Removed use of ioutil.ReadDir as it performs a stat syscall on each file which is not necerssary.

internal/psscanner/proclist.go

@@ -1,17 +1,12 @@
 package psscanner
 
 import (
-	"errors"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"os"
 	"strconv"
 )
 
-var procDirReader = func() ([]os.FileInfo, error) {
-	return ioutil.ReadDir("/proc")
-}
-
 type procList map[int]struct{}
 
 type pidProcessor interface {
@@ -37,15 +32,21 @@ func (pl procList) refresh(p pidProcessor) error {
 }
 
 func getPIDs() ([]int, error) {
-	proc, err := procDirReader()
+	f, err := dirOpen("/proc")
 	if err != nil {
 		return nil, fmt.Errorf("opening proc dir: %v", err)
 	}
+	defer f.Close()
+
+	names, err := f.Readdirnames(-1)
+	if err != nil {
+		return nil, fmt.Errorf("reading proc dir: %v", err)
+	}
 
 	pids := make([]int, 0)
-	for _, f := range proc {
+	for _, f := range names {
-		pid, err := file2Pid(f)
+		pid, err := strconv.Atoi(f)
-		if err != nil {
+		if err != nil || pid <= 0 {
 			continue
 		}
 		pids = append(pids, pid)
@@ -53,17 +54,11 @@ func getPIDs() ([]int, error) {
 	return pids, nil
 }
 
-var errNotAPid = errors.New("not a pid")
+type readDirNamesCloser interface {
-
+	Readdirnames(n int) (names []string, err error)
-func file2Pid(f os.FileInfo) (int, error) {
+	io.Closer
-	if !f.IsDir() {
-		return -1, errNotAPid
 }
 
-	pid, err := strconv.Atoi(f.Name())
+var dirOpen func(string) (readDirNamesCloser, error) = func(s string) (readDirNamesCloser, error) {
-	if err != nil || pid <= 0 {
+	return os.Open(s)
-		return -1, errNotAPid
-	}
-
-	return pid, nil
 }

internal/psscanner/proclist_test.go

@@ -3,31 +3,75 @@ package psscanner
 import (
 	"errors"
 	"fmt"
-	"os"
 	"reflect"
 	"strings"
 	"testing"
-	"time"
 )
 
 // GetPIDs
 
 func TestGetPIDs(t *testing.T) {
 	tests := []struct {
-		proc    []os.FileInfo
+		name        string
-		procErr error
+		proc        []string
+		procErrOpen error
+		procErrRead error
 		pids        []int
 		err         string
 	}{
-		{proc: []os.FileInfo{newMockDir("42"), newMockDir("somedir")}, procErr: nil, pids: []int{42}, err: ""},                   // reads numbers and ignores everything else
+		{
-		{proc: []os.FileInfo{newMockDir("42"), newMockFile("13")}, procErr: nil, pids: []int{42}, err: ""},                       // reads directories and ignores files
+			name:        "numbers-only",
-		{proc: []os.FileInfo{newMockDir("0"), newMockDir("-1")}, procErr: nil, pids: []int{}, err: ""},                           // ignores 0 and negative numbers
+			proc:        []string{"42", "somedir"},
-		{proc: []os.FileInfo{}, procErr: nil, pids: []int{}, err: ""},                                                            // can handle empty procfs
+			procErrOpen: nil,
-		{proc: []os.FileInfo{}, procErr: errors.New("file-system-error"), pids: nil, err: "opening proc dir: file-system-error"}, // returns errors
+			procErrRead: nil,
+			pids:        []int{42},
+			err:         "",
+		},
+		{
+			name:        "multiple-entries",
+			proc:        []string{"42", "13"},
+			procErrOpen: nil,
+			procErrRead: nil,
+			pids:        []int{42, 13},
+			err:         "",
+		},
+		{
+			name:        "ignores-lte-0",
+			proc:        []string{"0", "-1"},
+			procErrOpen: nil,
+			procErrRead: nil,
+			pids:        []int{},
+			err:         "",
+		},
+		{
+			name:        "empty-procfs",
+			proc:        []string{},
+			procErrOpen: nil,
+			procErrRead: nil,
+			pids:        []int{},
+			err:         "",
+		},
+		{
+			name:        "handle-open-error",
+			proc:        []string{},
+			procErrOpen: errors.New("file-system-error"),
+			procErrRead: nil,
+			pids:        nil,
+			err:         "opening proc dir: file-system-error",
+		},
+		{
+			name:        "handle-read-error",
+			proc:        []string{},
+			procErrOpen: nil,
+			procErrRead: errors.New("file-system-error"),
+			pids:        nil,
+			err:         "reading proc dir: file-system-error",
+		},
 	}
 
 	for _, tt := range tests {
-		restore := mockProcDirReader(tt.proc, tt.procErr)
+		t.Run(tt.name, func(t *testing.T) {
+			defer mockDir("/proc", tt.proc, tt.procErrRead, tt.procErrOpen, t)()
 			pids, err := getPIDs()
 			if !reflect.DeepEqual(pids, tt.pids) {
 				t.Errorf("Wrong pids returned: got %v but want %v", pids, tt.pids)
@@ -35,58 +79,53 @@ func TestGetPIDs(t *testing.T) {
 			if (err != nil || tt.err != "") && fmt.Sprintf("%v", err) != tt.err {
 				t.Errorf("Wrong error returned: got %v but want %s", err, tt.err)
 			}
-		restore()
+		})
 	}
 }
 
