From a3a4f4d061ed4fc1debbee0fe172a786c7c152d5 Mon Sep 17 00:00:00 2001
From: ksss <co000ri@gmail.com>
Date: Sat, 27 May 2017 13:29:38 +0900
Subject: IO#sysread Check for readable

---
 src/io.c   | 3 +++
 test/io.rb | 5 +++++
 2 files changed, 8 insertions(+)

diff --git a/src/io.c b/src/io.c
index 6d1b39cc5..e0de0ca36 100644
--- a/src/io.c
+++ b/src/io.c
@@ -637,6 +637,9 @@ mrb_io_sysread(mrb_state *mrb, mrb_value io)
   }
 
   fptr = (struct mrb_io *)io_get_open_fptr(mrb, io);
+  if (!fptr->readable) {
+    mrb_raise(mrb, E_IO_ERROR, "not opened for reading");
+  }
   ret = read(fptr->fd, RSTRING_PTR(buf), maxlen);
   switch (ret) {
     case 0: /* EOF */
diff --git a/test/io.rb b/test/io.rb
index 9ce8985f7..ee4309b57 100644
--- a/test/io.rb
+++ b/test/io.rb
@@ -238,6 +238,11 @@ assert('IO.sysopen, IO#sysread') do
   assert_raise(IOError) { io.sysread(1) }
   assert_raise(ArgumentError) { io.sysread(-1) }
   io.closed?
+
+  fd = IO.sysopen $mrbtest_io_wfname, "w"
+  io = IO.new fd, "w"
+  assert_raise(IOError) { io.sysread(1) }
+  io.close
 end
 
 assert('IO.sysopen, IO#syswrite') do
-- 
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