Add support for streaming stdout/stderr from Child invocations

lib/posix/spawn/child.rb

@@ -95,6 +95,13 @@ def initialize(*args)
           @options[:pgroup] = true
         end
         @options.delete(:chdir) if @options[:chdir].nil?
+        @streaming = false
+        if streams = @options.delete(:streams)
+          @stdout_block = streams[:stdout]
+          @stderr_block = streams[:stderr]
+
+          @streaming = !!@stdout_block || !!@stderr_block
+        end
         exec! if !@options.delete(:noexec)
       end
 
@@ -244,14 +251,30 @@ def read_and_write(input, stdin, stdout, stderr, timeout=nil, max=nil)
 
           # read from stdout and stderr streams
           ready[0].each do |fd|
-            buf = (fd == stdout) ? @out : @err
+            chunk = nil
             begin
-              buf << fd.readpartial(BUFSIZE)
+              chunk = fd.readpartial(BUFSIZE)
             rescue Errno::EAGAIN, Errno::EINTR
             rescue EOFError
               readers.delete(fd)
               fd.close
             end
+
+            if chunk
+              if fd == stdout
+                if @streaming && @stdout_block
+                  @stdout_block.call(chunk)
+                else
+                  @out << chunk
+                end
+              else
+                if @streaming && @stderr_block
+                  @stderr_block.call(chunk)
+                else
+                  @err << chunk
+                end
+              end
+            end
           end
 
           # keep tabs on the total amount of time we've spent here

test/test_child.rb

@@ -224,6 +224,36 @@ def test_utf8_input_long
     assert p.success?
   end
 
+  def test_streaming_stdout
+    stdout_buf = ""
+    stdout_stream = Proc.new do |chunk|
+      stdout_buf << chunk
+    end
+
+    input = "hello!"
+    p = Child.new('cat', :input => input, :streams => {
+      :stdout => stdout_stream
+    })
+
+    assert p.success?
+    assert_equal input, stdout_buf
+  end
+
+  def test_streaming_stderr
+    stderr_buf = ""
+    stderr_stream = Proc.new do |chunk|
+      stderr_buf << chunk
+    end
+
+    input = "hello!"
+    p = Child.new('ls', '-?', :input => input, :streams => {
+      :stderr => stderr_stream
+    })
+
+    refute p.success?
+    refute stderr_buf.empty?
+  end
+
   ##
   # Assertion Helpers