Don't hang on stderr

lib/terrapin/command_line/multi_pipe.rb

@@ -29,19 +29,51 @@ def close_write
       end
 
       def read
-        @stdout_output = read_stream(@stdout_in)
-        @stderr_output = read_stream(@stderr_in)
+        read_streams(@stdout_in, @stderr_in)
       end
 
       def close_read
-        @stdout_in.close
+        begin
+          @stdout_in.close
+        rescue IOError
+          # do nothing
+        end
+
+        begin
         @stderr_in.close
+        rescue IOError
+          # do nothing
+        end
+      end
+
+      def read_streams(output, error)
+        @stdout_output = ""
+        @stderr_output = ""
+        read_fds = [output, error]
+        while !read_fds.empty?
+          to_read, = IO.select(read_fds)
+          if to_read.include?(output)
+            @stdout_output << read_stream(output)
+            read_fds.delete(output) if output.closed?
+          end
+
+          if to_read.include?(error)
+            @stderr_output << read_stream(error)
+            read_fds.delete(error) if error.closed?
+          end
+        end
       end
 
       def read_stream(io)
         result = String.new
-        while partial_result = io.read(8192)
-          result << partial_result
+        begin
+          while partial_result = io.read_nonblock(8192)
+            result << partial_result
+          end
+        rescue EOFError, Errno::EPIPE
+          io.close
+        rescue Errno::EINTR, Errno::EWOULDBLOCK, Errno::EAGAIN
+          # do nothing
         end
         result
       end

spec/support/nonblocking_examples.rb

@@ -1,4 +1,17 @@
 shared_examples_for "a command that does not block" do
+  it "does not block if the command output a lot on stderr" do
+    cmd = Terrapin::CommandLine.new(
+      "ruby",
+      "-e '$stdout.puts %{hello}; $stderr.puts %{goodbye}*10_000'",
+      :swallow_stderr => false
+    )
+    Timeout.timeout(5) do
+      cmd.run
+    end
+    expect(cmd.command_output).to eq "hello\n"
+    expect(cmd.command_error_output).to eq "#{"goodbye" * 10_000}\n"
+  end
+
   it 'does not block if the command outputs a lot of data' do
     garbage_file = Tempfile.new("garbage")
     10.times{ garbage_file.write("A" * 1024 * 1024) }