[client] Log windows panics (#2829)

client/server/panic_generic.go

@@ -0,0 +1,7 @@
+//go:build !windows
+
+package server
+
+func handlePanicLog() error {
+	return nil
+}

client/server/panic_windows.go

@@ -0,0 +1,83 @@
+package server
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"syscall"
+
+	log "github.com/sirupsen/logrus"
+
+	"github.com/netbirdio/netbird/util"
+)
+
+const (
+	windowsPanicLogEnvVar = "NB_WINDOWS_PANIC_LOG"
+	// STD_ERROR_HANDLE ((DWORD)-12) = 4294967284
+	stdErrorHandle = ^uintptr(11)
+)
+
+var (
+	kernel32 = syscall.NewLazyDLL("kernel32.dll")
+
+	// https://learn.microsoft.com/en-us/windows/console/setstdhandle
+	setStdHandleFn = kernel32.NewProc("SetStdHandle")
+)
+
+func handlePanicLog() error {
+	logPath := os.Getenv(windowsPanicLogEnvVar)
+	if logPath == "" {
+		return nil
+	}
+
+	// Ensure the directory exists
+	logDir := filepath.Dir(logPath)
+	if err := os.MkdirAll(logDir, 0750); err != nil {
+		return fmt.Errorf("create panic log directory: %w", err)
+	}
+	if err := util.EnforcePermission(logPath); err != nil {
+		return fmt.Errorf("enforce permission on panic log file: %w", err)
+	}
+
+	// Open log file with append mode
+	f, err := os.OpenFile(logPath, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0644)
+	if err != nil {
+		return fmt.Errorf("open panic log file: %w", err)
+	}
+
+	// Redirect stderr to the file
+	if err = redirectStderr(f); err != nil {
+		if closeErr := f.Close(); closeErr != nil {
+			log.Warnf("failed to close file after redirect error: %v", closeErr)
+		}
+		return fmt.Errorf("redirect stderr: %w", err)
+	}
+
+	log.Infof("successfully configured panic logging to: %s", logPath)
+	return nil
+}
+
+// redirectStderr redirects stderr to the provided file
+func redirectStderr(f *os.File) error {
+	// Get the current process's stderr handle
+	if err := setStdHandle(f); err != nil {
+		return fmt.Errorf("failed to set stderr handle: %w", err)
+	}
+
+	// Also set os.Stderr for Go's standard library
+	os.Stderr = f
+
+	return nil
+}
+
+func setStdHandle(f *os.File) error {
+	handle := f.Fd()
+	r0, _, e1 := setStdHandleFn.Call(stdErrorHandle, handle)
+	if r0 == 0 {
+		if e1 != nil {
+			return e1
+		}
+		return syscall.EINVAL
+	}
+	return nil
+}

client/server/server.go

@@ -97,6 +97,10 @@ func (s *Server) Start() error {
 	defer s.mutex.Unlock()
 	state := internal.CtxGetState(s.rootCtx)
 
+	if err := handlePanicLog(); err != nil {
+		log.Warnf("failed to redirect stderr: %v", err)
+	}
+
 	if err := restoreResidualState(s.rootCtx); err != nil {
 		log.Warnf(errRestoreResidualState, err)
 	}