Refactor command execution to separate stdout and stderr

cmd/apply.go

@@ -253,7 +253,7 @@ func SetupVethDevices(netns string, devices map[string]config.VethDevice) error
 		peerNetns := values.Peer.Netns
 
 		slog.Debug("setup veth device", "netns", netns, "name", name, "addresses", values.Addresses, "routes", values.Routes,
-		"peer name", peerName, "peer netns", peerNetns, "peer addresses", values.Peer.Addresses, "peer routes", values.Peer.Routes)
+			"peer name", peerName, "peer netns", peerNetns, "peer addresses", values.Peer.Addresses, "peer routes", values.Peer.Routes)
 
 		// check if device is already exists in netns
 		_, err := n.ShowLink(name)
@@ -332,7 +332,7 @@ func RunPostScript(netns string, script string) error {
 	if err != nil {
 		return err
 	}
-	slog.Debug("post script output", "netns", netns, "script", script, "output", out)
+	slog.Debug("post script output", "netns", netns, "script", script, "stdout", out.Stdout, "stderr", out.Stderr)
 
 	return nil
 }

iproute2/base.go

@@ -22,8 +22,10 @@ SOFTWARE.
 package iproute2
 
 import (
+	"bytes"
 	"encoding/json"
 	"io"
+	"log/slog"
 	"os/exec"
 	"strings"
 	"syscall"
@@ -34,6 +36,11 @@ type BaseCommand struct {
 	prepend []string
 }
 
+type CommandOut struct {
+	Stdout string
+	Stderr string
+}
+
 func (b *BaseCommand) run(args ...string) error {
 	_, err := b.runIpCommand(args...)
 	return err
@@ -43,7 +50,11 @@ func (b *BaseCommand) runIpCommand(args ...string) (string, error) {
 	cmd := append([]string{b.path}, args...)
 	out, err := b.runCommand(cmd, nil)
 	if err == nil {
-		return out, nil
+		if out.Stderr != "" {
+			slog.Warn("ip command warning", "msg", out.Stderr)
+		}
+
+		return out.Stdout, nil
 	}
 
 	msg := err.Error()
@@ -58,7 +69,7 @@ func (b *BaseCommand) runIpCommand(args ...string) (string, error) {
 	return "", &UnknownError{Msg: err.Error()}
 }
 
-func (b *BaseCommand) runCommand(cmd []string, input *string) (string, error) {
+func (b *BaseCommand) runCommand(cmd []string, input *string) (*CommandOut, error) {
 	if b.prepend != nil {
 		cmd = append(b.prepend, cmd...)
 	}
@@ -73,24 +84,27 @@ func (b *BaseCommand) runCommand(cmd []string, input *string) (string, error) {
 	if input != nil {
 		stdin, err := c.StdinPipe()
 		if err != nil {
-			return "", err
+			return nil, err
 		}
 		go func() {
 			defer stdin.Close()
 			io.WriteString(stdin, *input)
 		}()
 	}
 
-	out, err := c.CombinedOutput()
-	if err != nil {
+	var stdout, stderr bytes.Buffer
+	c.Stdout = &stdout
+	c.Stderr = &stderr
+
+	if err := c.Run(); err != nil {
 		exitErr, _ := err.(*exec.ExitError)
 		status, _ := exitErr.Sys().(syscall.WaitStatus)
-		return "", &CommandError{
+		return nil, &CommandError{
 			ExitStatus: status.ExitStatus(),
-			Msg:        string(out),
+			Msg:        stderr.String(),
 		}
 	}
-	return string(out), nil
+	return &CommandOut{Stdout: stdout.String(), Stderr: stderr.String()}, nil
 }
 
 func (b *BaseCommand) AddLink(name string, linkType string, options ...string) error {

iproute2/iproute2.go

@@ -136,7 +136,7 @@ func (i *IpCmdWithNetns) Netns() string {
 	return i.netns
 }
 
-func (i *IpCmdWithNetns) ExecuteCommand(cmd string) (string, error) {
+func (i *IpCmdWithNetns) ExecuteCommand(cmd string) (*CommandOut, error) {
 	shell := []string{"/bin/bash"}
 	return i.runCommand(shell, &cmd)
 }