helper: use generic extra files interface

This replaces the pipes object and integrates context into helper process lifecycle.

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

helper/bwrap.go

@@ -1,111 +1,47 @@
 package helper
 
 import (
+	"context"
 	"errors"
 	"io"
 	"os"
-	"os/exec"
+	"slices"
 	"strconv"
 	"sync"
 
 	"git.gensokyo.uk/security/fortify/helper/bwrap"
+	"git.gensokyo.uk/security/fortify/helper/proc"
 )
 
 // BubblewrapName is the file name or path to bubblewrap.
 var BubblewrapName = "bwrap"
 
 type bubblewrap struct {
-	// bwrap child file name
+	// final args fd of bwrap process
+	argsFd uintptr
+
+	// name of the command to run in bwrap
 	name string
 
-	// bwrap pipes
-	control *pipes
-	// returns an array of arguments passed directly
-	// to the child process spawned by bwrap
-	argF func(argsFD, statFD int) []string
-
-	// pipes received by the child
-	// nil if no pipes are required
-	controlPt *pipes
-
 	lock sync.RWMutex
-	*exec.Cmd
+	*helperCmd
 }
 
-func (b *bubblewrap) StartNotify(ready chan error) error {
+func (b *bubblewrap) Start(ctx context.Context, stat bool) error {
 	b.lock.Lock()
 	defer b.lock.Unlock()
 
-	if ready != nil && b.controlPt == nil {
-		panic("attempted to start with status monitoring on a bwrap child initialised without pipes")
-	}
-
 	// 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.Process != nil {
+	if b.Cmd != nil && b.Cmd.Process != nil {
 		return errors.New("exec: already started")
 	}
 
-	// prepare bwrap pipe and args
-	if argsFD, _, err := b.control.prepareCmd(b.Cmd); err != nil {
-		return err
-	} else {
-		b.Cmd.Args = append(b.Cmd.Args, "--args", strconv.Itoa(argsFD), "--", b.name)
-	}
-
-	// prepare child args and pipes if enabled
-	if b.controlPt != nil {
-		b.controlPt.ready = ready
-		if argsFD, statFD, err := b.controlPt.prepareCmd(b.Cmd); err != nil {
-			return err
-		} else {
-			b.Cmd.Args = append(b.Cmd.Args, b.argF(argsFD, statFD)...)
-		}
-	} else {
-		b.Cmd.Args = append(b.Cmd.Args, b.argF(-1, -1)...)
-	}
-
-	if ready != nil {
-		b.Cmd.Env = append(b.Cmd.Env, FortifyHelper+"=1", FortifyStatus+"=1")
-	} else if b.controlPt != nil {
-		b.Cmd.Env = append(b.Cmd.Env, FortifyHelper+"=1", FortifyStatus+"=0")
-	} else {
-		b.Cmd.Env = append(b.Cmd.Env, FortifyHelper+"=1", FortifyStatus+"=-1")
-	}
-
-	if err := b.Cmd.Start(); err != nil {
-		return err
-	}
-
-	// write bwrap args first
-	if err := b.control.readyWriteArgs(); err != nil {
-		return err
-	}
-
-	// write child args if enabled
-	if b.controlPt != nil {
-		if err := b.controlPt.readyWriteArgs(); err != nil {
-			return err
-		}
-	}
-
-	return nil
-}
-
-func (b *bubblewrap) Close() error {
-	if b.controlPt == nil {
-		panic("attempted to close bwrap child initialised without pipes")
-	}
-
-	return b.controlPt.closeStatus()
-}
-
-func (b *bubblewrap) Start() error {
-	return b.StartNotify(nil)
-}
-
-func (b *bubblewrap) Unwrap() *exec.Cmd {
-	return b.Cmd
+	args := b.finalise(ctx, stat)
+	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(ctx, b.Cmd, b.files, b.extraFiles)
 }
 
 // MustNewBwrap initialises a new Bwrap instance with wt as the null-terminated argument writer.
@@ -130,27 +66,23 @@ func MustNewBwrap(
 // Function argF returns an array of arguments passed directly to the child process.
 func NewBwrap(
 	conf *bwrap.Config, name string,
-	wt io.WriterTo, argF func(argsFD, statFD int) []string,
+	wt io.WriterTo, argF func(argsFd, statFd int) []string,
 	extraFiles []*os.File,
 	syncFd *os.File,
 ) (Helper, error) {
 	b := new(bubblewrap)
 
-	b.argF = argF
 	b.name = name
-	if wt != nil {
-		b.controlPt = &pipes{args: wt}
-	}
+	b.helperCmd = newHelperCmd(b, BubblewrapName, wt, argF, extraFiles)
 
-	b.Cmd = execCommand(BubblewrapName)
-	b.control = new(pipes)
 	args := conf.Args()
-	if fdArgs, err := conf.FDArgs(syncFd, &extraFiles); err != nil {
-		return nil, err
-	} else if b.control.args, err = NewCheckedArgs(append(args, fdArgs...)); err != nil {
+	conf.FDArgs(syncFd, &args, b.extraFiles, &b.files)
+	if v, err := NewCheckedArgs(args); err != nil {
 		return nil, err
 	} else {
-		b.Cmd.ExtraFiles = extraFiles
+		f := proc.NewWriterTo(v)
+		b.argsFd = proc.InitFile(f, b.extraFiles)
+		b.files = append(b.files, f)
 	}
 
 	return b, nil