fix: redirect dns calls by configuring nsswitch config file in linux (#…

…1678)

* fix: redirect dns calls by configuring nsswitch config file in linux

linux distros like fedora uses systemd-resolve for dns resolution which makes unix socket with the application due to which keploy is not able to redirect them to proxy in test mode. This results in test failure. This is handled by editing the nsswitch.conf of /etc in linux to not use resolve in test mode

Signed-off-by: re-Tick <jain.ritik.1001@gmail.com>

---------

Signed-off-by: re-Tick <jain.ritik.1001@gmail.com>

pkg/service/test/test.go

@@ -9,6 +9,7 @@ import (
 	"os/exec"
 	"os/signal"
 	"path/filepath"
+	"runtime"
 	"sort"
 	"strconv"
 	"strings"
@@ -35,8 +36,9 @@ import (
 var Emoji = "\U0001F430" + " Keploy:"
 
 type tester struct {
-	logger *zap.Logger
-	mutex  sync.Mutex
+	logger        *zap.Logger
+	mutex         sync.Mutex
+	hostConfigStr string // hosts string in the nsswitch.conf of linux system. To restore the system hosts configuration after completion of test
 }
 type TestOptions struct {
 	MongoPassword      string
@@ -73,12 +75,79 @@ func NewTester(logger *zap.Logger) Tester {
 	}
 }
 
+// setting up the dns routing for the linux system
+func (t *tester) setupNsswitchConfig() error {
+	// Check if the nsswitch.conf present for the system
+	if _, err := os.Stat("/etc/nsswitch.conf"); err == nil {
+		// Read the current nsswitch.conf
+		data, err := os.ReadFile("/etc/nsswitch.conf")
+		if err != nil {
+			t.logger.Error("failed to read the nsswitch.conf file from system", zap.Error(err))
+			return err
+		}
+
+		// Replace the hosts field value if it exists
+		lines := strings.Split(string(data), "\n")
+		for i, line := range lines {
+			if strings.HasPrefix(line, "hosts:") {
+				t.hostConfigStr = lines[i]
+				lines[i] = "hosts: files dns"
+			}
+		}
+
+		// Write the modified nsswitch.conf back to the file
+		err = os.WriteFile("/etc/nsswitch.conf", []byte(strings.Join(lines, "\n")), 0644)
+		if err != nil {
+			t.logger.Error("failed to write the configuration to the nsswitch.conf file to redirect the DNS queries to proxy", zap.Error(err))
+			return err
+		}
+
+		t.logger.Debug("Successfully written to nsswitch config of linux")
+	}
+	return nil
+}
+
+// resetNsswitchConfig resets the hosts config of nsswitch of the system
+func (t *tester) resetNsswitchConfig() {
+	data, err := os.ReadFile("/etc/nsswitch.conf")
+	if err != nil {
+		t.logger.Error("failed to read the nsswitch.conf file from system", zap.Error(err))
+		return
+	}
+
+	// Replace the hosts field value if it exists with the actual system hosts value
+	lines := strings.Split(string(data), "\n")
+	for i, line := range lines {
+		if strings.HasPrefix(line, "hosts:") {
+			lines[i] = t.hostConfigStr
+		}
+	}
+
+	// Write the modified nsswitch.conf back to the file
+	err = os.WriteFile("/etc/nsswitch.conf", []byte(strings.Join(lines, "\n")), 0644)
+	if err != nil {
+		t.logger.Error("failed to write the configuration to the nsswitch.conf file to redirect the DNS queries to proxy", zap.Error(err))
+		return
+	}
+
+	t.logger.Debug("Successfully reset the nsswitch config of linux")
+}
+
 func (t *tester) InitialiseTest(cfg *TestConfig) (TestEnvironmentSetup, error) {
 	var (
 		returnVal TestEnvironmentSetup
 		err       error
 	)
 	returnVal.Storage = cfg.Storage
+
+	// setting up the dns routing for the fedora distro
+	if runtime.GOOS == "linux" {
+		err = t.setupNsswitchConfig()
+		if err != nil {
+			return returnVal, err
+		}
+	}
+
 	// capturing the code coverage for go bianries built by go-version 1.20^
 	if cfg.WithCoverage {
 
@@ -102,7 +171,7 @@ func (t *tester) InitialiseTest(cfg *TestConfig) (TestEnvironmentSetup, error) {
 				return returnVal, err
 			} else if err == nil && !dirInfo.IsDir() {
 				t.logger.Error("the goCoverDir is not a directory. Please provide a valid path to a directory for go coverage binaries.")
-				return returnVal, fmt.Errorf("the goCoverDir is not a directory. Please provide a valid path to a directory for go coverage binaries.")
+				return returnVal, fmt.Errorf("the goCoverDir is not a directory. Please provide a valid path to a directory for go coverage binaries")
 			} else if err != nil && os.IsNotExist(err) {
 				err := makeDirectory(cfg.CoverageReportPath)
 				if err != nil {
@@ -124,7 +193,7 @@ func (t *tester) InitialiseTest(cfg *TestConfig) (TestEnvironmentSetup, error) {
 	}
 
 	stopper := make(chan os.Signal, 1)
-	signal.Notify(stopper, os.Interrupt, os.Kill, syscall.SIGHUP, syscall.SIGINT, syscall.SIGQUIT, syscall.SIGTERM, syscall.SIGKILL)
+	signal.Notify(stopper, os.Interrupt, syscall.SIGHUP, syscall.SIGINT, syscall.SIGQUIT, syscall.SIGTERM)
 
 	models.SetMode(models.MODE_TEST)
 
@@ -140,7 +209,7 @@ func (t *tester) InitialiseTest(cfg *TestConfig) (TestEnvironmentSetup, error) {
 
 	select {
 	case <-stopper:
-		return returnVal, errors.New("Keploy was interupted by stopper")
+		return returnVal, errors.New("keploy was interupted by stopper")
 	default:
 		// load the ebpf hooks into the kernel
 		if err := returnVal.LoadedHooks.LoadHooks(cfg.AppCmd, cfg.AppContainer, 0, context.Background(), nil); err != nil {
@@ -151,7 +220,7 @@ func (t *tester) InitialiseTest(cfg *TestConfig) (TestEnvironmentSetup, error) {
 	select {
 	case <-stopper:
 		returnVal.LoadedHooks.Stop(true)
-		return returnVal, errors.New("Keploy was interupted by stopper")
+		return returnVal, errors.New("keploy was interupted by stopper")
 	default:
 		// start the proxy
 		returnVal.ProxySet = proxy.BootProxy(t.logger, proxy.Option{Port: cfg.Proxyport, MongoPassword: cfg.MongoPassword}, cfg.AppCmd, cfg.AppContainer, 0, "", cfg.PassThroughPorts, returnVal.LoadedHooks, context.Background(), cfg.Delay)
@@ -237,6 +306,14 @@ func (t *tester) Test(path string, testReportPath string, appCmd string, options
 		return false
 	}
 	initialisedValues, err := t.InitialiseTest(cfg)
+
+	// reset the hosts config in nsswitch.conf of the system
+	defer func() {
+		if t.hostConfigStr != "" {
+			t.resetNsswitchConfig()
+		}
+	}()
+
 	// Recover from panic and gracefully shutdown
 	defer initialisedValues.LoadedHooks.Recover(pkg.GenerateRandomID())
 	if err != nil {