stringio.c: padding in ungetbyte

* ext/stringio/stringio.c (strio_ungetbyte): pad with \000 when
  the current position is after the end.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@53181 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

3 files changed, 50 insertions, 7 deletions

diff --git a/ChangeLog b/ChangeLog
index ed442c63dc..b79c3d1bc5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Dec 18 12:09:21 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* ext/stringio/stringio.c (strio_ungetbyte): pad with \000 when
+	  the current position is after the end.
+
 Fri Dec 18 11:24:48 2015  Shugo Maeda  <shugo@ruby-lang.org>
 
 	* vm_method.c (rb_method_entry_make, check_override_opt_method):
diff --git a/ext/stringio/stringio.c b/ext/stringio/stringio.c
index 7c2c51dca8..23d7deba02 100644
--- a/ext/stringio/stringio.c
+++ b/ext/stringio/stringio.c
@@ -780,8 +780,9 @@ strio_ungetbyte(VALUE self, VALUE c)
 {
     struct StringIO *ptr = readable(self);
     char buf[1], *cp = buf;
-    long pos = ptr->pos, cl = 1;
+    long pos = ptr->pos, cl = 1, len, rest;
     VALUE str = ptr->string;
+    char *s;
 
     if (NIL_P(c)) return Qnil;
     if (FIXNUM_P(c)) {
@@ -794,19 +795,26 @@ strio_ungetbyte(VALUE self, VALUE c)
 	if (cl == 0) return Qnil;
     }
     check_modifiable(ptr);
-    rb_str_modify(str);
+    len = RSTRING_LEN(str);
+    rest = pos - len;
     if (cl > pos) {
-	char *s;
-	long rest = RSTRING_LEN(str) - pos;
-	rb_str_resize(str, rest + cl);
+	long ex = (rest < 0 ? cl-pos : cl+rest);
+	rb_str_modify_expand(str, ex);
+	rb_str_set_len(str, len + ex);
 	s = RSTRING_PTR(str);
-	memmove(s + cl, s + pos, rest);
+	if (rest < 0) memmove(s + cl, s + pos, -rest);
 	pos = 0;
     }
     else {
+	if (rest > 0) {
+	    rb_str_modify_expand(str, rest);
+	    rb_str_set_len(str, len + rest);
+	}
+	s = RSTRING_PTR(str);
+	if (rest > cl) memset(s + len, 0, rest - cl);
 	pos -= cl;
     }
-    memcpy(RSTRING_PTR(str) + pos, cp, cl);
+    memcpy(s + pos, cp, cl);
     ptr->pos = pos;
     RB_GC_GUARD(c);
     return Qnil;
diff --git a/test/stringio/test_stringio.rb b/test/stringio/test_stringio.rb
index af6efc684e..7b99d62f51 100644
--- a/test/stringio/test_stringio.rb
+++ b/test/stringio/test_stringio.rb
@@ -362,6 +362,11 @@ class TestStringIO < Test::Unit::TestCase
     t.ungetbyte("\xe7")
     t.ungetbyte("\xe7\xb4\x85")
     assert_equal("\u7d05\u7389bar\n", t.gets)
+    assert_equal("q\u7d05\u7389bar\n", s)
+    t.pos = 1
+    t.ungetbyte("\u{30eb 30d3 30fc}")
+    assert_equal(0, t.pos)
+    assert_equal("\u{30eb 30d3 30fc}\u7d05\u7389bar\n", s)
   end
 
   def test_ungetc
@@ -582,6 +587,31 @@ class TestStringIO < Test::Unit::TestCase
     assert_equal("b""\0""a", s.string)
   end
 
+  def test_ungetbyte_pos
+    b = '\\b00010001 \\B00010001 \\b1 \\B1 \\b000100011'
+    s = StringIO.new( b )
+    expected_pos = 0
+    while n = s.getbyte
+      assert_equal( expected_pos + 1, s.pos )
+
+      s.ungetbyte( n )
+      assert_equal( expected_pos, s.pos )
+      assert_equal( n, s.getbyte )
+
+      expected_pos += 1
+    end
+  end
+
+  def test_ungetbyte_padding
+    s = StringIO.new()
+    s.pos = 2
+    s.ungetbyte("a".ord)
+    assert_equal("\0""a", s.string)
+    s.pos = 0
+    s.ungetbyte("b".ord)
+    assert_equal("b""\0""a", s.string)
+  end
+
   def test_frozen
     s = StringIO.new
     s.freeze