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/bwrap.go

@@ -2,13 +2,11 @@ package helper
 
 import (
 	"context"
-	"errors"
 	"io"
 	"os"
 	"os/exec"
 	"slices"
 	"strconv"
-	"sync"
 	"syscall"
 
 	"git.gensokyo.uk/security/fortify/helper/bwrap"
@@ -18,34 +16,6 @@ import (
 // BubblewrapName is the file name or path to bubblewrap.
 var BubblewrapName = "bwrap"
 
-type bubblewrap struct {
-	// final args fd of bwrap process
-	argsFd uintptr
-
-	// name of the command to run in bwrap
-	name string
-
-	lock sync.RWMutex
-	*helperCmd
-}
-
-func (b *bubblewrap) Start() error {
-	b.lock.Lock()
-	defer b.lock.Unlock()
-
-	// Check for doubled Start calls before we defer failure cleanup. If the prior
-	// call to Start succeeded, we don't want to spuriously close its pipes.
-	if b.Cmd != nil && b.Cmd.Process != nil {
-		return errors.New("exec: already started")
-	}
-
-	args := b.finalise()
-	b.Cmd.Args = slices.Grow(b.Cmd.Args, 4+len(args))
-	b.Cmd.Args = append(b.Cmd.Args, "--args", strconv.Itoa(int(b.argsFd)), "--", b.name)
-	b.Cmd.Args = append(b.Cmd.Args, args...)
-	return proc.Fulfill(b.ctx, &b.ExtraFiles, b.Cmd.Start, b.files, b.extraFiles)
-}
-
 // MustNewBwrap initialises a new Bwrap instance with wt as the null-terminated argument writer.
 // If wt is nil, the child process spawned by bwrap will not get an argument pipe.
 // Function argF returns an array of arguments passed directly to the child process.
@@ -84,24 +54,25 @@ func NewBwrap(
 	extraFiles []*os.File,
 	syncFd *os.File,
 ) (Helper, error) {
-	b := new(bubblewrap)
-
-	b.name = name
-	b.helperCmd = newHelperCmd(ctx, BubblewrapName, wt, argF, stat, extraFiles)
+	b, args := newHelperCmd(ctx, BubblewrapName, wt, stat, argF, extraFiles)
 	if setpgid {
 		b.Cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
 	}
-	if cmdF != nil {
-		cmdF(b.helperCmd.Cmd)
-	}
 
+	var argsFd uintptr
 	if v, err := NewCheckedArgs(conf.Args(syncFd, b.extraFiles, &b.files)); err != nil {
 		return nil, err
 	} else {
 		f := proc.NewWriterTo(v)
-		b.argsFd = proc.InitFile(f, b.extraFiles)
+		argsFd = proc.InitFile(f, b.extraFiles)
 		b.files = append(b.files, f)
 	}
 
+	b.Args = slices.Grow(b.Args, 4+len(args))
+	b.Args = append(b.Args, "--args", strconv.Itoa(int(argsFd)), "--", name)
+	b.Args = append(b.Args, args...)
+	if cmdF != nil {
+		cmdF(b.Cmd)
+	}
 	return b, nil
 }