dbus: implement xdg-dbus-proxy wrapper

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

dbus/run.go

@@ -0,0 +1,134 @@
+package dbus
+
+import (
+	"errors"
+	"os"
+	"os/exec"
+)
+
+// Start launches the D-Bus proxy and sets up the Wait method.
+// ready should be buffered and should only be received from once.
+func (p *Proxy) Start(ready *chan bool) error {
+	p.lock.Lock()
+	defer p.lock.Unlock()
+
+	if p.seal == nil {
+		return errors.New("proxy not sealed")
+	}
+
+	// acquire pipes
+	if pr, pw, err := os.Pipe(); err != nil {
+		return err
+	} else {
+		p.statP[0], p.statP[1] = pr, pw
+	}
+	if pr, pw, err := os.Pipe(); err != nil {
+		return err
+	} else {
+		p.argsP[0], p.argsP[1] = pr, pw
+	}
+
+	p.cmd = exec.Command(p.path,
+		// ExtraFiles: If non-nil, entry i becomes file descriptor 3+i.
+		"--fd=3",
+		"--args=4",
+	)
+	p.cmd.Env = []string{}
+	p.cmd.ExtraFiles = []*os.File{p.statP[1], p.argsP[0]}
+	p.cmd.Stdout = os.Stdout
+	p.cmd.Stderr = os.Stderr
+	if err := p.cmd.Start(); err != nil {
+		return err
+	}
+
+	statsP, argsP := p.statP[0], p.argsP[1]
+
+	if _, err := argsP.Write([]byte(*p.seal)); err != nil {
+		if err1 := p.cmd.Process.Kill(); err1 != nil {
+			panic(err1)
+		}
+		return err
+	} else {
+		if err = argsP.Close(); err != nil {
+			if err1 := p.cmd.Process.Kill(); err1 != nil {
+				panic(err1)
+			}
+			return err
+		}
+	}
+
+	wait := make(chan error)
+	go func() {
+		// live out the lifespan of the process
+		wait <- p.cmd.Wait()
+	}()
+
+	read := make(chan error)
+	go func() {
+		n, err := statsP.Read(make([]byte, 1))
+		switch n {
+		case -1:
+			if err1 := p.cmd.Process.Kill(); err1 != nil {
+				panic(err1)
+			}
+			read <- err
+		case 0:
+			read <- err
+		case 1:
+			*ready <- true
+			read <- nil
+		default:
+			panic("unreachable") // unexpected read count
+		}
+	}()
+
+	p.wait = &wait
+	p.read = &read
+	p.ready = ready
+
+	return nil
+}
+
+// Wait waits for xdg-dbus-proxy to exit or fault.
+func (p *Proxy) Wait() error {
+	p.lock.RLock()
+	defer p.lock.RUnlock()
+
+	if p.wait == nil || p.read == nil {
+		return errors.New("proxy not running")
+	}
+
+	defer func() {
+		if err1 := p.statP[0].Close(); err1 != nil && !errors.Is(err1, os.ErrClosed) {
+			panic(err1)
+		}
+		if err1 := p.statP[1].Close(); err1 != nil && !errors.Is(err1, os.ErrClosed) {
+			panic(err1)
+		}
+
+		if err1 := p.argsP[0].Close(); err1 != nil && !errors.Is(err1, os.ErrClosed) {
+			panic(err1)
+		}
+		if err1 := p.argsP[1].Close(); err1 != nil && !errors.Is(err1, os.ErrClosed) {
+			panic(err1)
+		}
+
+	}()
+
+	select {
+	case err := <-*p.wait:
+		*p.ready <- false
+		return err
+	case err := <-*p.read:
+		if err != nil {
+			*p.ready <- false
+			return err
+		}
+		return <-*p.wait
+	}
+}
+
+// Close closes the status file descriptor passed to xdg-dbus-proxy, causing it to stop.
+func (p *Proxy) Close() error {
+	return p.statP[0].Close()
+}