Add Process.Parent() (#46)

Adds a `Parent()` method to `Process` and implements it for all platforms. This should make it easier for users of this library to traverse the process tree.

providers/darwin/process_darwin_amd64.go

@@ -85,6 +85,7 @@ func (s darwinSystem) Self() (types.Process, error) {
 }
 
 type process struct {
+	info *types.ProcessInfo
 	pid  int
 	cwd  string
 	exe  string
@@ -96,7 +97,20 @@ func (p *process) PID() int {
 	return p.pid
 }
 
+func (p *process) Parent() (types.Process, error) {
+	info, err := p.Info()
+	if err != nil {
+		return nil, err
+	}
+
+	return &process{pid: info.PPID}, nil
+}
+
 func (p *process) Info() (types.ProcessInfo, error) {
+	if p.info != nil {
+		return *p.info, nil
+	}
+
 	var task procTaskAllInfo
 	if err := getProcTaskAllInfo(p.pid, &task); err != nil {
 		return types.ProcessInfo{}, err
@@ -111,7 +125,7 @@ func (p *process) Info() (types.ProcessInfo, error) {
 		return types.ProcessInfo{}, err
 	}
 
-	return types.ProcessInfo{
+	p.info = &types.ProcessInfo{
 		Name: int8SliceToString(task.Pbsd.Pbi_name[:]),
 		PID:  p.pid,
 		PPID: int(task.Pbsd.Pbi_ppid),
@@ -120,7 +134,9 @@ func (p *process) Info() (types.ProcessInfo, error) {
 		Args: p.args,
 		StartTime: time.Unix(int64(task.Pbsd.Pbi_start_tvsec),
 			int64(task.Pbsd.Pbi_start_tvusec)*int64(time.Microsecond)),
-	}, nil
+	}
+
+	return *p.info, nil
 }
 
 func (p *process) User() (types.UserInfo, error) {

providers/linux/os_test.go

@@ -15,6 +15,8 @@
 // specific language governing permissions and limitations
 // under the License.
 
+// +build !windows
+
 package linux
 
 import (

providers/linux/process_linux.go

@@ -73,6 +73,20 @@ func (p *process) PID() int {
 	return p.Proc.PID
 }
 
+func (p *process) Parent() (types.Process, error) {
+	info, err := p.Info()
+	if err != nil {
+		return nil, err
+	}
+
+	proc, err := p.fs.NewProc(info.PPID)
+	if err != nil {
+		return nil, err
+	}
+
+	return &process{Proc: proc, fs: p.fs}, nil
+}
+
 func (p *process) path(pa ...string) string {
 	return p.fs.Path(append([]string{strconv.Itoa(p.PID())}, pa...)...)
 }

providers/windows/process_windows.go

@@ -79,6 +79,15 @@ func (p *process) PID() int {
 	return p.pid
 }
 
+func (p *process) Parent() (types.Process, error) {
+	info, err := p.Info()
+	if err != nil {
+		return nil, err
+	}
+
+	return newProcess(info.PPID)
+}
+
 func newProcess(pid int) (*process, error) {
 	p := &process{pid: pid}
 	if err := p.init(); err != nil {

system_test.go

@@ -115,6 +115,7 @@ func TestSelf(t *testing.T) {
 	assert.EqualValues(t, os.Getpid(), info.PID)
 	assert.EqualValues(t, os.Getppid(), info.PPID)
 	assert.Equal(t, os.Args, info.Args)
+	assert.WithinDuration(t, info.StartTime, time.Now(), 10*time.Second)
 
 	wd, err := os.Getwd()
 	if err != nil {
@@ -128,10 +129,11 @@ func TestSelf(t *testing.T) {
 	}
 	assert.Equal(t, exe, info.Exe)
 
+	parent, err := process.Parent()
 	if err != nil {
 		t.Fatal(err)
 	}
-	assert.WithinDuration(t, info.StartTime, time.Now(), 10*time.Second)
+	assert.EqualValues(t, os.Getppid(), parent.PID())
 
 	user, err := process.User()
 	if err != nil {

types/process.go

@@ -24,6 +24,7 @@ type Process interface {
 	Info() (ProcessInfo, error)
 	Memory() (MemoryInfo, error)
 	User() (UserInfo, error)
+	Parent() (Process, error)
 	PID() int
 }