chore: dry and modularize a bit

src/util.c

@@ -1,3 +1,5 @@
+#include <asm-generic/errno-base.h>
+#include <errno.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -53,6 +55,17 @@ void read_press(u_char* length, char* out) {
   }
 }
 
+bool read_press_nb(u_char* length, char* out, struct timeval* tv) {
+  fd_set fds;
+  FD_ZERO(&fds);
+  FD_SET(STDIN_FILENO, &fds);
+  int ret = select(STDIN_FILENO + 1, &fds, NULL, NULL, tv);
+  if ((ret < 0 && errno == EINTR) || ret == 0) return false;
+
+  read_press(length, out);
+  return true;
+}
+
 // https://stackoverflow.com/a/48040042
 static int selret_magic() {
   fd_set set;