change approach: redirect stderr to file instead using defer

Author: umbynos

main.go

@@ -111,6 +111,18 @@ func main() {
 		os.Exit(0)
 	}
 
+	// save crashreport to file
+	logFilename := "crashreport_" + time.Now().Format("20060102150405") + ".txt"
+	currDir, err := osext.ExecutableFolder()
+	if err != nil {
+		panic(err)
+	}
+	logFile, err := os.OpenFile(filepath.Join(currDir, logFilename), os.O_WRONLY|os.O_CREATE|os.O_SYNC|os.O_APPEND, 0644)
+	if err != nil {
+		log.Print("Cannot create file used for crash-report")
+	}
+	redirectStderr(logFile)
+
 	// Launch main loop in a goroutine
 	go loop()
 

redirect_stderr_unix.go

@@ -0,0 +1,20 @@
+// Log the panic under unix to the log file
+
+// +build !windows
+
+package main
+
+import (
+	"log"
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+// redirectStderr to the file passed in
+func redirectStderr(f *os.File) {
+	err := unix.Dup2(int(f.Fd()), int(os.Stderr.Fd()))
+	if err != nil {
+		log.Fatalf("Failed to redirect stderr to file: %v", err)
+	}
+}

redirect_stderr_win.go

@@ -0,0 +1,41 @@
+// Log the panic under windows to the log file
+//
+// Code from minix, via
+//
+// https://play.golang.org/p/kLtct7lSUg
+
+// +build windows
+
+package main
+
+import (
+	"log"
+	"os"
+	"syscall"
+)
+
+var (
+	kernel32         = syscall.MustLoadDLL("kernel32.dll")
+	procSetStdHandle = kernel32.MustFindProc("SetStdHandle")
+)
+
+func setStdHandle(stdhandle int32, handle syscall.Handle) error {
+	r0, _, e1 := syscall.Syscall(procSetStdHandle.Addr(), 2, uintptr(stdhandle), uintptr(handle), 0)
+	if r0 == 0 {
+		if e1 != 0 {
+			return error(e1)
+		}
+		return syscall.EINVAL
+	}
+	return nil
+}
+
+// redirectStderr to the file passed in
+func redirectStderr(f *os.File) {
+	err := setStdHandle(syscall.STD_ERROR_HANDLE, syscall.Handle(f.Fd()))
+	if err != nil {
+		log.Fatalf("Failed to redirect stderr to file: %v", err)
+	}
+	// SetStdHandle does not affect prior references to stderr
+	os.Stderr = f
+}