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

1 files changed, 3 insertions, 0 deletions

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):