Call `gzip` in subprocess instead of gzipping in Python in http_server.

mojo/devtools/common/devtoolslib/http_server.py

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import atexit
 import datetime
 import email.utils
 import errno
-import gzip
 import hashlib
 import logging
 import math
 import os.path
-import shutil
 import socket
+import subprocess
+import tempfile
 import threading
-import tempfile
 
 import SimpleHTTPServer
 import SocketServer
 
 _ZERO = datetime.timedelta(0)
 
 
 class UTC_TZINFO(datetime.tzinfo):
   """UTC time zone representation."""
 
@@ skipping 111 matching lines @@
 
     # pylint: disable=W0221
     def translate_path(self, path, gzipped=True):
       # Parent translate_path() will strip away the query string and fragment
       # identifier, but also will prepend the cwd to the path. relpath() gives
       # us the relative path back.
       normalized_path = os.path.relpath(
           SimpleHTTPServer.SimpleHTTPRequestHandler.translate_path(self, path))
 
       for prefix, local_base_path_list in mappings:
-        if normalized_path.startswith(prefix):
-          for local_base_path in local_base_path_list:
-            candidate = os.path.join(local_base_path,
-                                     normalized_path[len(prefix):])
-            if os.path.isfile(candidate):
-              if gzipped:
-                if not self.gzipped_file:
-                  self.gzipped_file = tempfile.NamedTemporaryFile(delete=False)
-                  self.original_file_name = candidate
-                  with open(candidate, 'rb') as source:
-                    with gzip.GzipFile(fileobj=self.gzipped_file) as target:
-                      shutil.copyfileobj(source, target)
-                  self.gzipped_file.close()
-                return self.gzipped_file.name
-              return candidate
-          else:
-            self.send_response(404)
-            return None
+        if not normalized_path.startswith(prefix):
+          continue
+
+        for local_base_path in local_base_path_list:
+          candidate = os.path.join(local_base_path,
+                                   normalized_path[len(prefix):])
+          if os.path.isfile(candidate):
+            if gzipped:
+              if not self.gzipped_file:
+                self.gzipped_file = tempfile.NamedTemporaryFile(delete=False)

[piotrt, 2015/08/25 11:55:23]

I would consider extracting lines 157-166? to a separate method
called f.e. _try_gzip(..) or something similar, to separate all the 
nested conditions from actual work being done. 

[ppi, 2015/08/25 12:07:43]

Good point, done.

+                self.original_file_name = candidate
+                try:
+                  subprocess.check_call(['gzip', '-c', candidate],
+                                        stdout=self.gzipped_file)
+                except Exception:
+                  print ('http_server: call to gzip failed, make sure that '
+                         'gzip is installed on the host.')
+                  raise
+                self.gzipped_file.close()
+              return self.gzipped_file.name
+            return candidate
+        else:
+          self.send_response(404)
+          return None
       self.send_response(404)
       return None
 
     def guess_type(self, path):
       # This is needed so that exploded Sky apps without shebang can still run
       # thanks to content-type mappings.
       # TODO(ppi): drop this part once we can rely on the Sky files declaring
       # correct shebang.
       actual_path = self.original_file_name or path
 
@@ skipping 43 matching lines @@
   except socket.error as v:
     error_code = v[0]
     print 'Failed to start http server for %s on port %d: %s.' % (
         str(mappings), host_port, os.strerror(error_code))
     if error_code == errno.EADDRINUSE:
       print ('  Run `fuser %d/tcp` to find out which process is using the port;'
              % host_port)
       print ('  or `fuser -k %d/tcp` terminate it.' % host_port)
     print '---'
     raise