one of the tokens.
func (s Session) sendWaiting(args []string, choices []Choice) (SendResult, error) {
	path, err := exec.LookPath("notify-send")
	if err != nil {
		return SendResult{}, errors.New("notify-send is not installed on this machine")
	}
	cmd := exec.Command(path, args...)
	cmd.Env = s.Env()
	if home := operatorHome(); exists(home) {
		cmd.Dir = home
	}
	out, err := cmd.StdoutPipe()
	if err != nil {
		return SendResult{}, err
	}
	var errOut capped
	cmd.Stderr = &errOut
	cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
	if err := cmd.Start(); err != nil {
		return SendResult{}, fmt.Errorf("notify-send: %w", err)
	}
	lines := bufio.NewReader(out)
	first := make(chan string, 1)
	go func() {
		line, _ := lines.ReadString('\n')
		first <- strings.TrimSpace(line)
	}()
	var idLine string
	select {
	case idLine = <-first:
	case <-time.After(busTimeout):
		_ = syscall.Kill(-cmd.Process.Pid, syscall.SIGKILL)
		_ = cmd.Wait()
		return SendResult{}, fmt.Errorf("notify-send did not answer an id within %s: %w", busTimeout, ErrTimedOut)
	}
	id, err := strconv.Atoi(idLine)
	if err != nil {
		_ = syscall.Kill(-cmd.Process.Pid, syscall.SIGKILL)
		_ = cmd.Wait()
		return SendResult{}, fmt.Errorf("notify-send answered no id: %q %s", idLine, strings.TrimSpace(errOut.String()))
	}
	go awaitAnswer(cmd, lines, id, choices)
	return SendResult{ID: id}, nil
}

// awaitAnswer reads what notify-send says when the notification ends, and says a chosen token.
func awaitAnswer(cmd *exec.Cmd, lines io.Reader, id int, choices []Choice) {
	timer := time.AfterFunc(AnswerWait, func() { _ = syscall.Kill(-cmd.Process.Pid, syscall.SIGTERM) })
	defer timer.Stop()
	rest, _ := io.ReadAll(io.LimitReader(lines, 4096))
	_ = cmd.Wait()
	if tok, ok := chosenToken(string(rest), choices); ok {
		body := map[string]any{"id": id, "token": tok, "machine": os.Getenv("MESH_NODE")}
		if err := emit(ChosenEvent, body); err != nil {
			fmt.Fprintf(os.Stderr, "[dunst] the operator chose an action on notification %d and it could not be said: %v\n", id, err)
		}
	}
}

// chosenToken is the token notify-send printed after the id, when it is one offered.
func chosenToken(rest string, choices []Choice) (string, bool) {
	for _, line := range strings.Split(rest, "\n") {
		line = strings.TrimSpace(line)
		for _, c := range choices {
			if line == c.Token {
				return c.Token, true
			}
		}
	}
	return "", false
}