From dfd6a516400b59aebe425b18cc481e23e8eb1575 Mon Sep 17 00:00:00 2001
From: Martin Magr <mmagr@redhat.com>
Date: Mon, 9 Aug 2021 22:45:04 +0200
Subject: [PATCH] Add system.GetOpenedFiles

Enables programatically find out about opened files from a given process.
---
 system/proc.go       | 32 ++++++++++++++++++++++++++------
 tests/system_test.go | 29 +++++++++++++++++++++++------
 2 files changed, 49 insertions(+), 12 deletions(-)

diff --git a/system/proc.go b/system/proc.go
index 271410a..0d05f82 100644
--- a/system/proc.go
+++ b/system/proc.go
@@ -11,18 +11,22 @@ import (
 
 // Modifiable constants
 var (
-	ProcLimitColumns = 4
-	ProcLimitPathFmt = "/proc/%d/limits"
-	splitRex         = regexp.MustCompile("  +")
+	ProcLimitColumns   = 4
+	ProcLimitPathFmt   = "/proc/%d/limits"
+	ProcOpenedFilesFmt = "/proc/%d/fd"
+	splitRex           = regexp.MustCompile("  +")
 )
 
-// GetProcLimits returns limits for the given process. Use -1 for actual process.
-func GetProcLimits(PID int) (map[string]map[string]interface{}, error) {
+func getProcPath(pathFmt string, PID int) string {
 	if PID == -1 {
 		PID = os.Getpid()
 	}
+	return fmt.Sprintf(pathFmt, PID)
+}
 
-	data, err := ioutil.ReadFile(fmt.Sprintf(ProcLimitPathFmt, PID))
+// GetProcLimits returns limits for the given process. Use -1 for actual process.
+func GetProcLimits(PID int) (map[string]map[string]interface{}, error) {
+	data, err := ioutil.ReadFile(getProcPath(ProcLimitPathFmt, PID))
 	if err != nil {
 		return nil, err
 	}
@@ -56,3 +60,19 @@ func GetProcLimits(PID int) (map[string]map[string]interface{}, error) {
 
 	return out, nil
 }
+
+// GetOpenedFiles returns count of opened files by the given process. Use -1 for actual process.
+func GetOpenedFiles(PID int) (int, error) {
+	dir, err := os.Open(getProcPath(ProcOpenedFilesFmt, PID))
+	if err != nil {
+		return -1, err
+	}
+
+	files, err := dir.Readdir(-1)
+	dir.Close()
+	if err != nil {
+		return -1, err
+	}
+
+	return len(files), nil
+}
diff --git a/tests/system_test.go b/tests/system_test.go
index fd687a9..4d85c18 100644
--- a/tests/system_test.go
+++ b/tests/system_test.go
@@ -1,6 +1,7 @@
 package tests
 
 import (
+	"fmt"
 	"io/ioutil"
 	"os"
 	"path"
@@ -34,13 +35,13 @@ func TestProcLimits(t *testing.T) {
 	require.NoError(t, err)
 	defer os.RemoveAll(tmpdir)
 
-	// save test content
-	file, err := os.Create(path.Join(tmpdir, "0_limits"))
-	require.NoError(t, err)
-	file.WriteString(procLimitData)
-	require.NoError(t, file.Close())
-
 	t.Run("Test parsed limit file", func(t *testing.T) {
+		// save test content
+		file, err := os.Create(path.Join(tmpdir, "0_limits"))
+		require.NoError(t, err)
+		file.WriteString(procLimitData)
+		require.NoError(t, file.Close())
+
 		system.ProcLimitPathFmt = path.Join(tmpdir, "%d_limits")
 
 		expected := map[string]map[string]interface{}{
@@ -131,4 +132,20 @@ func TestProcLimits(t *testing.T) {
 		assert.Equal(t, expected, parsed, "Did not parse correctly")
 	})
 
+	t.Run("Test opened files from process", func(t *testing.T) {
+		fdir := path.Join(tmpdir, "0")
+		err := os.Mkdir(fdir, 0755)
+		require.NoError(t, err)
+
+		for i := 0; i < 10; i++ {
+			file, err := os.Create(path.Join(fdir, fmt.Sprintf("socket%d", i)))
+			require.NoError(t, err)
+			require.NoError(t, file.Close())
+		}
+
+		system.ProcOpenedFilesFmt = path.Join(tmpdir, "%d")
+		fcount, err := system.GetOpenedFiles(0)
+		require.NoError(t, err)
+		assert.Equal(t, 10, fcount)
+	})
 }