Send stdout to /dev/null unless it is needed (#43)

'unrar' produces lots of output to stdout, and previously this
output was stored in a pipe with Subprocess.PIPE, which could get
filled up, causing everything to hang.

Almost all the of the time we do not care what uncompressors are
producing on stdout, so just send it to /dev/null. Add a way of
stopping this behaviour for the one uncompressor which currently
does read the output pipe.

dtrx/dtrx.py

@@ -295,8 +295,13 @@ def wait_for_exit(self, pipe):
                         % (self.filename)
                     )
 
+    def send_stdout_to_dev_null(self):
+        return True
+
     def run_pipes(self, final_stdout=None):
-        has_output_target = True if final_stdout else False
+        has_output_target = (
+            True if final_stdout or self.send_stdout_to_dev_null() else False
+        )
         if not self.pipes:
             return
         elif final_stdout is None:
@@ -713,6 +718,9 @@ def get_filenames(self):
                 yield line[fn_index:]
         self.archive.close()
 
+    def send_stdout_to_dev_null(self):
+        return False
+
     def timeout_check(self, pipe):
         nbs = NonblockingRead(pipe.stdout)
         errs = nbs.readlines()

tests/tests.yml

@@ -95,6 +95,13 @@
     cd test-1.23
     unar -D ../$1 || unrar x ../$1
 
+- name: many files .rar
+  filenames: test-lots-files.rar
+  baseline: |
+    mkdir test-lots-files
+    cd test-lots-files
+    unar -D ../$1 || unrar x ../$1
+
 - name: basic .arj
   filenames: test-1.23.arj
   baseline: |