commit d5895d2f6825bef56f7c8a23c191a27f12f3867e
Author: Loic Nageleisen <loic.nageleisen@gmail.com>
Date:   Tue Oct 30 15:57:34 2012 +0100

    working tee

diff --git a/tee.rb b/tee.rb
new file mode 100644
index 0000000..0180645
--- /dev/null
+++ b/tee.rb
@@ -0,0 +1,89 @@
+require 'digest/sha1'
+require 'digest/sha2'
+
+module Enumerable
+  def tee(*procs)
+    each { |i| procs.map { |p| p.call i } }
+  end
+end
+
+class IO
+  def chunks(chunk_size=1024)
+    Enumerator.new { |y| y << read(chunk_size) until eof? }
+  end
+
+  def each_chunk(chunk_size=nil)
+    chunks.each { |*args| yield *args }
+  end
+
+  def digest_with(digest, chunk_size=nil)
+    chunks(chunk_size).each { |chunk| digest << chunk }
+    digest
+  end
+
+  def sha256(chunk_size=nil)
+    digest_with Digest::SHA2.new(256), chunk_size
+  end
+
+  def fiber_chunks(chunk_size=1024)
+    Enumerator.new do |y|
+      until eof?
+        Fiber.yield
+        y << read(chunk_size)
+      end
+    end
+  end
+
+  def tee(*procs)
+    results = procs.map { nil }
+    ios = procs.map do |proc|
+      #IO.new
+      self
+    end
+    fibers = procs.map.with_index do |proc, i|
+      # set up communication
+      # start each proc, which will yield just before reading
+      Fiber.new do
+        results[i] = proc.call ios[i]
+      end
+    end.each { |fiber| fiber.resume }
+    prev_pos = tell
+    chunks.each do |chunk|
+      new_pos = tell
+      # for each proc
+      # - copy chunk into its dedicated IO stream
+      # - resume
+      procs.each.with_index do |proc, i|
+        ios[i].seek prev_pos
+        #ios[i].write chunk
+        fibers[i].resume
+        ios[i].seek new_pos
+      end
+      prev_pos = new_pos
+    end
+    results
+  end
+end
+
+
+File.open("tee.rb") do |f|
+
+  sha1_proc = lambda do |f|
+    digest = Digest::SHA1.new
+    f.fiber_chunks.each { |chunk| digest << chunk }
+    digest
+  end
+
+  sha2_proc = lambda do |f|
+    digest = Digest::SHA2.new(256)
+    f.fiber_chunks.each { |chunk| digest << chunk }
+    digest
+  end
+
+  puts_proc = lambda do |f|
+    f.fiber_chunks.each { |chunk| puts chunk }
+  end
+
+  p f.tee(sha1_proc, sha2_proc, puts_proc)
+
+end