dbus: implement xdg-dbus-proxy wrapper

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

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}}
+}