Issue #21151 has been updated by headius (Charles Nutter). Edit: previously I referred to non-writable state, but in actuality any state of `StringIO` or `IO` should be safe to read even if the object itself is frozen. There's no need for either type to be mutable just to read `sync` or `external_encoding` for example. ---------------------------------------- Bug #21151: IO and StringIO raise FrozenError even for read-only methods https://bugs.ruby-lang.org/issues/21151#change-114254 * Author: headius (Charles Nutter) * Status: Feedback * Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- Problem -------- While fixing a small [regression](https://github.com/ruby/stringio/issues/119) from my recent StringIO [fixes](https://github.com/ruby/stringio/issues/116) I discovered that a large number of read-only methods will fail if the StringIO is frozen. A few examples: ``` $ ruby -rstringio -e 's = StringIO.new; p s.lineno; s.freeze; p s.lineno' 0 -e:1:in 'StringIO#lineno': can't modify frozen StringIO: #<StringIO:0x0000000103711ea8> (FrozenError) from -e:1:in '<main>' $ ruby -rstringio -e 's = StringIO.new; p s.closed?; s.freeze; p s.closed?' false -e:1:in 'StringIO#closed?': can't modify frozen StringIO: #<StringIO:0x00000001008c1e68> (FrozenError) from -e:1:in '<main>' $ ruby -rstringio -e 's = StringIO.new; p s.eof?; s.freeze; p s.eof?' true -e:1:in 'StringIO#eof?': can't modify frozen StringIO: #<StringIO:0x000000011c171e80> (FrozenError) from -e:1:in '<main>' $ ruby -rstringio -e 's = StringIO.new; p s.pos; s.freeze; p s.pos' 0 -e:1:in 'StringIO#pos': can't modify frozen StringIO: #<StringIO:0x0000000105551df0> (FrozenError) from -e:1:in '<main>' ``` @kou pointed out that IO also raises for at least `lineno` and suggested I re-open the issue here. I still believe these read-only operations should be allowed on frozen IO or StringIO. Cause in StringIO ----------------- This is because the `StringIO` macro calls `get_strio` which calls `rb_io_taint_check` which calls `rb_check_frozen`. The `StringIO` macro is used in almost every method to access the rb_stringio_t data structure. A list of methods I believe should be operable when the StringIO is frozen (in stringio.c definition order): * string (returns underlying String but does not mutate anything) * lineno * pos * closed?/closed_read?/closed_write? * eof/eof? * sync * pid (a dummy method but it writes nothing) * fileno (dummy) * pread (by definition does not modify state) * isatty/tty? * size/length * external_encoding * internal_encoding In addition, `initialize_copy` probably should not require the original StringIO to be writable: ``` $ ruby -rstringio -e 's = StringIO.new("foo"); s.freeze; p s.dup' -e:1:in 'StringIO#initialize_copy': can't modify frozen StringIO: #<StringIO:0x0000000102eb1df8> (FrozenError) from -e:1:in 'Kernel#initialize_dup' from -e:1:in 'Kernel#dup' from -e:1:in '<main>' ``` The data from the original StringIO is unmodified by `initialize_copy`, other than the reference-counting `ptr->count` (which should not be subject to frozen checks). Cause in IO ----------- The `GetOpenFile` macro calls `RB_IO_POINTER` macro which calls `rb_io_taint_check` which calls `rb_check_frozen`. Methods in IO that should work on a frozen IO include those from the StringIO list above that currently raise. For example `lineno` uses `GetOpenFile` and raises, but `fileno` does not and does not raise. There's clearly some inconsistency here we can clean up. Origin ------ I believe most of the StringIO cases are caused by this change from 2011 that added frozen checks to StringIO (the class and the macro): https://github.com/ruby/ruby/commit/d8d9bac5c8b071135e50ad3f21c8a9b6a9c06e54 In IO, this behavior dates way back to 2000 by @matz himself: https://github.com/ruby/ruby/commit/087c83d7ceed6893afff93066937fb570ae4a115 Notes ----- Originally filed as https://github.com/ruby/stringio/issues/120. I have started to fix the StringIO cases for JRuby in https://github.com/ruby/stringio/pull/122. I could probably fix the C version of StringIO as well, but I'm a little more unsure about how to fix IO. -- https://bugs.ruby-lang.org/