#!/usr/bin/env ruby
# -*- encoding: binary -*-

# An example of using IO.tee, this is a limited version of the standard
# "tee" utility that requires stdin and stdout to both be pipes.
require 'io/splice'

usage = "filter_prog1 | #$0 DEST | filter_prog2"
dest = ARGV.shift or abort usage
$stdin.stat.pipe? or abort "stdin must be a pipe"
$stdout.stat.pipe? or abort "stdout must be a pipe"

dest = File.open(dest, 'wb')
out_fd = dest.fileno

stdin_fd = $stdin.fileno
stdout_fd = $stdout.fileno

begin
  nread = begin
    # "copy" data from stdin to stdout, without consuming stdin
    IO.tee(stdin_fd, stdout_fd, IO::Splice::PIPE_CAPA, 0)
  rescue EOFError
    break
  end

  # sends data to the file, consumes stdin
  nwritten = IO.splice(stdin_fd, nil, out_fd, nil, nread, 0)

  nwritten == nread or
    abort "short splice to file: #{nwritten} != #{nread}"
end while true