helper: combine helper ipc setup

The two-step args call is no longer necessary since stat is passed on initialisation.

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

helper/helper.go

@@ -2,9 +2,14 @@
 package helper
 
 import (
+	"context"
 	"fmt"
+	"io"
+	"os"
 	"os/exec"
 	"time"
+
+	"git.gensokyo.uk/security/fortify/helper/proc"
 )
 
 var (
@@ -28,3 +33,56 @@ type Helper interface {
 
 	fmt.Stringer
 }
+
+func newHelperFiles(
+	ctx context.Context,
+	wt io.WriterTo,
+	stat bool,
+	argF func(argsFd, statFd int) []string,
+	extraFiles []*os.File,
+) (hl *helperFiles, args []string) {
+	hl = new(helperFiles)
+	hl.ctx = ctx
+	hl.useArgsFd = wt != nil
+	hl.useStatFd = stat
+
+	hl.extraFiles = new(proc.ExtraFilesPre)
+	for _, f := range extraFiles {
+		_, v := hl.extraFiles.Append()
+		*v = f
+	}
+
+	argsFd := -1
+	if hl.useArgsFd {
+		f := proc.NewWriterTo(wt)
+		argsFd = int(proc.InitFile(f, hl.extraFiles))
+		hl.files = append(hl.files, f)
+	}
+
+	statFd := -1
+	if hl.useStatFd {
+		f := proc.NewStat(&hl.stat)
+		statFd = int(proc.InitFile(f, hl.extraFiles))
+		hl.files = append(hl.files, f)
+	}
+
+	args = argF(argsFd, statFd)
+	return
+}
+
+// helperFiles provides a generic wrapper around helper ipc.
+type helperFiles struct {
+	// whether argsFd is present
+	useArgsFd bool
+	// whether statFd is present
+	useStatFd bool
+
+	// closes statFd
+	stat io.Closer
+	// deferred extraFiles fulfillment
+	files []proc.File
+	// passed through to [proc.Fulfill] and [proc.InitFile]
+	extraFiles *proc.ExtraFilesPre
+
+	ctx context.Context
+}