From 1046eae7814930fb326371930715122d647457a2 Mon Sep 17 00:00:00 2001
From: nobu <nobu@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>
Date: Thu, 23 Nov 2017 07:10:56 +0000
Subject: io.c: read BOM only for reading

* io.c (io_strip_bom): just abandon detecting UTF encoding by BOM
  unless opened for reading.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60884 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
---
 io.c                      |  3 +++
 test/ruby/test_io_m17n.rb | 14 ++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/io.c b/io.c
index 6a9a273b41..ac2f246b51 100644
--- a/io.c
+++ b/io.c
@@ -5970,7 +5970,10 @@ static int
 io_strip_bom(VALUE io)
 {
     VALUE b1, b2, b3, b4;
+    rb_io_t *fptr;
 
+    GetOpenFile(io, fptr);
+    if (!(fptr->mode & FMODE_READABLE)) return 0;
     if (NIL_P(b1 = rb_io_getbyte(io))) return 0;
     switch (b1) {
       case INT2FIX(0xEF):
diff --git a/test/ruby/test_io_m17n.rb b/test/ruby/test_io_m17n.rb
index ccb124a46b..8ba34845fa 100644
--- a/test/ruby/test_io_m17n.rb
+++ b/test/ruby/test_io_m17n.rb
@@ -2168,6 +2168,20 @@ EOT
     assert_nil(enc)
   end
 
+  def test_bom_non_reading
+    with_tmpdir {
+      enc = nil
+      assert_nothing_raised(IOError) {
+        open("test", "w:bom|utf-8") {|f|
+          enc = f.external_encoding
+          f.print("abc")
+        }
+      }
+      assert_equal(Encoding::UTF_8, enc)
+      assert_equal("abc", File.binread("test"))
+    }
+  end
+
   def test_cbuf
     with_tmpdir {
       fn = "tst"
-- 
cgit v1.2.3