helper: helper.Helper interface

For upcoming bwrap implementation of helper.Helper

Signed-off-by: Ophestra Umiker <cat@ophivana.moe>

1 files changed, 93 insertions, 0 deletions

diff --git a/helper/direct.go b/helper/direct.go
new file mode 100644
index 00000000..24f9e75d
--- /dev/null
+++ b/helper/direct.go
@@ -0,0 +1,93 @@
+package helper
+
+import (
+	"errors"
+	"io"
+	"os/exec"
+	"sync"
+)
+
+// direct wraps *exec.Cmd and manages status and args fd.
+// Args is always 3 and status if set is always 4.
+type direct struct {
+	// helper pipes
+	// cannot be nil
+	p *pipes
+
+	// returns an array of arguments passed directly
+	// to the helper process
+	argF func(argsFD, statFD int) []string
+
+	lock sync.RWMutex
+	*exec.Cmd
+}
+
+func (h *direct) StartNotify(ready chan error) error {
+	h.lock.Lock()
+	defer h.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 h.Cmd.Process != nil {
+		return errors.New("exec: already started")
+	}
+
+	h.p.ready = ready
+	if argsFD, statFD, err := h.p.prepareCmd(h.Cmd); err != nil {
+		return err
+	} else {
+		h.Cmd.Args = append(h.Cmd.Args, h.argF(argsFD, statFD)...)
+	}
+
+	if ready != nil {
+		h.Cmd.Env = append(h.Cmd.Env, FortifyHelper+"=1", FortifyStatus+"=1")
+	} else {
+		h.Cmd.Env = append(h.Cmd.Env, FortifyHelper+"=1", FortifyStatus+"=0")
+	}
+
+	if err := h.Cmd.Start(); err != nil {
+		return err
+	}
+	if err := h.p.readyWriteArgs(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (h *direct) Wait() error {
+	h.lock.RLock()
+	defer h.lock.RUnlock()
+
+	if h.Cmd.Process == nil {
+		return errors.New("exec: not started")
+	}
+	if h.Cmd.ProcessState != nil {
+		return errors.New("exec: Wait was already called")
+	}
+
+	defer h.p.mustClosePipes()
+	return h.Cmd.Wait()
+}
+
+func (h *direct) Close() error {
+	return h.p.closeStatus()
+}
+
+func (h *direct) Start() error {
+	return h.StartNotify(nil)
+}
+
+func (h *direct) Unwrap() *exec.Cmd {
+	return h.Cmd
+}
+
+// New initialises a new direct Helper instance with wt as the null-terminated argument writer.
+// Function argF returns an array of arguments passed directly to the child process.
+func New(wt io.WriterTo, name string, argF func(argsFD, statFD int) []string) Helper {
+	if wt == nil {
+		panic("attempted to create helper with invalid argument writer")
+	}
+
+	return &direct{p: &pipes{args: wt}, argF: argF, Cmd: execCommand(name)}
+}