Should be true for close_on_exec flag

mrbgems/mruby-io/src/io.c

@@ -180,7 +180,7 @@ mrb_io_flags_to_modenum(mrb_state *mrb, int flags)
   return modenum;
 }
 
-void
+static void
 mrb_fd_cloexec(mrb_state *mrb, int fd)
 {
 #if defined(F_GETFD) && defined(F_SETFD) && defined(FD_CLOEXEC)
@@ -188,7 +188,8 @@ mrb_fd_cloexec(mrb_state *mrb, int fd)
 
   flags = fcntl(fd, F_GETFD);
   if (flags == -1) {
-    mrb_sys_fail(mrb, "fcntl");
+    mrb_bug(mrb, "mrb_fd_cloexec: fcntl(%S, F_GETFD) failed: %S",
+      mrb_fixnum_value(fd), mrb_fixnum_value(errno));
   }
   if (fd <= 2) {
     flags2 = flags & ~FD_CLOEXEC; /* Clear CLOEXEC for standard file descriptors: 0, 1, 2. */
@@ -198,7 +199,8 @@ mrb_fd_cloexec(mrb_state *mrb, int fd)
   }
   if (flags != flags2) {
     if (fcntl(fd, F_SETFD, flags2) == -1) {
-      mrb_sys_fail(mrb, "fcntl");
+      mrb_bug(mrb, "mrb_fd_cloexec: fcntl(%S, F_SETFD, %S) failed: %S",
+        mrb_fixnum_value(fd), mrb_fixnum_value(flags2), mrb_fixnum_value(errno));
     }
   }
 #endif
@@ -577,11 +579,17 @@ mrb_io_initialize_copy(mrb_state *mrb, mrb_value copy)
   if (failed) {
     mrb_sys_fail(mrb, 0);
   }
-  fptr_copy->fd2 = mrb_dup(mrb, fptr_orig->fd2, &failed);
-  if (failed) {
-    close(fptr_copy->fd);
-    mrb_sys_fail(mrb, 0);
+  mrb_fd_cloexec(mrb, fptr_copy->fd);
+
+  if (fptr_orig->fd2 != -1) {
+    fptr_copy->fd2 = mrb_dup(mrb, fptr_orig->fd2, &failed);
+    if (failed) {
+      close(fptr_copy->fd);
+      mrb_sys_fail(mrb, 0);
+    }
+    mrb_fd_cloexec(mrb, fptr_copy->fd2);
   }
+
   fptr_copy->pid = fptr_orig->pid;
   fptr_copy->readable = fptr_orig->readable;
   fptr_copy->writable = fptr_orig->writable;

mrbgems/mruby-io/test/io.rb

@@ -216,6 +216,7 @@ assert('IO#dup for readable') do
   dup = io.dup
   assert_true io != dup
   assert_true io.fileno != dup.fileno
+  assert_true dup.close_on_exec?
   assert_equal 'm', dup.sysread(1)
   assert_equal 'r', io.sysread(1)
   assert_equal 'u', dup.sysread(1)