Reland of Migrate DeviceUtils.ReadFile to adb_wrapper (try 3)

build/android/pylib/device/device_utils.py

 # Copyright 2014 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.
 
 """Provides a variety of device interactions based on adb.
 
 Eventually, this will be based on adb_wrapper.
 """
 # pylint: disable=W0613
 
@@ skipping 54 matching lines @@
     _DEFAULT_TIMEOUT, _DEFAULT_RETRIES)
 def RestartServer():
   """Restarts the adb server.
 
   Raises:
     CommandFailedError if we fail to kill or restart the server.
   """
   pylib.android_commands.AndroidCommands().RestartAdbServer()
 
 
+def _JoinLines(lines):
+  # makes sure that the last line is also terminated, and is more memory
+  # efficient than first appending an end-line to each line and then joining
+  # all of them together.
+  return ''.join(s for line in lines for s in (line, '\n'))
+
+
 class DeviceUtils(object):
 
   _VALID_SHELL_VARIABLE = re.compile('^[a-zA-Z_][a-zA-Z0-9_]*$')
 
   def __init__(self, device, default_timeout=_DEFAULT_TIMEOUT,
                default_retries=_DEFAULT_RETRIES):
     """DeviceUtils constructor.
 
     Args:
       device: Either a device serial, an existing AdbWrapper instance, or an
@@ skipping 779 matching lines @@
       CommandFailedError on failure.
       CommandTimeoutError on timeout.
     """
     # Create the base dir if it doesn't exist already
     dirname = os.path.dirname(host_path)
     if dirname and not os.path.exists(dirname):
       os.makedirs(dirname)
     self.adb.Pull(device_path, host_path)
 
   @decorators.WithTimeoutAndRetriesFromInstance()
-  def ReadFile(self, device_path, as_root=False, timeout=None, retries=None):
+  def ReadFile(self, device_path, as_root=False,
+               timeout=None, retries=None):
     """Reads the contents of a file from the device.
 
     Args:
       device_path: A string containing the absolute path of the file to read
                    from the device.
       as_root: A boolean indicating whether the read should be executed with
                root privileges.
       timeout: timeout in seconds
       retries: number of retries
 
     Returns:
-      The contents of the file at |device_path| as a list of lines.
+      The contents of |device_path| as a string. Contents are intepreted using
+      universal newlines, so the caller will see them encoded as '\n'. Also,
+      all lines will be terminated.
 
     Raises:
-      CommandFailedError if the file can't be read.
+      AdbCommandFailedError if the file can't be read.
       CommandTimeoutError on timeout.
       DeviceUnreachableError on missing device.
     """
-    # TODO(jbudorick) Evaluate whether we want to return a list of lines after
-    # the implementation switch, and if file not found should raise exception.
-    if as_root:
-      if not self.old_interface.CanAccessProtectedFileContents():
-        raise device_errors.CommandFailedError(
-          'Cannot read from %s with root privileges.' % device_path)
-      return self.old_interface.GetProtectedFileContents(device_path)
-    else:
-      return self.old_interface.GetFileContents(device_path)
+    return _JoinLines(self.RunShellCommand(
+        ['cat', device_path], as_root=as_root, check_return=True))
 
   @decorators.WithTimeoutAndRetriesFromInstance()
   def WriteFile(self, device_path, contents, as_root=False, force_push=False,
                 timeout=None, retries=None):
     """Writes |contents| to a file on the device.
 
     Args:
       device_path: A string containing the absolute path to the file to write
           on the device.
       contents: A string containing the data to write to the device.
@@ skipping 357 matching lines @@
     Returns:
       A Parallelizer operating over |devices|.
     """
     if not devices:
       devices = adb_wrapper.AdbWrapper.GetDevices()
     devices = [d if isinstance(d, cls) else cls(d) for d in devices]
     if async:
       return parallelizer.Parallelizer(devices)
     else:
       return parallelizer.SyncParallelizer(devices)