-func mockProcDirReader(proc []os.FileInfo, err error) (restore func()) {
+type MockDir struct {
-	oldFunc := procDirReader
+	names []string
-	procDirReader = func() ([]os.FileInfo, error) {
+	err   error
-		return proc, err
+}
+
+func (f *MockDir) Close() error {
+	return nil
+}
+
+func min(a, b int) int {
+	if a > b {
+		return b
+	}
+	return a
+}
+
+func (f *MockDir) Readdirnames(n int) (names []string, err error) {
+	if n < 0 {
+		return f.names, f.err
+	}
+	return f.names[:min(n, len(f.names))], f.err
+}
+
+// Hook/chain a mocked file into the "open" variable
+func mockDir(name string, names []string, errRead error, errOpen error, t *testing.T) func() {
+	oldopen := dirOpen
+	dirOpen = func(n string) (readDirNamesCloser, error) {
+		if name == n {
+			if testing.Verbose() {
+				t.Logf("opening mocked dir: %s", n)
+			}
+			return &MockDir{
+				names: names,
+				err:   errRead,
+			}, errOpen
+		}
+		return oldopen(n)
 	}
 	return func() {
-		procDirReader = oldFunc
+		dirOpen = oldopen
 	}
 }
 
-func newMockDir(name string) *mockFileInfo {
-	return &mockFileInfo{
-		name:  name,
-		isDir: true,
-	}
-}
-
-func newMockFile(name string) *mockFileInfo {
-	return &mockFileInfo{
-		name:  name,
-		isDir: false,
-	}
-}
-
-type mockFileInfo struct {
-	name  string
-	isDir bool
-}
-
-func (f *mockFileInfo) Name() string {
-	return f.name
-}
-func (f *mockFileInfo) Size() int64 {
-	return 0
-}
-func (f *mockFileInfo) Mode() os.FileMode {
-	return 0
-}
-func (f *mockFileInfo) ModTime() time.Time {
-	return time.Now()
-}
-func (f *mockFileInfo) IsDir() bool {
-	return f.isDir
-}
-func (f *mockFileInfo) Sys() interface{} {
-	return nil
-}
-
 type mockPidProcessor struct {
 	t    *testing.T
 	pids []int
@@ -124,7 +163,7 @@ func TestRefresh(t *testing.T) {
 			pidsProcessed: []int{3, 2},
 		},
 		{
-			name:          "nothing new",
+			name:          "nothing-new",
 			pl:            procList{1: unit, 2: unit, 3: unit},
 			newPids:       []int{1, 2, 3},
 			plAfter:       procList{1: unit, 2: unit, 3: unit},
@@ -134,7 +173,7 @@ func TestRefresh(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			defer mockPidList(tt.newPids)()
+			defer mockPidList(tt.newPids, t)()
 
 			m := &mockPidProcessor{t, []int{}}
 			tt.pl.refresh(m)
@@ -152,7 +191,24 @@ func TestRefresh(t *testing.T) {
 // separate test for failing, only one case where getPids fails
 func TestRefreshFail(t *testing.T) {
 	e := errors.New("file-system-error")
-	defer mockProcDirReader([]os.FileInfo{}, e)()
+	for _, tt := range []struct {
+		name    string
+		errRead error
+		errOpen error
+	}{
+		{
+			name:    "open-dir-fail",
+			errRead: nil,
+			errOpen: e,
+		},
+		{
+			name:    "read-dir-fail",
+			errRead: e,
+			errOpen: nil,
+		},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			defer mockDir("/proc", []string{}, tt.errRead, tt.errOpen, t)()
 			m := &mockPidProcessor{t, []int{}}
 			pl := procList{1: unit}
 			err := pl.refresh(m)
@@ -163,13 +219,15 @@ func TestRefreshFail(t *testing.T) {
 					t.Errorf("Unexpected error: %v", err)
 				}
 			}
+
+		})
+	}
 }
 
-func mockPidList(pids []int) func() {
+func mockPidList(pids []int, t *testing.T) func() {
-	dirs := make([]os.FileInfo, 0)
+	dirs := make([]string, 0)
 	for _, pid := range pids {
-		dirs = append(dirs, newMockDir(fmt.Sprintf("%d", pid)))
+		dirs = append(dirs, fmt.Sprintf("%d", pid))
 	}
-	restore := mockProcDirReader(dirs, nil)
+	return mockDir("/proc", dirs, nil, nil, t)
-	return restore
 }

internal/psscanner/psscanner_test.go

@@ -31,7 +31,7 @@ func TestRun(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			defer mockPidList(tt.pids)()
+			defer mockPidList(tt.pids, t)()
 			for _, pid := range tt.pids {
 				defer mockPidCmdLine(pid, []byte("the-command"), nil, nil, t)()
 				defer mockPidStatus(pid, []byte{}, nil, nil, t)() // don't mock read value since it's not worth it