From 730f2886b535709832494ebe8c98f88ba0a29cea Mon Sep 17 00:00:00 2001
From: kazu <kazu@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>
Date: Wed, 9 Jan 2019 12:55:20 +0000
Subject: [PATCH] Follow behaviour of IO#ungetbyte

see r65802 and [Bug #14359]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66760 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
---
 ext/stringio/stringio.c        | 19 +++++++++++++++----
 test/stringio/test_stringio.rb |  4 ++++
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/ext/stringio/stringio.c b/ext/stringio/stringio.c
index eb23109087..3cb46d99b9 100644
--- a/ext/stringio/stringio.c
+++ b/ext/stringio/stringio.c
@@ -803,16 +803,27 @@ static VALUE
 strio_ungetbyte(VALUE self, VALUE c)
 {
     struct StringIO *ptr = readable(self);
-    char buf[1], *cp = buf;
-    long cl = 1;
 
     check_modifiable(ptr);
     if (NIL_P(c)) return Qnil;
     if (FIXNUM_P(c)) {
-	buf[0] = (char)FIX2INT(c);
-	return strio_unget_bytes(ptr, buf, 1);
+        int i = FIX2INT(c);
+        if (0 <= i && i <= UCHAR_MAX) {
+            char buf[1];
+	    buf[0] = (char)i;
+	    return strio_unget_bytes(ptr, buf, 1);
+        }
+        else {
+            rb_raise(rb_eRangeError,
+                "integer %d too big to convert into `unsigned char'", i);
+        }
+    }
+    else if (RB_TYPE_P(c, T_BIGNUM)) {
+        rb_raise(rb_eRangeError, "bignum too big to convert into `unsigned char'");
     }
     else {
+        char *cp;
+        long cl;
 	SafeStringValue(c);
 	cp = RSTRING_PTR(c);
 	cl = RSTRING_LEN(c);
diff --git a/test/stringio/test_stringio.rb b/test/stringio/test_stringio.rb
index 89da34e4ec..b508d56310 100644
--- a/test/stringio/test_stringio.rb
+++ b/test/stringio/test_stringio.rb
@@ -452,6 +452,10 @@ class TestStringIO < Test::Unit::TestCase
     t.ungetbyte("\u{30eb 30d3 30fc}")
     assert_equal(0, t.pos)
     assert_equal("\u{30eb 30d3 30fc}\u7d05\u7389bar\n", s)
+
+    assert_raise(RangeError) {t.ungetbyte(-1)}
+    assert_raise(RangeError) {t.ungetbyte(256)}
+    assert_raise(RangeError) {t.ungetbyte(1<<64)}
   end
 
   def test_ungetc