dbus: implement xdg-dbus-proxy wrapper

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

dbus/config.go

@@ -0,0 +1,59 @@
+package dbus
+
+type Config struct {
+	See  []string `json:"see"`
+	Talk []string `json:"talk"`
+	Own  []string `json:"own"`
+
+	Log    bool `json:"log,omitempty"`
+	Filter bool `json:"filter"`
+}
+
+func (c *Config) Args(address, path string) (args []string) {
+	argc := 2 + len(c.See) + len(c.Talk) + len(c.Own)
+	if c.Log {
+		argc++
+	}
+	if c.Filter {
+		argc++
+	}
+
+	args = make([]string, 0, argc)
+	args = append(args, address, path)
+	for _, name := range c.See {
+		args = append(args, "--see="+name)
+	}
+	for _, name := range c.Talk {
+		args = append(args, "--talk="+name)
+	}
+	for _, name := range c.Own {
+		args = append(args, "--own="+name)
+	}
+	if c.Log {
+		args = append(args, "--log")
+	}
+	if c.Filter {
+		args = append(args, "--filter")
+	}
+
+	return
+}
+
+// NewConfig returns a reference to a Config struct with optional defaults.
+// If id is an empty string own defaults are omitted.
+func NewConfig(id string, defaults, mpris bool) (c *Config) {
+	c = &Config{Filter: true}
+
+	if defaults {
+		c.Talk = []string{"org.freedesktop.DBus", "org.freedesktop.portal.*", "org.freedesktop.Notifications"}
+
+		if id != "" {
+			c.Own = []string{id}
+			if mpris {
+				c.Own = append(c.Own, "org.mpris.MediaPlayer2."+id)
+			}
+		}
+	}
+
+	return
+}

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()
+}

dbus/setup.go

@@ -0,0 +1,73 @@
+package dbus
+
+import (
+	"errors"
+	"os"
+	"os/exec"
+	"strings"
+	"sync"
+)
+
+// Proxy holds references to a xdg-dbus-proxy process, and should never be copied.
+// Once sealed, configuration changes will no longer be possible and attempting to do so will result in a panic.
+type Proxy struct {
+	cmd *exec.Cmd
+
+	statP [2]*os.File
+	argsP [2]*os.File
+
+	address [2]string
+	path    string
+
+	wait  *chan error
+	read  *chan error
+	ready *chan bool
+
+	seal *string
+	lock sync.RWMutex
+}
+
+func (p *Proxy) String() string {
+	if p.cmd != nil {
+		return p.cmd.String()
+	}
+
+	if p.seal != nil {
+		return *p.seal
+	}
+
+	return "(unsealed dbus proxy)"
+}
+
+// Seal seals the Proxy instance.
+func (p *Proxy) Seal(c *Config) error {
+	p.lock.Lock()
+	defer p.lock.Unlock()
+
+	if p.seal != nil {
+		panic("dbus proxy sealed twice")
+	}
+	args := c.Args(p.address[0], p.address[1])
+
+	seal := strings.Builder{}
+	for _, arg := range args {
+		// reject argument strings containing null
+		for _, b := range arg {
+			if b == '\x00' {
+				return errors.New("argument contains null")
+			}
+		}
+
+		// write null terminated argument
+		seal.WriteString(arg)
+		seal.WriteByte('\x00')
+	}
+	v := seal.String()
+	p.seal = &v
+	return nil
+}
+
+// New returns a reference to a new unsealed Proxy.
+func New(binPath, address, path string) *Proxy {
+	return &Proxy{path: binPath, address: [2]string{address, path}}
+}