Provide a way to set path for File instances created with for_fd
IO.for_fd to instantiate an IO object from an existing file descriptor value. The logic for this simply calls the base
IO.new logic, which for all IO and subtypes simply wraps the given file descriptor.
When called against File, or other subtypes of IO, this has the side effect of creating an IO instance with that type, e.g.
File.for_fd will behave identically to
IO.for_fd except that the class of the resulting object will be File.
Unfortunately, this results in a File object that does not have any
path associated with it:
3.1.2 :001 > f = File.open('README.md') => #<File:README.md> 3.1.2 :002 > f.path => "README.md" 3.1.2 :003 > f2 = File.for_fd(f.fileno) => #<File:fd 5> 3.1.2 :004 > f2.path (irb):4:in `path': File is unnamed (TMPFILE?) (IOError) from (irb):4:in `<main>' from /home/headius/.rvm/rubies/ruby-3.1.2/lib/ruby/gems/3.1.0/gems/irb-1.4.1/exe/irb:11:in `<top (required)>' from /home/headius/.rvm/rubies/ruby-3.1.2/bin/irb:25:in `load' from /home/headius/.rvm/rubies/ruby-3.1.2/bin/irb:25:in `<main>'
I propose that there should be a way, via an extra parameter or a keyword argument, to provide a path when constructing a new File via
File.for_fd(fileno, path: "my/path")
This would necessitate a separate implementation for
File.for_fd unless we want to make it possible to set a path for all
for_fd calls (which may not make sense for many of them).
This came up while trying to implement a pure-Ruby (plus FFI) version of the "pty" library. Without overriding the
path function, it is not possible for the File object returned by
PTY.open to gain the "masterpty:" filename, and therefore it does not clearly indicate it is from a PTY.
See https://github.com/jruby/jruby/pull/7391, an attempt to match inspect output for these return values using
define_singleton_method. Providing a way to set the path would make this automatic without the singleton definition.
Updated by headius (Charles Nutter) 2 months ago
Looking at the linked PR again I realize that we would need this functionality for IO as well, in order for the IO object to have the "masterpty" marker. The File would still need help, so we can
for_fd but provide the slave name as path.
Updated by ko1 (Koichi Sasada) 20 days ago
It seems okay for
File.for_fd(fd, path: ...) but I'm not sure
IO.for_fd(fd, path: ...). Maybe it affects only
IO#path is not defined.
I think this functionality is also useful to label known IO such as:
p STDERR #=> #<IO:<STDERR>> p IO.for_fd(STDERR.to_i) #<IO:fd 2> p IO.for_fd(STDERR.to_i, path: '<STDERR>') #=> #<IO:<STDERR>>
name for strictly usage?