internal/helper: relocate from helper

This package is ugly and is pending removal only kept alive by xdg-dbus-proxy.

Its exported symbols are made available until v0.4.0 where it will be removed for #24.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/helper/container.go

@@ -0,0 +1,79 @@
+package helper
+
+import (
+	"context"
+	"errors"
+	"io"
+	"os"
+	"os/exec"
+	"slices"
+	"sync"
+
+	"hakurei.app/container"
+	"hakurei.app/container/check"
+	"hakurei.app/internal/helper/proc"
+	"hakurei.app/message"
+)
+
+// New initialises a Helper instance with wt as the null-terminated argument writer.
+func New(
+	ctx context.Context,
+	msg message.Msg,
+	pathname *check.Absolute, name string,
+	wt io.WriterTo,
+	stat bool,
+	argF func(argsFd, statFd int) []string,
+	cmdF func(z *container.Container),
+	extraFiles []*os.File,
+) Helper {
+	var args []string
+	h := new(helperContainer)
+	h.helperFiles, args = newHelperFiles(ctx, wt, stat, argF, extraFiles)
+	h.Container = container.NewCommand(ctx, msg, pathname, name, args...)
+	h.WaitDelay = WaitDelay
+	if cmdF != nil {
+		cmdF(h.Container)
+	}
+	return h
+}
+
+// helperContainer provides a [sandbox.Container] wrapper around helper ipc.
+type helperContainer struct {
+	started bool
+
+	mu sync.Mutex
+	*helperFiles
+	*container.Container
+}
+
+func (h *helperContainer) Start() error {
+	h.mu.Lock()
+	defer h.mu.Unlock()
+
+	if h.started {
+		return errors.New("helper: already started")
+	}
+	h.started = true
+
+	h.Env = slices.Grow(h.Env, 2)
+	if h.useArgsFd {
+		h.Env = append(h.Env, HakureiHelper+"=1")
+	} else {
+		h.Env = append(h.Env, HakureiHelper+"=0")
+	}
+	if h.useStatFd {
+		h.Env = append(h.Env, HakureiStatus+"=1")
+
+		// stat is populated on fulfill
+		h.Cancel = func(*exec.Cmd) error { return h.stat.Close() }
+	} else {
+		h.Env = append(h.Env, HakureiStatus+"=0")
+	}
+
+	return proc.Fulfill(h.helperFiles.ctx, &h.ExtraFiles, func() error {
+		if err := h.Container.Start(); err != nil {
+			return err
+		}
+		return h.Container.Serve()
+	}, h.files, h.extraFiles)
+}