target: Add Target.read_tree_values_flat(decode=None) parameter

Allow not decoding the values and keep them as bytestring, for when e.g.
sysfs files have binary content (e.g. exposed from device tree)

True decodes the bytestring, None attempts to decode and False does not
decode.

devlib/target.py

@@ -1363,7 +1363,7 @@ async def read_tree_tar_flat(self, path, depth=1, check_exit_code=True,
                 # if it is a file and not a folder
                 if content_f:
                     content = content_f.read()
-                    if decode_unicode:
+                    if decode_unicode in (True, None):
                         try:
                             content = content.decode('utf-8').strip()
                             if strip_null_chars:
@@ -1377,27 +1377,37 @@ async def read_tree_tar_flat(self, path, depth=1, check_exit_code=True,
         return result
 
     @asyn.asyncf
-    async def read_tree_values_flat(self, path, depth=1, check_exit_code=True):
+    async def read_tree_values_flat(self, path, depth=1, check_exit_code=True, decode=None):
         self.async_manager.track_access(
             asyn.PathAccess(namespace='target', path=path, mode='r')
         )
         command = 'read_tree_values {} {}'.format(quote(path), depth)
         output = await self._execute_util.asyn(command, as_root=self.is_rooted,
-                                    check_exit_code=check_exit_code)
-
+                                    check_exit_code=check_exit_code, decode=False)
         accumulator = defaultdict(list)
-        for entry in output.strip().split('\n'):
-            if ':' not in entry:
+        for entry in output.strip().splitlines():
+            if b':' not in entry:
                 continue
-            path, value = entry.strip().split(':', 1)
+            path, value = entry.strip().split(b':', 1)
             accumulator[path].append(value)
 
-        result = {k: '\n'.join(v).strip() for k, v in accumulator.items()}
+        if decode is None:
+            def do_decode(b):
+                try:
+                    return b.decode()
+                except UnicodeDecodeError:
+                    return b
+        elif decode:
+            do_decode = lambda b: b.decode()
+        else:
+            do_decode = lambda b: b
+
+        result = {k.decode(): do_decode(b'\n'.join(v).strip()) for k, v in accumulator.items()}
         return result
 
     @asyn.asyncf
     async def read_tree_values(self, path, depth=1, dictcls=dict,
-                         check_exit_code=True, tar=False, decode_unicode=True,
+                         check_exit_code=True, tar=False, decode_unicode=None,
                          strip_null_chars=True):
         """
         Reads the content of all files under a given tree
@@ -1415,7 +1425,7 @@ async def read_tree_values(self, path, depth=1, dictcls=dict,
         :returns: a tree-like dict with the content of files as leafs
         """
         if not tar:
-            value_map = await self.read_tree_values_flat.asyn(path, depth, check_exit_code)
+            value_map = await self.read_tree_values_flat.asyn(path, depth, check_exit_code, decode=decode_unicode)
         else:
             value_map = await self.read_tree_tar_flat.asyn(path, depth, check_exit_code,
                                                 decode_unicode,
@@ -1455,14 +1465,15 @@ async def _setup_shutils(self):
 
     @asyn.asyncf
     @call_conn
-    async def _execute_util(self, command, timeout=None, check_exit_code=True, as_root=False):
+    async def _execute_util(self, command, timeout=None, check_exit_code=True, as_root=False, decode=True):
         command = '{} {}'.format(quote(self.shutils), command)
-        return await self.execute.asyn(
-            command,
+        stdout, stderr = await self.execute_raw.asyn(
+            command=command,
             timeout=timeout,
             check_exit_code=check_exit_code,
-            as_root=as_root
+            as_root=as_root,
         )
+        return stdout.decode() if decode else stdout
 
     async def _extract_archive(self, path, cmd, dest=None):
         cmd = '{} ' + cmd  # busybox