From: "zzak (Zachary Scott)" Date: 2012-11-20T14:20:19+09:00 Subject: [ruby-core:49646] [ruby-trunk - Bug #5530] SEEK_SET malfunctions when used with 'append' File.open mode Issue #5530 has been updated by zzak (Zachary Scott). In anticipation of drbrain's change in rdoc, i've added r37744, see #7365. This should be reverted and treated similarly to kosaki-san's change in r37746 ---------------------------------------- Bug #5530: SEEK_SET malfunctions when used with 'append' File.open mode https://bugs.ruby-lang.org/issues/5530#change-33163 Author: jduck (Joshua J. Drake) Status: Closed Priority: Normal Assignee: drbrain (Eric Hodel) Category: lib Target version: 2.0.0 ruby -v: all The following code demonstrates the issue. As documented, IO#seek says "SEEK_SET" will move to a position relative to the start of the file. Using 'ab', it doesn't actually seek where it should. It's possible the documentation is just wrong here, either the code or documentation should change though. #!/usr/bin/env ruby modes = [ 'ab', 'wb', 'w+b', 'r+b' ] filename = '/tmp/test.txt' desired = "AABBBBAA" modes.each { |mode| File.unlink(filename) rescue nil File.open(filename, "wb") { |fd| fd.write('AAAAAAAA') } File.open(filename, mode) { |fd| fd.seek(2, IO::SEEK_SET) fd.write("BBBB") fd.close } data = '' File.open(filename, "rb") { |fd| data = fd.read(fd.stat.size) } puts "%3s #{data.inspect}" % mode } File.unlink(filename) puts "" Output:

fear:0:ruby$ rvm all ruby -v file_mode_test.rb
ruby 1.8.6 (2010-09-02 patchlevel 420) [x86_64-linux]
 ab "AAAAAAAABBBB"
 wb "\000\000BBBB"
w+b "\000\000BBBB"
r+b "AABBBBAA"

ruby 1.8.7 (2011-02-18 patchlevel 334) [x86_64-linux]
 ab "AAAAAAAABBBB"
 wb "\000\000BBBB"
w+b "\000\000BBBB"
r+b "AABBBBAA"

ruby 1.9.1p378 (2010-01-10 revision 26273) [x86_64-linux]
 ab "AAAAAAAABBBB"
 wb "\x00\x00BBBB"
w+b "\x00\x00BBBB"
r+b "AABBBBAA"

ruby 1.9.2p290 (2011-07-09 revision 32553) [x86_64-linux]
 ab "AAAAAAAABBBB"
 wb "\x00\x00BBBB"
w+b "\x00\x00BBBB"
r+b "AABBBBAA"

ruby 1.8.7 (2011-06-30 patchlevel 352) [x86_64-linux]
 ab "AAAAAAAABBBB"
 wb "\000\000BBBB"
w+b "\000\000BBBB"
r+b "AABBBBAA"

ruby 1.9.2p180 (2011-02-18 revision 30909) [x86_64-linux]
 ab "AAAAAAAABBBB"
 wb "\x00\x00BBBB"
w+b "\x00\x00BBBB"
r+b "AABBBBAA"

ruby 1.9.1p431 (2011-02-18 revision 30908) [x86_64-linux]
Error loading gem paths on load path in gem_prelude
can't modify frozen string
:69:in `force_encoding'
:69:in `set_home'
:38:in `dir'
:76:in `set_paths'
:47:in `path'
:286:in `push_all_highest_version_gems_on_load_path'
:355:in `'
 ab "AAAAAAAABBBB"
 wb "\x00\x00BBBB"
w+b "\x00\x00BBBB"
r+b "AABBBBAA"

ruby 1.9.3dev (2011-07-31 revision 32789) [x86_64-linux]
 ab "AAAAAAAABBBB"
 wb "\x00\x00BBBB"
w+b "\x00\x00BBBB"
r+b "AABBBBAA"

fear:0:ruby$
The other modes behave as expected. See also - http://dev.metasploit.com/redmine/issues/3199 -- http://bugs.ruby-lang.org/