Only include timestamp and colors in log if stderr is terminal

main.go

@@ -9,14 +9,31 @@ import (
 	"github.com/op/go-logging"
 	"github.com/subgraph/fw-daemon/nfqueue"
 	"sync"
+	"syscall"
+	"unsafe"
 )
 
 var log = logging.MustGetLogger("sgfw")
-var format = logging.MustStringFormatter(
+
+var logFormat = logging.MustStringFormatter(
+	"%{level:.4s} %{id:03x} %{message}",
+)
+var ttyFormat = logging.MustStringFormatter(
 	"%{color}%{time:15:04:05} ▶ %{level:.4s} %{id:03x}%{color:reset} %{message}",
 )
+const ioctlReadTermios = 0x5401
+
+func isTerminal(fd int) bool {
+	var termios syscall.Termios
+	_, _, err := syscall.Syscall6(syscall.SYS_IOCTL, uintptr(fd), ioctlReadTermios, uintptr(unsafe.Pointer(&termios)), 0, 0, 0)
+	return err == 0
+}
 
 func init() {
+	format := logFormat
+	if(isTerminal(int(os.Stderr.Fd()))) {
+		format = ttyFormat
+	}
 	backend := logging.NewLogBackend(os.Stderr, "", 0)
 	formatter := logging.NewBackendFormatter(backend, format)
 	leveler := logging.AddModuleLevel(formatter)